[Impeller] Switch from transient stencil to depth+stencil buffer.

Author: bdero

impeller/entity/entity_pass.cc

@@ -442,7 +442,7 @@ bool EntityPass::Render(ContentContext& renderer,
   // Setup a new root stencil with an optimal configuration if one wasn't
   // provided by the caller.
   else {
-    root_render_target.SetupStencilAttachment(
+    root_render_target.SetupDepthStencilAttachments(
         *renderer.GetContext(), *renderer.GetRenderTargetCache(),
         color0.texture->GetSize(),
         renderer.GetContext()->GetCapabilities()->SupportsOffscreenMSAA(),

impeller/renderer/render_target.cc

@@ -255,8 +255,8 @@ RenderTarget RenderTarget::CreateOffscreen(
   target.SetColorAttachment(color0, 0u);
 
   if (stencil_attachment_config.has_value()) {
-    target.SetupStencilAttachment(context, allocator, size, false, label,
-                                  stencil_attachment_config.value());
+    target.SetupDepthStencilAttachments(context, allocator, size, false, label,
+                                        stencil_attachment_config.value());
   } else {
     target.SetStencilAttachment(std::nullopt);
   }
@@ -347,43 +347,56 @@ RenderTarget RenderTarget::CreateOffscreenMSAA(
   // Create MSAA stencil texture.
 
   if (stencil_attachment_config.has_value()) {
-    target.SetupStencilAttachment(context, allocator, size, true, label,
-                                  stencil_attachment_config.value());
+    target.SetupDepthStencilAttachments(context, allocator, size, true, label,
+                                        stencil_attachment_config.value());
   } else {
     target.SetStencilAttachment(std::nullopt);
   }
 
   return target;
 }
 
-void RenderTarget::SetupStencilAttachment(
+void RenderTarget::SetupDepthStencilAttachments(
     const Context& context,
     RenderTargetAllocator& allocator,
     ISize size,
     bool msaa,
     const std::string& label,
     AttachmentConfig stencil_attachment_config) {
-  TextureDescriptor stencil_tex0;
-  stencil_tex0.storage_mode = stencil_attachment_config.storage_mode;
+  TextureDescriptor depth_stencil_texture_desc;
+  depth_stencil_texture_desc.storage_mode =
+      stencil_attachment_config.storage_mode;
   if (msaa) {
-    stencil_tex0.type = TextureType::kTexture2DMultisample;
-    stencil_tex0.sample_count = SampleCount::kCount4;
+    depth_stencil_texture_desc.type = TextureType::kTexture2DMultisample;
+    depth_stencil_texture_desc.sample_count = SampleCount::kCount4;
   }
-  stencil_tex0.format = context.GetCapabilities()->GetDefaultStencilFormat();
-  stencil_tex0.size = size;
-  stencil_tex0.usage =
+  depth_stencil_texture_desc.format =
+      context.GetCapabilities()->GetDefaultDepthStencilFormat();
+  depth_stencil_texture_desc.size = size;
+  depth_stencil_texture_desc.usage =
       static_cast<TextureUsageMask>(TextureUsage::kRenderTarget);
 
+  auto depth_stencil_texture =
+      allocator.CreateTexture(depth_stencil_texture_desc);
+  if (!depth_stencil_texture) {
+    return;  // Error messages are handled by `Allocator::CreateTexture`.
+  }
+
+  DepthAttachment depth0;
+  depth0.load_action = stencil_attachment_config.load_action;
+  depth0.store_action = stencil_attachment_config.store_action;
+  depth0.clear_depth = 0u;
+  depth0.texture = depth_stencil_texture;
+
   StencilAttachment stencil0;
   stencil0.load_action = stencil_attachment_config.load_action;
   stencil0.store_action = stencil_attachment_config.store_action;
   stencil0.clear_stencil = 0u;
-  stencil0.texture = allocator.CreateTexture(stencil_tex0);
+  stencil0.texture = depth_stencil_texture;
 
-  if (!stencil0.texture) {
-    return;  // Error messages are handled by `Allocator::CreateTexture`.
-  }
-  stencil0.texture->SetLabel(SPrintF("%s Stencil Texture", label.c_str()));
+  stencil0.texture->SetLabel(
+      SPrintF("%s Depth+Stencil Texture", label.c_str()));
+  SetDepthAttachment(std::move(depth0));
   SetStencilAttachment(std::move(stencil0));
 }
 
@@ -403,6 +416,9 @@ size_t RenderTarget::GetTotalAttachmentCount() const {
   if (stencil_.has_value()) {
     count++;
   }
+  if (depth_.has_value()) {
+    count++;
+  }
   return count;
 }
 

impeller/renderer/render_target.h

@@ -109,13 +109,13 @@ class RenderTarget final {
 
   bool IsValid() const;
 
-  void SetupStencilAttachment(const Context& context,
-                              RenderTargetAllocator& allocator,
-                              ISize size,
-                              bool msaa,
-                              const std::string& label = "Offscreen",
-                              AttachmentConfig stencil_attachment_config =
-                                  kDefaultStencilAttachmentConfig);
+  void SetupDepthStencilAttachments(const Context& context,
+                                    RenderTargetAllocator& allocator,
+                                    ISize size,
+                                    bool msaa,
+                                    const std::string& label = "Offscreen",
+                                    AttachmentConfig stencil_attachment_config =
+                                        kDefaultStencilAttachmentConfig);
 
   SampleCount GetSampleCount() const;
 

impeller/renderer/renderer_unittests.cc

@@ -1161,9 +1161,9 @@ TEST_P(RendererTest, StencilMask) {
       stencil_config.storage_mode = StorageMode::kHostVisible;
       auto render_target_allocator =
           RenderTargetAllocator(context->GetResourceAllocator());
-      render_target.SetupStencilAttachment(*context, render_target_allocator,
-                                           render_target.GetRenderTargetSize(),
-                                           true, "stencil", stencil_config);
+      render_target.SetupDepthStencilAttachments(
+          *context, render_target_allocator,
+          render_target.GetRenderTargetSize(), true, "stencil", stencil_config);
       // Fill the stencil buffer with an checkerboard pattern.
       const auto target_width = render_target.GetRenderTargetSize().width;
       const auto target_height = render_target.GetRenderTargetSize().height;