From 8e740b50bfde57103ef7e65fca0222a5837587e1 Mon Sep 17 00:00:00 2001
From: jonahwilliams <jonahwilliams@google.com>
Date: Tue, 26 Nov 2024 17:14:40 -0800
Subject: [PATCH 01/10] [Impeller] avoid heap allocation in RenderTarget
 object.

---
 impeller/display_list/canvas.cc               |  9 ++-
 impeller/entity/entity_pass_target.cc         |  2 +-
 .../entity/entity_pass_target_unittests.cc    | 20 ++-----
 impeller/entity/inline_pass_context.cc        | 15 +----
 impeller/entity/render_target_cache.cc        | 15 +++--
 .../entity/render_target_cache_unittests.cc   |  5 +-
 impeller/playground/playground.cc             |  8 +--
 .../renderer/backend/gles/render_pass_gles.cc |  9 ++-
 .../gles/test/surface_gles_unittests.cc       |  4 +-
 .../renderer/backend/metal/render_pass_mtl.mm |  7 ++-
 .../renderer/backend/vulkan/context_vk.cc     | 19 +++---
 .../backend/vulkan/render_pass_builder_vk.cc  | 58 +++++++++++++++---
 .../backend/vulkan/render_pass_builder_vk.h   | 11 +++-
 .../render_pass_builder_vk_unittests.cc       | 18 +++---
 .../vulkan/render_pass_cache_unittests.cc     |  3 +-
 .../vulkan/test/swapchain_unittests.cc        |  3 +-
 impeller/renderer/render_target.cc            | 59 ++++++++++++++++---
 impeller/renderer/render_target.h             | 14 ++---
 impeller/renderer/renderer_unittests.cc       |  8 ---
 19 files changed, 176 insertions(+), 111 deletions(-)

diff --git a/impeller/display_list/canvas.cc b/impeller/display_list/canvas.cc
index 7b26f02892904..f311094489fa3 100644
--- a/impeller/display_list/canvas.cc
+++ b/impeller/display_list/canvas.cc
@@ -14,6 +14,7 @@
 #include "flutter/fml/logging.h"
 #include "flutter/fml/trace_event.h"
 #include "impeller/base/validation.h"
+#include "impeller/core/formats.h"
 #include "impeller/display_list/color_filter.h"
 #include "impeller/display_list/image_filter.h"
 #include "impeller/display_list/skia_conversions.h"
@@ -856,7 +857,7 @@ void Canvas::DrawAtlas(const std::shared_ptr<AtlasContents>& atlas_contents,
 
 void Canvas::SetupRenderPass() {
   renderer_.GetRenderTargetCache()->Start();
-  auto color0 = render_target_.GetColorAttachments().find(0u)->second;
+  ColorAttachment color0 = render_target_.GetColor0();
 
   auto& stencil_attachment = render_target_.GetStencilAttachment();
   auto& depth_attachment = render_target_.GetDepthAttachment();
@@ -1463,8 +1464,7 @@ void Canvas::AddRenderEntityToCurrentPass(Entity& entity, bool reuse_depth) {
       RenderTarget& render_target = render_passes_.back()
                                         .inline_pass_context->GetPassTarget()
                                         .GetRenderTarget();
-      ColorAttachment attachment =
-          render_target.GetColorAttachments().find(0u)->second;
+      ColorAttachment attachment = render_target.GetColor0();
       // Attachment.clear color needs to be premultiplied at all times, but the
       // Color::Blend function requires unpremultiplied colors.
       attachment.clear_color = attachment.clear_color.Unpremultiply()
@@ -1591,8 +1591,7 @@ std::shared_ptr<Texture> Canvas::FlipBackdrop(Point global_pass_position,
   }
 
   if (should_use_onscreen) {
-    ColorAttachment color0 =
-        render_target_.GetColorAttachments().find(0u)->second;
+    ColorAttachment color0 = render_target_.GetColor0();
     // When MSAA is being used, we end up overriding the entire backdrop by
     // drawing the previous pass texture, and so we don't have to clear it and
     // can use kDontCare.
diff --git a/impeller/entity/entity_pass_target.cc b/impeller/entity/entity_pass_target.cc
index e9284de522675..a25d96e197d45 100644
--- a/impeller/entity/entity_pass_target.cc
+++ b/impeller/entity/entity_pass_target.cc
@@ -19,7 +19,7 @@ EntityPassTarget::EntityPassTarget(const RenderTarget& render_target,
 
 std::shared_ptr<Texture> EntityPassTarget::Flip(
     const ContentContext& renderer) {
-  auto color0 = target_.GetColorAttachments().find(0)->second;
+  ColorAttachment color0 = target_.GetColor0();
   if (!color0.resolve_texture) {
     VALIDATION_LOG << "EntityPassTarget Flip should never be called for a "
                       "non-MSAA target.";
diff --git a/impeller/entity/entity_pass_target_unittests.cc b/impeller/entity/entity_pass_target_unittests.cc
index cd22acbffdb5a..28aa97d3fd9b3 100644
--- a/impeller/entity/entity_pass_target_unittests.cc
+++ b/impeller/entity/entity_pass_target_unittests.cc
@@ -31,20 +31,14 @@ TEST_P(EntityPassTargetTest, SwapWithMSAATexture) {
 
   auto entity_pass_target = EntityPassTarget(render_target, false, false);
 
-  auto color0 = entity_pass_target.GetRenderTarget()
-                    .GetColorAttachments()
-                    .find(0u)
-                    ->second;
+  auto color0 = entity_pass_target.GetRenderTarget().GetColor0();
   auto msaa_tex = color0.texture;
   auto resolve_tex = color0.resolve_texture;
 
   FML_DCHECK(content_context);
   entity_pass_target.Flip(*content_context);
 
-  color0 = entity_pass_target.GetRenderTarget()
-               .GetColorAttachments()
-               .find(0u)
-               ->second;
+  color0 = entity_pass_target.GetRenderTarget().GetColor0();
 
   ASSERT_EQ(msaa_tex, color0.texture);
   ASSERT_NE(resolve_tex, color0.resolve_texture);
@@ -89,10 +83,7 @@ TEST_P(EntityPassTargetTest, SwapWithMSAAImplicitResolve) {
 
   auto entity_pass_target = EntityPassTarget(render_target, false, true);
 
-  auto color0 = entity_pass_target.GetRenderTarget()
-                    .GetColorAttachments()
-                    .find(0u)
-                    ->second;
+  auto color0 = entity_pass_target.GetRenderTarget().GetColor0();
   auto msaa_tex = color0.texture;
   auto resolve_tex = color0.resolve_texture;
 
@@ -101,10 +92,7 @@ TEST_P(EntityPassTargetTest, SwapWithMSAAImplicitResolve) {
   FML_DCHECK(content_context);
   entity_pass_target.Flip(*content_context);
 
-  color0 = entity_pass_target.GetRenderTarget()
-               .GetColorAttachments()
-               .find(0u)
-               ->second;
+  color0 = entity_pass_target.GetRenderTarget().GetColor0();
 
   ASSERT_NE(msaa_tex, color0.texture);
   ASSERT_NE(resolve_tex, color0.resolve_texture);
diff --git a/impeller/entity/inline_pass_context.cc b/impeller/entity/inline_pass_context.cc
index ac86af2139143..8c00550d272de 100644
--- a/impeller/entity/inline_pass_context.cc
+++ b/impeller/entity/inline_pass_context.cc
@@ -86,20 +86,12 @@ const std::shared_ptr<RenderPass>& InlinePassContext::GetRenderPass() {
     return pass_;
   }
 
-  if (pass_target_.GetRenderTarget().GetColorAttachments().empty()) {
-    VALIDATION_LOG << "Color attachment unexpectedly missing from the "
-                      "EntityPass render target.";
-    return pass_;
-  }
-
   command_buffer_->SetLabel("EntityPass Command Buffer");
 
   {
     // If the pass target has a resolve texture, then we're using MSAA.
-    bool is_msaa = pass_target_.GetRenderTarget()
-                       .GetColorAttachments()
-                       .find(0)
-                       ->second.resolve_texture != nullptr;
+    bool is_msaa =
+        pass_target_.GetRenderTarget().GetColor0().resolve_texture != nullptr;
     if (pass_count_ > 0 && is_msaa) {
       pass_target_.Flip(renderer_);
     }
@@ -107,8 +99,7 @@ const std::shared_ptr<RenderPass>& InlinePassContext::GetRenderPass() {
 
   // Find the color attachment a second time, since the target may have just
   // flipped.
-  auto color0 =
-      pass_target_.GetRenderTarget().GetColorAttachments().find(0)->second;
+  ColorAttachment color0 = pass_target_.GetRenderTarget().GetColor0();
   bool is_msaa = color0.resolve_texture != nullptr;
 
   if (pass_count_ > 0) {
diff --git a/impeller/entity/render_target_cache.cc b/impeller/entity/render_target_cache.cc
index dbfe0a9b50c63..fb9c8098f4b82 100644
--- a/impeller/entity/render_target_cache.cc
+++ b/impeller/entity/render_target_cache.cc
@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 #include "impeller/entity/render_target_cache.h"
+#include "impeller/core/formats.h"
 #include "impeller/renderer/render_target.h"
 
 namespace impeller {
@@ -52,10 +53,9 @@ RenderTarget RenderTargetCache::CreateOffscreen(
     const auto other_config = render_target_data.config;
     if (!render_target_data.used_this_frame && other_config == config) {
       render_target_data.used_this_frame = true;
-      auto color0 = render_target_data.render_target.GetColorAttachments()
-                        .find(0u)
-                        ->second;
-      auto depth = render_target_data.render_target.GetDepthAttachment();
+      ColorAttachment color0 = render_target_data.render_target.GetColor0();
+      std::optional<DepthAttachment> depth =
+          render_target_data.render_target.GetDepthAttachment();
       std::shared_ptr<Texture> depth_tex = depth ? depth->texture : nullptr;
       return RenderTargetAllocator::CreateOffscreen(
           context, size, mip_count, label, color_attachment_config,
@@ -102,10 +102,9 @@ RenderTarget RenderTargetCache::CreateOffscreenMSAA(
     const auto other_config = render_target_data.config;
     if (!render_target_data.used_this_frame && other_config == config) {
       render_target_data.used_this_frame = true;
-      auto color0 = render_target_data.render_target.GetColorAttachments()
-                        .find(0u)
-                        ->second;
-      auto depth = render_target_data.render_target.GetDepthAttachment();
+      ColorAttachment color0 = render_target_data.render_target.GetColor0();
+      std::optional<DepthAttachment> depth =
+          render_target_data.render_target.GetDepthAttachment();
       std::shared_ptr<Texture> depth_tex = depth ? depth->texture : nullptr;
       return RenderTargetAllocator::CreateOffscreenMSAA(
           context, size, mip_count, label, color_attachment_config,
diff --git a/impeller/entity/render_target_cache_unittests.cc b/impeller/entity/render_target_cache_unittests.cc
index 73493e7641c85..17ea9338f11e0 100644
--- a/impeller/entity/render_target_cache_unittests.cc
+++ b/impeller/entity/render_target_cache_unittests.cc
@@ -7,6 +7,7 @@
 #include "flutter/testing/testing.h"
 #include "impeller/base/validation.h"
 #include "impeller/core/allocator.h"
+#include "impeller/core/formats.h"
 #include "impeller/core/texture_descriptor.h"
 #include "impeller/entity/entity_playground.h"
 #include "impeller/entity/render_target_cache.h"
@@ -104,8 +105,8 @@ TEST_P(RenderTargetCacheTest, CachedTextureGetsNewAttachmentConfig) {
       *GetContext(), {100, 100}, 1, "Offscreen2", color_attachment_config);
   render_target_cache.End();
 
