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

@@ -8,6 +8,11 @@ void main()
   vec3 world_pos = point_object_to_world(pos);
   gl_Position = point_world_to_ndc(world_pos);
 
+#ifdef GPU_METAL
+  /* Small bias to always be on top of the geom. */
+  gl_Position.z -= 5e-5;
+#endif
+
   bool is_select = (nor.w > 0.0);
   bool is_hidden = (nor.w < 0.0);
 

source/blender/gpu/metal/mtl_shader_generator.mm

@@ -2606,14 +2606,28 @@ std::string MSLGeneratorInterface::generate_msl_vertex_out_struct(ShaderStage sh
    * is explicitly specified as a tf output. */
   bool first_attr_is_position = false;
   if (this->uses_gl_Position) {
-    out << "\tfloat4 _default_position_ [[position]];" << std::endl;
+
+    /* If Invariance is available, utilise this to consistently mitigate depth fighting artifacts
+     * by ensuring that vertex position is consistently calculated between subsequent passes
+     * with maximum precision. */
+    out << "\tfloat4 _default_position_ [[position]]";
+    if (@available(macos 11.0, *)) {
+      out << " [[invariant]]";
+    }
+    out << ";" << std::endl;
   }
   else {
     if (!this->uses_transform_feedback) {
       /* Use first output element for position. */
       BLI_assert(this->vertex_output_varyings.size() > 0);
       BLI_assert(this->vertex_output_varyings[0].type == "vec4");
-      out << "\tfloat4 " << this->vertex_output_varyings[0].name << " [[position]];" << std::endl;
+
+      /* Use invariance if available. See above for detail. */
+      out << "\tfloat4 " << this->vertex_output_varyings[0].name << " [[position]];";
+      if (@available(macos 11.0, *)) {
+        out << " [[invariant]]";
+      }
+      out << ";" << std::endl;
       first_attr_is_position = true;
     }
   }