Give the default render target a stencil buffer.

Author: chinmaygarde

impeller/playground/playground.mm

@@ -157,8 +157,26 @@ static void PlaygroundKeyCallback(GLFWwindow* window,
     color0.load_action = LoadAction::kClear;
     color0.store_action = StoreAction::kStore;
 
+    TextureDescriptor stencil_texture_descriptor;
+    stencil_texture_descriptor.format = PixelFormat::kD32FloatS8UNormInt;
+    stencil_texture_descriptor.size = color0_desc.size;
+    stencil_texture_descriptor.usage =
+        static_cast<TextureUsageMask>(TextureUsage::kShaderRead) |
+        static_cast<TextureUsageMask>(TextureUsage::kShaderWrite);
+    auto stencil_texture =
+        renderer_.GetContext()->GetPermanentsAllocator()->CreateTexture(
+            StorageMode::kDeviceTransient, stencil_texture_descriptor);
+    stencil_texture->SetLabel("PlaygroundMainStencil");
+
+    StencilAttachment stencil0;
+    stencil0.texture = stencil_texture;
+    stencil0.clear_stencil = 0;
+    stencil0.load_action = LoadAction::kClear;
+    stencil0.store_action = StoreAction::kStore;
+
     RenderTarget desc;
     desc.SetColorAttachment(color0, 0u);
+    desc.SetStencilAttachment(stencil0);
 
     Surface surface(desc);
 

impeller/renderer/pipeline.h

@@ -68,6 +68,10 @@ class PipelineT {
             context,
             Builder::MakeDefaultPipelineDescriptor(context))) {}
 
+  explicit PipelineT(const Context& context,
+                     std::optional<PipelineDescriptor> desc)
+      : pipeline_future_(CreatePipelineFuture(context, desc)) {}
+
   std::shared_ptr<Pipeline> WaitAndGet() {
     if (did_wait_) {
       return pipeline_;

impeller/renderer/pipeline_builder.h

@@ -104,6 +104,14 @@ struct PipelineBuilder {
       desc.SetColorAttachmentDescriptor(0u, std::move(color0));
     }
 
+    // Setup default stencil buffer descriptions.
+    {
+      StencilAttachmentDescriptor stencil0;
+      stencil0.depth_stencil_pass = StencilOperation::kIncrementClamp;
+      desc.SetStencilAttachmentDescriptors(stencil0);
+      desc.SetStencilPixelFormat(PixelFormat::kD32FloatS8UNormInt);
+    }
+
     return true;
   }
 };