From 4e4e9f6c4cc373cecd3d444b5f7787dd05944da7 Mon Sep 17 00:00:00 2001
From: Paul Wessel <pwessel@hawaii.edu>
Date: Sun, 16 Aug 2020 23:17:04 -1000
Subject: [PATCH 01/25] Enable painting the xz and yz back-walls in 3-D

let +g set xy plan color, while +x and +y optionally set the other two side.
---
 src/gmt_init.c    | 45 +++++++++++++++++++++++++++++++++++----------
 src/gmt_plot.c    | 38 +++++++++++++++++++++++++++-----------
 src/gmt_project.h |  4 ++--
 src/grdimage.c    |  6 +++---
 src/psbasemap.c   |  4 ++--
 src/pscoast.c     |  8 ++++----
 src/psrose.c      |  8 ++++----
 src/psternary.c   |  6 +++---
 8 files changed, 80 insertions(+), 39 deletions(-)

diff --git a/src/gmt_init.c b/src/gmt_init.c
index 07a4cce33d7..ab2e5b5df93 100644
--- a/src/gmt_init.c
+++ b/src/gmt_init.c
@@ -3749,7 +3749,7 @@ GMT_LOCAL int gmtinit_parse4_B_option (struct GMT_CTRL *GMT, char *in) {
 	gmtinit_handle_dosfile (GMT, in, 0);	/* Temporarily replace DOS files like X:/ with X;/ to avoid colon trouble */
 #endif
 
-	for (i = (int)strlen(in) - 1, ignore = false; !GMT->current.map.frame.paint && !error && i >= 0; i--) {	/** Look for +g<fill */
+	for (i = (int)strlen(in) - 1, ignore = false; !GMT->current.map.frame.paint[GMT_Z] && !error && i >= 0; i--) {	/** Look for +g<fill */
 		if (in[i] == ':') ignore = !ignore;
 		if (ignore) continue;	/* Not look inside text items */
 		if (in[i] == '+' && in[i+1] == 'o') {	/* Found +o<plon>/<plat> */
@@ -3775,9 +3775,9 @@ GMT_LOCAL int gmtinit_parse4_B_option (struct GMT_CTRL *GMT, char *in) {
 #ifdef _WIN32
 			gmtinit_handle_dosfile (GMT, out1, 1);	/* Undo any DOS files like X;/ back to X:/ */
 #endif
-			if (gmt_getfill (GMT, out1, &GMT->current.map.frame.fill)) error++;
+			if (gmt_getfill (GMT, out1, &GMT->current.map.frame.fill[GMT_Z])) error++;
 			if (!error) {
-				GMT->current.map.frame.paint = true;
+				GMT->current.map.frame.paint[GMT_Z] = true;
 				g = i;
 				in[g] = '\0';	/* Chop off +g for now */
 			}
@@ -4003,6 +4003,7 @@ bool gmtlib_B_is_frame (struct GMT_CTRL *GMT, char *in) {
 
 /*! . */
 GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
+	bool blank[2] = {false, false};
 	unsigned int pos = 0, k, error = 0;
 	char p[GMT_BUFSIZ] = {""}, text[GMT_BUFSIZ] = {""}, *mod = NULL;
 	double pole[2];
@@ -4018,8 +4019,9 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 	/* OK, here we are pretty sure this is a frame -B statement */
 
 	strncpy (text, in, GMT_BUFSIZ-1);
-	gmt_handle5_plussign (GMT, text, "bginot", 0);	/* Temporarily change double plus-signs to double ASCII 1 to avoid +<modifier> angst */
+	gmt_handle5_plussign (GMT, text, "bginotxy", 0);	/* Temporarily change double plus-signs to double ASCII 1 to avoid +<modifier> angst */
 	GMT->current.map.frame.header[0] = '\0';
+	gmt_M_memset (GMT->current.map.frame.paint, 3U, bool);
 
 	if ((mod = strchr (text, '+'))) {	/* Find start of modifiers, if any */
 		while ((gmt_strtok (mod, "+", &pos, p))) {	/* Parse any +<modifier> statements */
@@ -4028,11 +4030,11 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 					GMT->current.map.frame.draw_box = true;
 					break;
 				case 'g':	/* Paint the basemap interior */
-					if (p[1] == 0 || gmt_getfill (GMT, &p[1], &GMT->current.map.frame.fill)) {
+					if (p[1] == 0 || gmt_getfill (GMT, &p[1], &GMT->current.map.frame.fill[GMT_Z])) {
 						GMT_Report (GMT->parent, GMT_MSG_ERROR, "Bad +g<fill> argument %s\n", &p[1]);
 						error++;
 					}
-					GMT->current.map.frame.paint = true;
+					GMT->current.map.frame.paint[GMT_Z] = true;
 					break;
 				case 'i':	/* Turn on internal annotation for radiual or longitudinal axes when there is no other place to annotate */
 					GMT->current.map.frame.internal_annot = 1;	/* Longitude/angle */
@@ -4082,6 +4084,22 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 						gmtlib_enforce_rgb_triplets (GMT, GMT->current.map.frame.header, GMT_LEN256);	/* If @; is used, make sure the color information passed on to ps_text is in r/b/g format */
 					}
 					break;
+				case 'x':	/* Paint the basemap xz-plane for 3-D plots */
+					if (p[1] && gmt_getfill (GMT, &p[1], &GMT->current.map.frame.fill[GMT_X])) {
+						GMT_Report (GMT->parent, GMT_MSG_ERROR, "Bad +x<fill> argument %s\n", &p[1]);
+						error++;
+					}
+					blank[GMT_X] = !p[1];
+					GMT->current.map.frame.paint[GMT_X] = true;
+					break;
+				case 'y':	/* Paint the basemap yz-plane for 3-D plots */
+					if (p[1] && gmt_getfill (GMT, &p[1], &GMT->current.map.frame.fill[GMT_Y])) {
+						GMT_Report (GMT->parent, GMT_MSG_ERROR, "Bad +y<fill> argument %s\n", &p[1]);
+						error++;
+					}
+					blank[GMT_X] = !p[1];
+					GMT->current.map.frame.paint[GMT_Y] = true;
+					break;
 				default:
 					GMT_Report (GMT->parent, GMT_MSG_ERROR, "Option -B: Unrecognized frame modifier %s\n", p);
 					error++;
@@ -4091,6 +4109,12 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 		*mod = '\0';	/* Separate the modifiers from the frame selectors */
 	}
 
+	if (GMT->current.map.frame.paint[GMT_Z]) {
+		if (GMT->current.map.frame.paint[GMT_X] && blank[GMT_X])	/* Just +x means same as z-fill */
+			gmt_M_memcpy (&GMT->current.map.frame.fill[GMT_X], &GMT->current.map.frame.fill[GMT_Z], 1U, struct GMT_FILL);
+		if (GMT->current.map.frame.paint[GMT_Y] && blank[GMT_Y])	/* Just +x means same as z-fill */
+			gmt_M_memcpy (&GMT->current.map.frame.fill[GMT_Y], &GMT->current.map.frame.fill[GMT_Z], 1U, struct GMT_FILL);
+	}
 	/* Now parse the frame choices, if any */
 	error += gmtinit_decode5_wesnz (GMT, text, true);
 
@@ -4105,6 +4129,7 @@ void gmt_init_B (struct GMT_CTRL *GMT) {
 		for (k = 0; k < 6; k++) GMT->current.map.frame.axis[no].item[k].parent = no;
 		if (GMT->current.proj.xyz_projection[no] == GMT_TIME) GMT->current.map.frame.axis[no].type = GMT_TIME;
 	}
+	gmt_M_memset (GMT->current.map.frame.paint, 3U, bool);
 	GMT->common.B.string[0][0] = GMT->common.B.string[1][0] = '\0';
 	GMT->current.map.frame.init = true;
 	GMT->current.map.frame.draw = false;
@@ -12635,11 +12660,11 @@ GMT_LOCAL struct GMT_CTRL *gmtinit_begin_module_sub (struct GMTAPI_CTRL *API, co
 	GMT->common.p.active = GMT->common.s.active = GMT->common.t.active = GMT->common.colon.active = false;
 	gmt_M_memset (GMT->common.b.ncol, 2, int);
 
-	/* Initialize bg fill to white although we don't use it until GMT->current.map.frame.paint = true;
+	/* Initialize bg fill to white although we don't use it until GMT->current.map.frame.paint[GMT_Z] = true;
 	   But needed when using images with an transparency layer.
 	*/
 
-	GMT->current.map.frame.fill.rgb[0] = GMT->current.map.frame.fill.rgb[1] = GMT->current.map.frame.fill.rgb[2] = 1.0;
+	GMT->current.map.frame.fill[GMT_Z].rgb[0] = GMT->current.map.frame.fill[GMT_Z].rgb[1] = GMT->current.map.frame.fill[GMT_Z].rgb[2] = 1.0;
 
 	*Ccopy = Csave; /* Pass back out for safe-keeping by the module until gmt_end_module is called */
 
@@ -14303,8 +14328,8 @@ void gmt_end_module (struct GMT_CTRL *GMT, struct GMT_CTRL *Ccopy) {
 	gmtinit_free_user_media (GMT);	/* Free user-specified media formats */
 
 	/* Reset frame fill painting */
-	Ccopy->current.map.frame.paint = GMT->current.map.frame.paint;
-	gmt_M_memcpy (Ccopy->current.map.frame.fill.rgb, GMT->current.map.frame.fill.rgb, 3, double);
+	Ccopy->current.map.frame.paint[GMT_Z] = GMT->current.map.frame.paint[GMT_Z];
+	gmt_M_memcpy (Ccopy->current.map.frame.fill[GMT_Z].rgb, GMT->current.map.frame.fill[GMT_Z].rgb, 3, double);
 
 	/* GMT_IO */
 
diff --git a/src/gmt_plot.c b/src/gmt_plot.c
index 3045b99e86e..046ae29eaab 100644
--- a/src/gmt_plot.c
+++ b/src/gmt_plot.c
@@ -1556,6 +1556,21 @@ GMT_LOCAL void gmtplot_map_symbol_ns (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL
 	if (nc) gmt_M_free (GMT, xings);
 }
 
+GMT_LOCAL void gmtplot_z_walls (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL, double zmin, double zmax, int plane) {
+	double xx[4], yy[4];
+
+	if (!GMT->current.map.frame.paint[plane]) return;
+	fprintf (stderr, "Plot plane %d\n", plane);
+	xx[0] = xx[3] = (plane == GMT_Y) ? GMT->current.proj.rect[XLO] : GMT->current.proj.rect[YLO];
+	xx[1] = xx[2] = (plane == GMT_Y) ? GMT->current.proj.rect[XHI] : GMT->current.proj.rect[YHI];
+	PSL_command (GMT->PSL, "V\n");
+	gmt_setfill (GMT, &GMT->current.map.frame.fill[plane], 1);
+	yy[0] = yy[1] = gmt_z_to_zz (GMT, zmin);
+	yy[2] = yy[3] = gmt_z_to_zz (GMT, zmax);
+	PSL_plotpolygon (PSL, xx, yy, 4);
+	PSL_command (GMT->PSL, "U\n");
+}
+
 GMT_LOCAL void gmtplot_z_gridlines (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL, double zmin, double zmax, int plane) {
 	unsigned int k, i, nz, item[2] = {GMT_GRID_UPPER, GMT_GRID_LOWER};
 	double dz, zz, min, max, *z = NULL;
@@ -1563,7 +1578,6 @@ GMT_LOCAL void gmtplot_z_gridlines (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL,
 
 	min = (plane == GMT_Y) ? GMT->current.proj.rect[XLO] : GMT->current.proj.rect[YLO];
 	max = (plane == GMT_Y) ? GMT->current.proj.rect[XHI] : GMT->current.proj.rect[YHI];
-
 	for (k = 0; k < 2; k++) {
 		if (fabs (GMT->current.setting.map_grid_cross_size[k]) > 0.0) continue;
 
@@ -2628,9 +2642,11 @@ GMT_LOCAL bool gmtplot_is_fancy_boundary (struct GMT_CTRL *GMT) {
 GMT_LOCAL void gmtplot_vertical_wall (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL, int quadrant, double *nesw, bool back) {
 	int plane = (quadrant + 1) % 2;
 	gmt_plane_perspective (GMT, plane, nesw[quadrant % 4]);
-	PSL_plotbox (PSL, nesw[(quadrant+1)%4], GMT->current.proj.zmin, nesw[(quadrant+3)%4], GMT->current.proj.zmax);
-	if (back)
+	if (back) {
+		gmtplot_z_walls (GMT, PSL, GMT->common.R.wesn[ZLO], GMT->common.R.wesn[ZHI], 1-plane);
 		gmtplot_z_gridlines (GMT, PSL, GMT->common.R.wesn[ZLO], GMT->common.R.wesn[ZHI], plane);
+	}
+	PSL_plotbox (PSL, nesw[(quadrant+1)%4], GMT->current.proj.zmin, nesw[(quadrant+3)%4], GMT->current.proj.zmax);
 }
 
 GMT_LOCAL void gmtplot_timestamp (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL, double x, double y, unsigned int justify, char *U_label) {
@@ -7578,10 +7594,10 @@ struct PSL_CTRL *gmt_plotinit (struct GMT_CTRL *GMT, struct GMT_OPTION *options)
 
 	PSL = GMT->PSL;	/* Shorthand */
 
-	if (GMT->current.map.frame.paint) {	/* Must squirrel this away for now since we may call psbasemap during the movie-indicators below */
+	if (GMT->current.map.frame.paint[GMT_Z]) {	/* Must squirrel this away for now since we may call psbasemap during the movie-indicators below */
 		do_paint = true;
-		gmt_M_memcpy (&fill, &GMT->current.map.frame.fill, 1U, struct GMT_FILL);
-		GMT->current.map.frame.paint = false;	/* Turn off for now */
+		gmt_M_memcpy (&fill, &GMT->current.map.frame.fill[GMT_Z], 1U, struct GMT_FILL);
+		GMT->current.map.frame.paint[GMT_Z] = false;	/* Turn off for now */
 	}
 
 	PSL->internal.verbose = GMT->current.setting.verbose;		/* Inherit verbosity level from GMT */
@@ -8024,21 +8040,21 @@ struct PSL_CTRL *gmt_plotinit (struct GMT_CTRL *GMT, struct GMT_OPTION *options)
 		PSL_command (PSL, "}!\n");
 	}
 	if (do_paint) {	/* Reset any canvas coloring here */
-		GMT->current.map.frame.paint = true;
-		gmt_M_memcpy (&GMT->current.map.frame.fill, &fill, 1U, struct GMT_FILL);
+		GMT->current.map.frame.paint[GMT_Z] = true;
+		gmt_M_memcpy (&GMT->current.map.frame.fill[GMT_Z], &fill, 1U, struct GMT_FILL);
 	}
 
 	return (PSL);
 }
 
 void gmt_plotcanvas (struct GMT_CTRL *GMT) {
-	if (GMT->current.map.frame.paint) {	/* Paint the inside of the map with specified fill */
+	if (GMT->current.map.frame.paint[GMT_Z]) {	/* Paint the inside of the map (xy plane) with specified fill */
 		double *x = NULL, *y = NULL;
 		uint64_t np;
 		bool donut;
-		PSL_comment (GMT->PSL, "Fill the canvas %s\n", gmtlib_putfill (GMT, &GMT->current.map.frame.fill));
+		PSL_comment (GMT->PSL, "Fill the canvas %s\n", gmtlib_putfill (GMT, &GMT->current.map.frame.fill[GMT_Z]));
 		np = gmt_map_clip_path (GMT, &x, &y, &donut);
-		gmt_setfill (GMT, &GMT->current.map.frame.fill, 0);
+		gmt_setfill (GMT, &GMT->current.map.frame.fill[GMT_Z], 0);
 		PSL_plotpolygon (GMT->PSL, x, y, (int)((1 + donut) * np));
 		gmt_M_free (GMT, x);
 		gmt_M_free (GMT, y);
diff --git a/src/gmt_project.h b/src/gmt_project.h
index 0f09e0181c9..509e1771bd9 100644
--- a/src/gmt_project.h
+++ b/src/gmt_project.h
@@ -503,13 +503,13 @@ struct GMT_PLOT_AXIS {		/* Information for one time axis */
 struct GMT_PLOT_FRAME {		/* Various parameters for plotting of time axis boundaries */
 	struct GMT_PLOT_AXIS axis[3];	/* One each for x, y, and z */
 	char header[GMT_LEN256];	/* Plot title */
-	struct GMT_FILL fill;		/* Fill for the basemap inside, if paint == true */
+	struct GMT_FILL fill[3];		/* Fill for the basemap inside for planes x,y,z, if paint == true */
 	bool plotted_header;		/* true if header has been plotted */
 	bool init;			/* true if -B was used at all */
 	bool set;			/* true if -B was used to set any increments */
 	bool draw;			/* true if -B<int> was used, even -B0, as sign to draw axes */
 	bool drawz;			/* true if -B<int> was used, even -Bz0, as sign to draw z axes */
-	bool paint;			/* true if -B +g<fill> was used */
+	bool paint[3];			/* true if -B +x[<fill>], +y[<fill>], +g<fill> was used */
 	bool draw_box;			/* true if a 3-D Z-box is desired */
 	bool no_frame;			/* true if we just want gridlines but no frame, i.e +n was used */
 	bool check_side;		/* true if lon and lat annotations should be on x and y axis only */
diff --git a/src/grdimage.c b/src/grdimage.c
index 7bb1c7eb99f..2cc31908795 100644
--- a/src/grdimage.c
+++ b/src/grdimage.c
@@ -1260,9 +1260,9 @@ EXTERN_MSC int GMT_grdimage (void *V_API, int mode, void *args) {
 								   But what would it take to have a user selected bg color? */
 								double o, t;		/* o - opacity, t = transparency */
 								o = Img_proj->data[node_RGBA] / 255.0;	t = 1 - o;
-								rgb[0] = o * rgb[0] + t * GMT->current.map.frame.fill.rgb[0];
-								rgb[1] = o * rgb[1] + t * GMT->current.map.frame.fill.rgb[1];
-								rgb[2] = o * rgb[2] + t * GMT->current.map.frame.fill.rgb[2];
+								rgb[0] = o * rgb[0] + t * GMT->current.map.frame.fill[GMT_Z].rgb[0];
+								rgb[1] = o * rgb[1] + t * GMT->current.map.frame.fill[GMT_Z].rgb[1];
+								rgb[2] = o * rgb[2] + t * GMT->current.map.frame.fill[GMT_Z].rgb[2];
 								node_RGBA++;
 							}
 						}
diff --git a/src/psbasemap.c b/src/psbasemap.c
index e0c7b670827..72335ffd077 100644
--- a/src/psbasemap.c
+++ b/src/psbasemap.c
@@ -192,8 +192,8 @@ static int parse (struct GMT_CTRL *GMT, struct PSBASEMAP_CTRL *Ctrl, struct GMT_
 			case 'G':	/* Set canvas color */
 				if (gmt_M_compat_check (GMT, 4)) {
 					GMT_Report (API, GMT_MSG_COMPAT, "Option -G is deprecated; -B...+g%s was set instead, use this in the future.\n", opt->arg);
-					GMT->current.map.frame.paint = true;
-					if (gmt_getfill (GMT, opt->arg, &GMT->current.map.frame.fill)) {
+					GMT->current.map.frame.paint[GMT_Z] = true;
+					if (gmt_getfill (GMT, opt->arg, &GMT->current.map.frame.fill[GMT_Z])) {
 						gmt_fill_syntax (GMT, 'G', NULL, " ");
 						n_errors++;
 					}
diff --git a/src/pscoast.c b/src/pscoast.c
index 0557a777a0a..d99a50bedc1 100644
--- a/src/pscoast.c
+++ b/src/pscoast.c
@@ -149,8 +149,8 @@ static void *New_Ctrl (struct GMT_CTRL *GMT) {	/* Allocate and initialize a new
 
 	C->A.info.high = GSHHS_MAX_LEVEL;			/* Include all GSHHS levels */
 	C->D.set = 'l';						/* Low-resolution coastline data */
-	if (GMT->current.map.frame.paint)	/* Default Ocean color = Frame background color */
-		C->S.fill = GMT->current.map.frame.fill;
+	if (GMT->current.map.frame.paint[GMT_Z])	/* Default Ocean color = Frame background color */
+		C->S.fill = GMT->current.map.frame.fill[GMT_Z];
 	else
 		gmt_init_fill (GMT, &C->S.fill, 1.0, 1.0, 1.0);		/* Default Ocean color = white */
 	C->C.fill[LAKE] = C->C.fill[RIVER] = C->S.fill;		/* Default Lake/Riverlake color = Ocean color */
@@ -932,8 +932,8 @@ EXTERN_MSC int GMT_pscoast (void *V_API, int mode, void *args) {
 		clobber_background = true;
 		recursive = false;
 		if (!Ctrl->S.active) {	/* Since we are painting wet areas we must now reset them to white */
-			if (GMT->current.map.frame.paint)	/* Let ocean color match cancas fill color */
-				fill[0] = GMT->current.map.frame.fill;
+			if (GMT->current.map.frame.paint[GMT_Z])	/* Let ocean color match cancas fill color */
+				fill[0] = GMT->current.map.frame.fill[GMT_Z];
 			else
 				gmt_init_fill (GMT, &fill[0], 1.0, 1.0, 1.0);	/* Default Ocean color = white */
 		}
diff --git a/src/psrose.c b/src/psrose.c
index 56b1d305948..0b220dcb5bf 100644
--- a/src/psrose.c
+++ b/src/psrose.c
@@ -743,8 +743,8 @@ EXTERN_MSC int GMT_psrose (void *V_API, int mode, void *args) {
 		Return (GMT_PROJECTION_ERROR);
 	}
 
-	if (GMT->current.map.frame.paint) {	/* Until psrose uses a polar projection we must bypass the basemap fill and do it ourself here */
-		GMT->current.map.frame.paint = false;	/* Turn off so gmt_plotinit won't fill */
+	if (GMT->current.map.frame.paint[GMT_Z]) {	/* Until psrose uses a polar projection we must bypass the basemap fill and do it ourself here */
+		GMT->current.map.frame.paint[GMT_Z] = false;	/* Turn off so gmt_plotinit won't fill */
 		do_fill = true;
 	}
 	if ((PSL = gmt_plotinit (GMT, options)) == NULL) Return (GMT_RUNTIME_ERROR);
@@ -779,14 +779,14 @@ EXTERN_MSC int GMT_psrose (void *V_API, int mode, void *args) {
 
 	if (do_fill) {	/* Until psrose uses a polar projection we must bypass the basemap fill and do it ourself here */
 		double dim = 2.0 * Ctrl->S.scale;
-		GMT->current.map.frame.paint = true;	/* Restore original setting */
+		GMT->current.map.frame.paint[GMT_Z] = true;	/* Restore original setting */
 		if (half_only) {	/* Clip the bottom half of the circle */
 			double xc[4], yc[4];
 			xc[0] = xc[3] = -Ctrl->S.scale;	xc[1] = xc[2] = Ctrl->S.scale;
 			yc[0] = yc[1] = 0.0;	yc[2] = yc[3] = Ctrl->S.scale;
 			PSL_beginclipping (PSL, xc, yc, 4, GMT->session.no_rgb, 3);
 		}
-		gmt_setfill (GMT, &GMT->current.map.frame.fill, 0);
+		gmt_setfill (GMT, &GMT->current.map.frame.fill[GMT_Z], 0);
 		PSL_plotsymbol (PSL, 0.0, 0.0, &dim, PSL_CIRCLE);
 		if (half_only) PSL_endclipping (PSL, 1);		/* Reduce polygon clipping by one level */
 	}
diff --git a/src/psternary.c b/src/psternary.c
index 1201d7fbe92..635d56335b6 100644
--- a/src/psternary.c
+++ b/src/psternary.c
@@ -426,10 +426,10 @@ EXTERN_MSC int GMT_psternary (void *V_API, int mode, void *args) {
 	 * axis arguments.  We also must handle the canvas filling separately.  The three axis are 60 degrees
 	 * relative to each other and we do this directly with PSL calls. */
 
