Overlay: Wireframe: New method to avoid zfighting with geometry

This new method is only enabled if Overlay Smooth Wire is enabled.

This method gives really nice results but has some downside:
- Require a depth copy or loose the ability to write wire depth to the
  depth buffer and have correct depth ordering of wires. This patch use the former, with its associated cost.
- Require some depth sampling and prevent early depth test (i.e: has
  some performance impact).
- Has some relatively minor instability with geometry that are perpendicular
  to the view and intersecting with other geometry.

Pros:
- Compared to a fullpass approach this is surely going to have less
  performance impact and much higher quality.
- Removes the additional vertex offset. (see T74961)
- Fixes all half edges z-fighting.

{F8428014}

{F8428015}

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D7233

source/blender/draw/engines/overlay/overlay_antialiasing.c

@@ -113,16 +113,6 @@ void OVERLAY_antialiasing_init(OVERLAY_Data *vedata)
                                     GPU_ATTACHMENT_TEXTURE(color_tex),
                                     GPU_ATTACHMENT_TEXTURE(line_tex),
                                 });
-
-  if (pd->xray_enabled) {
-    DRW_texture_ensure_fullscreen_2d(&txl->temp_depth_tx, GPU_DEPTH24_STENCIL8, 0);
-
-    GPU_framebuffer_ensure_config(&fbl->overlay_xray_depth_copy_fb,
-                                  {
-                                      GPU_ATTACHMENT_TEXTURE(txl->temp_depth_tx),
-                                      GPU_ATTACHMENT_NONE,
-                                  });
-  }
 }
 
 void OVERLAY_antialiasing_cache_init(OVERLAY_Data *vedata)
@@ -168,6 +158,7 @@ void OVERLAY_antialiasing_cache_finish(OVERLAY_Data *vedata)
 {
   OVERLAY_FramebufferList *fbl = vedata->fbl;
   OVERLAY_TextureList *txl = vedata->txl;
+  OVERLAY_PassList *psl = vedata->psl;
   OVERLAY_PrivateData *pd = vedata->stl->pd;
   DefaultTextureList *dtxl = DRW_viewport_texture_list_get();
 
@@ -191,6 +182,22 @@ void OVERLAY_antialiasing_cache_finish(OVERLAY_Data *vedata)
                                    GPU_ATTACHMENT_TEXTURE(dtxl->color_overlay),
                                    GPU_ATTACHMENT_TEXTURE(txl->overlay_line_tx)});
   }
+
+  pd->antialiasing.do_depth_copy = !DRW_pass_is_empty(psl->wireframe_ps) ||
+                                   (pd->xray_enabled && pd->xray_opacity > 0.0f);
+  pd->antialiasing.do_depth_infront_copy = !DRW_pass_is_empty(psl->wireframe_xray_ps);
+
+  const bool do_wireframe = pd->antialiasing.do_depth_copy ||
+                            pd->antialiasing.do_depth_infront_copy;
+  if (pd->xray_enabled || do_wireframe) {
+    DRW_texture_ensure_fullscreen_2d(&txl->temp_depth_tx, GPU_DEPTH24_STENCIL8, 0);
+
+    GPU_framebuffer_ensure_config(&fbl->overlay_xray_depth_copy_fb,
+                                  {
+                                      GPU_ATTACHMENT_TEXTURE(txl->temp_depth_tx),
+                                      GPU_ATTACHMENT_NONE,
+                                  });
+  }
 }
 
 void OVERLAY_antialiasing_start(OVERLAY_Data *vedata)
@@ -217,18 +224,31 @@ void OVERLAY_xray_depth_copy(OVERLAY_Data *vedata)
   OVERLAY_FramebufferList *fbl = vedata->fbl;
   OVERLAY_PrivateData *pd = vedata->stl->pd;
 