-  auto color1 = target1.GetColorAttachments().find(0)->second;
-  auto color2 = target2.GetColorAttachments().find(0)->second;
+  ColorAttachment color1 = target1.GetColor0();
+  ColorAttachment color2 = target2.GetColor0();
   // The second color attachment should reuse the first attachment's texture
   // but with attributes from the second AttachmentConfig.
   EXPECT_EQ(color2.texture, color1.texture);
diff --git a/impeller/playground/playground.cc b/impeller/playground/playground.cc
index f588a54049480..fc7cbcd3140ea 100644
--- a/impeller/playground/playground.cc
+++ b/impeller/playground/playground.cc
@@ -284,12 +284,7 @@ bool Playground::OpenPlaygroundHere(
       }
       buffer->SetLabel("ImGui Command Buffer");
 
-      if (render_target.GetColorAttachments().empty()) {
-        VALIDATION_LOG << "render target attachments are empty.";
-        return false;
-      }
-
-      auto color0 = render_target.GetColorAttachments().find(0)->second;
+      auto color0 = render_target.GetColor0();
       color0.load_action = LoadAction::kLoad;
       if (color0.resolve_texture) {
         color0.texture = color0.resolve_texture;
@@ -297,7 +292,6 @@ bool Playground::OpenPlaygroundHere(
         color0.store_action = StoreAction::kStore;
       }
       render_target.SetColorAttachment(color0, 0);
-
       render_target.SetStencilAttachment(std::nullopt);
       render_target.SetDepthAttachment(std::nullopt);
 
diff --git a/impeller/renderer/backend/gles/render_pass_gles.cc b/impeller/renderer/backend/gles/render_pass_gles.cc
index 594fcfab0732f..6c9d45020dae8 100644
--- a/impeller/renderer/backend/gles/render_pass_gles.cc
+++ b/impeller/renderer/backend/gles/render_pass_gles.cc
@@ -11,6 +11,7 @@
 #include "fml/closure.h"
 #include "fml/logging.h"
 #include "impeller/base/validation.h"
+#include "impeller/core/formats.h"
 #include "impeller/renderer/backend/gles/context_gles.h"
 #include "impeller/renderer/backend/gles/device_buffer_gles.h"
 #include "impeller/renderer/backend/gles/formats_gles.h"
@@ -537,9 +538,11 @@ bool RenderPassGLES::OnEncodeCommands(const Context& context) const {
   if (!render_target.HasColorAttachment(0u)) {
     return false;
   }
-  const auto& color0 = render_target.GetColorAttachments().at(0u);
-  const auto& depth0 = render_target.GetDepthAttachment();
-  const auto& stencil0 = render_target.GetStencilAttachment();
+  const ColorAttachment& color0 = render_target.GetColor0();
+  const std::optional<DepthAttachment>& depth0 =
+      render_target.GetDepthAttachment();
+  const std::optional<StencilAttachment>& stencil0 =
+      render_target.GetStencilAttachment();
 
   auto pass_data = std::make_shared<RenderPassData>();
   pass_data->label = label_;
diff --git a/impeller/renderer/backend/gles/test/surface_gles_unittests.cc b/impeller/renderer/backend/gles/test/surface_gles_unittests.cc
index dbef03075a088..14b90907e7d81 100644
--- a/impeller/renderer/backend/gles/test/surface_gles_unittests.cc
+++ b/impeller/renderer/backend/gles/test/surface_gles_unittests.cc
@@ -21,8 +21,8 @@ TEST_P(SurfaceGLESTest, CanWrapNonZeroFBO) {
   ASSERT_TRUE(!!surface);
   ASSERT_TRUE(surface->IsValid());
   ASSERT_TRUE(surface->GetRenderTarget().HasColorAttachment(0));
-  const auto& texture = TextureGLES::Cast(
-      *(surface->GetRenderTarget().GetColorAttachments().at(0).texture));
+  const auto& texture =
+      TextureGLES::Cast(*(surface->GetRenderTarget().GetColor0().texture));
   auto wrapped = texture.GetFBO();
   ASSERT_TRUE(wrapped.has_value());
   // NOLINTNEXTLINE(bugprone-unchecked-optional-access)
diff --git a/impeller/renderer/backend/metal/render_pass_mtl.mm b/impeller/renderer/backend/metal/render_pass_mtl.mm
index 80cf59bb5f1f7..ddda56a9ec84a 100644
--- a/impeller/renderer/backend/metal/render_pass_mtl.mm
+++ b/impeller/renderer/backend/metal/render_pass_mtl.mm
@@ -104,8 +104,13 @@ static bool ConfigureStencilAttachment(
     const RenderTarget& desc) {
   auto result = [MTLRenderPassDescriptor renderPassDescriptor];
 
-  const auto& colors = desc.GetColorAttachments();
+  const ColorAttachment& color0 = desc.GetColor0();
+  if (!ConfigureColorAttachment(color0, result.colorAttachments[0u])) {
+    VALIDATION_LOG << "Could not configure color attachment at index 0";
+    return nil;
+  }
 
+  const auto& colors = desc.GetColorAttachments();
   for (const auto& color : colors) {
     if (!ConfigureColorAttachment(color.second,
                                   result.colorAttachments[color.first])) {
diff --git a/impeller/renderer/backend/vulkan/context_vk.cc b/impeller/renderer/backend/vulkan/context_vk.cc
index d793b3e9c61fd..8963fae083654 100644
--- a/impeller/renderer/backend/vulkan/context_vk.cc
+++ b/impeller/renderer/backend/vulkan/context_vk.cc
@@ -7,6 +7,7 @@
 #include <unordered_map>
 
 #include "fml/concurrent_message_loop.h"
+#include "impeller/core/formats.h"
 #include "impeller/renderer/backend/vulkan/command_queue_vk.h"
 #include "impeller/renderer/backend/vulkan/descriptor_pool_vk.h"
 #include "impeller/renderer/backend/vulkan/render_pass_builder_vk.h"
@@ -666,15 +667,15 @@ void ContextVK::InitializeCommonlyUsedShadersIfNeeded() const {
       rt_allocator.CreateOffscreenMSAA(*this, {1, 1}, 1);
 
   RenderPassBuilderVK builder;
-  for (const auto& [bind_point, color] : render_target.GetColorAttachments()) {
-    builder.SetColorAttachment(
-        bind_point,                                          //
-        color.texture->GetTextureDescriptor().format,        //
-        color.texture->GetTextureDescriptor().sample_count,  //
-        color.load_action,                                   //
-        color.store_action                                   //
-    );
-  }
+
+  const ColorAttachment& color = render_target.GetColor0();
+  builder.SetColorAttachment(
+      0u,                                                  //
+      color.texture->GetTextureDescriptor().format,        //
+      color.texture->GetTextureDescriptor().sample_count,  //
+      color.load_action,                                   //
+      color.store_action                                   //
+  );
 
   if (auto depth = render_target.GetDepthAttachment(); depth.has_value()) {
     builder.SetDepthStencilAttachment(
diff --git a/impeller/renderer/backend/vulkan/render_pass_builder_vk.cc b/impeller/renderer/backend/vulkan/render_pass_builder_vk.cc
index 77f5a3a1e9b14..32f62dddf1907 100644
--- a/impeller/renderer/backend/vulkan/render_pass_builder_vk.cc
+++ b/impeller/renderer/backend/vulkan/render_pass_builder_vk.cc
@@ -48,14 +48,27 @@ RenderPassBuilderVK& RenderPassBuilderVK::SetColorAttachment(
     desc.initialLayout = vk::ImageLayout::eUndefined;
   }
   desc.finalLayout = vk::ImageLayout::eGeneral;
-  colors_[index] = desc;
 
-  if (StoreActionPerformsResolve(store_action)) {
-    desc.storeOp = ToVKAttachmentStoreOp(store_action, true);
-    desc.samples = vk::SampleCountFlagBits::e1;
-    resolves_[index] = desc;
+  const bool performs_resolves = StoreActionPerformsResolve(store_action);
+  if (index == 0u) {
+    color0_ = desc;
+
+    if (performs_resolves) {
+      desc.storeOp = ToVKAttachmentStoreOp(store_action, true);
+      desc.samples = vk::SampleCountFlagBits::e1;
+      color0_resolve_ = desc;
+    } else {
+      color0_resolve_ = std::nullopt;
+    }
   } else {
-    resolves_.erase(index);
+    colors_[index] = desc;
+    if (performs_resolves) {
+      desc.storeOp = ToVKAttachmentStoreOp(store_action, true);
+      desc.samples = vk::SampleCountFlagBits::e1;
+      resolves_[index] = desc;
+    } else {
+      resolves_.erase(index);
+    }
   }
   return *this;
 }
@@ -100,8 +113,11 @@ vk::UniqueRenderPass RenderPassBuilderVK::Build(
     const vk::Device& device) const {
   // This must be less than `VkPhysicalDeviceLimits::maxColorAttachments` but we
   // are not checking.
-  const auto color_attachments_count =
+  auto color_attachments_count =
       colors_.empty() ? 0u : colors_.rbegin()->first + 1u;
+  if (color0_.has_value()) {
+    color_attachments_count++;
+  }
 
   std::vector<vk::AttachmentDescription> attachments;
 