-	if (GMT->current.map.frame.paint) {	/* Paint the inside of the map with specified fill */
-		gmt_setfill (GMT, &GMT->current.map.frame.fill, 0);
+	if (GMT->current.map.frame.paint[GMT_Z]) {	/* Paint the inside of the map with specified fill */
+		gmt_setfill (GMT, &GMT->current.map.frame.fill[GMT_Z], 0);
 		PSL_plotpolygon (PSL, tri_x, tri_y, 4);
-		GMT->current.map.frame.paint = false;
+		GMT->current.map.frame.paint[GMT_Z] = false;
 	}
 	/* Count how many of the three sides will be drawn */
 	if (GMT->current.map.frame.side[S_SIDE]) n_sides++;	/* The bottom (a) side */

From 360437f73dae8b1168988ff8c1e49a0c0630869e Mon Sep 17 00:00:00 2001
From: Paul Wessel <pwessel@hawaii.edu>
Date: Mon, 17 Aug 2020 19:48:39 -1000
Subject: [PATCH 02/25] Allow the 3-D box not to be plotted on top of figure

Until now, the +b did twh things: Turned on 3-D backwalls if gridlines were requested and draw the 3-D box, sometimes overprinting the main illustration.  This PR adds +B as an alternative.  Same as +b but does not draw the 3-D box outline.
---
 src/gmt_init.c    | 30 +++++++++++++++++-------------
 src/gmt_plot.c    | 24 +++++++++++++++---------
 src/gmt_project.h |  8 +++++++-
 3 files changed, 39 insertions(+), 23 deletions(-)

diff --git a/src/gmt_init.c b/src/gmt_init.c
index cb882b35bc3..f0376afbe37 100644
--- a/src/gmt_init.c
+++ b/src/gmt_init.c
@@ -2473,14 +2473,14 @@ GMT_LOCAL bool gmtinit_true_false_or_error (char *value, bool *answer) {
 }
 
 /*! . */
-GMT_LOCAL int gmtinit_decode4_wesnz (struct GMT_CTRL *GMT, const char *in, unsigned int side[], bool *draw_box, int part) {
+GMT_LOCAL int gmtinit_decode4_wesnz (struct GMT_CTRL *GMT, const char *in, unsigned int side[], unsigned int *draw_box, int part) {
 	/* Scans the WESNZwesnz+ flags at the end of string "in" and sets the side/drawbox parameters
 	 * and returns the length of the remaining string.  Assumes any +g<fill> has been removed from in.
 	 */
 
 	int i, k, orig_i;
-	unsigned int side_orig[5];
-	bool go = true, orig_draw_box = *draw_box;
+	unsigned int side_orig[5], orig_draw_box = *draw_box;
+	bool go = true;
 
 	GMT->current.map.frame.set_frame[part]++;
 	if (GMT->current.map.frame.set_frame[GMT_PRIMARY] > 1 || GMT->current.map.frame.set_frame[GMT_SECONDARY] > 1) {
@@ -2496,7 +2496,7 @@ GMT_LOCAL int gmtinit_decode4_wesnz (struct GMT_CTRL *GMT, const char *in, unsig
 	for (k = 0; go && i >= 0 && strchr ("WESNZwesnz+", in[i]); i--) {
 		if (k == 0 && part == 0) {	/* Wipe out default values when the first flag is found */
 			for (k = 0; k < 5; k++) side[k] = 0;
-			*draw_box = false;
+			*draw_box = GMT_3D_NONE;
 		}
 		if (in[i] == 's') {	/* Since s can mean both "draw south axis" and "seconds", check further */
 			if (side[S_SIDE]) go = false;	/* If S was set already then s probably means seconds */
@@ -2518,7 +2518,7 @@ GMT_LOCAL int gmtinit_decode4_wesnz (struct GMT_CTRL *GMT, const char *in, unsig
 			case 'n': side[N_SIDE] |= GMT_AXIS_BARB; break;
 			case 'z': side[Z_SIDE] |= GMT_AXIS_BARB; break;
 			/* Draw 3-D box */
-			case '+': *draw_box = true; break;
+			case '+': *draw_box = GMT_3D_BOX; break;
 		}
 	}
 	if (i >= 0 && in[i] == ',') i--;	/* Special case for -BCcustomfile,WESNwesn to avoid the filename being parsed for WESN */
@@ -3948,12 +3948,14 @@ GMT_LOCAL int gmtinit_decode5_wesnz (struct GMT_CTRL *GMT, const char *in, bool
 			/* Draw 3-D box */
 			case '+':
 				if (in[k+1] == 'b')	/* Got +b appended to MAP_FRAME_AXES, possibly */
-					GMT->current.map.frame.draw_box = true;
+					GMT->current.map.frame.draw_box = GMT_3D_BOX;
+				else if (in[k+1] == 'B')	/* Got +b appended to MAP_FRAME_AXES, possibly */
+					GMT->current.map.frame.draw_box = GMT_3D_WALL;
 				else if (in[k+1] == 'n')	/* Got +n appended to MAP_FRAME_AXES, means no frame nor annotations desired */
 					GMT->current.map.frame.no_frame = true;
 				else if (gmt_M_compat_check (GMT, 4)) {
 					GMT_Report (GMT->parent, GMT_MSG_COMPAT, "Modifier + in MAP_FRAME_AXES is deprecated; use +b instead.\n");
-					GMT->current.map.frame.draw_box = true;
+					GMT->current.map.frame.draw_box = GMT_3D_BOX;
 				}
 				else {
 					GMT_Report (GMT->parent, GMT_MSG_ERROR, "Modifier + in MAP_FRAME_AXES not recognized.\n");
@@ -4018,14 +4020,17 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 	/* OK, here we are pretty sure this is a frame -B statement */
 
 	strncpy (text, in, GMT_BUFSIZ-1);
-	gmt_handle5_plussign (GMT, text, "bginot", 0);	/* Temporarily change double plus-signs to double ASCII 1 to avoid +<modifier> angst */
+	gmt_handle5_plussign (GMT, text, "bBginot", 0);	/* Temporarily change double plus-signs to double ASCII 1 to avoid +<modifier> angst */
 	GMT->current.map.frame.header[0] = '\0';
 
 	if ((mod = strchr (text, '+'))) {	/* Find start of modifiers, if any */
 		while ((gmt_strtok (mod, "+", &pos, p))) {	/* Parse any +<modifier> statements */
 			switch (p[0]) {
 				case 'b':	/* Activate 3-D box and x-z, y-z gridlines (if selected) */
-					GMT->current.map.frame.draw_box = true;
+					GMT->current.map.frame.draw_box = GMT_3D_BOX;
+					break;
+				case 'B':	/* Activate 3-D box and x-z, y-z gridlines (if selected) */
+					GMT->current.map.frame.draw_box = GMT_3D_WALL;
 					break;
 				case 'g':	/* Paint the basemap interior */
 					if (p[1] == 0 || gmt_getfill (GMT, &p[1], &GMT->current.map.frame.fill)) {
@@ -5835,7 +5840,7 @@ void gmt_conf (struct GMT_CTRL *GMT) {
 	/* MAP_FRAME_AXES */
 	strcpy (GMT->current.setting.map_frame_axes, "WESNZ");
 	for (i = 0; i < 5; i++) GMT->current.map.frame.side[i] = 0;	/* Unset default settings */
-	GMT->current.map.frame.draw_box = false;
+	GMT->current.map.frame.draw_box = GMT_3D_NONE;
 	error += gmtinit_decode5_wesnz (GMT, "WESNZ", false);
 	/* MAP_DEFAULT_PEN */
 	error += gmt_getpen (GMT, "default,black", &GMT->current.setting.map_default_pen);
@@ -6545,8 +6550,7 @@ void gmtlib_explain_options (struct GMT_CTRL *GMT, char *options) {
 			gmt_message (GMT, "\t     To prepend a prefix to each annotation (e.g., $ 10, $ 20 ...), add +p<prefix>.\n");
 			gmt_message (GMT, "\t     To append a unit to each annotation (e.g., 5 km, 10 km ...), add +u<unit>.\n");
 			gmt_message (GMT, "\t     Cartesian x-axis takes optional +a<angle> for slanted or +an for orthogonal annotations [+ap].\n");
-			gmt_message (GMT, "\t     Cartesian y-axis takes optional +ap for parallel annotations [+an].\n");
-			gmt_message (GMT, "\t     Cartesian z-axis takes optional +an for parallel annotations [+an].\n");
+			gmt_message (GMT, "\t     Cartesian y- and z-axes take optional +ap for parallel annotations [+an].\n");
 			gmt_message (GMT, "\t     Geographic axes take optional +f for \"fancy\" annotations with W|E|S|N suffices.\n");
 			gmt_message (GMT, "\t     To label an axis, add +l<label>.  Use +L to enforce horizontal labels for y-axes.\n");
 			gmt_message (GMT, "\t     For another axis label on the opposite axis, use +s|S as well.\n");
@@ -9728,7 +9732,7 @@ unsigned int gmtlib_setparameter (struct GMT_CTRL *GMT, const char *keyword, cha
 		case GMTCASE_MAP_FRAME_AXES:
 			strncpy (GMT->current.setting.map_frame_axes, value, 5U);
 			for (i = 0; i < 5; i++) GMT->current.map.frame.side[i] = 0;	/* Unset default settings */
-			GMT->current.map.frame.draw_box = false;
+			GMT->current.map.frame.draw_box = GMT_3D_NONE;
 			error += (bool)gmtinit_decode5_wesnz (GMT, value, false);
 			break;
 
diff --git a/src/gmt_plot.c b/src/gmt_plot.c
index 75a30a85327..612d994f69d 100644
--- a/src/gmt_plot.c
+++ b/src/gmt_plot.c
@@ -1556,7 +1556,7 @@ GMT_LOCAL void gmtplot_map_symbol_ns (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL
 	if (nc) gmt_M_free (GMT, xings);
 }
 
-GMT_LOCAL void gmtplot_z_gridlines (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL, double zmin, double zmax, int plane) {
+GMT_LOCAL void gmtplot_z_gridlines (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL, double zmin, double zmax, int plane, bool back, unsigned int mode3d) {
 	unsigned int k, i, nz, item[2] = {GMT_GRID_UPPER, GMT_GRID_LOWER};
 	double dz, zz, min, max, *z = NULL;
 	char *plane_name[2] = {"y-z", "x-z"};
@@ -1583,8 +1583,14 @@ GMT_LOCAL void gmtplot_z_gridlines (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL,
 		}
 
 		PSL_setdash (PSL, NULL, 0);
-		gmt_M_free (GMT, z);
 	}
+	if (back && mode3d != GMT_3D_BOX) {
+		double z0 = gmt_z_to_zz (GMT, z[0]);
+		double z1 = gmt_z_to_zz (GMT, z[nz-1]);
+		PSL_plotsegment (PSL, min, z0, min, z1);
+		PSL_plotsegment (PSL, max, z0, max, z1);
+	}
+	gmt_M_free (GMT, z);
 }
 
 GMT_LOCAL int gmtplot_save_current_gridlines (struct GMT_CTRL *GMT) {
@@ -2625,12 +2631,12 @@ GMT_LOCAL bool gmtplot_is_fancy_boundary (struct GMT_CTRL *GMT) {
 	}
 }
 
-GMT_LOCAL void gmtplot_vertical_wall (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL, int quadrant, double *nesw, bool back) {
+GMT_LOCAL void gmtplot_vertical_wall (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL, int quadrant, double *nesw, bool back, unsigned int mode3d) {
 	int plane = (quadrant + 1) % 2;
 	gmt_plane_perspective (GMT, plane, nesw[quadrant % 4]);
-	PSL_plotbox (PSL, nesw[(quadrant+1)%4], GMT->current.proj.zmin, nesw[(quadrant+3)%4], GMT->current.proj.zmax);
+	if (mode3d == GMT_3D_BOX) PSL_plotbox (PSL, nesw[(quadrant+1)%4], GMT->current.proj.zmin, nesw[(quadrant+3)%4], GMT->current.proj.zmax);
 	if (back)
-		gmtplot_z_gridlines (GMT, PSL, GMT->common.R.wesn[ZLO], GMT->common.R.wesn[ZHI], plane);
+		gmtplot_z_gridlines (GMT, PSL, GMT->common.R.wesn[ZLO], GMT->common.R.wesn[ZHI], plane, back, mode3d);
 }
 
 GMT_LOCAL void gmtplot_timestamp (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL, double x, double y, unsigned int justify, char *U_label) {
@@ -5527,12 +5533,12 @@ void gmt_vertical_axis (struct GMT_CTRL *GMT, unsigned int mode) {
 		PSL_setfill (PSL, GMT->session.no_rgb, 1);
 		gmt_setpen (GMT, &GMT->current.setting.map_grid_pen[GMT_PRIMARY]);
 		if (fore) {
-			gmtplot_vertical_wall (GMT, PSL, GMT->current.proj.z_project.quadrant + 3, nesw, false);
-			gmtplot_vertical_wall (GMT, PSL, GMT->current.proj.z_project.quadrant    , nesw, false);
+			gmtplot_vertical_wall (GMT, PSL, GMT->current.proj.z_project.quadrant + 3, nesw, false, GMT->current.map.frame.draw_box);
+			gmtplot_vertical_wall (GMT, PSL, GMT->current.proj.z_project.quadrant    , nesw, false, GMT->current.map.frame.draw_box);
 		}
 		if (back) {
-			gmtplot_vertical_wall (GMT, PSL, GMT->current.proj.z_project.quadrant + 1, nesw, true);
-			gmtplot_vertical_wall (GMT, PSL, GMT->current.proj.z_project.quadrant + 2, nesw, true);
+			gmtplot_vertical_wall (GMT, PSL, GMT->current.proj.z_project.quadrant + 1, nesw, true, GMT->current.map.frame.draw_box);
+			gmtplot_vertical_wall (GMT, PSL, GMT->current.proj.z_project.quadrant + 2, nesw, true, GMT->current.map.frame.draw_box);
 		}
 	}
 
diff --git a/src/gmt_project.h b/src/gmt_project.h
index 0f09e0181c9..629647e078a 100644
--- a/src/gmt_project.h
+++ b/src/gmt_project.h
@@ -140,6 +140,12 @@ enum GMT_enum_zdown {GMT_ZDOWN_R = 0,	/* Default: Annotating radius */
 	GMT_ZDOWN_ZP	= 2,	/* Annotating planetary radius - r */
 	GMT_ZDOWN_ZR	= 3};	/* Annotating given radius - r */
 
+/* For drawing the 3-D backboard */
+enum GMT_enum_3Dmode {
+	GMT_3D_NONE = 0,	/* Default: No 3-D backboard */
+	GMT_3D_WALL	= 1,	/* Draw the backboard */
+	GMT_3D_BOX	= 2};	/* Draw the backboard and the 3-D wire box */
+
 /* gmt_M_is_periodic means the east and west meridians of a global map are separated */
 #define gmt_M_is_periodic(C) (gmt_M_is_cylindrical (C) || gmt_M_is_misc (C))
 
@@ -510,12 +516,12 @@ struct GMT_PLOT_FRAME {		/* Various parameters for plotting of time axis boundar
 	bool draw;			/* true if -B<int> was used, even -B0, as sign to draw axes */
 	bool drawz;			/* true if -B<int> was used, even -Bz0, as sign to draw z axes */
 	bool paint;			/* true if -B +g<fill> was used */
-	bool draw_box;			/* true if a 3-D Z-box is desired */
 	bool no_frame;			/* true if we just want gridlines but no frame, i.e +n was used */
 	bool check_side;		/* true if lon and lat annotations should be on x and y axis only */
 	bool primary;			/* true if current axis is primary, false if secondary */
 	bool set_both;			/* true if -B argument applies to both x and y axes */
 	bool obl_grid;			/* true if +o was given to draw oblique gridlines */
+	unsigned int draw_box;			/* 0 = no 3-D frame. 1 if 3-D Z-box is desired [default], 2 if no -Z box lines covering up the plot */
 	unsigned int internal_annot;	/* 1 (longitude) or 2 (latitude or radius) if +i was given to draw internal annotations */
 	unsigned int set_frame[2];	/* 1 if a -B<WESNframe> setting was given */
 	unsigned int horizontal;	/* 1 is S/N annotations should be parallel to axes, 2 if forced */

From a9dd71e20a89b8930453c418e1bba11fa0cf122d Mon Sep 17 00:00:00 2001
From: Paul Wessel <pwessel@hawaii.edu>
Date: Tue, 18 Aug 2020 21:59:01 -1000
Subject: [PATCH 03/25] Switch +B to +w instead for "wall"

---
 doc/rst/source/cookbook/options.rst |  8 ++++----
 doc/rst/source/explain_-B_full.rst_ |  8 ++++----
 src/gmt_init.c                      | 23 ++++++++++++-----------
 3 files changed, 20 insertions(+), 19 deletions(-)

diff --git a/doc/rst/source/cookbook/options.rst b/doc/rst/source/cookbook/options.rst
index 8c962595e42..d3f3c3d2598 100644
--- a/doc/rst/source/cookbook/options.rst
+++ b/doc/rst/source/cookbook/options.rst
@@ -287,7 +287,7 @@ tick, and gridline intervals, axes labels, and annotation units.
 
 The Frame settings are specified by
 
--  **-B**\ [*axes*][**+b**][**+g**\ *fill*][**+i**\ [*val*]][**+n**][**+o**\ *lon/lat*][**+t**\ *title*]
+-  **-B**\ [*axes*][**+b**\|\ **w**][**+g**\ *fill*][**+i**\ [*val*]][**+n**][**+o**\ *lon/lat*][**+t**\ *title*]
 
 Here, the optional *axes* dictates which of the axes should be drawn
 and possibly annotated.  By default, all 4 map boundaries (or plot axes)
@@ -300,9 +300,9 @@ any axis labels in addition to draw axis/tick-marks.  For 3-D plots you can
 also specify **Z** or **z**.  By default a single vertical axes will then be
 plotted at the most suitable map corner.  You can override this by appending
 any combination of corner ids **1234**, where **1** represents the lower left
-corner and the order goes counter-clockwise.  Append **+b** to draw the outline
-of the 3-D box defined by **-R**; this modifier is also needed to display
-gridlines in the x–z, y–z planes.  You may paint the
+corner and the order goes counter-clockwise.  Use **+w** to enable gridlines to be
+drawn on the x-z and y-z planes. Alternatively, append **+b** to also draw the outline
+of the 3-D cube defined by **-R**.  You may paint the
 map canvas by appending the **+g**\ *fill* modifier [Default is no fill].
 Use **+i** to annotate an internal meridian or parallel when the axis that normally
 would be drawn and annotated does not exist (e.g., azimuthal map with 360-degree range
diff --git a/doc/rst/source/explain_-B_full.rst_ b/doc/rst/source/explain_-B_full.rst_
index 568f3cfd4e0..9b4f74bcddd 100644
--- a/doc/rst/source/explain_-B_full.rst_
+++ b/doc/rst/source/explain_-B_full.rst_
@@ -3,7 +3,7 @@
 **-B**\ [**p**\|\ **s**]\ *parameters*
     Set map Frame and Axes parameters. The Frame parameters are specified by
 
-    **-B**\ [*axes*][**+b**][**+g**\ *fill*][**+i**\ [*val*]][**+n**][**+o**\ *lon/lat*][**+t**\ *title*]
+    **-B**\ [*axes*][**+b**\|\ **w**][**+g**\ *fill*][**+i**\ [*val*]][**+n**][**+o**\ *lon/lat*][**+t**\ *title*]
 
     where *axes* selects which axes to plot. By default, all 4 map boundaries
     (or plot axes) are plotted (named **W**, **E**, **S**, **N**). To customize,
@@ -15,9 +15,9 @@
     appearance of the vertical axis. By default a single vertical axes will be
     plotted at the most suitable map corner. Override the default by appending
     any combination of corner ids **1234**, where **1** represents the lower left
-    corner and the order goes counter-clockwise. Append **+b** to draw the outline of the 3-D
-    cube defined by **-R**; this modifier is also needed to display gridlines in
-    the x-z, y-z planes. Note that for 3-D views the title, if given, will be
+    corner and the order goes counter-clockwise.  Use **+w** to enable gridlines to be
+    drawn on the x-z and y-z planes. Alternatively, append **+b** to also draw the outline
+    of the 3-D cube defined by **-R**. Note that for 3-D views the title, if given, will be
     suppressed. You can paint the interior of the canvas with **+g**\ *fill*.
     Use **+i** to annotate an internal meridian or parallel when the axis that normally
     would be drawn and annotated does not exist (e.g., azimuthal map with 360-degree range
diff --git a/src/gmt_init.c b/src/gmt_init.c
index f0376afbe37..3b62393c66e 100644
--- a/src/gmt_init.c
+++ b/src/gmt_init.c
@@ -3949,7 +3949,7 @@ GMT_LOCAL int gmtinit_decode5_wesnz (struct GMT_CTRL *GMT, const char *in, bool
 			case '+':
 				if (in[k+1] == 'b')	/* Got +b appended to MAP_FRAME_AXES, possibly */
 					GMT->current.map.frame.draw_box = GMT_3D_BOX;
-				else if (in[k+1] == 'B')	/* Got +b appended to MAP_FRAME_AXES, possibly */
+				else if (in[k+1] == 'w')	/* Got +w appended to MAP_FRAME_AXES, possibly */
 					GMT->current.map.frame.draw_box = GMT_3D_WALL;
 				else if (in[k+1] == 'n')	/* Got +n appended to MAP_FRAME_AXES, means no frame nor annotations desired */
 					GMT->current.map.frame.no_frame = true;
@@ -3984,6 +3984,7 @@ GMT_LOCAL int gmtinit_decode5_wesnz (struct GMT_CTRL *GMT, const char *in, bool
 bool gmtlib_B_is_frame (struct GMT_CTRL *GMT, char *in) {
 	gmt_M_unused (GMT);
 	if (strstr (in, "+b")) return true;	/* Found a +b so likely frame */
+	if (strstr (in, "+w")) return true;	/* Found a +w so likely frame */
 	if (strstr (in, "+g")) return true;	/* Found a +g so likely frame */
 	if (strstr (in, "+i")) return true;	/* Found a +i so likely frame */
 	if (strstr (in, "+n")) return true;	/* Found a +n so likely frame */
@@ -4009,7 +4010,7 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 	char p[GMT_BUFSIZ] = {""}, text[GMT_BUFSIZ] = {""}, *mod = NULL;
 	double pole[2];
 
-	/* Parsing of -B<framesettings>: -B[<axes>][+b][+g<fill>][+n][+o<lon>/<lat>][+t<title>] */
+	/* Parsing of -B<framesettings>: -B[<axes>][+b|w][+g<fill>][+n][+o<lon>/<lat>][+t<title>] */
 
 	/* First determine that the given -B<in> string is indeed the framesetting option.  If not return -1 */
 