+  if (DRW_state_is_fbo() && pd->antialiasing.do_depth_copy) {
+    /* We copy the depth of the rendered geometry to be able to compare to the overlays depth. */
+    GPU_framebuffer_blit(
+        fbl->overlay_default_fb, 0, fbl->overlay_xray_depth_copy_fb, 0, GPU_DEPTH_BIT);
+  }
+
   if (DRW_state_is_fbo() && pd->xray_enabled) {
-    if (pd->xray_opacity > 0.0f) {
-      /* We copy the depth of the rendered geometry to be able to compare to the overlays depth. */
-      GPU_framebuffer_blit(
-          fbl->overlay_default_fb, 0, fbl->overlay_xray_depth_copy_fb, 0, GPU_DEPTH_BIT);
-    }
     /* We then clear to not occlude the overlays directly. */
     GPU_framebuffer_bind(fbl->overlay_default_fb);
     GPU_framebuffer_clear_depth(fbl->overlay_default_fb, 1.0f);
   }
 }
 
+void OVERLAY_xray_depth_infront_copy(OVERLAY_Data *vedata)
+{
+  OVERLAY_FramebufferList *fbl = vedata->fbl;
+  OVERLAY_PrivateData *pd = vedata->stl->pd;
+
+  if (DRW_state_is_fbo() && pd->antialiasing.do_depth_infront_copy) {
+    /* We copy the depth of the rendered geometry to be able to compare to the overlays depth. */
+    GPU_framebuffer_blit(
+        fbl->overlay_in_front_fb, 0, fbl->overlay_xray_depth_copy_fb, 0, GPU_DEPTH_BIT);
+  }
+}
+
 void OVERLAY_xray_fade_draw(OVERLAY_Data *vedata)
 {
   OVERLAY_PassList *psl = vedata->psl;

source/blender/draw/engines/overlay/overlay_engine.c

@@ -466,6 +466,8 @@ static void OVERLAY_draw_scene(void *vedata)
   OVERLAY_xray_fade_draw(vedata);
   OVERLAY_grid_draw(vedata);
 
+  OVERLAY_xray_depth_infront_copy(vedata);
+
   if (DRW_state_is_fbo()) {
     GPU_framebuffer_bind(fbl->overlay_line_in_front_fb);
   }

source/blender/draw/engines/overlay/overlay_private.h

@@ -293,6 +293,8 @@ typedef struct OVERLAY_PrivateData {
 
   struct {
     bool enabled;
+    bool do_depth_copy;
+    bool do_depth_infront_copy;
   } antialiasing;
   struct {
     bool show_handles;
@@ -411,6 +413,7 @@ void OVERLAY_antialiasing_start(OVERLAY_Data *vedata);
 void OVERLAY_antialiasing_end(OVERLAY_Data *vedata);
 void OVERLAY_xray_fade_draw(OVERLAY_Data *vedata);
 void OVERLAY_xray_depth_copy(OVERLAY_Data *vedata);
+void OVERLAY_xray_depth_infront_copy(OVERLAY_Data *vedata);
 
 bool OVERLAY_armature_is_pose_mode(Object *ob, const struct DRWContextState *draw_ctx);
 void OVERLAY_armature_cache_init(OVERLAY_Data *vedata);
@@ -613,7 +616,7 @@ GPUShader *OVERLAY_shader_particle_shape(void);
 GPUShader *OVERLAY_shader_pointcloud_dot(void);
 GPUShader *OVERLAY_shader_sculpt_mask(void);
 GPUShader *OVERLAY_shader_volume_velocity(bool use_needle);
-GPUShader *OVERLAY_shader_wireframe(void);
+GPUShader *OVERLAY_shader_wireframe(bool custom_bias);
 GPUShader *OVERLAY_shader_wireframe_select(void);
 GPUShader *OVERLAY_shader_xray_fade(void);
 

source/blender/draw/engines/overlay/overlay_shader.c

@@ -192,7 +192,7 @@ typedef struct OVERLAY_Shaders {
   GPUShader *volume_velocity_needle_sh;
   GPUShader *volume_velocity_sh;
   GPUShader *wireframe_select;
-  GPUShader *wireframe;
+  GPUShader *wireframe[2];
   GPUShader *xray_fade;
 } OVERLAY_Shaders;
 
@@ -1372,24 +1372,29 @@ GPUShader *OVERLAY_shader_wireframe_select(void)
   return sh_data->wireframe_select;
 }
 