@@ -111,6 +127,22 @@ vk::UniqueRenderPass RenderPassBuilderVK::Build(
                                                     kUnusedAttachmentReference);
   vk::AttachmentReference depth_stencil_ref = kUnusedAttachmentReference;
 
+  if (color0_.has_value()) {
+    vk::AttachmentReference color_ref;
+    color_ref.attachment = attachments.size();
+    color_ref.layout = vk::ImageLayout::eGeneral;
+    color_refs[0] = color_ref;
+    attachments.push_back(color0_.value());
+
+    if (color0_resolve_.has_value()) {
+      vk::AttachmentReference resolve_ref;
+      resolve_ref.attachment = attachments.size();
+      resolve_ref.layout = vk::ImageLayout::eGeneral;
+      resolve_refs[0] = resolve_ref;
+      attachments.push_back(color0_resolve_.value());
+    }
+  }
+
   for (const auto& color : colors_) {
     vk::AttachmentReference color_ref;
     color_ref.attachment = attachments.size();
@@ -207,4 +239,16 @@ RenderPassBuilderVK::GetDepthStencil() const {
   return depth_stencil_;
 }
 
+// Visible for testing.
+std::optional<vk::AttachmentDescription> RenderPassBuilderVK::GetColor0()
+    const {
+  return color0_;
+}
+
+// Visible for testing.
+std::optional<vk::AttachmentDescription> RenderPassBuilderVK::GetColor0Resolve()
+    const {
+  return color0_resolve_;
+}
+
 }  // namespace impeller
diff --git a/impeller/renderer/backend/vulkan/render_pass_builder_vk.h b/impeller/renderer/backend/vulkan/render_pass_builder_vk.h
index c3ed390e961b9..51c6313ec9583 100644
--- a/impeller/renderer/backend/vulkan/render_pass_builder_vk.h
+++ b/impeller/renderer/backend/vulkan/render_pass_builder_vk.h
@@ -54,10 +54,19 @@ class RenderPassBuilderVK {
   // Visible for testing.
   const std::optional<vk::AttachmentDescription>& GetDepthStencil() const;
 
+  // Visible for testing.
+  std::optional<vk::AttachmentDescription> GetColor0() const;
+
+  // Visible for testing.
+  std::optional<vk::AttachmentDescription> GetColor0Resolve() const;
+
  private:
+  std::optional<vk::AttachmentDescription> color0_;
+  std::optional<vk::AttachmentDescription> color0_resolve_;
+  std::optional<vk::AttachmentDescription> depth_stencil_;
+
   std::map<size_t, vk::AttachmentDescription> colors_;
   std::map<size_t, vk::AttachmentDescription> resolves_;
-  std::optional<vk::AttachmentDescription> depth_stencil_;
 };
 
 //------------------------------------------------------------------------------
diff --git a/impeller/renderer/backend/vulkan/render_pass_builder_vk_unittests.cc b/impeller/renderer/backend/vulkan/render_pass_builder_vk_unittests.cc
index 658ae2f54ac88..d280cdb6dfc23 100644
--- a/impeller/renderer/backend/vulkan/render_pass_builder_vk_unittests.cc
+++ b/impeller/renderer/backend/vulkan/render_pass_builder_vk_unittests.cc
@@ -40,9 +40,9 @@ TEST(RenderPassBuilder, RenderPassWithLoadOpUsesCurrentLayout) {
 
   EXPECT_TRUE(!!render_pass);
 
-  auto maybe_color = builder.GetColorAttachments().find(0u);
-  ASSERT_NE(maybe_color, builder.GetColorAttachments().end());
-  auto color = maybe_color->second;
+  auto maybe_color = builder.GetColor0();
+  ASSERT_TRUE(maybe_color.has_value());
+  auto color = maybe_color.value();
 
   EXPECT_EQ(color.initialLayout, vk::ImageLayout::eColorAttachmentOptimal);
   EXPECT_EQ(color.finalLayout, vk::ImageLayout::eGeneral);
@@ -66,9 +66,9 @@ TEST(RenderPassBuilder, CreatesRenderPassWithCombinedDepthStencil) {
 
   EXPECT_TRUE(!!render_pass);
 
-  auto maybe_color = builder.GetColorAttachments().find(0u);
-  ASSERT_NE(maybe_color, builder.GetColorAttachments().end());
-  auto color = maybe_color->second;
+  auto maybe_color = builder.GetColor0();
+  ASSERT_TRUE(maybe_color.has_value());
+  auto color = maybe_color.value();
 
   EXPECT_EQ(color.initialLayout, vk::ImageLayout::eUndefined);
   EXPECT_EQ(color.finalLayout, vk::ImageLayout::eGeneral);
@@ -135,9 +135,9 @@ TEST(RenderPassBuilder, CreatesMSAAResolveWithCorrectStore) {
 
   EXPECT_TRUE(!!render_pass);
 
-  auto maybe_color = builder.GetColorAttachments().find(0u);
-  ASSERT_NE(maybe_color, builder.GetColorAttachments().end());
-  auto color = maybe_color->second;
+  auto maybe_color = builder.GetColor0();
+  ASSERT_TRUE(maybe_color.has_value());
+  auto color = maybe_color.value();
 
   // MSAA Texture.
   EXPECT_EQ(color.initialLayout, vk::ImageLayout::eUndefined);
diff --git a/impeller/renderer/backend/vulkan/render_pass_cache_unittests.cc b/impeller/renderer/backend/vulkan/render_pass_cache_unittests.cc
index 055c91a3ccb10..51d42aee512b8 100644
--- a/impeller/renderer/backend/vulkan/render_pass_cache_unittests.cc
+++ b/impeller/renderer/backend/vulkan/render_pass_cache_unittests.cc
@@ -23,8 +23,7 @@ TEST_P(RendererTest, CachesRenderPassAndFramebuffer) {
 
   auto render_target =
       allocator->CreateOffscreenMSAA(*GetContext(), {100, 100}, 1);
-  auto resolve_texture =
-      render_target.GetColorAttachments().find(0u)->second.resolve_texture;
+  auto resolve_texture = render_target.GetColor0().resolve_texture;
   auto& texture_vk = TextureVK::Cast(*resolve_texture);
 
   EXPECT_EQ(texture_vk.GetCachedFramebuffer(), nullptr);
diff --git a/impeller/renderer/backend/vulkan/test/swapchain_unittests.cc b/impeller/renderer/backend/vulkan/test/swapchain_unittests.cc
index 7589f849a15e4..9594e2d75103a 100644
--- a/impeller/renderer/backend/vulkan/test/swapchain_unittests.cc
+++ b/impeller/renderer/backend/vulkan/test/swapchain_unittests.cc
@@ -86,8 +86,7 @@ TEST(SwapchainTest, CachesRenderPassOnSwapchainImage) {
     auto& depth = render_target.GetDepthAttachment();
     depth_stencil_textures.push_back(depth.has_value() ? depth->texture
                                                        : nullptr);
-    msaa_textures.push_back(
-        render_target.GetColorAttachments().find(0u)->second.texture);
+    msaa_textures.push_back(render_target.GetColor0().texture);
   }
 
   for (auto i = 1; i < 3; i++) {
diff --git a/impeller/renderer/render_target.cc b/impeller/renderer/render_target.cc
index dd70f9f202a9d..7de9db51fe0d8 100644
--- a/impeller/renderer/render_target.cc
+++ b/impeller/renderer/render_target.cc
@@ -28,6 +28,7 @@ bool RenderTarget::IsValid() const {
     return false;
   }
 
+#ifndef NDEBUG
   // Validate that all attachments are of the same size.
   {
     std::optional<ISize> size;
@@ -87,12 +88,18 @@ bool RenderTarget::IsValid() const {
       return false;
     }
   }
+#endif  // NDEBUG
 
   return true;
 }
 
 void RenderTarget::IterateAllAttachments(
     const std::function<bool(const Attachment& attachment)>& iterator) const {
+  if (color0_.has_value()) {
+    if (!iterator(color0_.value())) {
+      return;
+    }
+  }
   for (const auto& color : colors_) {
     if (!iterator(color.second)) {
       return;
@@ -113,13 +120,16 @@ void RenderTarget::IterateAllAttachments(
 }
 
 SampleCount RenderTarget::GetSampleCount() const {
-  if (auto found = colors_.find(0u); found != colors_.end()) {
-    return found->second.texture->GetTextureDescriptor().sample_count;
+  if (color0_.has_value()) {
+    return color0_.value().texture->GetTextureDescriptor().sample_count;
   }
   return SampleCount::kCount1;
 }
 
 bool RenderTarget::HasColorAttachment(size_t index) const {
+  if (index == 0u) {
+    return color0_.has_value();
+  }
   if (auto found = colors_.find(index); found != colors_.end()) {
     return true;
   }
@@ -127,6 +137,12 @@ bool RenderTarget::HasColorAttachment(size_t index) const {
 }
 
 std::optional<ISize> RenderTarget::GetColorAttachmentSize(size_t index) const {
+  if (index == 0u) {
+    if (color0_.has_value()) {
+      return color0_.value().texture->GetSize();
+    }
+    return std::nullopt;
+  }
   auto found = colors_.find(index);
 
   if (found == colors_.end()) {
@@ -142,12 +158,10 @@ ISize RenderTarget::GetRenderTargetSize() const {
 }
 
 std::shared_ptr<Texture> RenderTarget::GetRenderTargetTexture() const {
-  auto found = colors_.find(0u);
-  if (found == colors_.end()) {
+  if (!color0_.has_value()) {
     return nullptr;
   }
-  return found->second.resolve_texture ? found->second.resolve_texture
-                                       : found->second.texture;
+  return color0_->resolve_texture ? color0_->resolve_texture : color0_->texture;
 }
 
 PixelFormat RenderTarget::GetRenderTargetPixelFormat() const {
@@ -169,7 +183,12 @@ size_t RenderTarget::GetMaxColorAttacmentBindIndex() const {
 RenderTarget& RenderTarget::SetColorAttachment(
     const ColorAttachment& attachment,
     size_t index) {
-  if (attachment.IsValid()) {
+  if (!attachment.IsValid()) {
+    return *this;
+  }
+  if (index == 0u) {
+    color0_ = attachment;
+  } else {
     colors_[index] = attachment;
   }
   return *this;
@@ -195,6 +214,13 @@ RenderTarget& RenderTarget::SetStencilAttachment(
   return *this;
 }
 
