Fix T57650 UVEdit: selection not visible if behind unselected UVs

Use depth buffer to order the uv edges correctly to always draw selected
edges on top.
We still use the double drawing workaround for points to keep the smooth
antialiased display.

source/blender/editors/space_image/space_image.c

@@ -590,18 +590,17 @@ static void image_main_region_draw(const bContext *C, ARegion *ar)
    * olg context since we now use it for drawing the entire area */
   gpu_batch_presets_reset();
 
-  /* TODO(fclem) port to draw manager and remove the depth buffer allocation. */
   GPUViewport *viewport =
       ar->draw_buffer->viewport[ar->draw_buffer->stereo ? sima->iuser.multiview_eye : 0];
   DefaultFramebufferList *fbl = GPU_viewport_framebuffer_list_get(viewport);
-  GPU_framebuffer_bind(fbl->color_only_fb);
+  GPU_framebuffer_bind(fbl->default_fb);
 
   /* XXX not supported yet, disabling for now */
   scene->r.scemode &= ~R_COMP_CROP;
 
   /* clear and setup matrix */
   UI_GetThemeColor3fv(TH_BACK, col);
-  GPU_clear_color(col[0], col[1], col[2], 0.0);
+  GPU_clear_color(col[0], col[1], col[2], 0.0f);
   GPU_clear(GPU_COLOR_BIT);
 
   image_user_refresh_scene(C, sima);

source/blender/editors/uvedit/uvedit_draw.c

@@ -52,6 +52,7 @@
 #include "DEG_depsgraph_query.h"
 
 #include "GPU_batch.h"
+#include "GPU_framebuffer.h"
 #include "GPU_immediate.h"
 #include "GPU_immediate_util.h"
 #include "GPU_matrix.h"
@@ -300,8 +301,6 @@ static void draw_uvs(SpaceImage *sima, Scene *scene, Object *obedit, Depsgraph *
   uvedit_get_batches(eval_ob, sima, ts, &faces, &edges, &verts, &facedots);
 
   bool interpedges;
-  bool do_elem_order_fix = (ts->uv_flag & UV_SYNC_SELECTION) && (ts->selectmode & SCE_SELECT_FACE);
-  bool do_selected_edges = ((sima->flag & SI_NO_DRAWEDGES) == 0);
   bool draw_stretch = (sima->flag & SI_DRAW_STRETCH) != 0;
   if (ts->uv_flag & UV_SYNC_SELECTION) {
     interpedges = (ts->selectmode & SCE_SELECT_VERTEX) != 0;
@@ -378,37 +377,28 @@ static void draw_uvs(SpaceImage *sima, Scene *scene, Object *obedit, Depsgraph *
         break;
       }
       case SI_UVDT_OUTLINE: {
-        GPU_line_width(3.0f);
-        GPU_batch_program_set_builtin(edges, GPU_SHADER_2D_UNIFORM_COLOR);
-        GPU_batch_uniform_4f(edges, "color", 0.0f, 0.0f, 0.0f, 1.0f);
-        GPU_batch_draw(edges);
-
-        UI_GetThemeColor4fv(TH_WIRE_EDIT, col1);
-        UI_GetThemeColor4fv(TH_EDGE_SELECT, col2);
-
         /* We could modify the vbo's data filling
          * instead of modifying the provoking vert. */
         glProvokingVertex(GL_FIRST_VERTEX_CONVENTION);
 
-        GPU_line_width(1.0f);
+        UI_GetThemeColor4fv(TH_WIRE_EDIT, col1);
+        UI_GetThemeColor4fv(TH_EDGE_SELECT, col2);
+
         GPU_batch_program_set_builtin(
             edges, (interpedges) ? GPU_SHADER_2D_UV_EDGES_SMOOTH : GPU_SHADER_2D_UV_EDGES);
-        GPU_batch_uniform_4fv(edges, "edgeColor", col1);
-        GPU_batch_uniform_4fv(edges, "selectColor", do_selected_edges ? col2 : col1);
+        /* Black Outline. */
+        GPU_line_width(3.0f);
+        GPU_batch_uniform_4f(edges, "edgeColor", 0.0f, 0.0f, 0.0f, 1.0f);
+        GPU_batch_uniform_4f(edges, "selectColor", 0.0f, 0.0f, 0.0f, 1.0f);
         GPU_batch_draw(edges);
+        /* Inner Line. Use depth test to insure selection is drawn on top. */
+        GPU_depth_test(true);
+        GPU_line_width(1.0f);
+        GPU_batch_uniform_4fv(edges, "edgeColor", col1);
+        GPU_batch_uniform_4fv(edges, "selectColor", col2);
+        GPU_batch_draw(edges);
+        GPU_depth_test(false);
 