-GPUShader *OVERLAY_shader_wireframe(void)
+GPUShader *OVERLAY_shader_wireframe(bool custom_bias)
 {
   const DRWContextState *draw_ctx = DRW_context_state_get();
   const GPUShaderConfigData *sh_cfg = &GPU_shader_cfg_data[draw_ctx->sh_cfg];
   OVERLAY_Shaders *sh_data = &e_data.sh_data[draw_ctx->sh_cfg];
-  if (!sh_data->wireframe) {
-    sh_data->wireframe = GPU_shader_create_from_arrays({
+  if (!sh_data->wireframe[custom_bias]) {
+    sh_data->wireframe[custom_bias] = GPU_shader_create_from_arrays({
         .vert = (const char *[]){sh_cfg->lib,
                                  datatoc_common_view_lib_glsl,
                                  datatoc_common_globals_lib_glsl,
                                  datatoc_gpu_shader_common_obinfos_lib_glsl,
                                  datatoc_wireframe_vert_glsl,
                                  NULL},
-        .frag = (const char *[]){datatoc_common_view_lib_glsl, datatoc_wireframe_frag_glsl, NULL},
-        .defs = (const char *[]){sh_cfg->def, NULL},
+        .frag = (const char *[]){datatoc_common_view_lib_glsl,
+                                 datatoc_common_globals_lib_glsl,
+                                 datatoc_wireframe_frag_glsl,
+                                 NULL},
+        .defs = (const char *[]){sh_cfg->def,
+                                 custom_bias ? "#define CUSTOM_DEPTH_BIAS\n" : NULL,
+                                 NULL},
     });
   }
-  return sh_data->wireframe;
+  return sh_data->wireframe[custom_bias];
 }
 
 GPUShader *OVERLAY_shader_xray_fade(void)

source/blender/draw/engines/overlay/overlay_wireframe.c

@@ -51,6 +51,7 @@ void OVERLAY_wireframe_init(OVERLAY_Data *vedata)
 void OVERLAY_wireframe_cache_init(OVERLAY_Data *vedata)
 {
   OVERLAY_PassList *psl = vedata->psl;
+  OVERLAY_TextureList *txl = vedata->txl;
   OVERLAY_PrivateData *pd = vedata->stl->pd;
   const DRWContextState *draw_ctx = DRW_context_state_get();
   DRWShadingGroup *grp = NULL;
@@ -66,12 +67,14 @@ void OVERLAY_wireframe_cache_init(OVERLAY_Data *vedata)
 
   const bool use_select = (DRW_state_is_select() || DRW_state_is_depth());
   GPUShader *wires_sh = use_select ? OVERLAY_shader_wireframe_select() :
-                                     OVERLAY_shader_wireframe();
+                                     OVERLAY_shader_wireframe(pd->antialiasing.enabled);
 
   for (int xray = 0; xray < (is_material_shmode ? 1 : 2); xray++) {
     DRWState state = DRW_STATE_FIRST_VERTEX_CONVENTION | DRW_STATE_WRITE_COLOR |
                      DRW_STATE_WRITE_DEPTH | DRW_STATE_DEPTH_LESS_EQUAL;
     DRWPass *pass;
+    GPUTexture **depth_tx = (pd->xray_enabled || pd->xray_opacity > 0.0f) ? &txl->temp_depth_tx :
+                                                                            &txl->dummy_depth_tx;
 
     if (xray == 0) {
       DRW_PASS_CREATE(psl->wireframe_ps, state | pd->clipping_state);
@@ -85,6 +88,7 @@ void OVERLAY_wireframe_cache_init(OVERLAY_Data *vedata)
     for (int use_coloring = 0; use_coloring < 2; use_coloring++) {
       pd->wires_grp[xray][use_coloring] = grp = DRW_shgroup_create(wires_sh, pass);
       DRW_shgroup_uniform_block_persistent(grp, "globalsBlock", G_draw.block_ubo);
+      DRW_shgroup_uniform_texture_ref(grp, "depthTex", depth_tx);
       DRW_shgroup_uniform_float_copy(grp, "wireStepParam", pd->shdata.wire_step_param);
       DRW_shgroup_uniform_bool_copy(grp, "useColoring", use_coloring);
       DRW_shgroup_uniform_bool_copy(grp, "isTransform", (G.moving & G_TRANSFORM_OBJ) != 0);
@@ -92,10 +96,12 @@ void OVERLAY_wireframe_cache_init(OVERLAY_Data *vedata)
       DRW_shgroup_uniform_bool_copy(grp, "isRandomColor", is_random_color);
 
