[Impeller] Use booleans instead of counting backdrop reads.

impeller/entity/entity_pass.cc

@@ -110,7 +110,7 @@ void EntityPass::AddEntity(Entity entity) {
   }
 
   if (entity.GetBlendMode() > Entity::kLastPipelineBlendMode) {
-    advanced_blend_reads_from_pass_texture_ += 1;
+    advanced_blend_reads_from_pass_texture_ = true;
   }
   elements_.emplace_back(std::move(entity));
 }
@@ -277,10 +277,10 @@ EntityPass* EntityPass::AddSubpass(std::unique_ptr<EntityPass> pass) {
   pass->superpass_ = this;
 
   if (pass->backdrop_filter_proc_) {
-    backdrop_filter_reads_from_pass_texture_ += 1;
+    backdrop_filter_reads_from_pass_texture_ = true;
   }
   if (pass->blend_mode_ > Entity::kLastPipelineBlendMode) {
-    advanced_blend_reads_from_pass_texture_ += 1;
+    advanced_blend_reads_from_pass_texture_ = true;
   }
 
   auto subpass_pointer = pass.get();
@@ -299,9 +299,11 @@ void EntityPass::AddSubpassInline(std::unique_ptr<EntityPass> pass) {
     elements_.emplace_back(std::move(elements[i]));
   }
 
-  backdrop_filter_reads_from_pass_texture_ +=
+  backdrop_filter_reads_from_pass_texture_ =
+      backdrop_filter_reads_from_pass_texture_ ||
       pass->backdrop_filter_reads_from_pass_texture_;
-  advanced_blend_reads_from_pass_texture_ +=
+  advanced_blend_reads_from_pass_texture_ =
+      advanced_blend_reads_from_pass_texture_ ||
       pass->advanced_blend_reads_from_pass_texture_;
 }
 
@@ -366,10 +368,10 @@ static EntityPassTarget CreateRenderTarget(ContentContext& renderer,
       renderer.GetDeviceCapabilities().SupportsImplicitResolvingMSAA());
 }
 
-uint32_t EntityPass::GetTotalPassReads(ContentContext& renderer) const {
+bool EntityPass::DoesBackdropGetRead(ContentContext& renderer) const {
   return renderer.GetDeviceCapabilities().SupportsFramebufferFetch()
              ? backdrop_filter_reads_from_pass_texture_
-             : backdrop_filter_reads_from_pass_texture_ +
+             : backdrop_filter_reads_from_pass_texture_ ||
                    advanced_blend_reads_from_pass_texture_;
 }
 
@@ -413,11 +415,10 @@ bool EntityPass::Render(ContentContext& renderer,
   EntityPassClipStack clip_stack = EntityPassClipStack(
       Rect::MakeSize(root_render_target.GetRenderTargetSize()));
 
-  bool reads_from_onscreen_backdrop = GetTotalPassReads(renderer) > 0;
   // In this branch path, we need to render everything to an offscreen texture
   // and then blit the results onto the onscreen texture. If using this branch,
   // there's no need to set up a stencil attachment on the root render target.
-  if (reads_from_onscreen_backdrop) {
+  if (DoesBackdropGetRead(renderer)) {
     EntityPassTarget offscreen_target = CreateRenderTarget(
         renderer, root_render_target.GetRenderTargetSize(),
         GetRequiredMipCount(),
@@ -889,8 +890,7 @@ bool EntityPass::OnRender(
         pass_depth);
   }
 
-  InlinePassContext pass_context(renderer, pass_target,
-                                 GetTotalPassReads(renderer), GetElementCount(),
+  InlinePassContext pass_context(renderer, pass_target, GetElementCount(),
                                  collapsed_parent_pass);
   if (!pass_context.IsValid()) {
     VALIDATION_LOG << SPrintF("Pass context invalid (Depth=%d)", pass_depth);

impeller/entity/entity_pass.h

@@ -346,18 +346,18 @@ class EntityPass {
   ContentBoundsPromise bounds_promise_ = ContentBoundsPromise::kUnknown;
   int32_t required_mip_count_ = 1;
 
-  /// These values are incremented whenever something is added to the pass that
-  /// requires reading from the backdrop texture. Currently, this can happen in
-  /// the following scenarios:
+  /// These values indicate whether something has been added to the EntityPass
+  /// that requires reading from the backdrop texture. Currently, this can
+  /// happen in the following scenarios:
   ///   1. An entity with an "advanced blend" is added to the pass.
   ///   2. A subpass with a backdrop filter is added to the pass.
   /// These are tracked as separate values because we may ignore
-  /// blend_reads_from_pass_texture_ if the device supports framebuffer based
+  /// `blend_reads_from_pass_texture_` if the device supports framebuffer based
   /// advanced blends.
-  uint32_t advanced_blend_reads_from_pass_texture_ = 0;
-  uint32_t backdrop_filter_reads_from_pass_texture_ = 0;
+  bool advanced_blend_reads_from_pass_texture_ = false;
+  bool backdrop_filter_reads_from_pass_texture_ = false;
 
-  uint32_t GetTotalPassReads(ContentContext& renderer) const;
+  bool DoesBackdropGetRead(ContentContext& renderer) const;
 
   BackdropFilterProc backdrop_filter_proc_ = nullptr;
 

impeller/entity/inline_pass_context.cc

@@ -20,7 +20,6 @@ namespace impeller {
 InlinePassContext::InlinePassContext(
     const ContentContext& renderer,
     EntityPassTarget& pass_target,
-    uint32_t pass_texture_reads,
     uint32_t entity_count,
     std::optional<RenderPassResult> collapsed_parent_pass)
     : renderer_(renderer),

impeller/entity/inline_pass_context.h

@@ -25,7 +25,6 @@ class InlinePassContext {
   InlinePassContext(
       const ContentContext& renderer,
       EntityPassTarget& pass_target,
-      uint32_t pass_texture_reads,
       uint32_t entity_count,
       std::optional<RenderPassResult> collapsed_parent_pass = std::nullopt);