Revert "[Impeller] stencil buffer record/replay instead of MSAA storage. (flutter#47397)"

This reverts commit 04329c5.

Author: bdero

impeller/entity/entity_pass.cc

@@ -238,15 +238,18 @@ void EntityPass::AddSubpassInline(std::unique_ptr<EntityPass> pass) {
       pass->advanced_blend_reads_from_pass_texture_;
 }
 
-static const constexpr RenderTarget::AttachmentConfig kDefaultStencilConfig =
-    RenderTarget::AttachmentConfig{
-        .storage_mode = StorageMode::kDeviceTransient,
-        .load_action = LoadAction::kDontCare,
-        .store_action = StoreAction::kDontCare,
-    };
+static RenderTarget::AttachmentConfig GetDefaultStencilConfig(bool readable) {
+  return RenderTarget::AttachmentConfig{
+      .storage_mode = readable ? StorageMode::kDevicePrivate
+                               : StorageMode::kDeviceTransient,
+      .load_action = LoadAction::kDontCare,
+      .store_action = StoreAction::kDontCare,
+  };
+}
 
 static EntityPassTarget CreateRenderTarget(ContentContext& renderer,
                                            ISize size,
+                                           bool readable,
                                            const Color& clear_color) {
   auto context = renderer.GetContext();
 
@@ -267,8 +270,8 @@ static EntityPassTarget CreateRenderTarget(ContentContext& renderer,
             .resolve_storage_mode = StorageMode::kDevicePrivate,
             .load_action = LoadAction::kDontCare,
             .store_action = StoreAction::kMultisampleResolve,
-            .clear_color = clear_color},  // color_attachment_config
-        kDefaultStencilConfig             // stencil_attachment_config
+            .clear_color = clear_color},   // color_attachment_config
+        GetDefaultStencilConfig(readable)  // stencil_attachment_config
     );
   } else {
     target = RenderTarget::CreateOffscreen(
@@ -281,8 +284,8 @@ static EntityPassTarget CreateRenderTarget(ContentContext& renderer,
             .load_action = LoadAction::kDontCare,
             .store_action = StoreAction::kDontCare,
             .clear_color = clear_color,
-        },                     // color_attachment_config
-        kDefaultStencilConfig  // stencil_attachment_config
+        },                                 // color_attachment_config
+        GetDefaultStencilConfig(readable)  // stencil_attachment_config
     );
   }
 
@@ -340,7 +343,7 @@ bool EntityPass::Render(ContentContext& renderer,
   // there's no need to set up a stencil attachment on the root render target.
   if (reads_from_onscreen_backdrop) {
     auto offscreen_target = CreateRenderTarget(
-        renderer, root_render_target.GetRenderTargetSize(),
+        renderer, root_render_target.GetRenderTargetSize(), true,
         GetClearColorOrDefault(render_target.GetRenderTargetSize()));
 
     if (!OnRender(renderer,  // renderer
@@ -442,7 +445,8 @@ bool EntityPass::Render(ContentContext& renderer,
         *renderer.GetContext(), *renderer.GetRenderTargetCache(),
         color0.texture->GetSize(),
         renderer.GetContext()->GetCapabilities()->SupportsOffscreenMSAA(),
-        "ImpellerOnscreen", kDefaultStencilConfig);
+        "ImpellerOnscreen",
+        GetDefaultStencilConfig(reads_from_onscreen_backdrop));
   }
 
   // Set up the clear color of the root pass.
@@ -479,10 +483,10 @@ EntityPass::EntityResult EntityPass::GetEntityForElement(
   //--------------------------------------------------------------------------
   /// Setup entity element.
   ///
+
   if (const auto& entity = std::get_if<Entity>(&element)) {
     Entity element_entity = entity->Clone();
     element_entity.SetCapture(capture.CreateChild("Entity"));
-
     if (!global_pass_position.IsZero()) {
       // If the pass image is going to be rendered with a non-zero position,
       // apply the negative translation to entity copies before rendering them
@@ -497,9 +501,11 @@ EntityPass::EntityResult EntityPass::GetEntityForElement(
   //--------------------------------------------------------------------------
   /// Setup subpass element.
   ///
-  if (const auto& subpass_ptr =
-          std::get_if<std::unique_ptr<EntityPass>>(&element)) {
+
+  else if (const auto& subpass_ptr =
+               std::get_if<std::unique_ptr<EntityPass>>(&element)) {
     auto subpass = subpass_ptr->get();
+
     if (subpass->delegate_->CanElide()) {
       return EntityPass::EntityResult::Skip();
     }
@@ -602,6 +608,7 @@ EntityPass::EntityResult EntityPass::GetEntityForElement(
     auto subpass_target = CreateRenderTarget(
         renderer,                                        // renderer
         subpass_size,                                    // size
+        subpass->GetTotalPassReads(renderer) > 0,        // readable
         subpass->GetClearColorOrDefault(subpass_size));  // clear_color
 
     if (!subpass_target.IsValid()) {
@@ -675,6 +682,7 @@ EntityPass::EntityResult EntityPass::GetEntityForElement(
 
     return EntityPass::EntityResult::Success(std::move(element_entity));
   }
+
   FML_UNREACHABLE();
 }
 