@@ -4020,7 +4021,7 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 	/* OK, here we are pretty sure this is a frame -B statement */
 
 	strncpy (text, in, GMT_BUFSIZ-1);
-	gmt_handle5_plussign (GMT, text, "bBginot", 0);	/* Temporarily change double plus-signs to double ASCII 1 to avoid +<modifier> angst */
+	gmt_handle5_plussign (GMT, text, "bginotw", 0);	/* Temporarily change double plus-signs to double ASCII 1 to avoid +<modifier> angst */
 	GMT->current.map.frame.header[0] = '\0';
 
 	if ((mod = strchr (text, '+'))) {	/* Find start of modifiers, if any */
@@ -4029,7 +4030,7 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 				case 'b':	/* Activate 3-D box and x-z, y-z gridlines (if selected) */
 					GMT->current.map.frame.draw_box = GMT_3D_BOX;
 					break;
-				case 'B':	/* Activate 3-D box and x-z, y-z gridlines (if selected) */
+				case 'w':	/* Activate x-z, y-z gridlines and wall (if selected) */
 					GMT->current.map.frame.draw_box = GMT_3D_WALL;
 					break;
 				case 'g':	/* Paint the basemap interior */
@@ -4120,8 +4121,8 @@ void gmt_init_B (struct GMT_CTRL *GMT) {
 GMT_LOCAL int gmtinit_parse5_B_option (struct GMT_CTRL *GMT, char *in) {
 	/* GMT5 clean version based on new syntax:
 	 * Frame settings:
-	 *	-B[WESNwesnz|Z[1234]][+b][+g<fill>][+o<lon/lat>][+t<title>]
-	 *    		+b enables 3-D box and x-z, y-z gridlines.
+	 *	-B[WESNwesnz|Z[1234]][+b|w][+g<fill>][+o<lon/lat>][+t<title>]
+	 *    		+b|w enables  x-z, y-z gridlines and 3-D box [+b].
 	 *    		+g<fill> as plot interior fill [none].
 	 *    		+t<title> as plot title [none].
 	 *    		of one or more of w,e,s,n,z then only those axes will be drawn.
@@ -4167,8 +4168,8 @@ GMT_LOCAL int gmtinit_parse5_B_option (struct GMT_CTRL *GMT, char *in) {
 	if ((error = gmtinit_parse5_B_frame_setting (GMT, in)) >= 0) return (error);	/* Parsed the -B frame settings separately */
 	error = 0;	/* Reset since otherwise it is -1 */
 
-	if (strstr (in, "+b") || strstr (in, "+g") || strstr (in, "+i") || strstr (in, "+n") || strstr (in, "+o") || strstr (in, "+o") || strstr (in, "+t")) {
-		GMT_Report (GMT->parent, GMT_MSG_ERROR, "Option -B: Found frame setting modifiers (+b|g|i|n|o|p) mixed with axes settings!\n");
+	if (strstr (in, "+b") || strstr (in, "+g") || strstr (in, "+i") || strstr (in, "+n") || strstr (in, "+o") || strstr (in, "+o") || strstr (in, "+t") || strstr (in, "+w")) {
+		GMT_Report (GMT->parent, GMT_MSG_ERROR, "Option -B: Found frame setting modifiers (+b|g|i|n|o|p|W) mixed with axes settings!\n");
 		return (GMT_PARSE_ERROR);
 	}
 
@@ -6518,7 +6519,7 @@ void gmtlib_explain_options (struct GMT_CTRL *GMT, char *options) {
 
 			gmt_message (GMT, "\t-B Specify both (1) basemap frame settings and (2) axes parameters.\n");
 			gmt_message (GMT, "\t   Frame settings are modified via an optional single invocation of\n");
-			gmt_message (GMT, "\t     -B[<axes>][+b][+g<fill>][+i[<val>]][+n][+o<lon>/<lat>][+t<title>]\n");
+			gmt_message (GMT, "\t     -B[<axes>][+b|w][+g<fill>][+i[<val>]][+n][+o<lon>/<lat>][+t<title>]\n");
 			gmt_message (GMT, "\t   Axes parameters are specified via one or more invocations of\n");
 			gmt_message (GMT, "\t     -B[p|s][x|y|z]<info>\n\n");
 			gmt_message (GMT, "\t   1. Frame settings control which axes to plot, frame fill, title, and type of gridlines:\n");
@@ -6528,8 +6529,8 @@ void gmtlib_explain_options (struct GMT_CTRL *GMT, char *options) {
 			gmt_message (GMT, "\t     For 3-D plots the Z|z[<corners>][+b] controls the vertical axis.  The <corners> specifies\n");
 			gmt_message (GMT, "\t     at which corner(s) to erect the axis via a combination of 1,2,3,4; 1 means lower left corner,\n");
 			gmt_message (GMT, "\t     2 is lower right, etc., in a counter-clockwise order. [Default automatically selects one axis].\n");
-			gmt_message (GMT, "\t     The optional +b will erect a 3-D frame box to outline the 3-D domain [no frame box]. The +b\n");
-			gmt_message (GMT, "\t     is also required for x-z or y-z gridlines to be plotted (if such gridlines are selected below).\n");
+			gmt_message (GMT, "\t     The +w will enable x-z or y-z gridlines to be plotted (if such gridlines are selected below).\n");
+			gmt_message (GMT, "\t     Alternativelu, +b will also erect a 3-D frame box to outline the 3-D domain [no frame box].\n");
 			gmt_message (GMT, "\t     Append +g<fill> to paint the inside of the map region before further plotting [no fill].\n");
 			gmt_message (GMT, "\t     Append +i<val> to annotate along parallel or meridian <val> [0] when no such axes can be plotted.\n");
 			gmt_message (GMT, "\t     Append +n to have no frame and annotations whatsoever [Default is controlled by WESNZ/wesnz].\n");

From 3a08502e2bacb5199bfc1eefaa0538e830508164 Mon Sep 17 00:00:00 2001
From: Paul Wessel <pwessel@hawaii.edu>
Date: Wed, 19 Aug 2020 18:30:39 -1000
Subject: [PATCH 04/25] Better parsing and checking for +x +y

---
 src/gmt_init.c | 19 +++++++++++++++----
 src/gmt_plot.c |  4 ++--
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/src/gmt_init.c b/src/gmt_init.c
index dea62b6df4b..3489176256c 100644
--- a/src/gmt_init.c
+++ b/src/gmt_init.c
@@ -4097,7 +4097,7 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 						GMT_Report (GMT->parent, GMT_MSG_ERROR, "Bad +y<fill> argument %s\n", &p[1]);
 						error++;
 					}
-					blank[GMT_X] = !p[1];
+					blank[GMT_Y] = !p[1];
 					GMT->current.map.frame.paint[GMT_Y] = true;
 					break;
 				default:
@@ -4109,12 +4109,23 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 		*mod = '\0';	/* Separate the modifiers from the frame selectors */
 	}
 
-	if (GMT->current.map.frame.paint[GMT_Z]) {
-		if (GMT->current.map.frame.paint[GMT_X] && blank[GMT_X])	/* Just +x means same as z-fill */
+	if (GMT->current.map.frame.paint[GMT_X] && blank[GMT_X]) {	/* Just +x means same as z-fill */
+		if (GMT->current.map.frame.paint[GMT_Z])
 			gmt_M_memcpy (&GMT->current.map.frame.fill[GMT_X], &GMT->current.map.frame.fill[GMT_Z], 1U, struct GMT_FILL);
-		if (GMT->current.map.frame.paint[GMT_Y] && blank[GMT_Y])	/* Just +x means same as z-fill */
+		else {
+			GMT_Report (GMT->parent, GMT_MSG_ERROR, "Option -B: Modifier +x requires a fill argument if +g not set\n");
+			error++;
+		}
+	}
+	if (GMT->current.map.frame.paint[GMT_Y] && blank[GMT_Y]) {	/* Just +x means same as z-fill */
+		if (GMT->current.map.frame.paint[GMT_Z])
 			gmt_M_memcpy (&GMT->current.map.frame.fill[GMT_Y], &GMT->current.map.frame.fill[GMT_Z], 1U, struct GMT_FILL);
+		else {
+			GMT_Report (GMT->parent, GMT_MSG_ERROR, "Option -B: Modifier +y requires a fill argument if +g not set\n");
+			error++;
+		}
 	}
+
 	/* Now parse the frame choices, if any */
 	error += gmtinit_decode5_wesnz (GMT, text, true);
 
diff --git a/src/gmt_plot.c b/src/gmt_plot.c
index 11aadf83d32..d7d70fa89eb 100644
--- a/src/gmt_plot.c
+++ b/src/gmt_plot.c
@@ -1563,12 +1563,12 @@ GMT_LOCAL void gmtplot_z_walls (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL, doub
 	fprintf (stderr, "Plot plane %d\n", plane);
 	xx[0] = xx[3] = (plane == GMT_Y) ? GMT->current.proj.rect[XLO] : GMT->current.proj.rect[YLO];
 	xx[1] = xx[2] = (plane == GMT_Y) ? GMT->current.proj.rect[XHI] : GMT->current.proj.rect[YHI];
-	PSL_command (GMT->PSL, "V\n");
+	//PSL_command (GMT->PSL, "V\n");
 	gmt_setfill (GMT, &GMT->current.map.frame.fill[plane], 1);
 	yy[0] = yy[1] = gmt_z_to_zz (GMT, zmin);
 	yy[2] = yy[3] = gmt_z_to_zz (GMT, zmax);
 	PSL_plotpolygon (PSL, xx, yy, 4);
-	PSL_command (GMT->PSL, "U\n");
+	//PSL_command (GMT->PSL, "U\n");
 }
 
 GMT_LOCAL void gmtplot_z_gridlines (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL, double zmin, double zmax, int plane) {

From 6ac0bc2a74d9479ec17d222eb5b17ec94a8f245d Mon Sep 17 00:00:00 2001
From: Paul Wessel <pwessel@hawaii.edu>
Date: Wed, 19 Aug 2020 19:02:48 -1000
Subject: [PATCH 05/25] Add back-wall pen option via +w[pen]

---
 doc/rst/source/cookbook/options.rst |  6 +++---
 doc/rst/source/explain_-B_full.rst_ |  6 +++---
 src/gmt_init.c                      | 29 ++++++++++++++++++-----------
 src/gmt_plot.c                      |  9 ++++++++-
 src/gmt_project.h                   |  1 +
 5 files changed, 33 insertions(+), 18 deletions(-)

diff --git a/doc/rst/source/cookbook/options.rst b/doc/rst/source/cookbook/options.rst
index d3f3c3d2598..f35d17b7d6e 100644
--- a/doc/rst/source/cookbook/options.rst
+++ b/doc/rst/source/cookbook/options.rst
@@ -287,7 +287,7 @@ tick, and gridline intervals, axes labels, and annotation units.
 
 The Frame settings are specified by
 
--  **-B**\ [*axes*][**+b**\|\ **w**][**+g**\ *fill*][**+i**\ [*val*]][**+n**][**+o**\ *lon/lat*][**+t**\ *title*]
+-  **-B**\ [*axes*][**+b**][**+g**\ *fill*][**+i**\ [*val*]][**+n**][**+o**\ *lon/lat*][**+t**\ *title*][**+w**\ [*pen*]]
 
 Here, the optional *axes* dictates which of the axes should be drawn
 and possibly annotated.  By default, all 4 map boundaries (or plot axes)
@@ -300,8 +300,8 @@ any axis labels in addition to draw axis/tick-marks.  For 3-D plots you can
 also specify **Z** or **z**.  By default a single vertical axes will then be
 plotted at the most suitable map corner.  You can override this by appending
 any combination of corner ids **1234**, where **1** represents the lower left
-corner and the order goes counter-clockwise.  Use **+w** to enable gridlines to be
-drawn on the x-z and y-z planes. Alternatively, append **+b** to also draw the outline
+corner and the order goes counter-clockwise.  Use **+w** to draw the outlines of
+the x-z and y-z planes. Alternatively, append **+b** to also draw the front lines
 of the 3-D cube defined by **-R**.  You may paint the
 map canvas by appending the **+g**\ *fill* modifier [Default is no fill].
 Use **+i** to annotate an internal meridian or parallel when the axis that normally
diff --git a/doc/rst/source/explain_-B_full.rst_ b/doc/rst/source/explain_-B_full.rst_
index 9b4f74bcddd..c4fe01292d5 100644
--- a/doc/rst/source/explain_-B_full.rst_
+++ b/doc/rst/source/explain_-B_full.rst_
@@ -3,7 +3,7 @@
 **-B**\ [**p**\|\ **s**]\ *parameters*
     Set map Frame and Axes parameters. The Frame parameters are specified by
 
-    **-B**\ [*axes*][**+b**\|\ **w**][**+g**\ *fill*][**+i**\ [*val*]][**+n**][**+o**\ *lon/lat*][**+t**\ *title*]
+    **-B**\ [*axes*][**+b**][**+g**\ *fill*][**+i**\ [*val*]][**+n**][**+o**\ *lon/lat*][**+t**\ *title*][**+w**\ [*pen*]]
 
     where *axes* selects which axes to plot. By default, all 4 map boundaries
     (or plot axes) are plotted (named **W**, **E**, **S**, **N**). To customize,
@@ -15,8 +15,8 @@
     appearance of the vertical axis. By default a single vertical axes will be
     plotted at the most suitable map corner. Override the default by appending
     any combination of corner ids **1234**, where **1** represents the lower left
-    corner and the order goes counter-clockwise.  Use **+w** to enable gridlines to be
-    drawn on the x-z and y-z planes. Alternatively, append **+b** to also draw the outline
+    corner and the order goes counter-clockwise.  Use **+w** to draw the outlines of
+    the x-z and y-z planes. Alternatively, append **+b** to also draw the front lines
     of the 3-D cube defined by **-R**. Note that for 3-D views the title, if given, will be
     suppressed. You can paint the interior of the canvas with **+g**\ *fill*.
     Use **+i** to annotate an internal meridian or parallel when the axis that normally
diff --git a/src/gmt_init.c b/src/gmt_init.c
index 66648106d5e..0274f7117f7 100644
--- a/src/gmt_init.c
+++ b/src/gmt_init.c
@@ -4010,7 +4010,7 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 	char p[GMT_BUFSIZ] = {""}, text[GMT_BUFSIZ] = {""}, *mod = NULL;
 	double pole[2];
 
-	/* Parsing of -B<framesettings>: -B[<axes>][+b|w][+g<fill>][+n][+o<lon>/<lat>][+t<title>] */
+	/* Parsing of -B<framesettings>: -B[<axes>][+b][+g<fill>][+n][+o<lon>/<lat>][+t<title>][+w[<pen>]] */
 
 	/* First determine that the given -B<in> string is indeed the framesetting option.  If not return -1 */
 
@@ -4032,6 +4032,12 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 					break;
 				case 'w':	/* Activate x-z, y-z gridlines and wall (if selected) */
 					GMT->current.map.frame.draw_box = GMT_3D_WALL;
+					if (p[1] && gmt_getpen (GMT, &p[1], &GMT->current.map.frame.pen)) {
+						GMT_Report (GMT->parent, GMT_MSG_ERROR, "Bad +w<pen> argument %s\n", &p[1]);
+						error++;
+					}
+					else if (p[1] == 0)	/* Use grid pen as default */
+						gmt_M_memcpy (&GMT->current.map.frame.pen, &GMT->current.setting.map_grid_pen[GMT_PRIMARY], 1, struct GMT_PEN);
 					break;
 				case 'g':	/* Paint the basemap interior */
 					if (p[1] == 0 || gmt_getfill (GMT, &p[1], &GMT->current.map.frame.fill)) {
@@ -4121,10 +4127,11 @@ void gmt_init_B (struct GMT_CTRL *GMT) {
 GMT_LOCAL int gmtinit_parse5_B_option (struct GMT_CTRL *GMT, char *in) {
 	/* GMT5 clean version based on new syntax:
 	 * Frame settings:
-	 *	-B[WESNwesnz|Z[1234]][+b|w][+g<fill>][+o<lon/lat>][+t<title>]
-	 *    		+b|w enables  x-z, y-z gridlines and 3-D box [+b].
+	 *	-B[WESNwesnz|Z[1234]][+b][+g<fill>][+o<lon/lat>][+t<title>][+w[<pen>]]
+	 *    		+b draws 3-D box.
 	 *    		+g<fill> as plot interior fill [none].
 	 *    		+t<title> as plot title [none].
+	 *    		+w[<pen>] draws the outline of the xz and yz planes [no outline].
 	 *    		of one or more of w,e,s,n,z then only those axes will be drawn.
 	 *		Upper case letters means the chosen axes also will be annotated.
 	 *		Default is determined by MAP_FRAME_AXES setting [WESN].
@@ -6519,24 +6526,24 @@ void gmtlib_explain_options (struct GMT_CTRL *GMT, char *options) {
 
 			gmt_message (GMT, "\t-B Specify both (1) basemap frame settings and (2) axes parameters.\n");
 			gmt_message (GMT, "\t   Frame settings are modified via an optional single invocation of\n");
-			gmt_message (GMT, "\t     -B[<axes>][+b|w][+g<fill>][+i[<val>]][+n][+o<lon>/<lat>][+t<title>]\n");
+			gmt_message (GMT, "\t     -B[<axes>][+b][+g<fill>][+i[<val>]][+n][+o<lon>/<lat>][+t<title>][+w[<pen>]]\n");
 			gmt_message (GMT, "\t   Axes parameters are specified via one or more invocations of\n");
 			gmt_message (GMT, "\t     -B[p|s][x|y|z]<info>\n\n");
 			gmt_message (GMT, "\t   1. Frame settings control which axes to plot, frame fill, title, and type of gridlines:\n");
 			gmt_message (GMT, "\t     <axes> is a combination of W,E,S,N,Z and plots those axes only [Default is WESNZ (all)].\n");
 			gmt_message (GMT, "\t     Use lower case w,e,s,n,z just to draw and tick (but not annotate) those axes,\n");
 			gmt_message (GMT, "\t     and use l,r,b,t,u just to draw (but not annotate and tick) those axes.\n");
-			gmt_message (GMT, "\t     For 3-D plots the Z|z[<corners>][+b] controls the vertical axis.  The <corners> specifies\n");
-			gmt_message (GMT, "\t     at which corner(s) to erect the axis via a combination of 1,2,3,4; 1 means lower left corner,\n");
-			gmt_message (GMT, "\t     2 is lower right, etc., in a counter-clockwise order. [Default automatically selects one axis].\n");
-			gmt_message (GMT, "\t     The +w will enable x-z or y-z gridlines to be plotted (if such gridlines are selected below).\n");
-			gmt_message (GMT, "\t     Alternativelu, +b will also erect a 3-D frame box to outline the 3-D domain [no frame box].\n");
 			gmt_message (GMT, "\t     Append +g<fill> to paint the inside of the map region before further plotting [no fill].\n");
 			gmt_message (GMT, "\t     Append +i<val> to annotate along parallel or meridian <val> [0] when no such axes can be plotted.\n");
 			gmt_message (GMT, "\t     Append +n to have no frame and annotations whatsoever [Default is controlled by WESNZ/wesnz].\n");
 			gmt_message (GMT, "\t     Append +o<plon>/<plat> to draw oblique gridlines about this pole [regular gridlines].\n");
 			gmt_message (GMT, "\t     Note: the +o modifier is ignored unless gridlines are specified via the axes parameters (below).\n");
 			gmt_message (GMT, "\t     Append +t<title> to place a title over the map frame [no title].\n");
+			gmt_message (GMT, "\t     For 3-D plots the Z|z[<corners>] controls the vertical axis.  The <corners> specifies\n");
+			gmt_message (GMT, "\t     at which corner(s) to erect the z-axis via a combination of 1,2,3,4; 1 means lower left corner,\n");
+			gmt_message (GMT, "\t     2 is lower right, etc., in a counter-clockwise order [Default automatically selects one axis].\n");
+			gmt_message (GMT, "\t     The +w draws the outline of the xz and yz planes [no outlines].\n");
+			gmt_message (GMT, "\t     In addition, +b will erect a 3-D frame box to outline the 3-D domain [no frame box].\n");
 			gmt_message (GMT, "\t   2. Axes settings control the annotation, tick, and grid intervals and labels.\n");
 			gmt_message (GMT, "\t     The full axes specification is\n");
 			gmt_message (GMT, "\t       -B[p|s][x|y|z]<intervals>[+a<angle>|n|p][+f][+l|L<label>][+p<prefix>][+s|S<secondary_label>][+u<unit>]\n");
@@ -7663,8 +7670,8 @@ void gmt_syntax (struct GMT_CTRL *GMT, char option) {
 	switch (option) {
 
 		case 'B':	/* Tickmark option */
-			gmt_message (GMT, "\t-B[p|s][x|y|z]<intervals>[+a<angle>|n|p][+l|L<label>][+p<prefix>][+u<unit>] -B[<axes>][+b][+g<fill>][+o<lon>/<lat>][+t<title>] OR\n");
-			gmt_message (GMT, "\t-B[p|s][x|y|z][a|f|g]<tick>[m][l|p] -B[p|s][x|y|z][+l<label>][+p<prefix>][+u<unit>] -B[<axes>][+b][+g<fill>][+o<lon>/<lat>][+t<title>]\n");
+			gmt_message (GMT, "\t-B[p|s][x|y|z]<intervals>[+a<angle>|n|p][+l|L<label>][+p<prefix>][+u<unit>] -B[<axes>][+b][+g<fill>][+o<lon>/<lat>][+t<title>][+w[<pen>]] OR\n");
+			gmt_message (GMT, "\t-B[p|s][x|y|z][a|f|g]<tick>[m][l|p] -B[p|s][x|y|z][+l<label>][+p<prefix>][+u<unit>] -B[<axes>][+b][+g<fill>][+o<lon>/<lat>][+t<title>][+w[<pen>]]\n");
 			break;
 
 		case 'J':	/* Map projection option */
diff --git a/src/gmt_plot.c b/src/gmt_plot.c
index 612d994f69d..3e067ceba47 100644
--- a/src/gmt_plot.c
+++ b/src/gmt_plot.c
@@ -2634,7 +2634,14 @@ GMT_LOCAL bool gmtplot_is_fancy_boundary (struct GMT_CTRL *GMT) {
 GMT_LOCAL void gmtplot_vertical_wall (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL, int quadrant, double *nesw, bool back, unsigned int mode3d) {
 	int plane = (quadrant + 1) % 2;
 	gmt_plane_perspective (GMT, plane, nesw[quadrant % 4]);
-	if (mode3d == GMT_3D_BOX) PSL_plotbox (PSL, nesw[(quadrant+1)%4], GMT->current.proj.zmin, nesw[(quadrant+3)%4], GMT->current.proj.zmax);
+	if (mode3d == GMT_3D_WALL && back) {
+		PSL_setfill (PSL, GMT->session.no_rgb, 1);
+		gmt_setpen (GMT, &GMT->current.map.frame.pen);
+		PSL_plotbox (PSL, nesw[(quadrant+1)%4], GMT->current.proj.zmin, nesw[(quadrant+3)%4], GMT->current.proj.zmax);
+	}
+	if (mode3d == GMT_3D_BOX) {
+		PSL_plotbox (PSL, nesw[(quadrant+1)%4], GMT->current.proj.zmin, nesw[(quadrant+3)%4], GMT->current.proj.zmax);
+	}
 	if (back)
 		gmtplot_z_gridlines (GMT, PSL, GMT->common.R.wesn[ZLO], GMT->common.R.wesn[ZHI], plane, back, mode3d);
 }
diff --git a/src/gmt_project.h b/src/gmt_project.h
index 629647e078a..661fcbfba8d 100644
--- a/src/gmt_project.h
+++ b/src/gmt_project.h
@@ -510,6 +510,7 @@ struct GMT_PLOT_FRAME {		/* Various parameters for plotting of time axis boundar
 	struct GMT_PLOT_AXIS axis[3];	/* One each for x, y, and z */
 	char header[GMT_LEN256];	/* Plot title */
 	struct GMT_FILL fill;		/* Fill for the basemap inside, if paint == true */
+	struct GMT_PEN pen;		/* Pen for the 3-D back wall outlines */
 	bool plotted_header;		/* true if header has been plotted */
 	bool init;			/* true if -B was used at all */
 	bool set;			/* true if -B was used to set any increments */

From 898a1a919e88874e38e2a998be45018f4f23404b Mon Sep 17 00:00:00 2001
From: Paul Wessel <pwessel@hawaii.edu>
Date: Wed, 19 Aug 2020 19:48:54 -1000
Subject: [PATCH 06/25] Add option to paint back walls

---
 doc/rst/source/cookbook/options.rst |  6 ++--
 doc/rst/source/explain_-B_full.rst_ |  7 +++--
 src/gmt_init.c                      | 46 +++++++++++++++++------------
 src/gmt_plot.c                      | 12 ++++----
 src/gmt_project.h                   |  1 +
 5 files changed, 43 insertions(+), 29 deletions(-)

diff --git a/doc/rst/source/cookbook/options.rst b/doc/rst/source/cookbook/options.rst
index f35d17b7d6e..567bbd17586 100644
--- a/doc/rst/source/cookbook/options.rst
+++ b/doc/rst/source/cookbook/options.rst
@@ -287,7 +287,7 @@ tick, and gridline intervals, axes labels, and annotation units.
 