       pd->wires_all_grp[xray][use_coloring] = grp = DRW_shgroup_create(wires_sh, pass);
+      DRW_shgroup_uniform_texture_ref(grp, "depthTex", depth_tx);
       DRW_shgroup_uniform_float_copy(grp, "wireStepParam", 1.0f);
     }
 
     pd->wires_sculpt_grp[xray] = grp = DRW_shgroup_create(wires_sh, pass);
+    DRW_shgroup_uniform_texture_ref(grp, "depthTex", depth_tx);
     DRW_shgroup_uniform_float_copy(grp, "wireStepParam", 10.0f);
     DRW_shgroup_uniform_bool_copy(grp, "useColoring", false);
   }

source/blender/draw/engines/overlay/shaders/wireframe_frag.glsl

@@ -1,4 +1,7 @@
 
+/* Scene Depth texture copy for manual depth test. */
+uniform sampler2D depthTex;
+
 flat in vec2 edgeStart;
 
 #ifndef SELECT_EDGES
@@ -21,5 +24,32 @@ void main()
   lineOutput = pack_line_data(gl_FragCoord.xy, edgeStart, edgePos);
   fragColor.rgb = finalColor;
   fragColor.a = 1.0;
+
+#  ifdef CUSTOM_DEPTH_BIAS
+  vec2 dir = lineOutput.xy * 2.0 - 1.0;
+  bool dir_horiz = abs(dir.x) > abs(dir.y);
+
+  vec2 uv = gl_FragCoord.xy * sizeViewportInv.xy;
+  float depth_occluder = texture(depthTex, uv).r;
+  float depth_min = depth_occluder;
+
+  if (dir_horiz) {
+    depth_min = min(depth_min, texture(depthTex, uv + vec2(-sizeViewportInv.x, 0.0)).r);
+    depth_min = min(depth_min, texture(depthTex, uv + vec2(sizeViewportInv.x, 0.0)).r);
+  }
+  else {
+    depth_min = min(depth_min, texture(depthTex, uv + vec2(0, -sizeViewportInv.y)).r);
+    depth_min = min(depth_min, texture(depthTex, uv + vec2(0, sizeViewportInv.y)).r);
+  }
+
+  float delta = abs(depth_occluder - depth_min);
+
+  if (gl_FragCoord.z < (depth_occluder + delta) && gl_FragCoord.z > depth_occluder) {
+    gl_FragDepth = depth_occluder;
+  }
+  else {
+    gl_FragDepth = gl_FragCoord.z;
+  }
+#  endif
 #endif
 }

source/blender/draw/engines/overlay/shaders/wireframe_vert.glsl

@@ -110,19 +110,22 @@ void main()
   vec3 V = (is_persp) ? normalize(ViewMatrixInverse[3].xyz - wpos) : ViewMatrixInverse[2].xyz;
 
   float facing = dot(wnor, V);
+
+  gl_Position = point_world_to_ndc(wpos);
+
+#ifndef CUSTOM_DEPTH_BIAS
   float facing_ratio = clamp(1.0 - facing * facing, 0.0, 1.0);
   float flip = sign(facing);           /* Flip when not facing the normal (i.e.: backfacing). */
   float curvature = (1.0 - wd * 0.75); /* Avoid making things worse for curvy areas. */
   vec3 wofs = wnor * (facing_ratio * curvature * flip);
   wofs = normal_world_to_view(wofs);
 
-  gl_Position = point_world_to_ndc(wpos);
-
   /* Push vertex half a pixel (maximum) in normal direction. */
   gl_Position.xy += wofs.xy * sizeViewportInv.xy * gl_Position.w;
 
   /* Push the vertex towards the camera. Helps a bit. */
-  gl_Position.z -= facing_ratio * curvature * 1.0e-5 * gl_Position.w;
+  gl_Position.z -= facing_ratio * curvature * 1.0e-6 * gl_Position.w;
+#endif
 
   /* Convert to screen position [0..sizeVp]. */
   edgeStart = ((gl_Position.xy / gl_Position.w) * 0.5 + 0.5) * sizeViewport.xy;