Handle local coords in blender-style transforms.

Pressing XX/YY/ZZ will lock the transform to a local (rather than
global) axis.

This is achieved by temporarily toggling the local transform button. I
did this (vs handling it in the transform functions) for 3 reasons:

- Transform logic for translate/rotate (but not scale) appears to be
  tightly coupled to the gizmo
- This ensures the gizmo changes to indicate we're transforming
  locally/globally
- Toggling the button state in the UI also gives the user feedback about
  the nature of the transform.

The original state of the button is reset when the transform completes.

See godotengine/godot-proposals#1215.

editor/plugins/spatial_editor_plugin.cpp

@@ -752,6 +752,7 @@ void SpatialEditorViewport::_update_name() {
 
 void SpatialEditorViewport::_compute_edit(const Point2 &p_point) {
 
+	_edit.original_local = spatial_editor->are_local_coords_enabled();
 	_edit.click_ray = _get_ray(Vector2(p_point.x, p_point.y));
 	_edit.click_ray_pos = _get_ray_pos(Vector2(p_point.x, p_point.y));
 	_edit.plane = TRANSFORM_VIEW;
@@ -1384,6 +1385,7 @@ void SpatialEditorViewport::_sinput(const Ref<InputEvent> &p_event) {
 						}
 						undo_redo->commit_action();
 						_edit.mode = TRANSFORM_NONE;
+						spatial_editor->set_local_coords_enabled(_edit.original_local);
 						set_message("");
 					}
 
@@ -1980,30 +1982,42 @@ void SpatialEditorViewport::_sinput(const Ref<InputEvent> &p_event) {
 
 		if (_edit.mode != TRANSFORM_NONE) {
 			// We're actively transforming, handle keys specially
-			bool handled = true;
+			TransformPlane new_plane = TRANSFORM_VIEW;
+			String new_message;
 			if (ED_IS_SHORTCUT("spatial_editor/lock_transform_x", p_event)) {
-				_edit.plane = TRANSFORM_X_AXIS;
-				set_message(TTR("X-Axis Transform."), 2);
+				new_plane = TRANSFORM_X_AXIS;
+				new_message = TTR("X-Axis Transform.");
 			} else if (ED_IS_SHORTCUT("spatial_editor/lock_transform_y", p_event)) {
-				_edit.plane = TRANSFORM_Y_AXIS;
-				set_message(TTR("Y-Axis Transform."), 2);
+				new_plane = TRANSFORM_Y_AXIS;
+				new_message = TTR("Y-Axis Transform.");
 			} else if (ED_IS_SHORTCUT("spatial_editor/lock_transform_z", p_event)) {
-				_edit.plane = TRANSFORM_Z_AXIS;
-				set_message(TTR("Z-Axis Transform."), 2);
+				new_plane = TRANSFORM_Z_AXIS;
+				new_message = TTR("Z-Axis Transform.");
 			} else if (ED_IS_SHORTCUT("spatial_editor/lock_transform_yz", p_event)) {
-				_edit.plane = TRANSFORM_YZ;
-				set_message(TTR("YZ-Plane Transform."), 2);
+				new_plane = TRANSFORM_YZ;
+				new_message = TTR("YZ-Plane Transform.");
 			} else if (ED_IS_SHORTCUT("spatial_editor/lock_transform_xz", p_event)) {
-				_edit.plane = TRANSFORM_XZ;
-				set_message(TTR("XZ-Plane Transform."), 2);
+				new_plane = TRANSFORM_XZ;
+				new_message = TTR("XZ-Plane Transform.");
 			} else if (ED_IS_SHORTCUT("spatial_editor/lock_transform_xy", p_event)) {
-				_edit.plane = TRANSFORM_XY;
-				set_message(TTR("XY-Plane Transform."), 2);
-			} else {
-				handled = false;
+				new_plane = TRANSFORM_XY;
+				new_message = TTR("XY-Plane Transform.");
 			}
 
-			if (handled) {
+			if (new_plane != TRANSFORM_VIEW) {
+				if (new_plane != _edit.plane) {
+					// lock me once and get a global constraint
+					_edit.plane = new_plane;
+					spatial_editor->set_local_coords_enabled(false);
+				} else if (!spatial_editor->are_local_coords_enabled()) {
+					// lock me twice and get a local constraint
+					spatial_editor->set_local_coords_enabled(true);
+				} else {
+					// lock me thrice and we're back where we started
+					_edit.plane = TRANSFORM_VIEW;
+					spatial_editor->set_local_coords_enabled(false);
+				}
+				set_message(new_message, 2);
 				accept_event();
 				return;
 			}

editor/plugins/spatial_editor_plugin.h

@@ -364,6 +364,7 @@ class SpatialEditorViewport : public Control {
 		int gizmo_handle;
 		Variant gizmo_initial_value;
 		Vector3 gizmo_initial_pos;
+		bool original_local;
 	} _edit;
 
 	struct Cursor {
@@ -745,6 +746,7 @@ class SpatialEditor : public VBoxContainer {
 
 	ToolMode get_tool_mode() const { return tool_mode; }
 	bool are_local_coords_enabled() const { return tool_option_button[SpatialEditor::TOOL_OPT_LOCAL_COORDS]->is_pressed(); }
+	void set_local_coords_enabled(bool on) const { tool_option_button[SpatialEditor::TOOL_OPT_LOCAL_COORDS]->set_pressed(on); }
 	bool is_snap_enabled() const { return snap_enabled ^ snap_key_enabled; }
 	float get_translate_snap() const;
 	float get_rotate_snap() const;