 The Frame settings are specified by
 
--  **-B**\ [*axes*][**+b**][**+g**\ *fill*][**+i**\ [*val*]][**+n**][**+o**\ *lon/lat*][**+t**\ *title*][**+w**\ [*pen*]]
+-  **-B**\ [*axes*][**+b**][**+g**\ *fill*][**+i**\ [*val*]][**+n**][**+o**\ *lon/lat*][**+t**\ *title*][**+w**\ [*pen*]][**+x**\ [*fill*]][**+y**\ [*fill*]]
 
 Here, the optional *axes* dictates which of the axes should be drawn
 and possibly annotated.  By default, all 4 map boundaries (or plot axes)
@@ -302,7 +302,9 @@ plotted at the most suitable map corner.  You can override this by appending
 any combination of corner ids **1234**, where **1** represents the lower left
 corner and the order goes counter-clockwise.  Use **+w** to draw the outlines of
 the x-z and y-z planes. Alternatively, append **+b** to also draw the front lines
-of the 3-D cube defined by **-R**.  You may paint the
+of the 3-D cube defined by **-R**.  By default the back-walls are transparent.
+Use **+x** and **y** to paint them, using the same fill as the x-y plane if no fill
+is appended. You may paint the
 map canvas by appending the **+g**\ *fill* modifier [Default is no fill].
 Use **+i** to annotate an internal meridian or parallel when the axis that normally
 would be drawn and annotated does not exist (e.g., azimuthal map with 360-degree range
diff --git a/doc/rst/source/explain_-B_full.rst_ b/doc/rst/source/explain_-B_full.rst_
index c4fe01292d5..64d15c577d4 100644
--- a/doc/rst/source/explain_-B_full.rst_
+++ b/doc/rst/source/explain_-B_full.rst_
@@ -3,7 +3,7 @@
 **-B**\ [**p**\|\ **s**]\ *parameters*
     Set map Frame and Axes parameters. The Frame parameters are specified by
 
-    **-B**\ [*axes*][**+b**][**+g**\ *fill*][**+i**\ [*val*]][**+n**][**+o**\ *lon/lat*][**+t**\ *title*][**+w**\ [*pen*]]
+    **-B**\ [*axes*][**+b**][**+g**\ *fill*][**+i**\ [*val*]][**+n**][**+o**\ *lon/lat*][**+t**\ *title*][**+w**\ [*pen*]][**+x**\ [*fill*]][**+y**\ [*fill*]]
 
     where *axes* selects which axes to plot. By default, all 4 map boundaries
     (or plot axes) are plotted (named **W**, **E**, **S**, **N**). To customize,
@@ -17,8 +17,9 @@
     any combination of corner ids **1234**, where **1** represents the lower left
     corner and the order goes counter-clockwise.  Use **+w** to draw the outlines of
     the x-z and y-z planes. Alternatively, append **+b** to also draw the front lines
-    of the 3-D cube defined by **-R**. Note that for 3-D views the title, if given, will be
-    suppressed. You can paint the interior of the canvas with **+g**\ *fill*.
+    of the 3-D cube defined by **-R**. By default the back-walls are transparent.
+    Use **+x** and **y** to paint them, using the same fill as the x-y plane if no fill
+    is appended. You can paint the interior of the canvas with **+g**\ *fill*.
     Use **+i** to annotate an internal meridian or parallel when the axis that normally
     would be drawn and annotated does not exist (e.g., azimuthal map with 360-degree range
     has no latitude axis, and a global Hammer map has no longitude axis); optionally append the parallel or meridian [0].
diff --git a/src/gmt_init.c b/src/gmt_init.c
index 2efacf88b09..1d64a46cf33 100644
--- a/src/gmt_init.c
+++ b/src/gmt_init.c
@@ -3948,14 +3948,14 @@ GMT_LOCAL int gmtinit_decode5_wesnz (struct GMT_CTRL *GMT, const char *in, bool
 			/* Draw 3-D box */
 			case '+':
 				if (in[k+1] == 'b')	/* Got +b appended to MAP_FRAME_AXES, possibly */
-					GMT->current.map.frame.draw_box = GMT_3D_BOX;
+					GMT->current.map.frame.draw_box |= GMT_3D_BOX;
 				else if (in[k+1] == 'w')	/* Got +w appended to MAP_FRAME_AXES, possibly */
-					GMT->current.map.frame.draw_box = GMT_3D_WALL;
+					GMT->current.map.frame.draw_box |= GMT_3D_WALL;
 				else if (in[k+1] == 'n')	/* Got +n appended to MAP_FRAME_AXES, means no frame nor annotations desired */
 					GMT->current.map.frame.no_frame = true;
 				else if (gmt_M_compat_check (GMT, 4)) {
 					GMT_Report (GMT->parent, GMT_MSG_COMPAT, "Modifier + in MAP_FRAME_AXES is deprecated; use +b instead.\n");
-					GMT->current.map.frame.draw_box = GMT_3D_BOX;
+					GMT->current.map.frame.draw_box |= GMT_3D_BOX;
 				}
 				else {
 					GMT_Report (GMT->parent, GMT_MSG_ERROR, "Modifier + in MAP_FRAME_AXES not recognized.\n");
@@ -3984,12 +3984,14 @@ GMT_LOCAL int gmtinit_decode5_wesnz (struct GMT_CTRL *GMT, const char *in, bool
 bool gmtlib_B_is_frame (struct GMT_CTRL *GMT, char *in) {
 	gmt_M_unused (GMT);
 	if (strstr (in, "+b")) return true;	/* Found a +b so likely frame */
-	if (strstr (in, "+w")) return true;	/* Found a +w so likely frame */
 	if (strstr (in, "+g")) return true;	/* Found a +g so likely frame */
 	if (strstr (in, "+i")) return true;	/* Found a +i so likely frame */
 	if (strstr (in, "+n")) return true;	/* Found a +n so likely frame */
 	if (strstr (in, "+o")) return true;	/* Found a +o so likely frame */
 	if (strstr (in, "+t")) return true;	/* Found a +t so likely frame */
+	if (strstr (in, "+w")) return true;	/* Found a +w so likely frame */
+	if (strstr (in, "+s")) return true;	/* Found a +s so likely frame */
+	if (strstr (in, "+y")) return true;	/* Found a +y so likely frame */
 	if (strstr (in, "+a")) return false;	/* Found a +a so likely axis */
 	if (strstr (in, "+f")) return false;	/* Found a +f so likely axis */
 	if (strstr (in, "+l")) return false;	/* Found a +l so likely axis */
@@ -4011,7 +4013,7 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 	char p[GMT_BUFSIZ] = {""}, text[GMT_BUFSIZ] = {""}, *mod = NULL;
 	double pole[2];
 
-	/* Parsing of -B<framesettings>: -B[<axes>][+b][+g<fill>][+n][+o<lon>/<lat>][+t<title>][+w[<pen>]] */
+	/* Parsing of -B<framesettings>: -B[<axes>][+b][+g<fill>][+n][+o<lon>/<lat>][+t<title>][+w[<pen>]][+x[<fill>]][+y[<fill>]] */
 
 	/* First determine that the given -B<in> string is indeed the framesetting option.  If not return -1 */
 
@@ -4025,21 +4027,13 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 	gmt_handle5_plussign (GMT, text, "bginotwxy", 0);	/* Temporarily change double plus-signs to double ASCII 1 to avoid +<modifier> angst */
 	GMT->current.map.frame.header[0] = '\0';
 	gmt_M_memset (GMT->current.map.frame.paint, 3U, bool);
+	GMT->current.map.frame.draw_box = GMT_3D_NONE;
 
 	if ((mod = strchr (text, '+'))) {	/* Find start of modifiers, if any */
 		while ((gmt_strtok (mod, "+", &pos, p))) {	/* Parse any +<modifier> statements */
 			switch (p[0]) {
 				case 'b':	/* Activate 3-D box and x-z, y-z gridlines (if selected) */
-					GMT->current.map.frame.draw_box = GMT_3D_BOX;
-					break;
-				case 'w':	/* Activate x-z, y-z gridlines and wall (if selected) */
-					GMT->current.map.frame.draw_box = GMT_3D_WALL;
-					if (p[1] && gmt_getpen (GMT, &p[1], &GMT->current.map.frame.pen)) {
-						GMT_Report (GMT->parent, GMT_MSG_ERROR, "Bad +w<pen> argument %s\n", &p[1]);
-						error++;
-					}
-					else if (p[1] == 0)	/* Use grid pen as default */
-						gmt_M_memcpy (&GMT->current.map.frame.pen, &GMT->current.setting.map_grid_pen[GMT_PRIMARY], 1, struct GMT_PEN);
+					GMT->current.map.frame.draw_box |= GMT_3D_BOX;
 					break;
 				case 'g':	/* Paint the basemap interior */
 					if (p[1] == 0 || gmt_getfill (GMT, &p[1], &GMT->current.map.frame.fill[GMT_Z])) {
@@ -4096,6 +4090,16 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 						gmtlib_enforce_rgb_triplets (GMT, GMT->current.map.frame.header, GMT_LEN256);	/* If @; is used, make sure the color information passed on to ps_text is in r/b/g format */
 					}
 					break;
+				case 'w':	/* Activate x-z, y-z gridlines and wall (if selected) */
+					GMT->current.map.frame.draw_box |= GMT_3D_WALL;
+					GMT->current.map.frame.draw_wall = true;
+					if (p[1] && gmt_getpen (GMT, &p[1], &GMT->current.map.frame.pen)) {
+						GMT_Report (GMT->parent, GMT_MSG_ERROR, "Bad +w<pen> argument %s\n", &p[1]);
+						error++;
+					}
+					else if (p[1] == 0)	/* Use grid pen as default */
+						gmt_M_memcpy (&GMT->current.map.frame.pen, &GMT->current.setting.map_grid_pen[GMT_PRIMARY], 1, struct GMT_PEN);
+					break;
 				case 'x':	/* Paint the basemap xz-plane for 3-D plots */
 					if (p[1] && gmt_getfill (GMT, &p[1], &GMT->current.map.frame.fill[GMT_X])) {
 						GMT_Report (GMT->parent, GMT_MSG_ERROR, "Bad +x<fill> argument %s\n", &p[1]);
@@ -4103,6 +4107,7 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 					}
 					blank[GMT_X] = !p[1];
 					GMT->current.map.frame.paint[GMT_X] = true;
+					GMT->current.map.frame.draw_box |= GMT_3D_WALL;
 					break;
 				case 'y':	/* Paint the basemap yz-plane for 3-D plots */
 					if (p[1] && gmt_getfill (GMT, &p[1], &GMT->current.map.frame.fill[GMT_Y])) {
@@ -4111,6 +4116,7 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 					}
 					blank[GMT_Y] = !p[1];
 					GMT->current.map.frame.paint[GMT_Y] = true;
+					GMT->current.map.frame.draw_box |= GMT_3D_WALL;
 					break;
 				default:
 					GMT_Report (GMT->parent, GMT_MSG_ERROR, "Option -B: Unrecognized frame modifier %s\n", p);
@@ -4163,12 +4169,13 @@ void gmt_init_B (struct GMT_CTRL *GMT) {
 GMT_LOCAL int gmtinit_parse5_B_option (struct GMT_CTRL *GMT, char *in) {
 	/* GMT5 clean version based on new syntax:
 	 * Frame settings:
-	 *	-B[WESNwesnz|Z[1234]][+b][+g<fill>][+o<lon/lat>][+t<title>][+w[<pen>]]
+	 *	-B[WESNwesnz|Z[1234]][+b][+g<fill>][+o<lon/lat>][+t<title>][+w[<pen>]][+x[<fill>]][+y[<fill>]]
 	 *    		+b draws 3-D box.
 	 *    		+g<fill> as plot interior fill [none].
 	 *    		+t<title> as plot title [none].
 	 *    		+w[<pen>] draws the outline of the xz and yz planes [no outline].
 	 *    		of one or more of w,e,s,n,z then only those axes will be drawn.
+	 *    		+x and +y paints the back walls for xz and yz [with +g fill if not specified].
 	 *		Upper case letters means the chosen axes also will be annotated.
 	 *		Default is determined by MAP_FRAME_AXES setting [WESN].
 	 * Axis settings:
@@ -4211,7 +4218,7 @@ GMT_LOCAL int gmtinit_parse5_B_option (struct GMT_CTRL *GMT, char *in) {
 	if ((error = gmtinit_parse5_B_frame_setting (GMT, in)) >= 0) return (error);	/* Parsed the -B frame settings separately */
 	error = 0;	/* Reset since otherwise it is -1 */
 
-	if (strstr (in, "+b") || strstr (in, "+g") || strstr (in, "+i") || strstr (in, "+n") || strstr (in, "+o") || strstr (in, "+o") || strstr (in, "+t") || strstr (in, "+w")) {
+	if (strstr (in, "+b") || strstr (in, "+g") || strstr (in, "+i") || strstr (in, "+n") || strstr (in, "+o") || strstr (in, "+o") || strstr (in, "+t") || strstr (in, "+w") || strstr (in, "+x") || strstr (in, "+y")) {
 		GMT_Report (GMT->parent, GMT_MSG_ERROR, "Option -B: Found frame setting modifiers (+b|g|i|n|o|p|W) mixed with axes settings!\n");
 		return (GMT_PARSE_ERROR);
 	}
@@ -6579,6 +6586,7 @@ void gmtlib_explain_options (struct GMT_CTRL *GMT, char *options) {
 			gmt_message (GMT, "\t     at which corner(s) to erect the z-axis via a combination of 1,2,3,4; 1 means lower left corner,\n");
 			gmt_message (GMT, "\t     2 is lower right, etc., in a counter-clockwise order [Default automatically selects one axis].\n");
 			gmt_message (GMT, "\t     The +w draws the outline of the xz and yz planes [no outlines].\n");
+			gmt_message (GMT, "\t     The +x|y[<fill>] paint the xz and yz plane [no fill]. The +g<fill> is used if no fill is appended.\n");
 			gmt_message (GMT, "\t     In addition, +b will erect a 3-D frame box to outline the 3-D domain [no frame box].\n");
 			gmt_message (GMT, "\t   2. Axes settings control the annotation, tick, and grid intervals and labels.\n");
 			gmt_message (GMT, "\t     The full axes specification is\n");
@@ -7706,8 +7714,8 @@ void gmt_syntax (struct GMT_CTRL *GMT, char option) {
 	switch (option) {
 
 		case 'B':	/* Tickmark option */
-			gmt_message (GMT, "\t-B[p|s][x|y|z]<intervals>[+a<angle>|n|p][+l|L<label>][+p<prefix>][+u<unit>] -B[<axes>][+b][+g<fill>][+o<lon>/<lat>][+t<title>][+w[<pen>]] OR\n");
-			gmt_message (GMT, "\t-B[p|s][x|y|z][a|f|g]<tick>[m][l|p] -B[p|s][x|y|z][+l<label>][+p<prefix>][+u<unit>] -B[<axes>][+b][+g<fill>][+o<lon>/<lat>][+t<title>][+w[<pen>]]\n");
+			gmt_message (GMT, "\t-B[p|s][x|y|z]<intervals>[+a<angle>|n|p][+l|L<label>][+p<prefix>][+u<unit>] -B[<axes>][+b][+g<fill>][+o<lon>/<lat>][+t<title>][+w[<pen>]][+x[<fill>]][+y[<fill>]] OR\n");
+			gmt_message (GMT, "\t-B[p|s][x|y|z][a|f|g]<tick>[m][l|p] -B[p|s][x|y|z][+l<label>][+p<prefix>][+u<unit>] -B[<axes>][+b][+g<fill>][+o<lon>/<lat>][+t<title>][+w[<pen>]][+x[<fill>]][+y[<fill>]]\n");
 			break;
 
 		case 'J':	/* Map projection option */
diff --git a/src/gmt_plot.c b/src/gmt_plot.c
index 02f13ad0950..2f3d02723d8 100644
--- a/src/gmt_plot.c
+++ b/src/gmt_plot.c
@@ -1583,7 +1583,7 @@ GMT_LOCAL void gmtplot_z_gridlines (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL,
 
 		PSL_setdash (PSL, NULL, 0);
 	}
-	if (back && mode3d != GMT_3D_BOX) {
+	if (back && z && (mode3d & GMT_3D_BOX) == 0) {
 		double z0 = gmt_z_to_zz (GMT, z[0]);
 		double z1 = gmt_z_to_zz (GMT, z[nz-1]);
 		PSL_plotsegment (PSL, min, z0, min, z1);
@@ -2633,12 +2633,14 @@ GMT_LOCAL bool gmtplot_is_fancy_boundary (struct GMT_CTRL *GMT) {
 GMT_LOCAL void gmtplot_vertical_wall (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL, int quadrant, double *nesw, bool back, unsigned int mode3d) {
 	int plane = (quadrant + 1) % 2;
 	gmt_plane_perspective (GMT, plane, nesw[quadrant % 4]);
-	if (mode3d == GMT_3D_WALL && back) {
-		PSL_setfill (PSL, GMT->session.no_rgb, 1);
-		gmt_setpen (GMT, &GMT->current.map.frame.pen);
+	if (mode3d & GMT_3D_WALL && back) {
+		int wplane = 1 - plane;
+		double *rgb = (GMT->current.map.frame.paint[wplane]) ? GMT->current.map.frame.fill[wplane].rgb : GMT->session.no_rgb;
+		PSL_setfill (PSL, rgb, GMT->current.map.frame.draw_wall);
+		if (GMT->current.map.frame.draw_wall) gmt_setpen (GMT, &GMT->current.map.frame.pen);
 		PSL_plotbox (PSL, nesw[(quadrant+1)%4], GMT->current.proj.zmin, nesw[(quadrant+3)%4], GMT->current.proj.zmax);
 	}
-	if (mode3d == GMT_3D_BOX) {
+	if (mode3d & GMT_3D_BOX) {
 		PSL_plotbox (PSL, nesw[(quadrant+1)%4], GMT->current.proj.zmin, nesw[(quadrant+3)%4], GMT->current.proj.zmax);
 	}
 	if (back)
diff --git a/src/gmt_project.h b/src/gmt_project.h
index c3c836f17c8..2a4c4ad4a84 100644
--- a/src/gmt_project.h
+++ b/src/gmt_project.h
@@ -522,6 +522,7 @@ struct GMT_PLOT_FRAME {		/* Various parameters for plotting of time axis boundar
 	bool primary;			/* true if current axis is primary, false if secondary */
 	bool set_both;			/* true if -B argument applies to both x and y axes */
 	bool obl_grid;			/* true if +o was given to draw oblique gridlines */
+	bool draw_wall;			/* true if +w was given to draw backwall outline */
 	unsigned int draw_box;			/* 0 = no 3-D frame. 1 if 3-D Z-box is desired [default], 2 if no -Z box lines covering up the plot */
 	unsigned int internal_annot;	/* 1 (longitude) or 2 (latitude or radius) if +i was given to draw internal annotations */
 	unsigned int set_frame[2];	/* 1 if a -B<WESNframe> setting was given */

From 5350aed6f8e20100615afc33bfa1baf2913cccad Mon Sep 17 00:00:00 2001
From: Paul Wessel <pwessel@hawaii.edu>
Date: Wed, 19 Aug 2020 20:02:05 -1000
Subject: [PATCH 07/25] Clean up code

---
 src/gmt_init.c | 12 ++++++------
 src/gmt_plot.c |  6 +++---
 2 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/src/gmt_init.c b/src/gmt_init.c
index 1d64a46cf33..c68169c60d6 100644
--- a/src/gmt_init.c
+++ b/src/gmt_init.c
@@ -4090,9 +4090,9 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 						gmtlib_enforce_rgb_triplets (GMT, GMT->current.map.frame.header, GMT_LEN256);	/* If @; is used, make sure the color information passed on to ps_text is in r/b/g format */
 					}
 					break;
-				case 'w':	/* Activate x-z, y-z gridlines and wall (if selected) */
+				case 'w':	/* Set back-wall outline and optionally the pen to use */
 					GMT->current.map.frame.draw_box |= GMT_3D_WALL;
-					GMT->current.map.frame.draw_wall = true;
+					GMT->current.map.frame.draw_wall = true;	/* We will draw the outline of the walls */
 					if (p[1] && gmt_getpen (GMT, &p[1], &GMT->current.map.frame.pen)) {
 						GMT_Report (GMT->parent, GMT_MSG_ERROR, "Bad +w<pen> argument %s\n", &p[1]);
 						error++;
@@ -4127,19 +4127,19 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 		*mod = '\0';	/* Separate the modifiers from the frame selectors */
 	}
 
-	if (GMT->current.map.frame.paint[GMT_X] && blank[GMT_X]) {	/* Just +x means same as z-fill */
+	if (GMT->current.map.frame.paint[GMT_X] && blank[GMT_X]) {	/* Just +x means use the +g-fill */
 		if (GMT->current.map.frame.paint[GMT_Z])
 			gmt_M_memcpy (&GMT->current.map.frame.fill[GMT_X], &GMT->current.map.frame.fill[GMT_Z], 1U, struct GMT_FILL);
 		else {
-			GMT_Report (GMT->parent, GMT_MSG_ERROR, "Option -B: Modifier +x requires a fill argument if +g not set\n");
+			GMT_Report (GMT->parent, GMT_MSG_ERROR, "Option -B: Modifier +x requires a fill argument if +g was not set\n");
 			error++;
 		}
 	}
-	if (GMT->current.map.frame.paint[GMT_Y] && blank[GMT_Y]) {	/* Just +x means same as z-fill */
+	if (GMT->current.map.frame.paint[GMT_Y] && blank[GMT_Y]) {	/* Just +x means use the +g-fill */
 		if (GMT->current.map.frame.paint[GMT_Z])
 			gmt_M_memcpy (&GMT->current.map.frame.fill[GMT_Y], &GMT->current.map.frame.fill[GMT_Z], 1U, struct GMT_FILL);
 		else {
-			GMT_Report (GMT->parent, GMT_MSG_ERROR, "Option -B: Modifier +y requires a fill argument if +g not set\n");
+			GMT_Report (GMT->parent, GMT_MSG_ERROR, "Option -B: Modifier +y requires a fill argument if +g was not set\n");
 			error++;
 		}
 	}
diff --git a/src/gmt_plot.c b/src/gmt_plot.c
index 2f3d02723d8..357bfed7f26 100644
--- a/src/gmt_plot.c
+++ b/src/gmt_plot.c
@@ -1556,7 +1556,7 @@ GMT_LOCAL void gmtplot_map_symbol_ns (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL
 	if (nc) gmt_M_free (GMT, xings);
 }
 