-        if (do_elem_order_fix && do_selected_edges) {
-          /* We have problem in this mode when face order make some edges
-           * appear unselected because an adjacent face is not selected and
-           * render after the selected face.
-           * So, to avoid sorting edges by state we just render selected edges
-           * on top. A bit overkill but it's simple. */
-          GPU_blend(true);
-          GPU_batch_uniform_4fv(edges, "edgeColor", transparent);
-          GPU_batch_uniform_4fv(edges, "selectColor", col2);
-          GPU_batch_draw(edges);
-          GPU_blend(false);
-        }
         glProvokingVertex(GL_LAST_VERTEX_CONVENTION);
         break;
       }
@@ -429,25 +419,20 @@ static void draw_uvs(SpaceImage *sima, Scene *scene, Object *obedit, Depsgraph *
 
       GPU_batch_program_set_builtin(verts, GPU_SHADER_2D_UV_VERTS);
       GPU_batch_uniform_4f(verts, "vertColor", col1[0], col1[1], col1[2], 1.0f);
-      GPU_batch_uniform_4fv(verts, "selectColor", (do_elem_order_fix) ? transparent : col2);
+      GPU_batch_uniform_4fv(verts, "selectColor", transparent);
       GPU_batch_uniform_4fv(verts, "pinnedColor", pinned_col);
       GPU_batch_uniform_1f(verts, "pointSize", (pointsize + 1.5f) * M_SQRT2);
       GPU_batch_uniform_1f(verts, "outlineWidth", 0.75f);
       GPU_batch_draw(verts);
 
-      if (do_elem_order_fix) {
-        /* We have problem in this mode when face order make some verts
-         * appear unselected because an adjacent face is not selected and
-         * render after the selected face.
-         * So, to avoid sorting verts by state we just render selected verts
-         * on top. A bit overkill but it's simple. */
-        GPU_batch_uniform_4fv(verts, "vertColor", transparent);
-        GPU_batch_uniform_4fv(verts, "selectColor", col2);
-        GPU_batch_uniform_4fv(verts, "pinnedColor", pinned_col);
-        GPU_batch_uniform_1f(verts, "pointSize", (pointsize + 1.5f) * M_SQRT2);
-        GPU_batch_uniform_1f(verts, "outlineWidth", 0.75f);
-        GPU_batch_draw(verts);
-      }
+      /* We have problem in this mode when face order make some verts
+       * appear unselected because an adjacent face is not selected and
+       * render after the selected face.
+       * So, to avoid sorting verts by state we just render selected verts
+       * on top. A bit overkill but it's simple. */
+      GPU_batch_uniform_4fv(verts, "vertColor", transparent);
+      GPU_batch_uniform_4fv(verts, "selectColor", col2);
+      GPU_batch_draw(verts);
 
       GPU_blend(false);
       GPU_program_point_size(false);
@@ -502,6 +487,10 @@ void ED_uvedit_draw_main(SpaceImage *sima,
       uint objects_len = 0;
       Object **objects = BKE_view_layer_array_from_objects_in_edit_mode_unique_data_with_uvs(
           view_layer, ((View3D *)NULL), &objects_len);
+      if (objects_len > 0) {
+        GPU_clear_depth(1.0f);
+        GPU_clear(GPU_DEPTH_BIT);
+      }
       for (uint ob_index = 0; ob_index < objects_len; ob_index++) {
         Object *ob_iter = objects[ob_index];
         draw_uvs(sima, scene, ob_iter, depsgraph);

source/blender/gpu/GPU_framebuffer.h

@@ -209,6 +209,7 @@ void GPU_offscreen_viewport_data_get(GPUOffScreen *ofs,
                                      struct GPUTexture **r_depth);
 
 void GPU_clear_color(float red, float green, float blue, float alpha);
+void GPU_clear_depth(float depth);
 void GPU_clear(eGPUFrameBufferBits flags);
 
 #ifdef __cplusplus

source/blender/gpu/intern/gpu_framebuffer.c

@@ -1041,6 +1041,11 @@ void GPU_clear_color(float red, float green, float blue, float alpha)
   glClearColor(red, green, blue, alpha);
 }
 
+void GPU_clear_depth(float depth)
+{
+  glClearDepth(depth);
+}
+
 void GPU_clear(eGPUFrameBufferBits flags)
 {
   glClear(convert_buffer_bits_to_gl(flags));

source/blender/gpu/shaders/gpu_shader_2D_edituvs_edges_vert.glsl

@@ -19,13 +19,14 @@ flat out vec4 finalColor;
 
 void main()
 {
-  gl_Position = ModelViewProjectionMatrix * vec4(pos, 0.0, 1.0);
-
 #ifdef SMOOTH_COLOR
   bool is_select = (flag & VERT_UV_SELECT) != 0;
 #else
   bool is_select = (flag & EDGE_UV_SELECT) != 0;
 #endif
 
+  gl_Position = ModelViewProjectionMatrix * vec4(pos, 0.0, 1.0);
+  gl_Position.z = float(!is_select);
+
   finalColor = (is_select) ? selectColor : edgeColor;
 }