+ColorAttachment RenderTarget::GetColor0() const {
+  if (color0_.has_value()) {
+    return color0_.value();
+  }
+  return ColorAttachment{};
+}
+
 const std::map<size_t, ColorAttachment>& RenderTarget::GetColorAttachments()
     const {
   return colors_;
@@ -219,6 +245,9 @@ size_t RenderTarget::GetTotalAttachmentCount() const {
       count++;
     }
   }
+  if (color0_.has_value()) {
+    count++;
+  }
   if (depth_.has_value()) {
     count++;
   }
@@ -231,6 +260,10 @@ size_t RenderTarget::GetTotalAttachmentCount() const {
 std::string RenderTarget::ToString() const {
   std::stringstream stream;
 
+  if (color0_.has_value()) {
+    stream << SPrintF("Color[%zu]=(%s)", 0ul,
+                      ColorAttachmentToString(color0_.value()).c_str());
+  }
   for (const auto& [index, color] : colors_) {
     stream << SPrintF("Color[%zu]=(%s)", index,
                       ColorAttachmentToString(color).c_str());
@@ -248,6 +281,18 @@ std::string RenderTarget::ToString() const {
   return stream.str();
 }
 
+RenderTargetConfig RenderTarget::ToConfig() const {
+  if (color0_.has_value()) {
+    return RenderTargetConfig{};
+  }
+  const auto& color_attachment = color0_.value();
+  return RenderTargetConfig{
+      .size = color_attachment.texture->GetSize(),
+      .mip_count = color_attachment.texture->GetMipCount(),
+      .has_msaa = color_attachment.resolve_texture != nullptr,
+      .has_depth_stencil = depth_.has_value() && stencil_.has_value()};
+}
+
 RenderTargetAllocator::RenderTargetAllocator(
     std::shared_ptr<Allocator> allocator)
     : allocator_(std::move(allocator)) {}
diff --git a/impeller/renderer/render_target.h b/impeller/renderer/render_target.h
index 77f5bf43f5e38..b65ed33ff3e3d 100644
--- a/impeller/renderer/render_target.h
+++ b/impeller/renderer/render_target.h
@@ -109,6 +109,8 @@ class RenderTarget final {
 
   size_t GetMaxColorAttacmentBindIndex() const;
 
+  ColorAttachment GetColor0() const;
+
   const std::map<size_t, ColorAttachment>& GetColorAttachments() const;
 
   const std::optional<DepthAttachment>& GetDepthAttachment() const;
@@ -122,19 +124,13 @@ class RenderTarget final {
 
   std::string ToString() const;
 
-  RenderTargetConfig ToConfig() const {
-    auto& color_attachment = GetColorAttachments().find(0)->second;
-    return RenderTargetConfig{
-        .size = color_attachment.texture->GetSize(),
-        .mip_count = color_attachment.texture->GetMipCount(),
-        .has_msaa = color_attachment.resolve_texture != nullptr,
-        .has_depth_stencil = depth_.has_value() && stencil_.has_value()};
-  }
+  RenderTargetConfig ToConfig() const;
 
  private:
-  std::map<size_t, ColorAttachment> colors_;
+  std::optional<ColorAttachment> color0_;
   std::optional<DepthAttachment> depth_;
   std::optional<StencilAttachment> stencil_;
+  std::map<size_t, ColorAttachment> colors_;
 };
 
 /// @brief a wrapper around the impeller [Allocator] instance that can be used
diff --git a/impeller/renderer/renderer_unittests.cc b/impeller/renderer/renderer_unittests.cc
index 633ad6ddba897..0e84ea50cfd17 100644
--- a/impeller/renderer/renderer_unittests.cc
+++ b/impeller/renderer/renderer_unittests.cc
@@ -589,10 +589,6 @@ TEST_P(RendererTest, CanBlitTextureToTexture) {
       }
       pass->SetLabel("Playground Blit Pass");
 
-      if (render_target.GetColorAttachments().empty()) {
-        return false;
-      }
-
       // Blit `bridge` to the top left corner of the texture.
       pass->AddCopy(bridge, texture);
 
@@ -709,10 +705,6 @@ TEST_P(RendererTest, CanBlitTextureToBuffer) {
       }
       pass->SetLabel("Playground Blit Pass");
 
-      if (render_target.GetColorAttachments().empty()) {
-        return false;
-      }
-
       // Blit `bridge` to the top left corner of the texture.
       pass->AddCopy(bridge, device_buffer);
       pass->EncodeCommands(context->GetResourceAllocator());

From 5b4d07e4aeecd98b6a5e143abbcec0ea22bf4fd0 Mon Sep 17 00:00:00 2001
From: jonahwilliams <jonahwilliams@google.com>
Date: Tue, 26 Nov 2024 17:46:00 -0800
Subject: [PATCH 02/10] fix missing color attachments in vk render_pass.

---
 .../renderer/backend/vulkan/render_pass_vk.cc | 36 ++++++++++++++++---
 1 file changed, 32 insertions(+), 4 deletions(-)

diff --git a/impeller/renderer/backend/vulkan/render_pass_vk.cc b/impeller/renderer/backend/vulkan/render_pass_vk.cc
index 3808d84fd34c2..244795e21c912 100644
--- a/impeller/renderer/backend/vulkan/render_pass_vk.cc
+++ b/impeller/renderer/backend/vulkan/render_pass_vk.cc
@@ -56,6 +56,12 @@ static std::vector<vk::ClearValue> GetVKClearValues(
     const RenderTarget& target) {
   std::vector<vk::ClearValue> clears;
 
+  const ColorAttachment& color0 = target.GetColor0();
+  clears.emplace_back(VKClearValueFromColor(color0.clear_color));
+  if (color0.resolve_texture) {
+    clears.emplace_back(VKClearValueFromColor(color0.clear_color));
+  }
+
   for (const auto& [_, color] : target.GetColorAttachments()) {
     clears.emplace_back(VKClearValueFromColor(color.clear_color));
     if (color.resolve_texture) {
@@ -83,6 +89,22 @@ SharedHandleVK<vk::RenderPass> RenderPassVK::CreateVKRenderPass(
     const std::shared_ptr<CommandBufferVK>& command_buffer) const {
   RenderPassBuilderVK builder;
 
+  const ColorAttachment& color0 = render_target_.GetColor0();
+  builder.SetColorAttachment(
+      0u,                                                   //
+      color0.texture->GetTextureDescriptor().format,        //
+      color0.texture->GetTextureDescriptor().sample_count,  //
+      color0.load_action,                                   //
+      color0.store_action,                                  //
+      TextureVK::Cast(*color0.texture).GetLayout()          //
+  );
+  TextureVK::Cast(*color0.texture)
+      .SetLayoutWithoutEncoding(vk::ImageLayout::eGeneral);
+  if (color0.resolve_texture) {
+    TextureVK::Cast(*color0.resolve_texture)
+        .SetLayoutWithoutEncoding(vk::ImageLayout::eGeneral);
+  }
+
   for (const auto& [bind_point, color] : render_target_.GetColorAttachments()) {
     builder.SetColorAttachment(
         bind_point,                                          //
@@ -137,10 +159,8 @@ RenderPassVK::RenderPassVK(const std::shared_ptr<const Context>& context,
                            const RenderTarget& target,
                            std::shared_ptr<CommandBufferVK> command_buffer)
     : RenderPass(context, target), command_buffer_(std::move(command_buffer)) {
-  color_image_vk_ =
-      render_target_.GetColorAttachments().find(0u)->second.texture;
-  resolve_image_vk_ =
-      render_target_.GetColorAttachments().find(0u)->second.resolve_texture;
+  color_image_vk_ = render_target_.GetColor0().texture;
+  resolve_image_vk_ = render_target_.GetColor0().resolve_texture;
 
   const auto& vk_context = ContextVK::Cast(*context);
   command_buffer_vk_ = command_buffer_->GetCommandBuffer();
@@ -254,6 +274,14 @@ SharedHandleVK<vk::Framebuffer> RenderPassVK::CreateVKFramebuffer(
   // This bit must be consistent to ensure compatibility with the pass created
   // earlier. Follow this order: Color attachments, then depth-stencil, then
   // stencil.
+  const ColorAttachment color0 = render_target_.GetColor0();
+  attachments.emplace_back(
+      TextureVK::Cast(*color0.texture).GetRenderTargetView());
+  if (color0.resolve_texture) {
+    attachments.emplace_back(
+        TextureVK::Cast(*color0.resolve_texture).GetRenderTargetView());
+  }
+
   for (const auto& [_, color] : render_target_.GetColorAttachments()) {
     // The bind point doesn't matter here since that information is present in
     // the render pass.

From 24450c427295733b3ca99bcb93530eeefc8b4482 Mon Sep 17 00:00:00 2001
From: Jonah Williams <jonahwilliams@google.com>
Date: Tue, 26 Nov 2024 19:26:14 -0800
Subject: [PATCH 03/10] Update render_target.cc

---
 impeller/renderer/render_target.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/impeller/renderer/render_target.cc b/impeller/renderer/render_target.cc
index 7de9db51fe0d8..80b1416e2ceb6 100644
--- a/impeller/renderer/render_target.cc
+++ b/impeller/renderer/render_target.cc
@@ -261,7 +261,7 @@ std::string RenderTarget::ToString() const {
   std::stringstream stream;
 
   if (color0_.has_value()) {
-    stream << SPrintF("Color[%zu]=(%s)", 0ul,
+    stream << SPrintF("Color[%d]=(%s)", 0,
                       ColorAttachmentToString(color0_.value()).c_str());
   }
   for (const auto& [index, color] : colors_) {

From 61c4ff56c16765d299a718fb322d05a3d9a4cc54 Mon Sep 17 00:00:00 2001
From: jonahwilliams <jonahwilliams@google.com>
Date: Tue, 26 Nov 2024 23:03:23 -0800
Subject: [PATCH 04/10] lint workarounds.