-GMT_LOCAL void gmtplot_z_gridlines (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL, double zmin, double zmax, int plane, bool back, unsigned int mode3d) {
+GMT_LOCAL void gmtplot_z_gridlines (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL, double zmin, double zmax, int plane, unsigned int mode3d) {
 	unsigned int k, i, nz, item[2] = {GMT_GRID_UPPER, GMT_GRID_LOWER};
 	double dz, zz, min, max, *z = NULL;
 	char *plane_name[2] = {"y-z", "x-z"};
@@ -1583,7 +1583,7 @@ GMT_LOCAL void gmtplot_z_gridlines (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL,
 
 		PSL_setdash (PSL, NULL, 0);
 	}
-	if (back && z && (mode3d & GMT_3D_BOX) == 0) {
+	if (z && (mode3d & GMT_3D_BOX) == 0) {
 		double z0 = gmt_z_to_zz (GMT, z[0]);
 		double z1 = gmt_z_to_zz (GMT, z[nz-1]);
 		PSL_plotsegment (PSL, min, z0, min, z1);
@@ -2644,7 +2644,7 @@ GMT_LOCAL void gmtplot_vertical_wall (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL
 		PSL_plotbox (PSL, nesw[(quadrant+1)%4], GMT->current.proj.zmin, nesw[(quadrant+3)%4], GMT->current.proj.zmax);
 	}
 	if (back)
-		gmtplot_z_gridlines (GMT, PSL, GMT->common.R.wesn[ZLO], GMT->common.R.wesn[ZHI], plane, back, mode3d);
+		gmtplot_z_gridlines (GMT, PSL, GMT->common.R.wesn[ZLO], GMT->common.R.wesn[ZHI], plane, mode3d);
 }
 
 GMT_LOCAL void gmtplot_timestamp (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL, double x, double y, unsigned int justify, char *U_label) {

From fa7dbdd4d5ea121bb4a40e5d89307b7d38ba0ad6 Mon Sep 17 00:00:00 2001
From: Paul Wessel <pwessel@hawaii.edu>
Date: Wed, 19 Aug 2020 20:11:50 -1000
Subject: [PATCH 08/25] Ensure 3-D title on top

---
 src/gmt_plot.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/gmt_plot.c b/src/gmt_plot.c
index 357bfed7f26..d7babebddaf 100644
--- a/src/gmt_plot.c
+++ b/src/gmt_plot.c
@@ -5480,7 +5480,7 @@ void gmt_map_basemap (struct GMT_CTRL *GMT) {
 
 	PSL_setdash (PSL, NULL, 0);	/* To ensure no dashed pens are set prior */
 
-	gmt_vertical_axis (GMT, GMT->current.plot.mode_3D);
+	if (GMT->current.proj.three_D && GMT->current.map.frame.drawz) GMT->current.map.frame.plotted_header = true;	/* Just so it is not plotted by gmtplot_map_boundary first */
 
 	if (GMT->current.proj.got_azimuths) gmt_M_uint_swap (GMT->current.map.frame.side[E_SIDE], GMT->current.map.frame.side[W_SIDE]);	/* Temporary swap to trick justify machinery */
 
@@ -5505,6 +5505,10 @@ void gmt_map_basemap (struct GMT_CTRL *GMT) {
 
 	PSL_setdash (PSL, NULL, 0);
 
+	if (GMT->current.proj.three_D && GMT->current.map.frame.drawz) GMT->current.map.frame.plotted_header = false;	/* Now we can plot the title [if selected via -B+t] */
+
+	gmt_vertical_axis (GMT, GMT->current.plot.mode_3D);
+
 	PSL_comment (PSL, "End of basemap\n");
 
 	for (side = 0; side < 4; side++) {	/* Reset annotation crowdedness arrays */

From 20d57fad51b821b60b82373a614140738f2f3d9b Mon Sep 17 00:00:00 2001
From: Paul Wessel <pwessel@hawaii.edu>
Date: Wed, 19 Aug 2020 22:55:11 -1000
Subject: [PATCH 09/25] Finalize xz and yz gridlines

---
 doc/rst/source/cookbook/options.rst |  6 +++--
 doc/rst/source/explain_-B_full.rst_ |  6 ++---
 src/gmt_plot.c                      | 38 +++++++++++++++++++++++------
 3 files changed, 37 insertions(+), 13 deletions(-)

diff --git a/doc/rst/source/cookbook/options.rst b/doc/rst/source/cookbook/options.rst
index 567bbd17586..562cc813614 100644
--- a/doc/rst/source/cookbook/options.rst
+++ b/doc/rst/source/cookbook/options.rst
@@ -290,14 +290,16 @@ The Frame settings are specified by
 -  **-B**\ [*axes*][**+b**][**+g**\ *fill*][**+i**\ [*val*]][**+n**][**+o**\ *lon/lat*][**+t**\ *title*][**+w**\ [*pen*]][**+x**\ [*fill*]][**+y**\ [*fill*]]
 
 Here, the optional *axes* dictates which of the axes should be drawn
-and possibly annotated.  By default, all 4 map boundaries (or plot axes)
+and possibly annotated.  By default, all four map boundaries (or plot axes)
 are plotted (denoted **W**, **E**, **S**, **N**). To change this selection,
 append the codes for those you want (e.g., **WSn**). In this example,
 the lower case **n** denotes to draw the axis and (major and minor) tick
 marks on the "northern" (top) edge of the plot. The upper case **WS** will
 annotate the "western" and "southern" axes with numerals and plot the
 any axis labels in addition to draw axis/tick-marks.  For 3-D plots you can
-also specify **Z** or **z**.  By default a single vertical axes will then be
+also specify **Z** or **z**.  To *just* draw an axis without annotation and
+ticks you can use the **l**\ (eft), **r**\ (ight), **b**\ (ottom), **t**\ (op)
+and (for 3-D) **u**\ (p) codes. By default, a single vertical axes will then be
 plotted at the most suitable map corner.  You can override this by appending
 any combination of corner ids **1234**, where **1** represents the lower left
 corner and the order goes counter-clockwise.  Use **+w** to draw the outlines of
diff --git a/doc/rst/source/explain_-B_full.rst_ b/doc/rst/source/explain_-B_full.rst_
index 64d15c577d4..a4ad61fc83c 100644
--- a/doc/rst/source/explain_-B_full.rst_
+++ b/doc/rst/source/explain_-B_full.rst_
@@ -5,19 +5,19 @@
 
     **-B**\ [*axes*][**+b**][**+g**\ *fill*][**+i**\ [*val*]][**+n**][**+o**\ *lon/lat*][**+t**\ *title*][**+w**\ [*pen*]][**+x**\ [*fill*]][**+y**\ [*fill*]]
 
-    where *axes* selects which axes to plot. By default, all 4 map boundaries
+    where *axes* selects which axes to plot. By default, all four map boundaries
     (or plot axes) are plotted (named **W**, **E**, **S**, **N**). To customize,
     append the codes for those you want (e.g., **WSn**). Upper case means plot
     and annotate while lower case just plots and ticks the specified axes.
     To *just* draw an axis without annotation and ticks you can use the **l**\ (eft),
-    **r**\ (ight), **b**\ (ottom), **t**\ (opt) and (for 3-D) **u**\ (p) codes. If a 3-D basemap
+    **r**\ (ight), **b**\ (ottom), **t**\ (op) and (for 3-D) **u**\ (p) codes. If a 3-D basemap
     is selected with **-p** and **-Jz**, append **Z**, **z**, or **u** to control the
     appearance of the vertical axis. By default a single vertical axes will be
     plotted at the most suitable map corner. Override the default by appending
     any combination of corner ids **1234**, where **1** represents the lower left
     corner and the order goes counter-clockwise.  Use **+w** to draw the outlines of
     the x-z and y-z planes. Alternatively, append **+b** to also draw the front lines
-    of the 3-D cube defined by **-R**. By default the back-walls are transparent.
+    of the 3-D cube defined by **-R**. By default, the back-walls are transparent.
     Use **+x** and **y** to paint them, using the same fill as the x-y plane if no fill
     is appended. You can paint the interior of the canvas with **+g**\ *fill*.
     Use **+i** to annotate an internal meridian or parallel when the axis that normally
diff --git a/src/gmt_plot.c b/src/gmt_plot.c
index d7babebddaf..7e8c68fa32b 100644
--- a/src/gmt_plot.c
+++ b/src/gmt_plot.c
@@ -1556,13 +1556,21 @@ GMT_LOCAL void gmtplot_map_symbol_ns (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL
 	if (nc) gmt_M_free (GMT, xings);
 }
 
-GMT_LOCAL void gmtplot_z_gridlines (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL, double zmin, double zmax, int plane, unsigned int mode3d) {
-	unsigned int k, i, nz, item[2] = {GMT_GRID_UPPER, GMT_GRID_LOWER};
-	double dz, zz, min, max, *z = NULL;
+GMT_LOCAL void gmtplot_z_gridlines (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL, double zmin, double zmax, int plane, unsigned int mode3d, int quadrant) {
+	unsigned int k, i, nz, n, item[2] = {GMT_GRID_UPPER, GMT_GRID_LOWER};
+	int qplane = 1 - plane;
+	double dz, zz, dd, min, max, z0, z1, xx, dummy, value, *z = NULL, *d = NULL;
 	char *plane_name[2] = {"y-z", "x-z"};
 
-	min = (plane == GMT_Y) ? GMT->current.proj.rect[XLO] : GMT->current.proj.rect[YLO];
-	max = (plane == GMT_Y) ? GMT->current.proj.rect[XHI] : GMT->current.proj.rect[YHI];
+	if (qplane == GMT_X) {
+		value = (quadrant == 4) ? GMT->common.R.wesn[YHI] : GMT->common.R.wesn[YLO];
+		min = GMT->current.proj.rect[XLO];	max = GMT->current.proj.rect[XHI];
+	}
+	else {
+		value = (quadrant == 3) ? GMT->common.R.wesn[XHI] : GMT->common.R.wesn[XLO];
+		min = GMT->current.proj.rect[YLO];	max = GMT->current.proj.rect[YHI];
+	}
+
 	for (k = 0; k < 2; k++) {
 		if (fabs (GMT->current.setting.map_grid_cross_size[k]) > 0.0) continue;
 
@@ -1580,12 +1588,26 @@ GMT_LOCAL void gmtplot_z_gridlines (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL,
 			zz = gmt_z_to_zz (GMT, z[i]);
 			PSL_plotsegment (PSL, min, zz, max, zz);
 		}
+		z0 = gmt_z_to_zz (GMT, z[0]);
+		z1 = gmt_z_to_zz (GMT, z[nz-1]);
+
+		dd = gmtlib_get_map_interval (GMT, &GMT->current.map.frame.axis[qplane].item[item[k]]);
+		if (!GMT->current.map.frame.axis[qplane].item[item[k]].active || fabs(dd) == 0.0) continue;
+		n = gmtlib_coordinate_array (GMT, GMT->common.R.wesn[2*qplane], GMT->common.R.wesn[2*qplane+1], &GMT->current.map.frame.axis[qplane].item[item[k]], &d, NULL);
+		for (i = 0; i < n; i++) {	/* Here z acts as y and x|y acts as x */
+			/* Draw one horizontal line */
+			if (qplane == GMT_X)	/* The "x" are projection x or longitude */
+				gmt_geo_to_xy (GMT, d[i], value, &xx, &dummy);
+			else	/* The "x" are projection y or latitude */
+				gmt_geo_to_xy (GMT, value, d[i], &dummy, &xx);
+
+			PSL_plotsegment (PSL, xx, z0, xx, z1);
+		}
+		gmt_M_free (GMT, d);
 
 		PSL_setdash (PSL, NULL, 0);
 	}
 	if (z && (mode3d & GMT_3D_BOX) == 0) {
-		double z0 = gmt_z_to_zz (GMT, z[0]);
-		double z1 = gmt_z_to_zz (GMT, z[nz-1]);
 		PSL_plotsegment (PSL, min, z0, min, z1);
 		PSL_plotsegment (PSL, max, z0, max, z1);
 	}
@@ -2644,7 +2666,7 @@ GMT_LOCAL void gmtplot_vertical_wall (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL
 		PSL_plotbox (PSL, nesw[(quadrant+1)%4], GMT->current.proj.zmin, nesw[(quadrant+3)%4], GMT->current.proj.zmax);
 	}
 	if (back)
-		gmtplot_z_gridlines (GMT, PSL, GMT->common.R.wesn[ZLO], GMT->common.R.wesn[ZHI], plane, mode3d);
+		gmtplot_z_gridlines (GMT, PSL, GMT->common.R.wesn[ZLO], GMT->common.R.wesn[ZHI], plane, mode3d, quadrant);
 }
 
 GMT_LOCAL void gmtplot_timestamp (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL, double x, double y, unsigned int justify, char *U_label) {

From 3bbd139c97b4698372cfddc6bc326b683c8d139e Mon Sep 17 00:00:00 2001
From: Paul Wessel <pwessel@hawaii.edu>
Date: Wed, 19 Aug 2020 23:04:48 -1000
Subject: [PATCH 10/25] Fix docs

---
 doc/rst/source/cookbook/options.rst |  8 ++++----
 doc/rst/source/explain_-B_full.rst_ | 13 +++++++------
 src/gmt_init.c                      | 10 +++++-----
 3 files changed, 16 insertions(+), 15 deletions(-)

diff --git a/doc/rst/source/cookbook/options.rst b/doc/rst/source/cookbook/options.rst
index 562cc813614..929b4fc9ac6 100644
--- a/doc/rst/source/cookbook/options.rst
+++ b/doc/rst/source/cookbook/options.rst
@@ -303,11 +303,11 @@ and (for 3-D) **u**\ (p) codes. By default, a single vertical axes will then be
 plotted at the most suitable map corner.  You can override this by appending
 any combination of corner ids **1234**, where **1** represents the lower left
 corner and the order goes counter-clockwise.  Use **+w** to draw the outlines of
-the x-z and y-z planes. Alternatively, append **+b** to also draw the front lines
+the x-z and y-z planes [no outlines] and optionally append the *pen* to use
+[:term:`MAP_GRID_PEN_PRIMARY]. Alternatively, append **+b** to also draw the front lines
 of the 3-D cube defined by **-R**.  By default the back-walls are transparent.
-Use **+x** and **y** to paint them, using the same fill as the x-y plane if no fill
-is appended. You may paint the
-map canvas by appending the **+g**\ *fill* modifier [Default is no fill].
+Use **+x** and **+y** to paint them, using the same fill as the x-y plane if no fill
+is appended. You may paint the map canvas by appending the **+g**\ *fill* modifier [Default is no fill].
 Use **+i** to annotate an internal meridian or parallel when the axis that normally
 would be drawn and annotated does not exist (e.g., azimuthal map with 360-degree range
 has no latitude axis, and a global Hammer map has no longitude axis);
diff --git a/doc/rst/source/explain_-B_full.rst_ b/doc/rst/source/explain_-B_full.rst_
index a4ad61fc83c..ae0e4f3ed43 100644
--- a/doc/rst/source/explain_-B_full.rst_
+++ b/doc/rst/source/explain_-B_full.rst_
@@ -10,15 +10,16 @@
     append the codes for those you want (e.g., **WSn**). Upper case means plot
     and annotate while lower case just plots and ticks the specified axes.
     To *just* draw an axis without annotation and ticks you can use the **l**\ (eft),
-    **r**\ (ight), **b**\ (ottom), **t**\ (op) and (for 3-D) **u**\ (p) codes. If a 3-D basemap
-    is selected with **-p** and **-Jz**, append **Z**, **z**, or **u** to control the
-    appearance of the vertical axis. By default a single vertical axes will be
-    plotted at the most suitable map corner. Override the default by appending
+    **r**\ (ight), **b**\ (ottom), **t**\ (op) and (for 3-D) **u**\ (p) codes.
+    If a 3-D basemap is selected with **-p** and **-Jz**, append **Z**, **z**, or
+    **u** to control the appearance of the vertical axis. By default a single vertical
+    axes will be plotted at the most suitable map corner. Override the default by appending
     any combination of corner ids **1234**, where **1** represents the lower left
     corner and the order goes counter-clockwise.  Use **+w** to draw the outlines of
-    the x-z and y-z planes. Alternatively, append **+b** to also draw the front lines
+    the x-z and y-z planes [no outline] and optionally append the *pen* to use
+    [:term:`MAP_GRID_PEN_PRIMARY]. Alternatively, append **+b** to also draw the front lines
     of the 3-D cube defined by **-R**. By default, the back-walls are transparent.
-    Use **+x** and **y** to paint them, using the same fill as the x-y plane if no fill
+    Use **+x** and **+y** to paint them, using the same fill as the x-y plane if no fill
     is appended. You can paint the interior of the canvas with **+g**\ *fill*.
     Use **+i** to annotate an internal meridian or parallel when the axis that normally
     would be drawn and annotated does not exist (e.g., azimuthal map with 360-degree range
diff --git a/src/gmt_init.c b/src/gmt_init.c
index c68169c60d6..205b459d925 100644
--- a/src/gmt_init.c
+++ b/src/gmt_init.c
@@ -4032,17 +4032,17 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 	if ((mod = strchr (text, '+'))) {	/* Find start of modifiers, if any */
 		while ((gmt_strtok (mod, "+", &pos, p))) {	/* Parse any +<modifier> statements */
 			switch (p[0]) {
-				case 'b':	/* Activate 3-D box and x-z, y-z gridlines (if selected) */
+				case 'b':	/* Draw 3-D box */
 					GMT->current.map.frame.draw_box |= GMT_3D_BOX;
 					break;
-				case 'g':	/* Paint the basemap interior */
+				case 'g':	/* Paint the basemap x-y plane */
 					if (p[1] == 0 || gmt_getfill (GMT, &p[1], &GMT->current.map.frame.fill[GMT_Z])) {
 						GMT_Report (GMT->parent, GMT_MSG_ERROR, "Bad +g<fill> argument %s\n", &p[1]);
 						error++;
 					}
 					GMT->current.map.frame.paint[GMT_Z] = true;
 					break;
-				case 'i':	/* Turn on internal annotation for radiual or longitudinal axes when there is no other place to annotate */
+				case 'i':	/* Turn on internal annotation for radial or longitudinal axes when there is no outside place to annotate */
 					GMT->current.map.frame.internal_annot = 1;	/* Longitude/angle */
 					if (GMT->current.proj.projection == GMT_POLAR)	/* Optional argument is an angle, not longitude, so atof will do */
 						GMT->current.map.frame.internal_arg = (p[1]) ? atof (&p[1]) : GMT->common.R.wesn[XLO];
@@ -4127,7 +4127,7 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 		*mod = '\0';	/* Separate the modifiers from the frame selectors */
 	}
 
-	if (GMT->current.map.frame.paint[GMT_X] && blank[GMT_X]) {	/* Just +x means use the +g-fill */
+	if (GMT->current.map.frame.paint[GMT_X] && blank[GMT_X]) {	/* Just +x means use the +g-fill (which must exist) */
 		if (GMT->current.map.frame.paint[GMT_Z])
 			gmt_M_memcpy (&GMT->current.map.frame.fill[GMT_X], &GMT->current.map.frame.fill[GMT_Z], 1U, struct GMT_FILL);
 		else {
@@ -4135,7 +4135,7 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 			error++;
 		}
 	}
-	if (GMT->current.map.frame.paint[GMT_Y] && blank[GMT_Y]) {	/* Just +x means use the +g-fill */
+	if (GMT->current.map.frame.paint[GMT_Y] && blank[GMT_Y]) {	/* Just +x means use the +g-fill (which must exist) */
 		if (GMT->current.map.frame.paint[GMT_Z])
 			gmt_M_memcpy (&GMT->current.map.frame.fill[GMT_Y], &GMT->current.map.frame.fill[GMT_Z], 1U, struct GMT_FILL);
 		else {

From cbbcf389ae2c17942c637cfbee039acf4f4228ff Mon Sep 17 00:00:00 2001
From: Paul Wessel <pwessel@hawaii.edu>
Date: Wed, 19 Aug 2020 23:50:01 -1000
Subject: [PATCH 11/25] typos

---
 doc/rst/source/cookbook/options.rst | 2 +-
 doc/rst/source/explain_-B_full.rst_ | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/doc/rst/source/cookbook/options.rst b/doc/rst/source/cookbook/options.rst
index 929b4fc9ac6..b548e84868a 100644
--- a/doc/rst/source/cookbook/options.rst
+++ b/doc/rst/source/cookbook/options.rst
@@ -304,7 +304,7 @@ plotted at the most suitable map corner.  You can override this by appending
 any combination of corner ids **1234**, where **1** represents the lower left
 corner and the order goes counter-clockwise.  Use **+w** to draw the outlines of
 the x-z and y-z planes [no outlines] and optionally append the *pen* to use
-[:term:`MAP_GRID_PEN_PRIMARY]. Alternatively, append **+b** to also draw the front lines
+[:term:`MAP_GRID_PEN_PRIMARY`]. Alternatively, append **+b** to also draw the front lines
 of the 3-D cube defined by **-R**.  By default the back-walls are transparent.
 Use **+x** and **+y** to paint them, using the same fill as the x-y plane if no fill
 is appended. You may paint the map canvas by appending the **+g**\ *fill* modifier [Default is no fill].
diff --git a/doc/rst/source/explain_-B_full.rst_ b/doc/rst/source/explain_-B_full.rst_
index ae0e4f3ed43..05746e28412 100644
--- a/doc/rst/source/explain_-B_full.rst_
+++ b/doc/rst/source/explain_-B_full.rst_
@@ -17,7 +17,7 @@
     any combination of corner ids **1234**, where **1** represents the lower left
     corner and the order goes counter-clockwise.  Use **+w** to draw the outlines of
     the x-z and y-z planes [no outline] and optionally append the *pen* to use
-    [:term:`MAP_GRID_PEN_PRIMARY]. Alternatively, append **+b** to also draw the front lines
+    [:term:`MAP_GRID_PEN_PRIMARY`]. Alternatively, append **+b** to also draw the front lines
     of the 3-D cube defined by **-R**. By default, the back-walls are transparent.
     Use **+x** and **+y** to paint them, using the same fill as the x-y plane if no fill
     is appended. You can paint the interior of the canvas with **+g**\ *fill*.

