[Impeller] Don't use unnecessary stencil attachments (flutter#39537)

Author: bdero

impeller/entity/contents/content_context.cc

@@ -121,6 +121,10 @@ void ContentContextOptions::ApplyToPipelineDescriptor(
   }
   desc.SetColorAttachmentDescriptor(0u, color0);
 
+  if (!has_stencil_attachment) {
+    desc.ClearStencilAttachments();
+  }
+
   if (desc.GetFrontStencilAttachmentDescriptor().has_value()) {
     StencilAttachmentDescriptor stencil =
         desc.GetFrontStencilAttachmentDescriptor().value();

impeller/entity/contents/content_context.h

@@ -179,17 +179,29 @@ using GeometryColorPipeline =
 using YUVToRGBFilterPipeline =
     RenderPipelineT<YuvToRgbFilterVertexShader, YuvToRgbFilterFragmentShader>;
 
+/// Pipeline state configuration.
+///
+/// Each unique combination of these options requires a different pipeline state
+/// object to be built. This struct is used as a key for the per-pipeline
+/// variant cache.
+///
+/// When adding fields to this key, reliant features should take care to limit
+/// the combinatorical explosion of variations. A sufficiently complicated
+/// Flutter application may easily require building hundreds of PSOs in total,
+/// but they shouldn't require e.g. 10s of thousands.
 struct ContentContextOptions {
   SampleCount sample_count = SampleCount::kCount1;
   BlendMode blend_mode = BlendMode::kSourceOver;
   CompareFunction stencil_compare = CompareFunction::kEqual;
   StencilOperation stencil_operation = StencilOperation::kKeep;
   PrimitiveType primitive_type = PrimitiveType::kTriangle;
+  bool has_stencil_attachment = true;
 
   struct Hash {
     constexpr std::size_t operator()(const ContentContextOptions& o) const {
       return fml::HashCombine(o.sample_count, o.blend_mode, o.stencil_compare,
-                              o.stencil_operation, o.primitive_type);
+                              o.stencil_operation, o.primitive_type,
+                              o.has_stencil_attachment);
     }
   };
 
@@ -200,7 +212,8 @@ struct ContentContextOptions {
              lhs.blend_mode == rhs.blend_mode &&
              lhs.stencil_compare == rhs.stencil_compare &&
              lhs.stencil_operation == rhs.stencil_operation &&
-             lhs.primitive_type == rhs.primitive_type;
+             lhs.primitive_type == rhs.primitive_type &&
+             lhs.has_stencil_attachment == rhs.has_stencil_attachment;
     }
   };
 

impeller/entity/contents/contents.cc

@@ -16,13 +16,17 @@ namespace impeller {
 ContentContextOptions OptionsFromPass(const RenderPass& pass) {
   ContentContextOptions opts;
   opts.sample_count = pass.GetRenderTarget().GetSampleCount();
+  opts.has_stencil_attachment =
+      pass.GetRenderTarget().GetStencilAttachment().has_value();
   return opts;
 }
 
 ContentContextOptions OptionsFromPassAndEntity(const RenderPass& pass,
                                                const Entity& entity) {
   ContentContextOptions opts;
   opts.sample_count = pass.GetRenderTarget().GetSampleCount();
+  opts.has_stencil_attachment =
+      pass.GetRenderTarget().GetStencilAttachment().has_value();
   opts.blend_mode = entity.GetBlendMode();
   return opts;
 }

impeller/entity/contents/scene_contents.cc

@@ -45,16 +45,20 @@ bool SceneContents::Render(const ContentContext& renderer,
   }
 
   RenderTarget subpass_target = RenderTarget::CreateOffscreenMSAA(
-      *renderer.GetContext(),            // context
-      ISize(coverage.value().size),      // size
-      "SceneContents",                   // label
-      StorageMode::kDeviceTransient,     // color_storage_mode
-      StorageMode::kDevicePrivate,       // color_resolve_storage_mode
-      LoadAction::kClear,                // color_load_action
-      StoreAction::kMultisampleResolve,  // color_store_action
-      StorageMode::kDeviceTransient,     // stencil_storage_mode
-      LoadAction::kDontCare,             // stencil_load_action
-      StoreAction::kDontCare             // stencil_store_action
+      *renderer.GetContext(),        // context
+      ISize(coverage.value().size),  // size
+      "SceneContents",               // label
+      RenderTarget::AttachmentConfigMSAA{
+          .storage_mode = StorageMode::kDeviceTransient,
+          .resolve_storage_mode = StorageMode::kDevicePrivate,
+          .load_action = LoadAction::kClear,
+          .store_action = StoreAction::kMultisampleResolve,
+      },  // color_attachment_config
+      RenderTarget::AttachmentConfig{
+          .storage_mode = StorageMode::kDeviceTransient,
+          .load_action = LoadAction::kDontCare,
+          .store_action = StoreAction::kDontCare,
+      }  // stencil_attachment_config
   );
   if (!subpass_target.IsValid()) {
     return false;

impeller/entity/entity_pass.cc

@@ -156,31 +156,39 @@ static RenderTarget CreateRenderTarget(ContentContext& renderer,
 
