[Impeller] avoid heap allocation in RenderTarget object. (#56829)

All render targets created by flutter have a single color attachment. Lets specialize that case in impeller::RenderTarget by creating a field for that attachment description instead of placing it in a hashmap.

Author: Jonah Williams

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"
@@ -853,7 +854,7 @@ 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_.GetColorAttachment(0);
 
   auto& stencil_attachment = render_target_.GetStencilAttachment();
   auto& depth_attachment = render_target_.GetDepthAttachment();
@@ -1460,8 +1461,7 @@ 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.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()
@@ -1588,8 +1588,7 @@ 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_.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.

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_.GetColorAttachment(0);
   if (!color0.resolve_texture) {
     VALIDATION_LOG << "EntityPassTarget Flip should never be called for a "
                       "non-MSAA target.";

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().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()
-               .GetColorAttachments()
-               .find(0u)
-               ->second;
+  color0 = entity_pass_target.GetRenderTarget().GetColorAttachment(0);
 
   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().GetColorAttachment(0);
   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().GetColorAttachment(0);
 
   ASSERT_NE(msaa_tex, color0.texture);
   ASSERT_NE(resolve_tex, color0.resolve_texture);

impeller/entity/inline_pass_context.cc

@@ -86,29 +86,21 @@ 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().GetColorAttachment(0).resolve_texture !=
+        nullptr;
     if (pass_count_ > 0 && is_msaa) {
       pass_target_.Flip(renderer_);
     }
   }
 
   // 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().GetColorAttachment(0);
   bool is_msaa = color0.resolve_texture != nullptr;
 
   if (pass_count_ > 0) {

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 +53,10 @@ 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.GetColorAttachment(0);
+      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 +103,10 @@ 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.GetColorAttachment(0);
+      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,

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.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);

impeller/playground/playground.cc

@@ -284,20 +284,14 @@ 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.GetColorAttachment(0);
       color0.load_action = LoadAction::kLoad;
       if (color0.resolve_texture) {
         color0.texture = color0.resolve_texture;
         color0.resolve_texture = nullptr;
         color0.store_action = StoreAction::kStore;
       }
       render_target.SetColorAttachment(color0, 0);
-
       render_target.SetStencilAttachment(std::nullopt);
       render_target.SetDepthAttachment(std::nullopt);
 

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"
@@ -550,9 +551,11 @@ 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.GetColorAttachment(0);
+  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_;

impeller/renderer/backend/gles/test/surface_gles_unittests.cc

@@ -22,7 +22,7 @@ TEST_P(SurfaceGLESTest, CanWrapNonZeroFBO) {
   ASSERT_TRUE(surface->IsValid());
   ASSERT_TRUE(surface->GetRenderTarget().HasColorAttachment(0));
   const auto& texture = TextureGLES::Cast(
-      *(surface->GetRenderTarget().GetColorAttachments().at(0).texture));
+      *(surface->GetRenderTarget().GetColorAttachment(0).texture));
   auto wrapped = texture.GetFBO();
   ASSERT_TRUE(wrapped.has_value());
   // NOLINTNEXTLINE(bugprone-unchecked-optional-access)

impeller/renderer/backend/metal/render_pass_mtl.mm

@@ -104,15 +104,15 @@ static bool ConfigureStencilAttachment(
     const RenderTarget& desc) {
   auto result = [MTLRenderPassDescriptor renderPassDescriptor];
 
-  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;
-    }
+  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& depth = desc.GetDepthAttachment();