From 58d831264a818c805e0a2a3f3e8b53730a646b6c Mon Sep 17 00:00:00 2001
From: Paul Wessel <pwessel@hawaii.edu>
Date: Thu, 20 Aug 2020 10:01:20 -1000
Subject: [PATCH 12/25] Let wall outline cover up any gridlines in the same
 place

---
 src/gmt_plot.c | 22 +++++++++++++++-------
 1 file changed, 15 insertions(+), 7 deletions(-)

diff --git a/src/gmt_plot.c b/src/gmt_plot.c
index 7e8c68fa32b..71acb19be9d 100644
--- a/src/gmt_plot.c
+++ b/src/gmt_plot.c
@@ -1607,7 +1607,7 @@ GMT_LOCAL void gmtplot_z_gridlines (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL,
 
 		PSL_setdash (PSL, NULL, 0);
 	}
-	if (z && (mode3d & GMT_3D_BOX) == 0) {
+	if (!GMT->current.map.frame.draw_wall && z && (mode3d & GMT_3D_BOX) == 0) {
 		PSL_plotsegment (PSL, min, z0, min, z1);
 		PSL_plotsegment (PSL, max, z0, max, z1);
 	}
@@ -2657,16 +2657,24 @@ GMT_LOCAL void gmtplot_vertical_wall (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL
 	gmt_plane_perspective (GMT, plane, nesw[quadrant % 4]);
 	if (mode3d & GMT_3D_WALL && back) {
 		int wplane = 1 - plane;
-		double *rgb = (GMT->current.map.frame.paint[wplane]) ? GMT->current.map.frame.fill[wplane].rgb : GMT->session.no_rgb;
-		PSL_setfill (PSL, rgb, GMT->current.map.frame.draw_wall);
-		if (GMT->current.map.frame.draw_wall) gmt_setpen (GMT, &GMT->current.map.frame.pen);
-		PSL_plotbox (PSL, nesw[(quadrant+1)%4], GMT->current.proj.zmin, nesw[(quadrant+3)%4], GMT->current.proj.zmax);
+		if (GMT->current.map.frame.paint[wplane]) {	/* First paint the back wall */
+			PSL_setfill (PSL, GMT->current.map.frame.fill[wplane].rgb, 0);
+			PSL_plotbox (PSL, nesw[(quadrant+1)%4], GMT->current.proj.zmin, nesw[(quadrant+3)%4], GMT->current.proj.zmax);
+		}
+		if (back)
+			gmtplot_z_gridlines (GMT, PSL, GMT->common.R.wesn[ZLO], GMT->common.R.wesn[ZHI], plane, mode3d, quadrant);
+
+		if (GMT->current.map.frame.draw_wall) {
+			PSL_setfill (PSL, GMT->session.no_rgb, 1);
+			gmt_setpen (GMT, &GMT->current.map.frame.pen);
+			PSL_plotbox (PSL, nesw[(quadrant+1)%4], GMT->current.proj.zmin, nesw[(quadrant+3)%4], GMT->current.proj.zmax);
+		}
 	}
+	else if (back)
+		gmtplot_z_gridlines (GMT, PSL, GMT->common.R.wesn[ZLO], GMT->common.R.wesn[ZHI], plane, mode3d, quadrant);
 	if (mode3d & GMT_3D_BOX) {
 		PSL_plotbox (PSL, nesw[(quadrant+1)%4], GMT->current.proj.zmin, nesw[(quadrant+3)%4], GMT->current.proj.zmax);
 	}
-	if (back)
-		gmtplot_z_gridlines (GMT, PSL, GMT->common.R.wesn[ZLO], GMT->common.R.wesn[ZHI], plane, mode3d, quadrant);
 }
 
 GMT_LOCAL void gmtplot_timestamp (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL, double x, double y, unsigned int justify, char *U_label) {

From bace2d98165b0e7c95ae898944de94bf78cc9a0b Mon Sep 17 00:00:00 2001
From: Paul Wessel <pwessel@hawaii.edu>
Date: Thu, 20 Aug 2020 10:31:19 -1000
Subject: [PATCH 13/25] Implicitly set +w if z-gridlines selected

---
 src/gmt_plot.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/gmt_plot.c b/src/gmt_plot.c
index 71acb19be9d..aee51c98d46 100644
--- a/src/gmt_plot.c
+++ b/src/gmt_plot.c
@@ -5561,6 +5561,11 @@ void gmt_vertical_axis (struct GMT_CTRL *GMT, unsigned int mode) {
 	if (!GMT->current.proj.three_D) return;
 	if (!GMT->current.map.frame.drawz) return;
 
+	if (GMT->current.map.frame.axis[GMT_Z].item[GMT_GRID_UPPER].active || GMT->current.map.frame.axis[GMT_Z].item[GMT_GRID_LOWER].active) {
+		GMT->current.map.frame.draw_box |= GMT_3D_WALL;
+		GMT->current.map.frame.draw_wall = true;
+	}
+
 	nesw[0] = GMT->current.proj.rect[YHI], nesw[1] = GMT->current.proj.rect[XHI], nesw[2] = GMT->current.proj.rect[YLO], nesw[3] = GMT->current.proj.rect[XLO];
 
 	fore = mode & 2, back = mode & 1;

From 7b6b80b1e9837589441d250084100b3da658e548 Mon Sep 17 00:00:00 2001
From: Paul Wessel <pwessel@hawaii.edu>
Date: Thu, 20 Aug 2020 11:05:09 -1000
Subject: [PATCH 14/25] Draw portal, not box for backwall outlines

---
 src/gmt_plot.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/src/gmt_plot.c b/src/gmt_plot.c
index aee51c98d46..11fba544bed 100644
--- a/src/gmt_plot.c
+++ b/src/gmt_plot.c
@@ -2654,7 +2654,12 @@ GMT_LOCAL bool gmtplot_is_fancy_boundary (struct GMT_CTRL *GMT) {
 
 GMT_LOCAL void gmtplot_vertical_wall (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL, int quadrant, double *nesw, bool back, unsigned int mode3d) {
 	int plane = (quadrant + 1) % 2;
+	double xx[4], yy[4];
 	gmt_plane_perspective (GMT, plane, nesw[quadrant % 4]);
+	if (back) {
+		xx[0] = xx[1] = nesw[(quadrant+1)%4];	xx[2] = xx[3] = nesw[(quadrant+3)%4];
+		yy[0] = yy[3] = GMT->current.proj.zmin;	yy[1] = yy[2] = GMT->current.proj.zmax;
+	}
 	if (mode3d & GMT_3D_WALL && back) {
 		int wplane = 1 - plane;
 		if (GMT->current.map.frame.paint[wplane]) {	/* First paint the back wall */
@@ -2665,15 +2670,15 @@ GMT_LOCAL void gmtplot_vertical_wall (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL
 			gmtplot_z_gridlines (GMT, PSL, GMT->common.R.wesn[ZLO], GMT->common.R.wesn[ZHI], plane, mode3d, quadrant);
 
 		if (GMT->current.map.frame.draw_wall) {
-			PSL_setfill (PSL, GMT->session.no_rgb, 1);
 			gmt_setpen (GMT, &GMT->current.map.frame.pen);
-			PSL_plotbox (PSL, nesw[(quadrant+1)%4], GMT->current.proj.zmin, nesw[(quadrant+3)%4], GMT->current.proj.zmax);
+			PSL_plotline (PSL, xx, yy, 4, PSL_MOVE|PSL_STROKE);
 		}
 	}
 	else if (back)
 		gmtplot_z_gridlines (GMT, PSL, GMT->common.R.wesn[ZLO], GMT->common.R.wesn[ZHI], plane, mode3d, quadrant);
 	if (mode3d & GMT_3D_BOX) {
-		PSL_plotbox (PSL, nesw[(quadrant+1)%4], GMT->current.proj.zmin, nesw[(quadrant+3)%4], GMT->current.proj.zmax);
+		gmt_setpen (GMT, &GMT->current.map.frame.pen);
+		PSL_plotline (PSL, xx, yy, 4, PSL_MOVE|PSL_STROKE);
 	}
 }
 

From 28562a5ca7395f10f0957090730f1d6567822efd Mon Sep 17 00:00:00 2001
From: Paul Wessel <pwessel@hawaii.edu>
Date: Thu, 20 Aug 2020 11:36:45 -1000
Subject: [PATCH 15/25] let +g set all, while adding +x|y|z for individual
 control

---
 src/gmt_init.c | 36 ++++++++++++++++++++++++++----------
 1 file changed, 26 insertions(+), 10 deletions(-)

diff --git a/src/gmt_init.c b/src/gmt_init.c
index 205b459d925..663c7389e69 100644
--- a/src/gmt_init.c
+++ b/src/gmt_init.c
@@ -4008,12 +4008,12 @@ bool gmtlib_B_is_frame (struct GMT_CTRL *GMT, char *in) {
 
 /*! . */
 GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
-	bool blank[2] = {false, false};
+	bool blank[2] = {false, false}, did_g = false;
 	unsigned int pos = 0, k, error = 0;
 	char p[GMT_BUFSIZ] = {""}, text[GMT_BUFSIZ] = {""}, *mod = NULL;
 	double pole[2];
 
-	/* Parsing of -B<framesettings>: -B[<axes>][+b][+g<fill>][+n][+o<lon>/<lat>][+t<title>][+w[<pen>]][+x[<fill>]][+y[<fill>]] */
+	/* Parsing of -B<framesettings>: -B[<axes>][+b][+g<fill>][+n][+o<lon>/<lat>][+t<title>][+w[<pen>]][+x[<fill>]][+y[<fill>]][+z[<fill>]] */
 
 	/* First determine that the given -B<in> string is indeed the framesetting option.  If not return -1 */
 
@@ -4024,7 +4024,7 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 	/* OK, here we are pretty sure this is a frame -B statement */
 
 	strncpy (text, in, GMT_BUFSIZ-1);
-	gmt_handle5_plussign (GMT, text, "bginotwxy", 0);	/* Temporarily change double plus-signs to double ASCII 1 to avoid +<modifier> angst */
+	gmt_handle5_plussign (GMT, text, "bginotwxyz", 0);	/* Temporarily change double plus-signs to double ASCII 1 to avoid +<modifier> angst */
 	GMT->current.map.frame.header[0] = '\0';
 	gmt_M_memset (GMT->current.map.frame.paint, 3U, bool);
 	GMT->current.map.frame.draw_box = GMT_3D_NONE;
@@ -4040,7 +4040,7 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 						GMT_Report (GMT->parent, GMT_MSG_ERROR, "Bad +g<fill> argument %s\n", &p[1]);
 						error++;
 					}
-					GMT->current.map.frame.paint[GMT_Z] = true;
+					GMT->current.map.frame.paint[GMT_Z] = did_g = true;
 					break;
 				case 'i':	/* Turn on internal annotation for radial or longitudinal axes when there is no outside place to annotate */
 					GMT->current.map.frame.internal_annot = 1;	/* Longitude/angle */
@@ -4118,6 +4118,14 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 					GMT->current.map.frame.paint[GMT_Y] = true;
 					GMT->current.map.frame.draw_box |= GMT_3D_WALL;
 					break;
+				case 'z':	/* Paint the basemap xy-plane for 3-D plots */
+					if (p[1] && gmt_getfill (GMT, &p[1], &GMT->current.map.frame.fill[GMT_Z])) {
+						GMT_Report (GMT->parent, GMT_MSG_ERROR, "Bad +z<fill> argument %s\n", &p[1]);
+						error++;
+					}
+					GMT->current.map.frame.paint[GMT_Z] = true;
+					GMT->current.map.frame.draw_box |= GMT_3D_WALL;
+					break;
 				default:
 					GMT_Report (GMT->parent, GMT_MSG_ERROR, "Option -B: Unrecognized frame modifier %s\n", p);
 					error++;
@@ -4143,6 +4151,14 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 			error++;
 		}
 	}
+	if (!GMT->current.map.frame.paint[GMT_X] && did_g) {	/* Let +g set all sides not already set */
+		gmt_M_memcpy (&GMT->current.map.frame.fill[GMT_X], &GMT->current.map.frame.fill[GMT_Z], 1U, struct GMT_FILL);
+		GMT->current.map.frame.paint[GMT_X] = true;
+	}
+	if (!GMT->current.map.frame.paint[GMT_Y] && did_g) {	/* Let +g set all sides not already set */
+		gmt_M_memcpy (&GMT->current.map.frame.fill[GMT_Y], &GMT->current.map.frame.fill[GMT_Z], 1U, struct GMT_FILL);
+		GMT->current.map.frame.paint[GMT_Y] = true;
+	}
 
 	/* Now parse the frame choices, if any */
 	error += gmtinit_decode5_wesnz (GMT, text, true);
@@ -4169,13 +4185,13 @@ void gmt_init_B (struct GMT_CTRL *GMT) {
 GMT_LOCAL int gmtinit_parse5_B_option (struct GMT_CTRL *GMT, char *in) {
 	/* GMT5 clean version based on new syntax:
 	 * Frame settings:
-	 *	-B[WESNwesnz|Z[1234]][+b][+g<fill>][+o<lon/lat>][+t<title>][+w[<pen>]][+x[<fill>]][+y[<fill>]]
+	 *	-B[WESNwesnz|Z[1234]][+b][+g<fill>][+o<lon/lat>][+t<title>][+w[<pen>]][+x[<fill>]][+y[<fill>]][+z[<fill>]]
 	 *    		+b draws 3-D box.
-	 *    		+g<fill> as plot interior fill [none].
+	 *    		+g<fill> as plot interior fill and backwalls (if 3-D) [none].
 	 *    		+t<title> as plot title [none].
 	 *    		+w[<pen>] draws the outline of the xz and yz planes [no outline].
 	 *    		of one or more of w,e,s,n,z then only those axes will be drawn.
-	 *    		+x and +y paints the back walls for xz and yz [with +g fill if not specified].
+	 *    		+x, +y, +z paints the back walls for xz, yz, xy [with +g fill if not specified].
 	 *		Upper case letters means the chosen axes also will be annotated.
 	 *		Default is determined by MAP_FRAME_AXES setting [WESN].
 	 * Axis settings:
@@ -4218,7 +4234,7 @@ GMT_LOCAL int gmtinit_parse5_B_option (struct GMT_CTRL *GMT, char *in) {
 	if ((error = gmtinit_parse5_B_frame_setting (GMT, in)) >= 0) return (error);	/* Parsed the -B frame settings separately */
 	error = 0;	/* Reset since otherwise it is -1 */
 
-	if (strstr (in, "+b") || strstr (in, "+g") || strstr (in, "+i") || strstr (in, "+n") || strstr (in, "+o") || strstr (in, "+o") || strstr (in, "+t") || strstr (in, "+w") || strstr (in, "+x") || strstr (in, "+y")) {
+	if (strstr (in, "+b") || strstr (in, "+g") || strstr (in, "+i") || strstr (in, "+n") || strstr (in, "+o") || strstr (in, "+o") || strstr (in, "+t") || strstr (in, "+w") || strstr (in, "+x") || strstr (in, "+y") || strstr (in, "+z")) {
 		GMT_Report (GMT->parent, GMT_MSG_ERROR, "Option -B: Found frame setting modifiers (+b|g|i|n|o|p|W) mixed with axes settings!\n");
 		return (GMT_PARSE_ERROR);
 	}
@@ -6569,7 +6585,7 @@ void gmtlib_explain_options (struct GMT_CTRL *GMT, char *options) {
 
 			gmt_message (GMT, "\t-B Specify both (1) basemap frame settings and (2) axes parameters.\n");
 			gmt_message (GMT, "\t   Frame settings are modified via an optional single invocation of\n");
-			gmt_message (GMT, "\t     -B[<axes>][+b][+g<fill>][+i[<val>]][+n][+o<lon>/<lat>][+t<title>][+w[<pen>]]\n");
+			gmt_message (GMT, "\t     -B[<axes>][+b][+g<fill>][+i[<val>]][+n][+o<lon>/<lat>][+t<title>][+w[<pen>]][+x<fill>][+y<fill>][+z<fill>]\n");
 			gmt_message (GMT, "\t   Axes parameters are specified via one or more invocations of\n");
 			gmt_message (GMT, "\t     -B[p|s][x|y|z]<info>\n\n");
 			gmt_message (GMT, "\t   1. Frame settings control which axes to plot, frame fill, title, and type of gridlines:\n");
@@ -6586,7 +6602,7 @@ void gmtlib_explain_options (struct GMT_CTRL *GMT, char *options) {
 			gmt_message (GMT, "\t     at which corner(s) to erect the z-axis via a combination of 1,2,3,4; 1 means lower left corner,\n");
 			gmt_message (GMT, "\t     2 is lower right, etc., in a counter-clockwise order [Default automatically selects one axis].\n");
 			gmt_message (GMT, "\t     The +w draws the outline of the xz and yz planes [no outlines].\n");
-			gmt_message (GMT, "\t     The +x|y[<fill>] paint the xz and yz plane [no fill]. The +g<fill> is used if no fill is appended.\n");
+			gmt_message (GMT, "\t     The +x|y|z[<fill>] paint the xz, yz, xy plane [no fill]. The +g<fill> is used if no fill is appended.\n");
 			gmt_message (GMT, "\t     In addition, +b will erect a 3-D frame box to outline the 3-D domain [no frame box].\n");
 			gmt_message (GMT, "\t   2. Axes settings control the annotation, tick, and grid intervals and labels.\n");
 			gmt_message (GMT, "\t     The full axes specification is\n");

From 18d040b9e488e5e7895998d6eb0af9a15217eeb0 Mon Sep 17 00:00:00 2001
From: Paul Wessel <pwessel@hawaii.edu>
Date: Thu, 20 Aug 2020 12:12:16 -1000
Subject: [PATCH 16/25] update docs

---
 doc/rst/source/cookbook/options.rst |  8 +++---
 doc/rst/source/explain_-B_full.rst_ |  8 +++---
 src/gmt_init.c                      | 43 +++++++++--------------------
 3 files changed, 21 insertions(+), 38 deletions(-)

diff --git a/doc/rst/source/cookbook/options.rst b/doc/rst/source/cookbook/options.rst
index b548e84868a..617f8a20dfe 100644
--- a/doc/rst/source/cookbook/options.rst
+++ b/doc/rst/source/cookbook/options.rst
@@ -287,7 +287,7 @@ tick, and gridline intervals, axes labels, and annotation units.
 
 The Frame settings are specified by
 
--  **-B**\ [*axes*][**+b**][**+g**\ *fill*][**+i**\ [*val*]][**+n**][**+o**\ *lon/lat*][**+t**\ *title*][**+w**\ [*pen*]][**+x**\ [*fill*]][**+y**\ [*fill*]]
+-  **-B**\ [*axes*][**+b**][**+g**\ *fill*][**+i**\ [*val*]][**+n**][**+o**\ *lon/lat*][**+t**\ *title*][**+w**\ [*pen*]][**+x**\ *fill*][**+y**\ *fill*][**+z**\ *fill*]
 
 Here, the optional *axes* dictates which of the axes should be drawn
 and possibly annotated.  By default, all four map boundaries (or plot axes)
@@ -305,9 +305,9 @@ any combination of corner ids **1234**, where **1** represents the lower left
 corner and the order goes counter-clockwise.  Use **+w** to draw the outlines of
 the x-z and y-z planes [no outlines] and optionally append the *pen* to use
 [:term:`MAP_GRID_PEN_PRIMARY`]. Alternatively, append **+b** to also draw the front lines
-of the 3-D cube defined by **-R**.  By default the back-walls are transparent.
-Use **+x** and **+y** to paint them, using the same fill as the x-y plane if no fill
-is appended. You may paint the map canvas by appending the **+g**\ *fill* modifier [Default is no fill].
+of the 3-D cube defined by **-R**.  You can paint the interior of the canvas with
+**+g**\ *fill* (this also sets fill for the two back-walls in 3-D).
+Use **+x**, **+y**, and **+z** to control the painting per plane [Default is no fill].
 Use **+i** to annotate an internal meridian or parallel when the axis that normally
 would be drawn and annotated does not exist (e.g., azimuthal map with 360-degree range
 has no latitude axis, and a global Hammer map has no longitude axis);
diff --git a/doc/rst/source/explain_-B_full.rst_ b/doc/rst/source/explain_-B_full.rst_
index 05746e28412..43d53a502c8 100644
--- a/doc/rst/source/explain_-B_full.rst_
+++ b/doc/rst/source/explain_-B_full.rst_
@@ -3,7 +3,7 @@
 **-B**\ [**p**\|\ **s**]\ *parameters*
     Set map Frame and Axes parameters. The Frame parameters are specified by
 
-    **-B**\ [*axes*][**+b**][**+g**\ *fill*][**+i**\ [*val*]][**+n**][**+o**\ *lon/lat*][**+t**\ *title*][**+w**\ [*pen*]][**+x**\ [*fill*]][**+y**\ [*fill*]]
+    **-B**\ [*axes*][**+b**][**+g**\ *fill*][**+i**\ [*val*]][**+n**][**+o**\ *lon/lat*][**+t**\ *title*][**+w**\ [*pen*]][**+x**\ *fill*][**+y**\ *fill*][**+z**\ *fill*]
 
     where *axes* selects which axes to plot. By default, all four map boundaries
     (or plot axes) are plotted (named **W**, **E**, **S**, **N**). To customize,
@@ -18,9 +18,9 @@
     corner and the order goes counter-clockwise.  Use **+w** to draw the outlines of
     the x-z and y-z planes [no outline] and optionally append the *pen* to use
     [:term:`MAP_GRID_PEN_PRIMARY`]. Alternatively, append **+b** to also draw the front lines
-    of the 3-D cube defined by **-R**. By default, the back-walls are transparent.
-    Use **+x** and **+y** to paint them, using the same fill as the x-y plane if no fill
-    is appended. You can paint the interior of the canvas with **+g**\ *fill*.
+    of the 3-D cube defined by **-R**. You can paint the interior of the canvas with
+    **+g**\ *fill* (this also sets fill for the two back-walls in 3-D).
+    Use **+x**, **+y**, and **+z** to control the painting per plane [Default is no fill]. 
     Use **+i** to annotate an internal meridian or parallel when the axis that normally
     would be drawn and annotated does not exist (e.g., azimuthal map with 360-degree range
     has no latitude axis, and a global Hammer map has no longitude axis); optionally append the parallel or meridian [0].
diff --git a/src/gmt_init.c b/src/gmt_init.c
index 663c7389e69..d097094df0b 100644
--- a/src/gmt_init.c
+++ b/src/gmt_init.c
@@ -3990,8 +3990,9 @@ bool gmtlib_B_is_frame (struct GMT_CTRL *GMT, char *in) {
 	if (strstr (in, "+o")) return true;	/* Found a +o so likely frame */
 	if (strstr (in, "+t")) return true;	/* Found a +t so likely frame */
 	if (strstr (in, "+w")) return true;	/* Found a +w so likely frame */
-	if (strstr (in, "+s")) return true;	/* Found a +s so likely frame */
+	if (strstr (in, "+x")) return true;	/* Found a +x so likely frame */
 	if (strstr (in, "+y")) return true;	/* Found a +y so likely frame */
+	if (strstr (in, "+z")) return true;	/* Found a +z so likely frame */
 	if (strstr (in, "+a")) return false;	/* Found a +a so likely axis */
 	if (strstr (in, "+f")) return false;	/* Found a +f so likely axis */
 	if (strstr (in, "+l")) return false;	/* Found a +l so likely axis */
@@ -4008,12 +4009,12 @@ bool gmtlib_B_is_frame (struct GMT_CTRL *GMT, char *in) {
 
 /*! . */
 GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
-	bool blank[2] = {false, false}, did_g = false;
+	bool did_g = false;
 	unsigned int pos = 0, k, error = 0;
 	char p[GMT_BUFSIZ] = {""}, text[GMT_BUFSIZ] = {""}, *mod = NULL;
 	double pole[2];
 
-	/* Parsing of -B<framesettings>: -B[<axes>][+b][+g<fill>][+n][+o<lon>/<lat>][+t<title>][+w[<pen>]][+x[<fill>]][+y[<fill>]][+z[<fill>]] */
+	/* Parsing of -B<framesettings>: -B[<axes>][+b][+g<fill>][+n][+o<lon>/<lat>][+t<title>][+w[<pen>]][+x<fill>][+y<fill>][+z<fill>] */
 