---
 .../backend/vulkan/render_pass_builder_vk_unittests.cc   | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/impeller/renderer/backend/vulkan/render_pass_builder_vk_unittests.cc b/impeller/renderer/backend/vulkan/render_pass_builder_vk_unittests.cc
index d280cdb6dfc23..85d277385cbc5 100644
--- a/impeller/renderer/backend/vulkan/render_pass_builder_vk_unittests.cc
+++ b/impeller/renderer/backend/vulkan/render_pass_builder_vk_unittests.cc
@@ -42,6 +42,9 @@ TEST(RenderPassBuilder, RenderPassWithLoadOpUsesCurrentLayout) {
 
   auto maybe_color = builder.GetColor0();
   ASSERT_TRUE(maybe_color.has_value());
+  if (!maybe_color.has_value()) {
+    return;
+  }
   auto color = maybe_color.value();
 
   EXPECT_EQ(color.initialLayout, vk::ImageLayout::eColorAttachmentOptimal);
@@ -68,6 +71,9 @@ TEST(RenderPassBuilder, CreatesRenderPassWithCombinedDepthStencil) {
 
   auto maybe_color = builder.GetColor0();
   ASSERT_TRUE(maybe_color.has_value());
+  if (!maybe_color.has_value()) {
+    return;
+  }
   auto color = maybe_color.value();
 
   EXPECT_EQ(color.initialLayout, vk::ImageLayout::eUndefined);
@@ -137,6 +143,9 @@ TEST(RenderPassBuilder, CreatesMSAAResolveWithCorrectStore) {
 
   auto maybe_color = builder.GetColor0();
   ASSERT_TRUE(maybe_color.has_value());
+  if (!maybe_color.has_value()) {
+    return;
+  }
   auto color = maybe_color.value();
 
   // MSAA Texture.

From b6de222c1dcbe16685f4fe4fcb1ce46e5604d6fb Mon Sep 17 00:00:00 2001
From: Jonah Williams <jonahwilliams@google.com>
Date: Tue, 26 Nov 2024 23:41:31 -0800
Subject: [PATCH 05/10] Update render_target.cc

---
 impeller/renderer/render_target.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/impeller/renderer/render_target.cc b/impeller/renderer/render_target.cc
index 80b1416e2ceb6..c133c74096ecc 100644
--- a/impeller/renderer/render_target.cc
+++ b/impeller/renderer/render_target.cc
@@ -282,7 +282,7 @@ std::string RenderTarget::ToString() const {
 }
 
 RenderTargetConfig RenderTarget::ToConfig() const {
-  if (color0_.has_value()) {
+  if (!color0_.has_value()) {
     return RenderTargetConfig{};
   }
   const auto& color_attachment = color0_.value();

From c65046afe87988e93e67e209217bb60e5ecdcbe7 Mon Sep 17 00:00:00 2001
From: jonahwilliams <jonahwilliams@google.com>
Date: Wed, 27 Nov 2024 11:44:13 -0800
Subject: [PATCH 06/10] ++

---
 .../render_pass_builder_vk_unittests.cc       | 29 +++++++++++--------
 1 file changed, 17 insertions(+), 12 deletions(-)

diff --git a/impeller/renderer/backend/vulkan/render_pass_builder_vk_unittests.cc b/impeller/renderer/backend/vulkan/render_pass_builder_vk_unittests.cc
index 85d277385cbc5..2aa44c42de0db 100644
--- a/impeller/renderer/backend/vulkan/render_pass_builder_vk_unittests.cc
+++ b/impeller/renderer/backend/vulkan/render_pass_builder_vk_unittests.cc
@@ -40,12 +40,12 @@ TEST(RenderPassBuilder, RenderPassWithLoadOpUsesCurrentLayout) {
 
   EXPECT_TRUE(!!render_pass);
 
-  auto maybe_color = builder.GetColor0();
+  std::optional<vk::AttachmentDescription> maybe_color = builder.GetColor0();
   ASSERT_TRUE(maybe_color.has_value());
   if (!maybe_color.has_value()) {
     return;
   }
-  auto color = maybe_color.value();
+  vk::AttachmentDescription color = maybe_color.value();
 
   EXPECT_EQ(color.initialLayout, vk::ImageLayout::eColorAttachmentOptimal);
   EXPECT_EQ(color.finalLayout, vk::ImageLayout::eGeneral);
@@ -69,24 +69,25 @@ TEST(RenderPassBuilder, CreatesRenderPassWithCombinedDepthStencil) {
 
   EXPECT_TRUE(!!render_pass);
 
-  auto maybe_color = builder.GetColor0();
+  std::optional<vk::AttachmentDescription> maybe_color = builder.GetColor0();
   ASSERT_TRUE(maybe_color.has_value());
   if (!maybe_color.has_value()) {
     return;
   }
-  auto color = maybe_color.value();
+  vk::AttachmentDescription color = maybe_color.value();
 
   EXPECT_EQ(color.initialLayout, vk::ImageLayout::eUndefined);
   EXPECT_EQ(color.finalLayout, vk::ImageLayout::eGeneral);
   EXPECT_EQ(color.loadOp, vk::AttachmentLoadOp::eClear);
   EXPECT_EQ(color.storeOp, vk::AttachmentStoreOp::eStore);
 
-  auto maybe_depth_stencil = builder.GetDepthStencil();
+  std::optional<vk::AttachmentDescription> maybe_depth_stencil =
+      builder.GetDepthStencil();
   ASSERT_TRUE(maybe_depth_stencil.has_value());
   if (!maybe_depth_stencil.has_value()) {
     return;
   }
-  auto depth_stencil = maybe_depth_stencil.value();
+  vk::AttachmentDescription depth_stencil = maybe_depth_stencil.value();
 
   EXPECT_EQ(depth_stencil.initialLayout, vk::ImageLayout::eUndefined);
   EXPECT_EQ(depth_stencil.finalLayout,
@@ -112,12 +113,13 @@ TEST(RenderPassBuilder, CreatesRenderPassWithOnlyStencil) {
 
   EXPECT_TRUE(!!render_pass);
 
-  auto maybe_depth_stencil = builder.GetDepthStencil();
+  std::optional<vk::AttachmentDescription> maybe_depth_stencil =
+      builder.GetDepthStencil();
   ASSERT_TRUE(maybe_depth_stencil.has_value());
   if (!maybe_depth_stencil.has_value()) {
     return;
   }
-  auto depth_stencil = maybe_depth_stencil.value();
+  vk::AttachmentDescription depth_stencil = maybe_depth_stencil.value();
 
   EXPECT_EQ(depth_stencil.initialLayout, vk::ImageLayout::eUndefined);
   EXPECT_EQ(depth_stencil.finalLayout,
@@ -146,7 +148,7 @@ TEST(RenderPassBuilder, CreatesMSAAResolveWithCorrectStore) {
   if (!maybe_color.has_value()) {
     return;
   }
-  auto color = maybe_color.value();
+  vk::AttachmentDescription color = maybe_color.value();
 
   // MSAA Texture.
   EXPECT_EQ(color.initialLayout, vk::ImageLayout::eUndefined);
@@ -154,9 +156,12 @@ TEST(RenderPassBuilder, CreatesMSAAResolveWithCorrectStore) {
   EXPECT_EQ(color.loadOp, vk::AttachmentLoadOp::eClear);
   EXPECT_EQ(color.storeOp, vk::AttachmentStoreOp::eDontCare);
 
-  auto maybe_resolve = builder.GetResolves().find(0u);
-  ASSERT_NE(maybe_resolve, builder.GetResolves().end());
-  auto resolve = maybe_resolve->second;
+  auto maybe_resolve = builder.GetColor0Resolve();
+  ASSERT_TRUE(maybe_resolve.has_value());
+  if (!maybe_resolve.has_value()) {
+    return;
+  }
+  vk::AttachmentDescription resolve = maybe_resolve.value();
 
   // MSAA Resolve Texture.
   EXPECT_EQ(resolve.initialLayout, vk::ImageLayout::eUndefined);

From 132748a81ae9dd0a3a1e83d8b8e8542d41f734e3 Mon Sep 17 00:00:00 2001
From: jonahwilliams <jonahwilliams@google.com>
Date: Mon, 2 Dec 2024 12:07:33 -0800
Subject: [PATCH 07/10] fixup flutter gpu.

---
 impeller/renderer/backend/metal/render_pass_mtl.mm | 2 +-
 impeller/renderer/render_target.cc                 | 4 ++++
 impeller/renderer/render_target.h                  | 2 ++
 lib/gpu/render_pass.cc                             | 4 ++++
 4 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/impeller/renderer/backend/metal/render_pass_mtl.mm b/impeller/renderer/backend/metal/render_pass_mtl.mm
index ddda56a9ec84a..8365e6749aee8 100644
--- a/impeller/renderer/backend/metal/render_pass_mtl.mm
+++ b/impeller/renderer/backend/metal/render_pass_mtl.mm
@@ -105,7 +105,7 @@ static bool ConfigureStencilAttachment(
   auto result = [MTLRenderPassDescriptor renderPassDescriptor];
 
   const ColorAttachment& color0 = desc.GetColor0();
-  if (!ConfigureColorAttachment(color0, result.colorAttachments[0u])) {
+  if (!ConfigureColorAttachment(color0, result.colorAttachments[0])) {
     VALIDATION_LOG << "Could not configure color attachment at index 0";
     return nil;
   }
diff --git a/impeller/renderer/render_target.cc b/impeller/renderer/render_target.cc
index c133c74096ecc..a280b683c91db 100644
--- a/impeller/renderer/render_target.cc
+++ b/impeller/renderer/render_target.cc
@@ -221,6 +221,10 @@ ColorAttachment RenderTarget::GetColor0() const {
   return ColorAttachment{};
 }
 
+bool RenderTarget::HasColor0() const {
+  return color0_.has_value();
+}
+
 const std::map<size_t, ColorAttachment>& RenderTarget::GetColorAttachments()
     const {
   return colors_;
diff --git a/impeller/renderer/render_target.h b/impeller/renderer/render_target.h
index b65ed33ff3e3d..0038d0901e75f 100644
--- a/impeller/renderer/render_target.h
+++ b/impeller/renderer/render_target.h
@@ -111,6 +111,8 @@ class RenderTarget final {
 
   ColorAttachment GetColor0() const;
 
+  bool HasColor0() const;
+
   const std::map<size_t, ColorAttachment>& GetColorAttachments() const;
 
   const std::optional<DepthAttachment>& GetDepthAttachment() const;
diff --git a/lib/gpu/render_pass.cc b/lib/gpu/render_pass.cc
index 3987d823f5a22..154539edfaa01 100644
--- a/lib/gpu/render_pass.cc
+++ b/lib/gpu/render_pass.cc
@@ -105,6 +105,10 @@ RenderPass::GetOrCreatePipeline() {
 
   pipeline_desc.SetSampleCount(render_target_.GetSampleCount());
 
+  if (render_target_.HasColor0()) {
+    auto& color = GetColorAttachmentDescriptor(0);
+    color.format = render_target_.GetRenderTargetPixelFormat();
+  }
   for (const auto& it : render_target_.GetColorAttachments()) {
     auto& color = GetColorAttachmentDescriptor(it.first);
     color.format = render_target_.GetRenderTargetPixelFormat();

From 2f912f6263c9bbefd25c4099452dea6f1aaeed23 Mon Sep 17 00:00:00 2001
From: jonahwilliams <jonahwilliams@google.com>
Date: Mon, 2 Dec 2024 17:34:42 -0800
Subject: [PATCH 08/10] hide specialization of color0 attachment.