@@ -699,15 +707,6 @@ bool EntityPass::RenderElement(Entity& element_entity,
   // blit the non-MSAA resolve texture of the previous pass to MSAA textures
   // (let alone a transient one).
   if (result.backdrop_texture) {
-    // Restore any clips that were recorded before the backdrop filter was
-    // applied.
-    auto& replay_entities = clip_replay_->GetReplayEntities();
-    for (const auto& entity : replay_entities) {
-      if (!entity.Render(renderer, *result.pass)) {
-        VALIDATION_LOG << "Failed to render entity for clip restore.";
-      }
-    }
-
     auto size_rect = Rect::MakeSize(result.pass->GetRenderTargetSize());
     auto msaa_backdrop_contents = TextureContents::MakeRect(size_rect);
     msaa_backdrop_contents->SetStencilEnabled(false);
@@ -815,7 +814,6 @@ bool EntityPass::RenderElement(Entity& element_entity,
 #endif
 
   element_entity.SetClipDepth(element_entity.GetClipDepth() - clip_depth_floor);
-  clip_replay_->RecordEntity(element_entity, clip_coverage.type);
   if (!element_entity.Render(renderer, *result.pass)) {
     VALIDATION_LOG << "Failed to render entity.";
     return false;
@@ -1167,24 +1165,4 @@ void EntityPass::SetEnableOffscreenCheckerboard(bool enabled) {
   enable_offscreen_debug_checkerboard_ = enabled;
 }
 
-EntityPassClipRecorder::EntityPassClipRecorder() {}
-
-void EntityPassClipRecorder::RecordEntity(const Entity& entity,
-                                          Contents::ClipCoverage::Type type) {
-  switch (type) {
-    case Contents::ClipCoverage::Type::kNoChange:
-      return;
-    case Contents::ClipCoverage::Type::kAppend:
-      rendered_clip_entities_.push_back(entity.Clone());
-      break;
-    case Contents::ClipCoverage::Type::kRestore:
-      rendered_clip_entities_.pop_back();
-      break;
-  }
-}
-
-const std::vector<Entity>& EntityPassClipRecorder::GetReplayEntities() const {
-  return rendered_clip_entities_;
-}
-
 }  // namespace impeller

impeller/entity/entity_pass.h

@@ -21,7 +21,6 @@
 namespace impeller {
 
 class ContentContext;
-class EntityPassClipRecorder;
 
 class EntityPass {
  public:
@@ -295,8 +294,6 @@ class EntityPass {
   bool flood_clip_ = false;
   bool enable_offscreen_debug_checkerboard_ = false;
   std::optional<Rect> bounds_limit_;
-  std::unique_ptr<EntityPassClipRecorder> clip_replay_ =
-      std::make_unique<EntityPassClipRecorder>();
 
   /// These values are incremented whenever something is added to the pass that
   /// requires reading from the backdrop texture. Currently, this can happen in
@@ -321,26 +318,6 @@ class EntityPass {
   EntityPass& operator=(const EntityPass&) = delete;
 };
 
-/// @brief A class that tracks all clips that have been recorded in the current
-///        entity pass stencil.
-///
-///        These clips are replayed when restoring the backdrop so that the
-///        stencil buffer is left in an identical state.
-class EntityPassClipRecorder {
- public:
-  EntityPassClipRecorder();
-
-  ~EntityPassClipRecorder() = default;
-
-  /// @brief Record the entity based on the provided coverage [type].
-  void RecordEntity(const Entity& entity, Contents::ClipCoverage::Type type);
-
-  const std::vector<Entity>& GetReplayEntities() const;
-
- private:
-  std::vector<Entity> rendered_clip_entities_;
-};
-
 }  // namespace impeller
 
 #endif  // FLUTTER_IMPELLER_ENTITY_ENTITY_PASS_H_

impeller/entity/inline_pass_context.cc

@@ -23,6 +23,7 @@ InlinePassContext::InlinePassContext(
     : context_(std::move(context)),
       pass_target_(pass_target),
       entity_count_(entity_count),
+      total_pass_reads_(pass_texture_reads),
       is_collapsed_(collapsed_parent_pass.has_value()) {
   if (collapsed_parent_pass.has_value()) {
     pass_ = collapsed_parent_pass.value().pass;
@@ -141,9 +142,17 @@ InlinePassContext::RenderPassResult InlinePassContext::GetRenderPass(
     return {};
   }
 
-  stencil->load_action = LoadAction::kClear;
-  stencil->store_action = StoreAction::kDontCare;
+  // Only clear the stencil if this is the very first pass of the
+  // layer.
+  stencil->load_action =
+      pass_count_ > 0 ? LoadAction::kLoad : LoadAction::kClear;
+  // If we're on the last pass of the layer, there's no need to store the
+  // stencil because nothing needs to read it.
+  stencil->store_action = pass_count_ == total_pass_reads_
+                              ? StoreAction::kDontCare
+                              : StoreAction::kStore;
   pass_target_.target_.SetStencilAttachment(stencil.value());
+
   pass_target_.target_.SetColorAttachment(color0, 0);
 
   pass_ = command_buffer_->CreateRenderPass(pass_target_.GetRenderTarget());

impeller/entity/inline_pass_context.h

@@ -51,7 +51,7 @@ class InlinePassContext {
   std::shared_ptr<RenderPass> pass_;
   uint32_t pass_count_ = 0;
   uint32_t entity_count_ = 0;
-
+  uint32_t total_pass_reads_ = 0;
   // Whether this context is collapsed into a parent entity pass.
   bool is_collapsed_ = false;