   if (context->SupportsOffscreenMSAA()) {
     return RenderTarget::CreateOffscreenMSAA(
-        *context,                          // context
-        size,                              // size
-        "EntityPass",                      // label
-        StorageMode::kDeviceTransient,     // color_storage_mode
-        StorageMode::kDevicePrivate,       // color_resolve_storage_mode
-        LoadAction::kDontCare,             // color_load_action
-        StoreAction::kMultisampleResolve,  // color_store_action
-        readable ? StorageMode::kDevicePrivate
-                 : StorageMode::kDeviceTransient,  // stencil_storage_mode
-        LoadAction::kDontCare,                     // stencil_load_action
-        StoreAction::kDontCare                     // stencil_store_action
+        *context,      // context
+        size,          // size
+        "EntityPass",  // label
+        RenderTarget::AttachmentConfigMSAA{
+            .storage_mode = StorageMode::kDeviceTransient,
+            .resolve_storage_mode = StorageMode::kDevicePrivate,
+            .load_action = LoadAction::kDontCare,
+            .store_action = StoreAction::kMultisampleResolve,
+        },  // color_attachment_config
+        RenderTarget::AttachmentConfig{
+            .storage_mode = readable ? StorageMode::kDevicePrivate
+                                     : StorageMode::kDeviceTransient,
+            .load_action = LoadAction::kDontCare,
+            .store_action = StoreAction::kDontCare,
+        }  // stencil_attachment_config
     );
   }
 
   return RenderTarget::CreateOffscreen(
-      *context,                     // context
-      size,                         // size
-      "EntityPass",                 // label
-      StorageMode::kDevicePrivate,  // color_storage_mode
-      LoadAction::kDontCare,        // color_load_action
-      StoreAction::kDontCare,       // color_store_action
-      readable ? StorageMode::kDevicePrivate
-               : StorageMode::kDeviceTransient,  // stencil_storage_mode
-      LoadAction::kDontCare,                     // stencil_load_action
-      StoreAction::kDontCare                     // stencil_store_action
+      *context,      // context
+      size,          // size
+      "EntityPass",  // label
+      RenderTarget::AttachmentConfig{
+          .storage_mode = StorageMode::kDevicePrivate,
+          .load_action = LoadAction::kDontCare,
+          .store_action = StoreAction::kDontCare,
+      },  // color_attachment_config
+      RenderTarget::AttachmentConfig{
+          .storage_mode = readable ? StorageMode::kDevicePrivate
+                                   : StorageMode::kDeviceTransient,
+          .load_action = LoadAction::kDontCare,
+          .store_action = StoreAction::kDontCare,
+      }  // stencil_attachment_config
   );
 }
 

impeller/playground/imgui/imgui_impl_impeller.cc

@@ -94,10 +94,8 @@ bool ImGui_ImplImpeller_Init(
     auto desc = impeller::PipelineBuilder<impeller::ImguiRasterVertexShader,
                                           impeller::ImguiRasterFragmentShader>::
         MakeDefaultPipelineDescriptor(*context);
-    desc->SetStencilPixelFormat(impeller::PixelFormat::kUnknown);
-    desc->SetStencilAttachmentDescriptors(std::nullopt);
-    desc->SetDepthPixelFormat(impeller::PixelFormat::kUnknown);
-    desc->SetDepthStencilAttachmentDescriptor(std::nullopt);
+    desc->ClearStencilAttachments();
+    desc->ClearDepthAttachment();
 
     bd->pipeline =
         context->GetPipelineLibrary()->GetPipeline(std::move(desc)).Get();

impeller/renderer/pipeline_descriptor.cc

@@ -153,6 +153,26 @@ PipelineDescriptor& PipelineDescriptor::SetStencilAttachmentDescriptors(
   return *this;
 }
 
+void PipelineDescriptor::ClearStencilAttachments() {
+  back_stencil_attachment_descriptor_.reset();
+  front_stencil_attachment_descriptor_.reset();
+  SetStencilPixelFormat(impeller::PixelFormat::kUnknown);
+}
+
+void PipelineDescriptor::ClearDepthAttachment() {
+  depth_attachment_descriptor_.reset();
+  SetDepthPixelFormat(impeller::PixelFormat::kUnknown);
+}
+
+void PipelineDescriptor::ClearColorAttachment(size_t index) {
+  if (color_attachment_descriptors_.find(index) ==
+      color_attachment_descriptors_.end()) {
+    return;
+  }
+
+  color_attachment_descriptors_.erase(index);
+}
+
 void PipelineDescriptor::ResetAttachments() {
   color_attachment_descriptors_.clear();
   depth_attachment_descriptor_.reset();

impeller/renderer/pipeline_descriptor.h

@@ -83,6 +83,12 @@ class PipelineDescriptor final : public Comparable<PipelineDescriptor> {
       std::optional<StencilAttachmentDescriptor> front,
       std::optional<StencilAttachmentDescriptor> back);
 
+  void ClearStencilAttachments();
+
+  void ClearDepthAttachment();
+
+  void ClearColorAttachment(size_t index);
+
   std::optional<StencilAttachmentDescriptor>
   GetFrontStencilAttachmentDescriptor() const;