---
 impeller/display_list/canvas.cc               |   6 +-
 impeller/entity/entity_pass_target.cc         |   2 +-
 .../entity/entity_pass_target_unittests.cc    |   8 +-
 impeller/entity/inline_pass_context.cc        |   5 +-
 impeller/entity/render_target_cache.cc        |   6 +-
 .../entity/render_target_cache_unittests.cc   |   4 +-
 impeller/playground/playground.cc             |   2 +-
 .../renderer/backend/gles/render_pass_gles.cc |   2 +-
 .../gles/test/surface_gles_unittests.cc       |   4 +-
 .../renderer/backend/metal/render_pass_mtl.mm |  21 ++--
 .../renderer/backend/vulkan/context_vk.cc     |  19 ++--
 .../vulkan/render_pass_cache_unittests.cc     |   2 +-
 .../renderer/backend/vulkan/render_pass_vk.cc | 104 +++++++-----------
 .../vulkan/test/swapchain_unittests.cc        |   2 +-
 impeller/renderer/render_target.cc            |  38 +++++--
 impeller/renderer/render_target.h             |  18 ++-
 lib/gpu/render_pass.cc                        |  15 ++-
 17 files changed, 128 insertions(+), 130 deletions(-)

diff --git a/impeller/display_list/canvas.cc b/impeller/display_list/canvas.cc
index f311094489fa3..4aaa83372bf1a 100644
--- a/impeller/display_list/canvas.cc
+++ b/impeller/display_list/canvas.cc
@@ -857,7 +857,7 @@ void Canvas::DrawAtlas(const std::shared_ptr<AtlasContents>& atlas_contents,
 
 void Canvas::SetupRenderPass() {
   renderer_.GetRenderTargetCache()->Start();
-  ColorAttachment color0 = render_target_.GetColor0();
+  ColorAttachment color0 = render_target_.GetColorAttachment(0);
 
   auto& stencil_attachment = render_target_.GetStencilAttachment();
   auto& depth_attachment = render_target_.GetDepthAttachment();
@@ -1464,7 +1464,7 @@ void Canvas::AddRenderEntityToCurrentPass(Entity& entity, bool reuse_depth) {
       RenderTarget& render_target = render_passes_.back()
                                         .inline_pass_context->GetPassTarget()
                                         .GetRenderTarget();
-      ColorAttachment attachment = render_target.GetColor0();
+      ColorAttachment attachment = render_target.GetColorAttachment(0);
       // Attachment.clear color needs to be premultiplied at all times, but the
       // Color::Blend function requires unpremultiplied colors.
       attachment.clear_color = attachment.clear_color.Unpremultiply()
@@ -1591,7 +1591,7 @@ std::shared_ptr<Texture> Canvas::FlipBackdrop(Point global_pass_position,
   }
 
   if (should_use_onscreen) {
-    ColorAttachment color0 = render_target_.GetColor0();
+    ColorAttachment color0 = render_target_.GetColorAttachment(0);
     // When MSAA is being used, we end up overriding the entire backdrop by
     // drawing the previous pass texture, and so we don't have to clear it and
     // can use kDontCare.
diff --git a/impeller/entity/entity_pass_target.cc b/impeller/entity/entity_pass_target.cc
index a25d96e197d45..db9c917b27add 100644
--- a/impeller/entity/entity_pass_target.cc
+++ b/impeller/entity/entity_pass_target.cc
@@ -19,7 +19,7 @@ EntityPassTarget::EntityPassTarget(const RenderTarget& render_target,
 
 std::shared_ptr<Texture> EntityPassTarget::Flip(
     const ContentContext& renderer) {
-  ColorAttachment color0 = target_.GetColor0();
+  ColorAttachment color0 = target_.GetColorAttachment(0);
   if (!color0.resolve_texture) {
     VALIDATION_LOG << "EntityPassTarget Flip should never be called for a "
                       "non-MSAA target.";
diff --git a/impeller/entity/entity_pass_target_unittests.cc b/impeller/entity/entity_pass_target_unittests.cc
index 28aa97d3fd9b3..4a72138a70e19 100644
--- a/impeller/entity/entity_pass_target_unittests.cc
+++ b/impeller/entity/entity_pass_target_unittests.cc
@@ -31,14 +31,14 @@ TEST_P(EntityPassTargetTest, SwapWithMSAATexture) {
 
   auto entity_pass_target = EntityPassTarget(render_target, false, false);
 
-  auto color0 = entity_pass_target.GetRenderTarget().GetColor0();
+  auto color0 = entity_pass_target.GetRenderTarget().GetColorAttachment(0);
   auto msaa_tex = color0.texture;
   auto resolve_tex = color0.resolve_texture;
 
   FML_DCHECK(content_context);
   entity_pass_target.Flip(*content_context);
 
-  color0 = entity_pass_target.GetRenderTarget().GetColor0();
+  color0 = entity_pass_target.GetRenderTarget().GetColorAttachment(0);
 
   ASSERT_EQ(msaa_tex, color0.texture);
   ASSERT_NE(resolve_tex, color0.resolve_texture);
@@ -83,7 +83,7 @@ TEST_P(EntityPassTargetTest, SwapWithMSAAImplicitResolve) {
 
   auto entity_pass_target = EntityPassTarget(render_target, false, true);
 
-  auto color0 = entity_pass_target.GetRenderTarget().GetColor0();
+  auto color0 = entity_pass_target.GetRenderTarget().GetColorAttachment(0);
   auto msaa_tex = color0.texture;
   auto resolve_tex = color0.resolve_texture;
 
@@ -92,7 +92,7 @@ TEST_P(EntityPassTargetTest, SwapWithMSAAImplicitResolve) {
   FML_DCHECK(content_context);
   entity_pass_target.Flip(*content_context);
 
-  color0 = entity_pass_target.GetRenderTarget().GetColor0();
+  color0 = entity_pass_target.GetRenderTarget().GetColorAttachment(0);
 
   ASSERT_NE(msaa_tex, color0.texture);
   ASSERT_NE(resolve_tex, color0.resolve_texture);
diff --git a/impeller/entity/inline_pass_context.cc b/impeller/entity/inline_pass_context.cc
index 8c00550d272de..82d94a614ec5d 100644
--- a/impeller/entity/inline_pass_context.cc
+++ b/impeller/entity/inline_pass_context.cc
@@ -91,7 +91,8 @@ const std::shared_ptr<RenderPass>& InlinePassContext::GetRenderPass() {
   {
     // If the pass target has a resolve texture, then we're using MSAA.
     bool is_msaa =
-        pass_target_.GetRenderTarget().GetColor0().resolve_texture != nullptr;
+        pass_target_.GetRenderTarget().GetColorAttachment(0).resolve_texture !=
+        nullptr;
     if (pass_count_ > 0 && is_msaa) {
       pass_target_.Flip(renderer_);
     }
@@ -99,7 +100,7 @@ const std::shared_ptr<RenderPass>& InlinePassContext::GetRenderPass() {
 
   // Find the color attachment a second time, since the target may have just
   // flipped.
-  ColorAttachment color0 = pass_target_.GetRenderTarget().GetColor0();
+  ColorAttachment color0 = pass_target_.GetRenderTarget().GetColorAttachment(0);
   bool is_msaa = color0.resolve_texture != nullptr;
 
   if (pass_count_ > 0) {
diff --git a/impeller/entity/render_target_cache.cc b/impeller/entity/render_target_cache.cc
index fb9c8098f4b82..43c85fcbed790 100644
--- a/impeller/entity/render_target_cache.cc
+++ b/impeller/entity/render_target_cache.cc
@@ -53,7 +53,8 @@ RenderTarget RenderTargetCache::CreateOffscreen(
     const auto other_config = render_target_data.config;
     if (!render_target_data.used_this_frame && other_config == config) {
       render_target_data.used_this_frame = true;
-      ColorAttachment color0 = render_target_data.render_target.GetColor0();
+      ColorAttachment color0 =
+          render_target_data.render_target.GetColorAttachment(0);
       std::optional<DepthAttachment> depth =
           render_target_data.render_target.GetDepthAttachment();
       std::shared_ptr<Texture> depth_tex = depth ? depth->texture : nullptr;
@@ -102,7 +103,8 @@ RenderTarget RenderTargetCache::CreateOffscreenMSAA(
     const auto other_config = render_target_data.config;
     if (!render_target_data.used_this_frame && other_config == config) {
       render_target_data.used_this_frame = true;
-      ColorAttachment color0 = render_target_data.render_target.GetColor0();
+      ColorAttachment color0 =
+          render_target_data.render_target.GetColorAttachment(0);
       std::optional<DepthAttachment> depth =
           render_target_data.render_target.GetDepthAttachment();
       std::shared_ptr<Texture> depth_tex = depth ? depth->texture : nullptr;
diff --git a/impeller/entity/render_target_cache_unittests.cc b/impeller/entity/render_target_cache_unittests.cc
index 17ea9338f11e0..2684e322c587e 100644
--- a/impeller/entity/render_target_cache_unittests.cc
+++ b/impeller/entity/render_target_cache_unittests.cc
@@ -105,8 +105,8 @@ TEST_P(RenderTargetCacheTest, CachedTextureGetsNewAttachmentConfig) {
       *GetContext(), {100, 100}, 1, "Offscreen2", color_attachment_config);
   render_target_cache.End();
 
-  ColorAttachment color1 = target1.GetColor0();
-  ColorAttachment color2 = target2.GetColor0();
+  ColorAttachment color1 = target1.GetColorAttachment(0);
+  ColorAttachment color2 = target2.GetColorAttachment(0);
   // The second color attachment should reuse the first attachment's texture
   // but with attributes from the second AttachmentConfig.
   EXPECT_EQ(color2.texture, color1.texture);
diff --git a/impeller/playground/playground.cc b/impeller/playground/playground.cc
index fc7cbcd3140ea..1ef9f17f134d8 100644
--- a/impeller/playground/playground.cc
+++ b/impeller/playground/playground.cc
@@ -284,7 +284,7 @@ bool Playground::OpenPlaygroundHere(
       }
       buffer->SetLabel("ImGui Command Buffer");
 