 	/* First determine that the given -B<in> string is indeed the framesetting option.  If not return -1 */
 
@@ -4035,7 +4036,7 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 				case 'b':	/* Draw 3-D box */
 					GMT->current.map.frame.draw_box |= GMT_3D_BOX;
 					break;
-				case 'g':	/* Paint the basemap x-y plane */
+				case 'g':	/* Paint the basemap x-y plane and for 3-D back walls */
 					if (p[1] == 0 || gmt_getfill (GMT, &p[1], &GMT->current.map.frame.fill[GMT_Z])) {
 						GMT_Report (GMT->parent, GMT_MSG_ERROR, "Bad +g<fill> argument %s\n", &p[1]);
 						error++;
@@ -4101,20 +4102,18 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 						gmt_M_memcpy (&GMT->current.map.frame.pen, &GMT->current.setting.map_grid_pen[GMT_PRIMARY], 1, struct GMT_PEN);
 					break;
 				case 'x':	/* Paint the basemap xz-plane for 3-D plots */
-					if (p[1] && gmt_getfill (GMT, &p[1], &GMT->current.map.frame.fill[GMT_X])) {
-						GMT_Report (GMT->parent, GMT_MSG_ERROR, "Bad +x<fill> argument %s\n", &p[1]);
+					if (p[1] == 0 || gmt_getfill (GMT, &p[1], &GMT->current.map.frame.fill[GMT_X])) {
+						GMT_Report (GMT->parent, GMT_MSG_ERROR, "Bad +x<fill> argument %s (or possibly missing)\n", &p[1]);
 						error++;
 					}
-					blank[GMT_X] = !p[1];
 					GMT->current.map.frame.paint[GMT_X] = true;
 					GMT->current.map.frame.draw_box |= GMT_3D_WALL;
 					break;
 				case 'y':	/* Paint the basemap yz-plane for 3-D plots */
-					if (p[1] && gmt_getfill (GMT, &p[1], &GMT->current.map.frame.fill[GMT_Y])) {
-						GMT_Report (GMT->parent, GMT_MSG_ERROR, "Bad +y<fill> argument %s\n", &p[1]);
+					if (p[1] == 0 || gmt_getfill (GMT, &p[1], &GMT->current.map.frame.fill[GMT_Y])) {
+						GMT_Report (GMT->parent, GMT_MSG_ERROR, "Bad +y<fill> argument %s (or possibly missing)\n", &p[1]);
 						error++;
 					}
-					blank[GMT_Y] = !p[1];
 					GMT->current.map.frame.paint[GMT_Y] = true;
 					GMT->current.map.frame.draw_box |= GMT_3D_WALL;
 					break;
@@ -4135,22 +4134,6 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 		*mod = '\0';	/* Separate the modifiers from the frame selectors */
 	}
 
-	if (GMT->current.map.frame.paint[GMT_X] && blank[GMT_X]) {	/* Just +x means use the +g-fill (which must exist) */
-		if (GMT->current.map.frame.paint[GMT_Z])
-			gmt_M_memcpy (&GMT->current.map.frame.fill[GMT_X], &GMT->current.map.frame.fill[GMT_Z], 1U, struct GMT_FILL);
-		else {
-			GMT_Report (GMT->parent, GMT_MSG_ERROR, "Option -B: Modifier +x requires a fill argument if +g was not set\n");
-			error++;
-		}
-	}
-	if (GMT->current.map.frame.paint[GMT_Y] && blank[GMT_Y]) {	/* Just +x means use the +g-fill (which must exist) */
-		if (GMT->current.map.frame.paint[GMT_Z])
-			gmt_M_memcpy (&GMT->current.map.frame.fill[GMT_Y], &GMT->current.map.frame.fill[GMT_Z], 1U, struct GMT_FILL);
-		else {
-			GMT_Report (GMT->parent, GMT_MSG_ERROR, "Option -B: Modifier +y requires a fill argument if +g was not set\n");
-			error++;
-		}
-	}
 	if (!GMT->current.map.frame.paint[GMT_X] && did_g) {	/* Let +g set all sides not already set */
 		gmt_M_memcpy (&GMT->current.map.frame.fill[GMT_X], &GMT->current.map.frame.fill[GMT_Z], 1U, struct GMT_FILL);
 		GMT->current.map.frame.paint[GMT_X] = true;
@@ -4185,7 +4168,7 @@ void gmt_init_B (struct GMT_CTRL *GMT) {
 GMT_LOCAL int gmtinit_parse5_B_option (struct GMT_CTRL *GMT, char *in) {
 	/* GMT5 clean version based on new syntax:
 	 * Frame settings:
-	 *	-B[WESNwesnz|Z[1234]][+b][+g<fill>][+o<lon/lat>][+t<title>][+w[<pen>]][+x[<fill>]][+y[<fill>]][+z[<fill>]]
+	 *	-B[WESNwesnz|Z[1234]][+b][+g<fill>][+o<lon/lat>][+t<title>][+w[<pen>]][+x<fill>][+y<fill>][+z<fill>]
 	 *    		+b draws 3-D box.
 	 *    		+g<fill> as plot interior fill and backwalls (if 3-D) [none].
 	 *    		+t<title> as plot title [none].
@@ -6602,7 +6585,7 @@ void gmtlib_explain_options (struct GMT_CTRL *GMT, char *options) {
 			gmt_message (GMT, "\t     at which corner(s) to erect the z-axis via a combination of 1,2,3,4; 1 means lower left corner,\n");
 			gmt_message (GMT, "\t     2 is lower right, etc., in a counter-clockwise order [Default automatically selects one axis].\n");
 			gmt_message (GMT, "\t     The +w draws the outline of the xz and yz planes [no outlines].\n");
-			gmt_message (GMT, "\t     The +x|y|z[<fill>] paint the xz, yz, xy plane [no fill]. The +g<fill> is used if no fill is appended.\n");
+			gmt_message (GMT, "\t     The +x|y|z[<fill>] paint the xz, yz, xy plane [no fill]. The +g<fill> sets all three planes.\n");
 			gmt_message (GMT, "\t     In addition, +b will erect a 3-D frame box to outline the 3-D domain [no frame box].\n");
 			gmt_message (GMT, "\t   2. Axes settings control the annotation, tick, and grid intervals and labels.\n");
 			gmt_message (GMT, "\t     The full axes specification is\n");
@@ -7730,8 +7713,8 @@ void gmt_syntax (struct GMT_CTRL *GMT, char option) {
 	switch (option) {
 
 		case 'B':	/* Tickmark option */
-			gmt_message (GMT, "\t-B[p|s][x|y|z]<intervals>[+a<angle>|n|p][+l|L<label>][+p<prefix>][+u<unit>] -B[<axes>][+b][+g<fill>][+o<lon>/<lat>][+t<title>][+w[<pen>]][+x[<fill>]][+y[<fill>]] OR\n");
-			gmt_message (GMT, "\t-B[p|s][x|y|z][a|f|g]<tick>[m][l|p] -B[p|s][x|y|z][+l<label>][+p<prefix>][+u<unit>] -B[<axes>][+b][+g<fill>][+o<lon>/<lat>][+t<title>][+w[<pen>]][+x[<fill>]][+y[<fill>]]\n");
+			gmt_message (GMT, "\t-B[p|s][x|y|z]<intervals>[+a<angle>|n|p][+l|L<label>][+p<prefix>][+u<unit>] -B[<axes>][+b][+g<fill>][+o<lon>/<lat>][+t<title>][+w[<pen>]][+x<fill>][+y<fill>][+z<fill>] OR\n");
+			gmt_message (GMT, "\t-B[p|s][x|y|z][a|f|g]<tick>[m][l|p] -B[p|s][x|y|z][+l<label>][+p<prefix>][+u<unit>] -B[<axes>][+b][+g<fill>][+o<lon>/<lat>][+t<title>][+w[<pen>]][+x<fill>][+y<fill>][+z<fill>]\n");
 			break;
 
 		case 'J':	/* Map projection option */

From 2eae99436ae266f4005112551c62531ff3d96180 Mon Sep 17 00:00:00 2001
From: Paul Wessel <pwessel@hawaii.edu>
Date: Thu, 20 Aug 2020 15:38:51 -1000
Subject: [PATCH 17/25] Ensure +b sets the wall

---
 src/gmt_init.c | 2 +-
 src/gmt_plot.c | 6 ++----
 2 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/src/gmt_init.c b/src/gmt_init.c
index d097094df0b..c7caba4fe26 100644
--- a/src/gmt_init.c
+++ b/src/gmt_init.c
@@ -4034,7 +4034,7 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 		while ((gmt_strtok (mod, "+", &pos, p))) {	/* Parse any +<modifier> statements */
 			switch (p[0]) {
 				case 'b':	/* Draw 3-D box */
-					GMT->current.map.frame.draw_box |= GMT_3D_BOX;
+					GMT->current.map.frame.draw_box |= (GMT_3D_BOX|GMT_3D_WALL);
 					break;
 				case 'g':	/* Paint the basemap x-y plane and for 3-D back walls */
 					if (p[1] == 0 || gmt_getfill (GMT, &p[1], &GMT->current.map.frame.fill[GMT_Z])) {
diff --git a/src/gmt_plot.c b/src/gmt_plot.c
index 11fba544bed..01441cc533d 100644
--- a/src/gmt_plot.c
+++ b/src/gmt_plot.c
@@ -2656,10 +2656,8 @@ GMT_LOCAL void gmtplot_vertical_wall (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL
 	int plane = (quadrant + 1) % 2;
 	double xx[4], yy[4];
 	gmt_plane_perspective (GMT, plane, nesw[quadrant % 4]);
-	if (back) {
-		xx[0] = xx[1] = nesw[(quadrant+1)%4];	xx[2] = xx[3] = nesw[(quadrant+3)%4];
-		yy[0] = yy[3] = GMT->current.proj.zmin;	yy[1] = yy[2] = GMT->current.proj.zmax;
-	}
+	xx[0] = xx[1] = nesw[(quadrant+1)%4];	xx[2] = xx[3] = nesw[(quadrant+3)%4];
+	yy[0] = yy[3] = GMT->current.proj.zmin;	yy[1] = yy[2] = GMT->current.proj.zmax;
 	if (mode3d & GMT_3D_WALL && back) {
 		int wplane = 1 - plane;
 		if (GMT->current.map.frame.paint[wplane]) {	/* First paint the back wall */

From 3d75efb9fbd18428d998b3a447d0b2ede377273e Mon Sep 17 00:00:00 2001
From: Paul Wessel <pwessel@hawaii.edu>
Date: Thu, 20 Aug 2020 16:24:38 -1000
Subject: [PATCH 18/25] Adjust gridline spacing

Let the annotation interval always be the auto gridline spacing, and make first-orer allowances for perspective view when selecting the "width" of the axes.
---
 src/gmt_map.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/src/gmt_map.c b/src/gmt_map.c
index 858aa48ae17..c1e431ab237 100644
--- a/src/gmt_map.c
+++ b/src/gmt_map.c
@@ -6584,7 +6584,7 @@ void gmt_auto_frame_interval (struct GMT_CTRL *GMT, unsigned int axis, unsigned
 	double Hmaj[4] = {2.0, 3.0, 6.0, 12.0}, Hsub[4] = {1.0, 1.0, 3.0, 3.0};
 	double Omaj[4] = {3.0, 6.0}, Osub[4] = {1.0, 3.0};
 	double Dmaj[4] = {2.0, 3.0, 7.0, 14.0}, Dsub[4] = {1.0, 1.0, 1.0, 7.0};
-	double d, f, p, *maj = defmaj, *sub = defsub;
+	double d, f, p, sxy = 1.0, sz = 1.0, *maj = defmaj, *sub = defsub;
 	struct GMT_PLOT_AXIS *A = &GMT->current.map.frame.axis[axis];
 	struct GMT_PLOT_AXIS_ITEM *T;
 
@@ -6595,21 +6595,24 @@ void gmt_auto_frame_interval (struct GMT_CTRL *GMT, unsigned int axis, unsigned
 		!(A->item[item+2].active && A->item[item+2].interval == 0.0) &&
 		!(A->item[item+4].active && A->item[item+4].interval == 0.0)) return;
 
+	if (GMT->current.proj.three_D) {	/* Make an approximate adjustment to the "sizes" given a perspective view */
+		sxy = 1.0 - cosd (GMT->current.proj.z_project.view_elevation);
+		sz  = 1.0 - fabs (sind (GMT->current.proj.z_project.view_elevation));
+	}
 	/* f = frame width/height (inch); d = domain width/height (world coordinates) */
 	if (axis == GMT_X) {
-		f = fabs (GMT->current.proj.rect[XHI] - GMT->current.proj.rect[XLO]);
+		f = sxy * fabs (GMT->current.proj.rect[XHI] - GMT->current.proj.rect[XLO]);
 		d = fabs (GMT->common.R.wesn[XHI] - GMT->common.R.wesn[XLO]);
 	}
 	else if (axis == GMT_Y) {
-		f = fabs (GMT->current.proj.rect[YHI] - GMT->current.proj.rect[YLO]);
+		f = sxy * fabs (GMT->current.proj.rect[YHI] - GMT->current.proj.rect[YLO]);
 		d = fabs (GMT->common.R.wesn[YHI] - GMT->common.R.wesn[YLO]);
 	}
 	else {
-		f = fabs (GMT->current.proj.zmax - GMT->current.proj.zmin);
+		f = sz * fabs (GMT->current.proj.zmax - GMT->current.proj.zmin);
 		d = fabs (GMT->common.R.wesn[ZHI] - GMT->common.R.wesn[ZLO]);
 	}
 	f *= GMT->session.u2u[GMT_INCH][GMT_PT];	/* Change to points */
-
 	/* First guess of interval */
 	d *= MAX (0.05, MIN (5.0 * GMT->current.setting.font_annot[item].size / f, 0.20));
 
@@ -6678,7 +6681,8 @@ void gmt_auto_frame_interval (struct GMT_CTRL *GMT, unsigned int axis, unsigned
 	/* Finally set grid interval (if annotation set as well, use major, otherwise minor interval) */
 	T = &A->item[item+4];
 	if (T->active && T->interval == 0.0) {
-		T->interval = set_a ? d : f, T->generated = true;
+		/* T->interval = set_a ? d : f, T->generated = true; Commented out because f is too fine for gridline spacing, even if no annotations */
+		T->interval = d, T->generated = true;
 		snprintf (tmp, GMT_LEN16, "g%g", T->interval); strcat (string, tmp);
 		if (is_time) T->unit = unit, strcat (string, sunit);
 	}

From 33419e0f95c5cb87ca4177514577b14ffc67dbe6 Mon Sep 17 00:00:00 2001
From: Paul Wessel <pwessel@hawaii.edu>
Date: Thu, 20 Aug 2020 17:33:42 -1000
Subject: [PATCH 19/25] Revert gridline choice for now

---
 src/gmt_map.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/gmt_map.c b/src/gmt_map.c
index c1e431ab237..f1554f5c81f 100644
--- a/src/gmt_map.c
+++ b/src/gmt_map.c
@@ -6681,8 +6681,8 @@ void gmt_auto_frame_interval (struct GMT_CTRL *GMT, unsigned int axis, unsigned
 	/* Finally set grid interval (if annotation set as well, use major, otherwise minor interval) */
 	T = &A->item[item+4];
 	if (T->active && T->interval == 0.0) {
-		/* T->interval = set_a ? d : f, T->generated = true; Commented out because f is too fine for gridline spacing, even if no annotations */
-		T->interval = d, T->generated = true;
+		T->interval = set_a ? d : f, T->generated = true; /* Commented out because f is too fine for gridline spacing, even if no annotations */
+		// T->interval = d, T->generated = true;
 		snprintf (tmp, GMT_LEN16, "g%g", T->interval); strcat (string, tmp);
 		if (is_time) T->unit = unit, strcat (string, sunit);
 	}

From d9fc4c40b4f54e717f910dbcf3ef8ba832d2e36b Mon Sep 17 00:00:00 2001
From: Paul Wessel <pwessel@hawaii.edu>
Date: Sat, 22 Aug 2020 14:36:03 -1000
Subject: [PATCH 20/25] Address meaning of +x +y and set above/below annotation
 for z-axis

---
 doc/rst/source/cookbook/options.rst |  2 +-
 doc/rst/source/explain_-B_full.rst_ |  2 +-
 src/gmt_init.c                      | 29 +++++++++++++++++------------
 src/gmt_plot.c                      | 18 +++++++++++++++++-
 4 files changed, 36 insertions(+), 15 deletions(-)

diff --git a/doc/rst/source/cookbook/options.rst b/doc/rst/source/cookbook/options.rst
index 617f8a20dfe..c49a5f38813 100644
--- a/doc/rst/source/cookbook/options.rst
+++ b/doc/rst/source/cookbook/options.rst
@@ -307,7 +307,7 @@ the x-z and y-z planes [no outlines] and optionally append the *pen* to use
 [:term:`MAP_GRID_PEN_PRIMARY`]. Alternatively, append **+b** to also draw the front lines
 of the 3-D cube defined by **-R**.  You can paint the interior of the canvas with
 **+g**\ *fill* (this also sets fill for the two back-walls in 3-D).
-Use **+x**, **+y**, and **+z** to control the painting per plane [Default is no fill].
+Use **+x**, **+y**, and **+z** to control the painting of planes *yz*, *xz* and *xy*, respectively [Default is no fill].
 Use **+i** to annotate an internal meridian or parallel when the axis that normally
 would be drawn and annotated does not exist (e.g., azimuthal map with 360-degree range
 has no latitude axis, and a global Hammer map has no longitude axis);
diff --git a/doc/rst/source/explain_-B_full.rst_ b/doc/rst/source/explain_-B_full.rst_
index 43d53a502c8..3fbc88b3986 100644
--- a/doc/rst/source/explain_-B_full.rst_
+++ b/doc/rst/source/explain_-B_full.rst_
@@ -20,7 +20,7 @@
     [:term:`MAP_GRID_PEN_PRIMARY`]. Alternatively, append **+b** to also draw the front lines
     of the 3-D cube defined by **-R**. You can paint the interior of the canvas with
     **+g**\ *fill* (this also sets fill for the two back-walls in 3-D).
-    Use **+x**, **+y**, and **+z** to control the painting per plane [Default is no fill]. 
+    Use **+x**, **+y**, and **+z** to control the painting of planes *yz*, *xz* and *xy*, respectively [Default is no fill]. 
     Use **+i** to annotate an internal meridian or parallel when the axis that normally
     would be drawn and annotated does not exist (e.g., azimuthal map with 360-degree range
     has no latitude axis, and a global Hammer map has no longitude axis); optionally append the parallel or meridian [0].
diff --git a/src/gmt_init.c b/src/gmt_init.c
index c7caba4fe26..dfe81ac3e4a 100644
--- a/src/gmt_init.c
+++ b/src/gmt_init.c
@@ -4013,6 +4013,7 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 	unsigned int pos = 0, k, error = 0;
 	char p[GMT_BUFSIZ] = {""}, text[GMT_BUFSIZ] = {""}, *mod = NULL;
 	double pole[2];
+	struct GMT_FILL F;
 
 	/* Parsing of -B<framesettings>: -B[<axes>][+b][+g<fill>][+n][+o<lon>/<lat>][+t<title>][+w[<pen>]][+x<fill>][+y<fill>][+z<fill>] */
 
@@ -4037,11 +4038,11 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 					GMT->current.map.frame.draw_box |= (GMT_3D_BOX|GMT_3D_WALL);
 					break;
 				case 'g':	/* Paint the basemap x-y plane and for 3-D back walls */
-					if (p[1] == 0 || gmt_getfill (GMT, &p[1], &GMT->current.map.frame.fill[GMT_Z])) {
+					if (p[1] == 0 || gmt_getfill (GMT, &p[1], &F)) {
 						GMT_Report (GMT->parent, GMT_MSG_ERROR, "Bad +g<fill> argument %s\n", &p[1]);
 						error++;
 					}
-					GMT->current.map.frame.paint[GMT_Z] = did_g = true;
+					did_g = true;
 					break;
 				case 'i':	/* Turn on internal annotation for radial or longitudinal axes when there is no outside place to annotate */
 					GMT->current.map.frame.internal_annot = 1;	/* Longitude/angle */
@@ -4101,20 +4102,20 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 					else if (p[1] == 0)	/* Use grid pen as default */
 						gmt_M_memcpy (&GMT->current.map.frame.pen, &GMT->current.setting.map_grid_pen[GMT_PRIMARY], 1, struct GMT_PEN);
 					break;
-				case 'x':	/* Paint the basemap xz-plane for 3-D plots */
-					if (p[1] == 0 || gmt_getfill (GMT, &p[1], &GMT->current.map.frame.fill[GMT_X])) {
+				case 'x':	/* Paint the basemap yz-plane for 3-D plots */
+					if (p[1] == 0 || gmt_getfill (GMT, &p[1], &GMT->current.map.frame.fill[GMT_Y])) {
 						GMT_Report (GMT->parent, GMT_MSG_ERROR, "Bad +x<fill> argument %s (or possibly missing)\n", &p[1]);
 						error++;
 					}
-					GMT->current.map.frame.paint[GMT_X] = true;
+					GMT->current.map.frame.paint[GMT_Y] = true;
 					GMT->current.map.frame.draw_box |= GMT_3D_WALL;
 					break;
-				case 'y':	/* Paint the basemap yz-plane for 3-D plots */
-					if (p[1] == 0 || gmt_getfill (GMT, &p[1], &GMT->current.map.frame.fill[GMT_Y])) {
+				case 'y':	/* Paint the basemap xz-plane for 3-D plots */
+					if (p[1] == 0 || gmt_getfill (GMT, &p[1], &GMT->current.map.frame.fill[GMT_X])) {
 						GMT_Report (GMT->parent, GMT_MSG_ERROR, "Bad +y<fill> argument %s (or possibly missing)\n", &p[1]);
 						error++;
 					}
-					GMT->current.map.frame.paint[GMT_Y] = true;
+					GMT->current.map.frame.paint[GMT_X] = true;
 					GMT->current.map.frame.draw_box |= GMT_3D_WALL;
 					break;
 				case 'z':	/* Paint the basemap xy-plane for 3-D plots */
@@ -4135,13 +4136,17 @@ GMT_LOCAL int gmtinit_parse5_B_frame_setting (struct GMT_CTRL *GMT, char *in) {
 	}
 
 	if (!GMT->current.map.frame.paint[GMT_X] && did_g) {	/* Let +g set all sides not already set */
-		gmt_M_memcpy (&GMT->current.map.frame.fill[GMT_X], &GMT->current.map.frame.fill[GMT_Z], 1U, struct GMT_FILL);
+		gmt_M_memcpy (&GMT->current.map.frame.fill[GMT_X], &F, 1U, struct GMT_FILL);
 		GMT->current.map.frame.paint[GMT_X] = true;
 	}
 	if (!GMT->current.map.frame.paint[GMT_Y] && did_g) {	/* Let +g set all sides not already set */
-		gmt_M_memcpy (&GMT->current.map.frame.fill[GMT_Y], &GMT->current.map.frame.fill[GMT_Z], 1U, struct GMT_FILL);
+		gmt_M_memcpy (&GMT->current.map.frame.fill[GMT_Y], &F, 1U, struct GMT_FILL);
 		GMT->current.map.frame.paint[GMT_Y] = true;
 	}
+	if (!GMT->current.map.frame.paint[GMT_Z] && did_g) {	/* Let +g set all sides not already set */
+		gmt_M_memcpy (&GMT->current.map.frame.fill[GMT_Z], &F, 1U, struct GMT_FILL);
+		GMT->current.map.frame.paint[GMT_Z] = true;
+	}
 
