Add geometry shader to pipeline

 - This follows on the previous commit; rendering modes can now be
   switched by pressing 'M'. Currently, the alternate mode only moves
   some processing to the geometry shader, and adds an annoying
   time-dependent movement of line segments so I can verify it's working
   and the normal calculation looks alright.

 - Next up: trying to generate triangles in the geometry shader instead
   of just copying the line segments.

l_system_3d.c

@@ -46,7 +46,7 @@ static void FreeApplicationState(ApplicationState *s) {
 // Recomputes the scene's projection matrix based on s->aspect_ratio.
 static void UpdateProjectionMatrix(ApplicationState *s) {
   glm_mat4_identity(s->shared_uniforms.projection);
-  glm_perspective(45.0, s->aspect_ratio, 0.01, 100.0,
+  glm_perspective(45.0, s->aspect_ratio, 1.0, 100.0,
     s->shared_uniforms.projection);
 }
 
@@ -297,7 +297,9 @@ static void UpdateCamera(ApplicationState *s) {
   glm_vec3_zero(target);
   glm_vec3_zero(up);
   up[1] = 1.0;
-  tmp = glfwGetTime() / 4.0;
+  tmp = glfwGetTime();
+  s->shared_uniforms.current_time = tmp;
+  tmp /= 4.0;
   position[0] = sin(tmp) * 5.0;
   position[1] = 2.0;
   position[2] = cos(tmp) * 5.0;

l_system_3d.h

@@ -14,7 +14,8 @@ typedef struct {
   vec4 camera_position;
   float size_scale;
   float geometry_thickness;
-  float pad[2];
+  float current_time;
+  float pad[1];
 } SharedUniforms;
 
 // Maintains global data about the running program.

pipes_shader.geom

@@ -1,6 +1,6 @@
 #version 330 core
 layout (lines) in;
-layout (triangle_strip, max_vertices = 4) out;
+layout (line_strip, max_vertices = 2) out;
 
 in VS_OUT {
   vec3 position;
@@ -18,40 +18,33 @@ out GS_OUT {
   vec4 color;
 } gs_out;
 
+uniform mat4 model;
+uniform mat3 normal;
+
 //INCLUDE_SHARED_UNIFORMS
 
+// Returns a value that oscillates between 0 and 1 based on time.
+float timeOffset() {
+  return (sin(shared_uniforms.current_time * 3) + 1.0) * 0.5;
+}
+
 void main() {
-  vec3 right = gs_in[0].right;
-  vec3 forward = gs_in[0].forward;
-  vec3 bottom = gs_in[0].position;
-  vec3 top = gs_in[0].position;
-  // NOTE: verify this is in the correct order.
+  gs_out.forward = normal * gs_in[0].forward;
+  gs_out.up = normal * gs_in[0].up;
+  gs_out.right = normal * gs_in[0].right;
+  gs_out.color = gs_in[1].color;
+
   mat4 projView = shared_uniforms.projection * shared_uniforms.view;
-  // The normal vectors don't change.
-  gs_out.forward = forward;
-  gs_out.up = gs_in[0].up;
-  gs_out.right = right;
-  //gs_out.color = gs_in[1].color;
-  gs_out.color = vec4(0.5, 0.3, 1.0, 1.0);
-
-  float half_rect_width = 0.5 * shared_uniforms.geometry_thickness *
-    shared_uniforms.size_scale;
-
-  // Bottom left
-  gs_out.frag_position = bottom - (right * half_rect_width);
-  gl_Position = projView * vec4(gs_out.frag_position, 1.0);
+  vec4 pos_tmp = model * vec4(gs_in[0].position, 1);
+  pos_tmp += normalize(vec4(gs_out.right, 1.0)) * timeOffset();
+  gs_out.frag_position = pos_tmp.xyz;
+  gl_Position = projView * pos_tmp;
   EmitVertex();
-  // Bottom right
-  gs_out.frag_position = bottom + (right * half_rect_width);
-  gl_Position = projView * vec4(gs_out.frag_position, 1.0);
-  EmitVertex();
-  // Top right
-  gs_out.frag_position = top + (right * half_rect_width);
-  gl_Position = projView * vec4(gs_out.frag_position, 1.0);
-  EmitVertex();
-  // Top left
-  gs_out.frag_position = top - (right * half_rect_width);
-  gl_Position = projView * vec4(gs_out.frag_position, 1.0);
+
+  pos_tmp = model * vec4(gs_in[1].position, 1);
+  pos_tmp += normalize(vec4(gs_out.right, 1.0)) * timeOffset();
+  gs_out.frag_position = pos_tmp.xyz;
+  gl_Position = projView * pos_tmp;
   EmitVertex();
   EndPrimitive();
 }

pipes_shader.vert

@@ -7,9 +7,6 @@ layout (location = 3) in vec4 color_in;
 // Added to the location of each vertex to center the overall mesh on 0,0,0.
 uniform vec3 location_offset;
 
-uniform mat4 model;
-uniform mat3 normal;
-
 out VS_OUT {
   vec3 position;
   vec3 forward;
@@ -21,9 +18,9 @@ out VS_OUT {
 //INCLUDE_SHARED_UNIFORMS
 
 void main() {
-  vs_out.position = (model * vec4(position_in + location_offset, 1.0)).xyz;
-  vs_out.forward = normalize(normal * forward_in);
-  vs_out.up = normalize(normal * up_in);
-  vs_out.right = normalize(cross(vs_out.forward, vs_out.up));
+  vs_out.position = position_in + location_offset;
+  vs_out.forward = forward_in;
+  vs_out.up = up_in;
   vs_out.color = color_in;
+  vs_out.right = normalize(cross(forward_in, up_in));
 }

shared_uniforms.glsl

@@ -4,6 +4,7 @@ layout(std140) uniform SharedUniforms {
   vec4 camera_position;
   float size_scale;
   float geometry_thickness;
-  float pad[2];
+  float current_time;
+  float pad[1];
 } shared_uniforms;
 

simple_shader.vert

@@ -22,8 +22,9 @@ out VS_OUT {
 //INCLUDE_SHARED_UNIFORMS
 
 void main() {
-  gl_Position = shared_uniforms.projection * shared_uniforms.view * model *
-    vec4(position_in + location_offset, 1.0);
+  vec4 loc_tmp = model * vec4(position_in + location_offset, 1.0);
+  gl_Position = shared_uniforms.projection * shared_uniforms.view * loc_tmp;
+  vs_out.frag_position = loc_tmp.xyz;
   vs_out.color = color_in;
   vs_out.forward = normal * forward_in;
   vs_out.up = normal * up_in;
@@ -34,6 +35,4 @@ void main() {
   if (normal[0][0] == 0.0001) {
     vs_out.color[0] *= 0.9999;
   }
-
-  vs_out.frag_position = vec3(model * vec4(position_in + location_offset, 1.0));
 }