-      auto color0 = render_target.GetColor0();
+      auto color0 = render_target.GetColorAttachment(0);
       color0.load_action = LoadAction::kLoad;
       if (color0.resolve_texture) {
         color0.texture = color0.resolve_texture;
diff --git a/impeller/renderer/backend/gles/render_pass_gles.cc b/impeller/renderer/backend/gles/render_pass_gles.cc
index 6c9d45020dae8..0da1c79c7bd6c 100644
--- a/impeller/renderer/backend/gles/render_pass_gles.cc
+++ b/impeller/renderer/backend/gles/render_pass_gles.cc
@@ -538,7 +538,7 @@ bool RenderPassGLES::OnEncodeCommands(const Context& context) const {
   if (!render_target.HasColorAttachment(0u)) {
     return false;
   }
-  const ColorAttachment& color0 = render_target.GetColor0();
+  const ColorAttachment& color0 = render_target.GetColorAttachment(0);
   const std::optional<DepthAttachment>& depth0 =
       render_target.GetDepthAttachment();
   const std::optional<StencilAttachment>& stencil0 =
diff --git a/impeller/renderer/backend/gles/test/surface_gles_unittests.cc b/impeller/renderer/backend/gles/test/surface_gles_unittests.cc
index 14b90907e7d81..a039e03786c22 100644
--- a/impeller/renderer/backend/gles/test/surface_gles_unittests.cc
+++ b/impeller/renderer/backend/gles/test/surface_gles_unittests.cc
@@ -21,8 +21,8 @@ TEST_P(SurfaceGLESTest, CanWrapNonZeroFBO) {
   ASSERT_TRUE(!!surface);
   ASSERT_TRUE(surface->IsValid());
   ASSERT_TRUE(surface->GetRenderTarget().HasColorAttachment(0));
-  const auto& texture =
-      TextureGLES::Cast(*(surface->GetRenderTarget().GetColor0().texture));
+  const auto& texture = TextureGLES::Cast(
+      *(surface->GetRenderTarget().GetColorAttachment(0).texture));
   auto wrapped = texture.GetFBO();
   ASSERT_TRUE(wrapped.has_value());
   // NOLINTNEXTLINE(bugprone-unchecked-optional-access)
diff --git a/impeller/renderer/backend/metal/render_pass_mtl.mm b/impeller/renderer/backend/metal/render_pass_mtl.mm
index 8365e6749aee8..cd0fbbeb0219c 100644
--- a/impeller/renderer/backend/metal/render_pass_mtl.mm
+++ b/impeller/renderer/backend/metal/render_pass_mtl.mm
@@ -104,22 +104,17 @@ static bool ConfigureStencilAttachment(
     const RenderTarget& desc) {
   auto result = [MTLRenderPassDescriptor renderPassDescriptor];
 
-  const ColorAttachment& color0 = desc.GetColor0();
-  if (!ConfigureColorAttachment(color0, result.colorAttachments[0])) {
-    VALIDATION_LOG << "Could not configure color attachment at index 0";
+  bool configured_attachment = desc.IterateAllColorAttachments(
+      [&result](size_t index, const ColorAttachment& attachment) -> bool {
+        return ConfigureColorAttachment(attachment,
+                                        result.colorAttachments[index]);
+      });
+
+  if (!configured_attachment) {
+    VALIDATION_LOG << "Could not configure color attachments";
     return nil;
   }
 
-  const auto& colors = desc.GetColorAttachments();
-  for (const auto& color : colors) {
-    if (!ConfigureColorAttachment(color.second,
-                                  result.colorAttachments[color.first])) {
-      VALIDATION_LOG << "Could not configure color attachment at index "
-                     << color.first;
-      return nil;
-    }
-  }
-
   const auto& depth = desc.GetDepthAttachment();
 
   if (depth.has_value() &&
diff --git a/impeller/renderer/backend/vulkan/context_vk.cc b/impeller/renderer/backend/vulkan/context_vk.cc
index 8963fae083654..62da661cf7e84 100644
--- a/impeller/renderer/backend/vulkan/context_vk.cc
+++ b/impeller/renderer/backend/vulkan/context_vk.cc
@@ -668,14 +668,17 @@ void ContextVK::InitializeCommonlyUsedShadersIfNeeded() const {
 
   RenderPassBuilderVK builder;
 
-  const ColorAttachment& color = render_target.GetColor0();
-  builder.SetColorAttachment(
-      0u,                                                  //
-      color.texture->GetTextureDescriptor().format,        //
-      color.texture->GetTextureDescriptor().sample_count,  //
-      color.load_action,                                   //
-      color.store_action                                   //
-  );
+  render_target.IterateAllColorAttachments(
+      [&builder](size_t index, const ColorAttachment& attachment) -> bool {
+        builder.SetColorAttachment(
+            index,                                                    //
+            attachment.texture->GetTextureDescriptor().format,        //
+            attachment.texture->GetTextureDescriptor().sample_count,  //
+            attachment.load_action,                                   //
+            attachment.store_action                                   //
+        );
+        return true;
+      });
 
   if (auto depth = render_target.GetDepthAttachment(); depth.has_value()) {
     builder.SetDepthStencilAttachment(
diff --git a/impeller/renderer/backend/vulkan/render_pass_cache_unittests.cc b/impeller/renderer/backend/vulkan/render_pass_cache_unittests.cc
index 51d42aee512b8..f4b470ebe2a3f 100644
--- a/impeller/renderer/backend/vulkan/render_pass_cache_unittests.cc
+++ b/impeller/renderer/backend/vulkan/render_pass_cache_unittests.cc
@@ -23,7 +23,7 @@ TEST_P(RendererTest, CachesRenderPassAndFramebuffer) {
 
   auto render_target =
       allocator->CreateOffscreenMSAA(*GetContext(), {100, 100}, 1);
-  auto resolve_texture = render_target.GetColor0().resolve_texture;
+  auto resolve_texture = render_target.GetColorAttachment(0).resolve_texture;
   auto& texture_vk = TextureVK::Cast(*resolve_texture);
 
   EXPECT_EQ(texture_vk.GetCachedFramebuffer(), nullptr);
diff --git a/impeller/renderer/backend/vulkan/render_pass_vk.cc b/impeller/renderer/backend/vulkan/render_pass_vk.cc
index 244795e21c912..1bbebd409cce6 100644
--- a/impeller/renderer/backend/vulkan/render_pass_vk.cc
+++ b/impeller/renderer/backend/vulkan/render_pass_vk.cc
@@ -56,18 +56,14 @@ static std::vector<vk::ClearValue> GetVKClearValues(
     const RenderTarget& target) {
   std::vector<vk::ClearValue> clears;
 
-  const ColorAttachment& color0 = target.GetColor0();
-  clears.emplace_back(VKClearValueFromColor(color0.clear_color));
-  if (color0.resolve_texture) {
-    clears.emplace_back(VKClearValueFromColor(color0.clear_color));
-  }
-
-  for (const auto& [_, color] : target.GetColorAttachments()) {
-    clears.emplace_back(VKClearValueFromColor(color.clear_color));
-    if (color.resolve_texture) {
-      clears.emplace_back(VKClearValueFromColor(color.clear_color));
-    }
-  }
+  target.IterateAllColorAttachments(
+      [&clears](size_t index, const ColorAttachment& attachment) -> bool {
+        clears.emplace_back(VKClearValueFromColor(attachment.clear_color));
+        if (attachment.resolve_texture) {
+          clears.emplace_back(VKClearValueFromColor(attachment.clear_color));
+        }
+        return true;
+      });
 
   const auto& depth = target.GetDepthAttachment();
   const auto& stencil = target.GetStencilAttachment();
@@ -89,38 +85,24 @@ SharedHandleVK<vk::RenderPass> RenderPassVK::CreateVKRenderPass(
     const std::shared_ptr<CommandBufferVK>& command_buffer) const {
   RenderPassBuilderVK builder;
 
-  const ColorAttachment& color0 = render_target_.GetColor0();
-  builder.SetColorAttachment(
-      0u,                                                   //
-      color0.texture->GetTextureDescriptor().format,        //
-      color0.texture->GetTextureDescriptor().sample_count,  //
-      color0.load_action,                                   //
-      color0.store_action,                                  //
-      TextureVK::Cast(*color0.texture).GetLayout()          //
-  );
-  TextureVK::Cast(*color0.texture)
-      .SetLayoutWithoutEncoding(vk::ImageLayout::eGeneral);
-  if (color0.resolve_texture) {
-    TextureVK::Cast(*color0.resolve_texture)
-        .SetLayoutWithoutEncoding(vk::ImageLayout::eGeneral);
-  }
-
-  for (const auto& [bind_point, color] : render_target_.GetColorAttachments()) {
-    builder.SetColorAttachment(
-        bind_point,                                          //
-        color.texture->GetTextureDescriptor().format,        //
-        color.texture->GetTextureDescriptor().sample_count,  //
-        color.load_action,                                   //
-        color.store_action,                                  //
-        TextureVK::Cast(*color.texture).GetLayout()          //
-    );
-    TextureVK::Cast(*color.texture)
-        .SetLayoutWithoutEncoding(vk::ImageLayout::eGeneral);
-    if (color.resolve_texture) {
-      TextureVK::Cast(*color.resolve_texture)
-          .SetLayoutWithoutEncoding(vk::ImageLayout::eGeneral);
-    }
-  }
+  render_target_.IterateAllColorAttachments(
+      [&](size_t bind_point, const ColorAttachment& attachment) -> bool {
+        builder.SetColorAttachment(
+            bind_point,                                               //
+            attachment.texture->GetTextureDescriptor().format,        //
+            attachment.texture->GetTextureDescriptor().sample_count,  //
+            attachment.load_action,                                   //
+            attachment.store_action,                                  //
+            TextureVK::Cast(*attachment.texture).GetLayout()          //
+        );
+        TextureVK::Cast(*attachment.texture)
+            .SetLayoutWithoutEncoding(vk::ImageLayout::eGeneral);
+        if (attachment.resolve_texture) {
+          TextureVK::Cast(*attachment.resolve_texture)
+              .SetLayoutWithoutEncoding(vk::ImageLayout::eGeneral);
+        }
+        return true;
+      });
 