 	/* Now parse the frame choices, if any */
 	error += gmtinit_decode5_wesnz (GMT, text, true);
@@ -4174,7 +4179,7 @@ GMT_LOCAL int gmtinit_parse5_B_option (struct GMT_CTRL *GMT, char *in) {
 	 *    		+t<title> as plot title [none].
 	 *    		+w[<pen>] draws the outline of the xz and yz planes [no outline].
 	 *    		of one or more of w,e,s,n,z then only those axes will be drawn.
-	 *    		+x, +y, +z paints the back walls for xz, yz, xy [with +g fill if not specified].
+	 *    		+x, +y, +z paints the back walls for yz, xz, xy [with +g fill if not specified].
 	 *		Upper case letters means the chosen axes also will be annotated.
 	 *		Default is determined by MAP_FRAME_AXES setting [WESN].
 	 * Axis settings:
@@ -6585,7 +6590,7 @@ void gmtlib_explain_options (struct GMT_CTRL *GMT, char *options) {
 			gmt_message (GMT, "\t     at which corner(s) to erect the z-axis via a combination of 1,2,3,4; 1 means lower left corner,\n");
 			gmt_message (GMT, "\t     2 is lower right, etc., in a counter-clockwise order [Default automatically selects one axis].\n");
 			gmt_message (GMT, "\t     The +w draws the outline of the xz and yz planes [no outlines].\n");
-			gmt_message (GMT, "\t     The +x|y|z[<fill>] paint the xz, yz, xy plane [no fill]. The +g<fill> sets all three planes.\n");
+			gmt_message (GMT, "\t     The +x|y|z[<fill>] paint the yz, xz, xy planes [no fill]. The +g<fill> sets all three planes.\n");
 			gmt_message (GMT, "\t     In addition, +b will erect a 3-D frame box to outline the 3-D domain [no frame box].\n");
 			gmt_message (GMT, "\t   2. Axes settings control the annotation, tick, and grid intervals and labels.\n");
 			gmt_message (GMT, "\t     The full axes specification is\n");
diff --git a/src/gmt_plot.c b/src/gmt_plot.c
index 01441cc533d..0a8ae944225 100644
--- a/src/gmt_plot.c
+++ b/src/gmt_plot.c
@@ -5555,6 +5555,20 @@ void gmt_map_basemap (struct GMT_CTRL *GMT) {
 	PSL_setcolor (PSL, GMT->current.setting.map_default_pen.rgb, PSL_IS_STROKE);
 }
 
+GMT_LOCAL bool gmtplot_z_axis_side (struct GMT_CTRL *GMT, unsigned int axis, unsigned int quadrant) {
+	bool below;
+	axis++;	/* 1-4 */
+	switch (axis) {
+		case 1: below = (quadrant == 2);	break;
+		case 2: below = (quadrant != 3);	break;
+		case 3: below = (quadrant != 2);	break;
+		case 4: below = (quadrant == 3);	break;
+		default: below = true;	/* Just to avoid Coverity issues */
+	}
+	fprintf (stderr, "Zaxis = %d quadrant = %d below = %d\n", axis, quadrant, below);
+	return below;
+}
+
 void gmt_vertical_axis (struct GMT_CTRL *GMT, unsigned int mode) {
 	/* Mode means: 1 = background walls and title, 2 = foreground walls and axis, 3 = all */
 	unsigned int fore, back, old_plane, form;
@@ -5596,6 +5610,7 @@ void gmt_vertical_axis (struct GMT_CTRL *GMT, unsigned int mode) {
 
 	if (fore && GMT->current.map.frame.side[Z_SIDE]) {
 		unsigned int k, n_z, quadrant, corner_to_quadrant[5] = {0, 2, 1, 4, 3}, z_axis[4];	/* Given corner ID 1-4, return quadrant, or vice versa (0 is unused) */
+		bool below;
 		gmt_M_memcpy (z_axis, GMT->current.map.frame.z_axis, 4, unsigned int);
 		for (k = n_z = 0; k < 4; k++)	/* Count # of vertical axes specified; if 0 then we do an auto-select */
 			if (z_axis[k]) n_z++;
@@ -5604,13 +5619,14 @@ void gmt_vertical_axis (struct GMT_CTRL *GMT, unsigned int mode) {
 		for (k = 0; k < 4; k++) {
 			if (z_axis[k] == 0) continue;	/* Not drawing this vertical axis */
 			quadrant = corner_to_quadrant[k+1];	/* Given corner (k+1), return quadrant */
+			below = gmtplot_z_axis_side (GMT, k, GMT->current.proj.z_project.quadrant);
 			gmt_xyz_to_xy (GMT, nesw[(quadrant/2*2+1)%4], nesw[((quadrant+1)/2*2)%4], GMT->common.R.wesn[ZLO], &xx, &yy);
 			/* Restrict reduced azimuth to -45 to 45 range */
 			az = GMT->current.proj.z_project.view_azimuth - 90.0 - floor ((GMT->current.proj.z_project.view_azimuth - 45.0) / 90.0) * 90.0;
 			PSL_command (PSL, "/PSL_GPP matrix currentmatrix def [%.12g %.12g %.12g %.12g %.12g %.12g] concat\n",
 				cosd(az), sind(az) * GMT->current.proj.z_project.sin_el, 0.0, GMT->current.proj.z_project.cos_el, xx * PSL->internal.x2ix, yy * PSL->internal.y2iy);
 			gmt_xy_axis (GMT, 0.0, -GMT->common.R.wesn[ZLO], GMT->current.proj.zmax - GMT->current.proj.zmin, GMT->common.R.wesn[ZLO],
-				GMT->common.R.wesn[ZHI], &GMT->current.map.frame.axis[GMT_Z], true, GMT->current.map.frame.side[Z_SIDE]);
+				GMT->common.R.wesn[ZHI], &GMT->current.map.frame.axis[GMT_Z], below, GMT->current.map.frame.side[Z_SIDE]);
 			PSL_command (PSL, "PSL_GPP setmatrix\n");
 		}
 	}

From 410efae4f3c59e1ae3fbf84db2967d06d89f3d40 Mon Sep 17 00:00:00 2001
From: Paul Wessel <pwessel@hawaii.edu>
Date: Sat, 22 Aug 2020 14:54:13 -1000
Subject: [PATCH 21/25] remove printstatement

---
 src/gmt_plot.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/src/gmt_plot.c b/src/gmt_plot.c
index 0a8ae944225..a0315ffb122 100644
--- a/src/gmt_plot.c
+++ b/src/gmt_plot.c
@@ -5565,7 +5565,6 @@ GMT_LOCAL bool gmtplot_z_axis_side (struct GMT_CTRL *GMT, unsigned int axis, uns
 		case 4: below = (quadrant == 3);	break;
 		default: below = true;	/* Just to avoid Coverity issues */
 	}
-	fprintf (stderr, "Zaxis = %d quadrant = %d below = %d\n", axis, quadrant, below);
 	return below;
 }
 

From 3aa852d13643994f34841ba7ee77837967bbe7d1 Mon Sep 17 00:00:00 2001
From: Paul Wessel <pwessel@hawaii.edu>
Date: Sat, 22 Aug 2020 17:40:49 -1000
Subject: [PATCH 22/25] Separate 3-D box lines from wall drawing

---
 src/gmt_plot.c | 38 +++++++++++++++++++++++++++-----------
 1 file changed, 27 insertions(+), 11 deletions(-)

diff --git a/src/gmt_plot.c b/src/gmt_plot.c
index a0315ffb122..38c8c19d8f8 100644
--- a/src/gmt_plot.c
+++ b/src/gmt_plot.c
@@ -2653,31 +2653,41 @@ GMT_LOCAL bool gmtplot_is_fancy_boundary (struct GMT_CTRL *GMT) {
 }
 
 GMT_LOCAL void gmtplot_vertical_wall (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL, int quadrant, double *nesw, bool back, unsigned int mode3d) {
-	int plane = (quadrant + 1) % 2;
+	/* Draws the two vertical walls in the back of the 3-D plot */
+	int plane = (quadrant + 1) % 2;	/* Black magic that gives us GMT_X (for yz plane) or GMT_Y (for xz plane) */
 	double xx[4], yy[4];
 	gmt_plane_perspective (GMT, plane, nesw[quadrant % 4]);
+	/* Assign the coordinates of the four corners of the wall (hence assumed to be rectangular) */
 	xx[0] = xx[1] = nesw[(quadrant+1)%4];	xx[2] = xx[3] = nesw[(quadrant+3)%4];
 	yy[0] = yy[3] = GMT->current.proj.zmin;	yy[1] = yy[2] = GMT->current.proj.zmax;
-	if (mode3d & GMT_3D_WALL && back) {
-		int wplane = 1 - plane;
-		if (GMT->current.map.frame.paint[wplane]) {	/* First paint the back wall */
+	if (mode3d & GMT_3D_WALL && back) {	/* Called for one of the back walls and we wish to draw it */
+		int wplane = 1 - plane;	/* Get integer for the correct plain side */
+		if (GMT->current.map.frame.paint[wplane]) {	/* First paint the back wall, with no outline drawn */
 			PSL_setfill (PSL, GMT->current.map.frame.fill[wplane].rgb, 0);
 			PSL_plotbox (PSL, nesw[(quadrant+1)%4], GMT->current.proj.zmin, nesw[(quadrant+3)%4], GMT->current.proj.zmax);
 		}
-		if (back)
+		if (back)	/* Gridlines was requested, so draw those now */
 			gmtplot_z_gridlines (GMT, PSL, GMT->common.R.wesn[ZLO], GMT->common.R.wesn[ZHI], plane, mode3d, quadrant);
 
-		if (GMT->current.map.frame.draw_wall) {
+		if (GMT->current.map.frame.draw_wall) {	/* We wanted the outline of the back-wall drawn, do now to overwrite any perimeter gridlines */
 			gmt_setpen (GMT, &GMT->current.map.frame.pen);
 			PSL_plotline (PSL, xx, yy, 4, PSL_MOVE|PSL_STROKE);
 		}
 	}
-	else if (back)
+	else if (back)	/* Get here if no back-walls were filled our outlined */
 		gmtplot_z_gridlines (GMT, PSL, GMT->common.R.wesn[ZLO], GMT->common.R.wesn[ZHI], plane, mode3d, quadrant);
-	if (mode3d & GMT_3D_BOX) {
-		gmt_setpen (GMT, &GMT->current.map.frame.pen);
-		PSL_plotline (PSL, xx, yy, 4, PSL_MOVE|PSL_STROKE);
-	}
+}
+
+GMT_LOCAL void gmtplot_cube_box (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL, int quadrant, double *nesw) {
+	/* Draws the 3-D cube lines */
+	int plane = (quadrant + 1) % 2;	/* Black magic that gives us GMT_X (for yz plane) or GMT_Y (for xz plane) */
+	double xx[4], yy[4];
+	gmt_plane_perspective (GMT, plane, nesw[quadrant % 4]);
+	/* Assign the coordinates of the four corners of the wall (hence assumed to be rectangular) */
+	xx[0] = xx[1] = nesw[(quadrant+1)%4];	xx[2] = xx[3] = nesw[(quadrant+3)%4];
+	yy[0] = yy[3] = GMT->current.proj.zmin;	yy[1] = yy[2] = GMT->current.proj.zmax;
+	gmt_setpen (GMT, &GMT->current.map.frame.pen);
+	PSL_plotline (PSL, xx, yy, 4, PSL_MOVE|PSL_STROKE);
 }
 
 GMT_LOCAL void gmtplot_timestamp (struct GMT_CTRL *GMT, struct PSL_CTRL *PSL, double x, double y, unsigned int justify, char *U_label) {
@@ -5603,6 +5613,12 @@ void gmt_vertical_axis (struct GMT_CTRL *GMT, unsigned int mode) {
 			gmtplot_vertical_wall (GMT, PSL, GMT->current.proj.z_project.quadrant + 1, nesw, true, GMT->current.map.frame.draw_box);
 			gmtplot_vertical_wall (GMT, PSL, GMT->current.proj.z_project.quadrant + 2, nesw, true, GMT->current.map.frame.draw_box);
 		}
+		if (GMT->current.map.frame.draw_box & GMT_3D_BOX) {
+			gmtplot_cube_box (GMT, PSL, GMT->current.proj.z_project.quadrant + 3, nesw);
+			gmtplot_cube_box (GMT, PSL, GMT->current.proj.z_project.quadrant    , nesw);
+			gmtplot_cube_box (GMT, PSL, GMT->current.proj.z_project.quadrant + 1, nesw);
+			gmtplot_cube_box (GMT, PSL, GMT->current.proj.z_project.quadrant + 2, nesw);
+		}
 	}
 
 	/* Vertical axis */

From 44cf8507df8bfdaa3cf0133e006894cb5dfaef34 Mon Sep 17 00:00:00 2001
From: Paul Wessel <pwessel@hawaii.edu>
Date: Sat, 22 Aug 2020 19:02:09 -1000
Subject: [PATCH 23/25] Update gmtparse_B_arg_inspector for new +i,w,x,y,z
 modifiers

---
 src/gmt_parse.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/src/gmt_parse.c b/src/gmt_parse.c
index 815cf048f87..20107a2f5ec 100644
--- a/src/gmt_parse.c
+++ b/src/gmt_parse.c
@@ -86,7 +86,7 @@ GMT_LOCAL int gmtparse_B_arg_inspector (struct GMT_CTRL *GMT, char *in) {
 	int gmt4 = 0, gmt5 = 0, n_digits = 0, n_colons = 0, n_slashes = 0, colon_text = 0, wesn_at_end = 0;
 	bool ignore = false;	/* true if inside a colon-separated string under GMT4 style assumption */
 	bool ignore5 = false;	/* true if label, title, prefix, suffix */
-	bool custom = false;	/* True if -B[p|s][x|y|z]c<filename> was given; then we relax checing for .c (old second) */
+	bool custom = false;	/* True if -B[p|s][x|y|z]c<filename> was given; then we relax checking for .c (old second) */
 	char mod = 0;
 
 	if (!in || in[0] == 0) return (9);	/* Just a safety precaution, 9 means "either" syntax but it is an empty string */
@@ -124,10 +124,12 @@ GMT_LOCAL int gmtparse_B_arg_inspector (struct GMT_CTRL *GMT, char *in) {
 		if (ignore) continue;	/* Don't look inside a title or label */
 		switch (in[k]) {
 			case '/': if (mod == 0) n_slashes++; break;	/* Only GMT4 uses slashes */
-			case '+':	/* Plus, might be GMT5 modifier switch */
+			case '+':	/* Plus, might be a GMT5 modifier switch */
 				if      (k < last && in[k+1] == 'u') {mod = 'u'; ignore5 = true;  gmt5++;}	/* unit (suffix) settings */
 				else if (k < last && in[k+1] == 'b') {mod = 'b'; ignore5 = false; gmt5++;}	/* 3-D box settings */
 				else if (k < last && in[k+1] == 'g') {mod = 'g'; ignore5 = false; gmt5++;}	/* fill settings */
+				else if (k < last && in[k+1] == 'i') {mod = 'i'; ignore5 = false; gmt5++;}	/* internal annotation settings */
+				else if (k < last && in[k+1] == 'n') {mod = 'n'; ignore5 = true;  gmt5++;}	/* Turn off frames and annotations */
 				else if (k < last && in[k+1] == 'o') {mod = 'o'; ignore5 = false; gmt5++;}	/* oblique pole settings */
 				else if (k < last && in[k+1] == 'p') {mod = 'p'; ignore5 = true;  gmt5++;}	/* prefix settings */
 				else if (k < last && in[k+1] == 'l') {mod = 'l'; ignore5 = true;  gmt5++;}	/* Label */
@@ -135,7 +137,10 @@ GMT_LOCAL int gmtparse_B_arg_inspector (struct GMT_CTRL *GMT, char *in) {
 				else if (k < last && in[k+1] == 's') {mod = 's'; ignore5 = true;  gmt5++;}	/* Secondary label */
 				else if (k < last && in[k+1] == 'S') {mod = 'S'; ignore5 = true;  gmt5++;}	/* Forced horizontal Secondary lLabel */
 				else if (k < last && in[k+1] == 't') {mod = 't'; ignore5 = true;  gmt5++;}	/* title */
-				else if (k < last && in[k+1] == 'n') {mod = 'n'; ignore5 = true;  gmt5++;}	/* Turn off frames and annotations */
+				else if (k < last && in[k+1] == 'w') {mod = 'w'; ignore5 = false; gmt5++;}	/* Pen for walls */
+				else if (k < last && in[k+1] == 'x') {mod = 'x'; ignore5 = false; gmt5++;}	/* Paint for yz plane */
+				else if (k < last && in[k+1] == 'y') {mod = 'y'; ignore5 = false; gmt5++;}	/* Paint for xz plane */
+				else if (k < last && in[k+1] == 'z') {mod = 'z'; ignore5 = false; gmt5++;}	/* Paint for xy plane */
 				else if (k && (in[k-1] == 'Z' || in[k-1] == 'z')) {ignore5 = false; gmt4++;}	/* Z-axis with 3-D box */
 				break;
 			case 'c':	/* If following a number this is unit c for seconds in GMT4 */

From 824689881c76657427a9fd753f8555d4b0f06deb Mon Sep 17 00:00:00 2001
From: Paul Wessel <pwessel@hawaii.edu>
Date: Sat, 22 Aug 2020 19:43:00 -1000
Subject: [PATCH 24/25] Update module lists

---
 doc/rst/source/modules-classic.rst | 4 ++++
 doc/rst/source/modules.rst         | 4 ++++
 2 files changed, 8 insertions(+)

diff --git a/doc/rst/source/modules-classic.rst b/doc/rst/source/modules-classic.rst
index 6330dd91926..ce334222ef0 100644
--- a/doc/rst/source/modules-classic.rst
+++ b/doc/rst/source/modules-classic.rst
@@ -37,6 +37,7 @@ All modules are requested via a call to the :doc:`gmt` program.
     filter1d
     fitcircle
     gmt2kml
+    gmtbinstats
     gmtconnect
     gmtconvert
     gmtdefaults
@@ -192,6 +193,7 @@ Core Modules
     - :doc:`filter1d`
     - :doc:`fitcircle`
     - :doc:`gmt2kml`
+    - :doc:`gmtbinstats`
     - :doc:`gmtconnect`
     - :doc:`gmtconvert`
     - :doc:`gmtdefaults`
@@ -572,6 +574,8 @@ Miscellaneous
 +-----------------------+-----------------------+
 | :doc:`grdgdal`        | |grdgdal_purpose|     |
 +-----------------------+-----------------------+
+| :doc:`gmtbinstats`    | |gmtbinstats_purpose| |
++-----------------------+-----------------------+
 | :doc:`gmtwhich`       | |gmtwhich_purpose|    |
 +-----------------------+-----------------------+
 | :doc:`gmtwhich`       | |gmtwhich_purpose|    |
diff --git a/doc/rst/source/modules.rst b/doc/rst/source/modules.rst
index b93ead2b6bf..7ca9440f7ea 100644
--- a/doc/rst/source/modules.rst
+++ b/doc/rst/source/modules.rst
@@ -45,6 +45,7 @@ All modules are requested via a call to the :doc:`gmt` program.
    filter1d
    fitcircle
    gmt2kml
+   gmtbinstats
    gmtconnect
    gmtconvert
    gmtdefaults
@@ -207,6 +208,7 @@ Core Modules
     - :doc:`filter1d`
     - :doc:`fitcircle`
     - :doc:`gmt2kml`
+    - :doc:`gmtbinstats`
     - :doc:`gmtconnect`
     - :doc:`gmtconvert`
     - :doc:`gmtdefaults`
@@ -601,6 +603,8 @@ Miscellaneous
 +-----------------------+-----------------------+
 | :doc:`grdgdal`        | |grdgdal_purpose|     |
 +-----------------------+-----------------------+
+| :doc:`gmtbinstats`    | |gmtbinstats_purpose| |
++-----------------------+-----------------------+
 | :doc:`gmtwhich`       | |gmtwhich_purpose|    |
 +-----------------------+-----------------------+
 | :doc:`kml2gmt`        | |kml2gmt_purpose|     |

From 9fae472f20acf6813e6d1b0d5d838b19b0137ff2 Mon Sep 17 00:00:00 2001
From: Dongdong Tian <seisman.info@gmail.com>
Date: Sun, 23 Aug 2020 13:11:15 -0400
Subject: [PATCH 25/25] Revert "Update module lists"

This reverts commit 824689881c76657427a9fd753f8555d4b0f06deb.
---
 doc/rst/source/modules-classic.rst | 4 ----
 doc/rst/source/modules.rst         | 4 ----
 2 files changed, 8 deletions(-)

diff --git a/doc/rst/source/modules-classic.rst b/doc/rst/source/modules-classic.rst
index ce334222ef0..6330dd91926 100644
--- a/doc/rst/source/modules-classic.rst
+++ b/doc/rst/source/modules-classic.rst
@@ -37,7 +37,6 @@ All modules are requested via a call to the :doc:`gmt` program.
     filter1d
     fitcircle
     gmt2kml
-    gmtbinstats
     gmtconnect
     gmtconvert
     gmtdefaults
@@ -193,7 +192,6 @@ Core Modules
     - :doc:`filter1d`
     - :doc:`fitcircle`
     - :doc:`gmt2kml`
-    - :doc:`gmtbinstats`
     - :doc:`gmtconnect`
     - :doc:`gmtconvert`
     - :doc:`gmtdefaults`
@@ -574,8 +572,6 @@ Miscellaneous
 +-----------------------+-----------------------+
 | :doc:`grdgdal`        | |grdgdal_purpose|     |
 +-----------------------+-----------------------+
-| :doc:`gmtbinstats`    | |gmtbinstats_purpose| |
-+-----------------------+-----------------------+
 | :doc:`gmtwhich`       | |gmtwhich_purpose|    |
 +-----------------------+-----------------------+
 | :doc:`gmtwhich`       | |gmtwhich_purpose|    |
diff --git a/doc/rst/source/modules.rst b/doc/rst/source/modules.rst
index 7ca9440f7ea..b93ead2b6bf 100644
--- a/doc/rst/source/modules.rst
+++ b/doc/rst/source/modules.rst
@@ -45,7 +45,6 @@ All modules are requested via a call to the :doc:`gmt` program.
    filter1d
    fitcircle
    gmt2kml
-   gmtbinstats
    gmtconnect
    gmtconvert
    gmtdefaults
@@ -208,7 +207,6 @@ Core Modules
     - :doc:`filter1d`
     - :doc:`fitcircle`
     - :doc:`gmt2kml`
-    - :doc:`gmtbinstats`
     - :doc:`gmtconnect`
     - :doc:`gmtconvert`
     - :doc:`gmtdefaults`
@@ -603,8 +601,6 @@ Miscellaneous
 +-----------------------+-----------------------+
 | :doc:`grdgdal`        | |grdgdal_purpose|     |
 +-----------------------+-----------------------+
-| :doc:`gmtbinstats`    | |gmtbinstats_purpose| |
-+-----------------------+-----------------------+
 | :doc:`gmtwhich`       | |gmtwhich_purpose|    |
 +-----------------------+-----------------------+
 | :doc:`kml2gmt`        | |kml2gmt_purpose|     |