Overlay-Next: Fix discrepancy with xray fade and in-front

This require another depth buffer for correct merging
of overlays. Hopefully we can remove this mandatory
allocation later.

source/blender/draw/engines/overlay/overlay_next_instance.cc

@@ -384,7 +384,9 @@ void Instance::draw(Manager &manager)
     /* For X-ray we render the scene to a separate depth buffer. */
     resources.xray_depth_tx.acquire(render_size, GPU_DEPTH24_STENCIL8);
     resources.depth_target_tx.wrap(resources.xray_depth_tx);
-    resources.depth_target_in_front_tx.wrap(resources.xray_depth_tx);
+    /* TODO(fclem): Remove mandatory allocation. */
+    resources.xray_depth_in_front_tx.acquire(render_size, GPU_DEPTH24_STENCIL8);
+    resources.depth_target_in_front_tx.wrap(resources.xray_depth_in_front_tx);
   }
   else {
     /* TODO(fclem): Remove mandatory allocation. */
@@ -469,6 +471,7 @@ void Instance::draw(Manager &manager)
   resources.line_tx.release();
   resources.overlay_tx.release();
   resources.xray_depth_tx.release();
+  resources.xray_depth_in_front_tx.release();
   resources.depth_in_front_alloc_tx.release();
   resources.color_overlay_alloc_tx.release();
   resources.color_render_alloc_tx.release();
@@ -523,7 +526,7 @@ void Instance::draw_v3d(Manager &manager, View &view)
 
   regular.prepass.draw(resources.overlay_line_fb, manager, view);
 
-  if (!state.xray_enabled && state.v3d && state.v3d->shading.type > OB_SOLID) {
+  if (state.xray_enabled || (state.v3d && state.v3d->shading.type > OB_SOLID)) {
     /* If workbench is not enabled, the infront buffer might contain garbage. */
     GPU_framebuffer_bind(resources.overlay_line_in_front_fb);
     GPU_framebuffer_clear_depth(resources.overlay_line_in_front_fb, 1.0f);

source/blender/draw/engines/overlay/overlay_next_private.hh

@@ -354,6 +354,7 @@ struct Resources : public select::SelectMap {
   TextureFromPool overlay_tx = {"overlay_tx"};
   /* Target containing depth of overlays when xray is enabled. */
   TextureFromPool xray_depth_tx = {"xray_depth_tx"};
+  TextureFromPool xray_depth_in_front_tx = {"xray_depth_in_front_tx"};
 
   /* Texture that are usually allocated inside. These are fallback when they aren't.
    * They are then wrapped inside the #TextureRefs below. */

source/blender/draw/engines/overlay/overlay_next_shader.cc

@@ -357,6 +357,7 @@ ShaderModule::ShaderModule(const SelectionType selection_type, const bool clippi
 
   xray_fade = shader("overlay_xray_fade", [](gpu::shader::ShaderCreateInfo &info) {
     info.sampler(2, ImageType::DEPTH_2D, "xrayDepthTexInfront");
+    info.sampler(3, ImageType::DEPTH_2D, "depthTexInfront");
   });
 
   /** Selectable Shaders */

source/blender/draw/engines/overlay/overlay_next_xray_fade.hh

@@ -43,6 +43,7 @@ class XrayFade {
       /* TODO(fclem): Confusing. The meaning of xray depth texture changed between legacy engine
        * and overlay next. To be renamed after shaders are not shared anymore. */
       pass.bind_texture("depthTex", &res.xray_depth_tx);
+      pass.bind_texture("depthTexInfront", &res.xray_depth_in_front_tx);
       pass.bind_texture("xrayDepthTex", &res.depth_tx);
       pass.bind_texture("xrayDepthTexInfront", &res.depth_in_front_tx);
       pass.push_constant("opacity", 1.0f - state.xray_opacity);

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

@@ -4,18 +4,38 @@
 
 void main()
 {
-  float depth = texture(depthTex, uvcoordsvar.xy).r;
-  float depth_xray = texture(xrayDepthTex, uvcoordsvar.xy).r;
 #ifdef OVERLAY_NEXT
-  float depth_xray_infront = texture(xrayDepthTexInfront, uvcoordsvar.xy).r;
-  if (((depth_xray_infront == 1.0) && (depth > depth_xray)) || (depth > depth_xray_infront)) {
-    fragColor = vec4(opacity);
-  }
-  else {
+  /* TODO(fclem): Cleanup naming. Here the xray depth mean the scene depth (from workbench) and
+   * simple depth is the overlay depth. */
+  float depth_infront = textureLod(depthTexInfront, uvcoordsvar.xy, 0.0).r;
+  float depth_xray_infront = textureLod(xrayDepthTexInfront, uvcoordsvar.xy, 0.0).r;
+  if (depth_infront != 1.0) {
+    if (depth_xray_infront < depth_infront) {
+      fragColor = vec4(opacity);
+      return;
+    }
+
     discard;
     return;
   }
+
+  float depth = textureLod(depthTex, uvcoordsvar.xy, 0.0).r;
+  float depth_xray = textureLod(xrayDepthTex, uvcoordsvar.xy, 0.0).r;
+  /* Merge infront depth. */
+  if (depth_xray_infront != 1.0) {
+    depth_xray = 0.0;
+  }
+
+  if (depth_xray < depth) {
+    fragColor = vec4(opacity);
+    return;
+  }
+
+  discard;
+  return;
 #else
+  float depth = texture(depthTex, uvcoordsvar.xy).r;
+  float depth_xray = texture(xrayDepthTex, uvcoordsvar.xy).r;
   fragColor = vec4((depth < 1.0 && depth > depth_xray) ? opacity : 1.0);
 #endif
 }