   if (auto depth = render_target_.GetDepthAttachment(); depth.has_value()) {
     builder.SetDepthStencilAttachment(
@@ -159,8 +141,9 @@ RenderPassVK::RenderPassVK(const std::shared_ptr<const Context>& context,
                            const RenderTarget& target,
                            std::shared_ptr<CommandBufferVK> command_buffer)
     : RenderPass(context, target), command_buffer_(std::move(command_buffer)) {
-  color_image_vk_ = render_target_.GetColor0().texture;
-  resolve_image_vk_ = render_target_.GetColor0().resolve_texture;
+  const ColorAttachment& color0 = render_target_.GetColorAttachment(0);
+  color_image_vk_ = color0.texture;
+  resolve_image_vk_ = color0.resolve_texture;
 
   const auto& vk_context = ContextVK::Cast(*context);
   command_buffer_vk_ = command_buffer_->GetCommandBuffer();
@@ -274,24 +257,19 @@ SharedHandleVK<vk::Framebuffer> RenderPassVK::CreateVKFramebuffer(
   // This bit must be consistent to ensure compatibility with the pass created
   // earlier. Follow this order: Color attachments, then depth-stencil, then
   // stencil.
-  const ColorAttachment color0 = render_target_.GetColor0();
-  attachments.emplace_back(
-      TextureVK::Cast(*color0.texture).GetRenderTargetView());
-  if (color0.resolve_texture) {
-    attachments.emplace_back(
-        TextureVK::Cast(*color0.resolve_texture).GetRenderTargetView());
-  }
+  render_target_.IterateAllColorAttachments(
+      [&attachments](size_t index, const ColorAttachment& attachment) -> bool {
+        // The bind point doesn't matter here since that information is present
+        // in the render pass.
+        attachments.emplace_back(
+            TextureVK::Cast(*attachment.texture).GetRenderTargetView());
+        if (attachment.resolve_texture) {
+          attachments.emplace_back(TextureVK::Cast(*attachment.resolve_texture)
+                                       .GetRenderTargetView());
+        }
+        return true;
+      });
 
-  for (const auto& [_, color] : render_target_.GetColorAttachments()) {
-    // The bind point doesn't matter here since that information is present in
-    // the render pass.
-    attachments.emplace_back(
-        TextureVK::Cast(*color.texture).GetRenderTargetView());
-    if (color.resolve_texture) {
-      attachments.emplace_back(
-          TextureVK::Cast(*color.resolve_texture).GetRenderTargetView());
-    }
-  }
   if (auto depth = render_target_.GetDepthAttachment(); depth.has_value()) {
     attachments.emplace_back(
         TextureVK::Cast(*depth->texture).GetRenderTargetView());
diff --git a/impeller/renderer/backend/vulkan/test/swapchain_unittests.cc b/impeller/renderer/backend/vulkan/test/swapchain_unittests.cc
index 9594e2d75103a..4347df46aa561 100644
--- a/impeller/renderer/backend/vulkan/test/swapchain_unittests.cc
+++ b/impeller/renderer/backend/vulkan/test/swapchain_unittests.cc
@@ -86,7 +86,7 @@ TEST(SwapchainTest, CachesRenderPassOnSwapchainImage) {
     auto& depth = render_target.GetDepthAttachment();
     depth_stencil_textures.push_back(depth.has_value() ? depth->texture
                                                        : nullptr);
-    msaa_textures.push_back(render_target.GetColor0().texture);
+    msaa_textures.push_back(render_target.GetColorAttachment(0).texture);
   }
 
   for (auto i = 1; i < 3; i++) {
diff --git a/impeller/renderer/render_target.cc b/impeller/renderer/render_target.cc
index a280b683c91db..b3621e706b659 100644
--- a/impeller/renderer/render_target.cc
+++ b/impeller/renderer/render_target.cc
@@ -93,6 +93,22 @@ bool RenderTarget::IsValid() const {
   return true;
 }
 
+bool RenderTarget::IterateAllColorAttachments(
+    const std::function<bool(size_t index, const ColorAttachment& attachment)>&
+        iterator) const {
+  if (color0_.has_value()) {
+    if (!iterator(0, color0_.value())) {
+      return false;
+    }
+  }
+  for (const auto& [index, attachment] : colors_) {
+    if (!iterator(index, attachment)) {
+      return false;
+    }
+  }
+  return true;
+}
+
 void RenderTarget::IterateAllAttachments(
     const std::function<bool(const Attachment& attachment)>& iterator) const {
   if (color0_.has_value()) {
@@ -214,22 +230,20 @@ RenderTarget& RenderTarget::SetStencilAttachment(
   return *this;
 }
 
-ColorAttachment RenderTarget::GetColor0() const {
-  if (color0_.has_value()) {
-    return color0_.value();
+ColorAttachment RenderTarget::GetColorAttachment(size_t index) const {
+  if (index == 0) {
+    if (color0_.has_value()) {
+      return color0_.value();
+    }
+    return ColorAttachment{};
+  }
+  std::map<size_t, ColorAttachment>::const_iterator it = colors_.find(index);
+  if (it != colors_.end()) {
+    return it->second;
   }
   return ColorAttachment{};
 }
 
-bool RenderTarget::HasColor0() const {
-  return color0_.has_value();
-}
-
-const std::map<size_t, ColorAttachment>& RenderTarget::GetColorAttachments()
-    const {
-  return colors_;
-}
-
 const std::optional<DepthAttachment>& RenderTarget::GetDepthAttachment() const {
   return depth_;
 }
diff --git a/impeller/renderer/render_target.h b/impeller/renderer/render_target.h
index 0038d0901e75f..e7d1fb73df60c 100644
--- a/impeller/renderer/render_target.h
+++ b/impeller/renderer/render_target.h
@@ -102,6 +102,13 @@ class RenderTarget final {
   RenderTarget& SetColorAttachment(const ColorAttachment& attachment,
                                    size_t index);
 
+  /// @brief Get the color attachment at [index].
+  ///
+  /// This function does not validate whether or not the attachment was
+  /// previously defined and will return a default constructed attachment
+  /// if none is set.
+  ColorAttachment GetColorAttachment(size_t index) const;
+
   RenderTarget& SetDepthAttachment(std::optional<DepthAttachment> attachment);
 
   RenderTarget& SetStencilAttachment(
@@ -109,18 +116,17 @@ class RenderTarget final {
 
   size_t GetMaxColorAttacmentBindIndex() const;
 
-  ColorAttachment GetColor0() const;
-
-  bool HasColor0() const;
-
-  const std::map<size_t, ColorAttachment>& GetColorAttachments() const;
-
   const std::optional<DepthAttachment>& GetDepthAttachment() const;
 
   const std::optional<StencilAttachment>& GetStencilAttachment() const;
 
   size_t GetTotalAttachmentCount() const;
 
+  bool IterateAllColorAttachments(
+      const std::function<bool(size_t index,
+                               const ColorAttachment& attachment)>& iterator)
+      const;
+
   void IterateAllAttachments(
       const std::function<bool(const Attachment& attachment)>& iterator) const;
 
diff --git a/lib/gpu/render_pass.cc b/lib/gpu/render_pass.cc
index 154539edfaa01..a566567a9484f 100644
--- a/lib/gpu/render_pass.cc
+++ b/lib/gpu/render_pass.cc
@@ -105,14 +105,13 @@ RenderPass::GetOrCreatePipeline() {
 
   pipeline_desc.SetSampleCount(render_target_.GetSampleCount());
 
-  if (render_target_.HasColor0()) {
-    auto& color = GetColorAttachmentDescriptor(0);
-    color.format = render_target_.GetRenderTargetPixelFormat();
-  }
-  for (const auto& it : render_target_.GetColorAttachments()) {
-    auto& color = GetColorAttachmentDescriptor(it.first);
-    color.format = render_target_.GetRenderTargetPixelFormat();
-  }
+  render_target_.IterateAllColorAttachments(
+      [&](size_t index, const impeller::ColorAttachment& attachment) -> bool {
+        auto& color = GetColorAttachmentDescriptor(index);
+        color.format = render_target_.GetRenderTargetPixelFormat();
+        return true;
+      });
+
   pipeline_desc.SetColorAttachmentDescriptors(color_descriptors_);
 
   {

From 52d2674a859a95e2229f2e036ad3752cc2fa871e Mon Sep 17 00:00:00 2001
From: jonahwilliams <jonahwilliams@google.com>
Date: Mon, 2 Dec 2024 17:36:22 -0800
Subject: [PATCH 09/10] add comment.

---
 impeller/renderer/render_target.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/impeller/renderer/render_target.h b/impeller/renderer/render_target.h
index e7d1fb73df60c..a7a1e0bd32c9a 100644
--- a/impeller/renderer/render_target.h
+++ b/impeller/renderer/render_target.h
@@ -138,6 +138,9 @@ class RenderTarget final {
   std::optional<ColorAttachment> color0_;
   std::optional<DepthAttachment> depth_;
   std::optional<StencilAttachment> stencil_;
+  // Note: color0 is stored in the color0_ field above and not in this map,
+  // to avoid heap allocations for the commonly created render target formats
+  // in Flutter.
   std::map<size_t, ColorAttachment> colors_;
 };
 

From 21902829d3e3412e5fc1f04bb7fb391a14748f2e Mon Sep 17 00:00:00 2001
From: jonahwilliams <jonahwilliams@google.com>
Date: Tue, 3 Dec 2024 09:20:44 -0800
Subject: [PATCH 10/10] ++

---
 impeller/renderer/backend/vulkan/render_pass_builder_vk.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/impeller/renderer/backend/vulkan/render_pass_builder_vk.h b/impeller/renderer/backend/vulkan/render_pass_builder_vk.h
index 51c6313ec9583..4e9632d9a6d13 100644
--- a/impeller/renderer/backend/vulkan/render_pass_builder_vk.h
+++ b/impeller/renderer/backend/vulkan/render_pass_builder_vk.h
@@ -8,6 +8,7 @@
 #include <map>
 #include <optional>
 
+#include "flutter/fml/macros.h"
 #include "impeller/core/formats.h"
 #include "impeller/renderer/backend/vulkan/context_vk.h"
 #include "impeller/renderer/backend/vulkan/vk.h"
@@ -65,6 +66,7 @@ class RenderPassBuilderVK {
   std::optional<vk::AttachmentDescription> color0_resolve_;
   std::optional<vk::AttachmentDescription> depth_stencil_;
 
+  // Color attachment 0 is stored in the field above and not in these maps.
   std::map<size_t, vk::AttachmentDescription> colors_;
   std::map<size_t, vk::AttachmentDescription> resolves_;
 };