[Blink] Have DrawingBuffer set TransferableResource::alpha_type directly

This CL changes DrawingBuffer to directly set the `alpha_type` field on
the TransferableResource that it prepares rather than indirecting
through TextureLayer to do so. It also eliminates
TextureLayer::SetPremultipliedAlpha() [there were no other production
callsites] to ensure that the field doesn't get overwritten.

A few notes:

* The TransferableResource that the TextureLayer created by
  DrawingBuffer ends up with is the one created via
  PrepareTransferableResource [1]
* The TransferableResource defaults to premultiplied and is created
  fresh on every invocation to `PrepareTransferableResource()`, so we
  need to set `alpha_type` explicitly only if setting it to
  unpremultiplied
* The TextureLayer that DrawingBuffer creates will have SetNeedsCommit()
  called on it independently of the current call to
  SetPremultipliedAlpha() via the call to SetHitTestable() [2][3][4]

[1] https://source.chromium.org/chromium/chromium/src/+/main:cc/layers/texture_layer.cc;l=171-172?q=TextureLayer::Update&ss=chromium
[2] https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/platform/graphics/gpu/drawing_buffer.cc;l=1?q=drawing_buffer.cc&sq=&ss=chromium
[3] https://source.chromium.org/chromium/chromium/src/+/main:cc/layers/layer.cc;l=880;drc=02446d66622a0a811448be7bb4ac8939c5b00aa9
[4] https://source.chromium.org/chromium/chromium/src/+/main:cc/layers/layer.cc;l=870-876;drc=02446d66622a0a811448be7bb4ac8939c5b00aa9
[5] https://source.chromium.org/chromium/chromium/src/+/main:cc/layers/layer.h;drc=02446d66622a0a811448be7bb4ac8939c5b00aa9;l=1054

Bug: 410591523
Change-Id: Ia14e8d8892ec040f0f7c3d251686b295cc231d19
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6549640
Reviewed-by: Antonio Sartori <antoniosartori@chromium.org>
Reviewed-by: Vasiliy Telezhnikov <vasilyt@chromium.org>
Commit-Queue: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1461192}

cc/layers/texture_layer.cc

@@ -30,7 +30,6 @@ scoped_refptr<TextureLayer> TextureLayer::Create(TextureLayerClient* client) {
 TextureLayer::TextureLayer(TextureLayerClient* client)
     : client_(client),
       uv_bottom_right_(1.f, 1.f),
-      premultiplied_alpha_(true),
       blend_background_color_(false),
       force_texture_to_opaque_(false),
       needs_set_resource_(false) {}
@@ -62,13 +61,6 @@ void TextureLayer::SetUV(const gfx::PointF& top_left,
   SetNeedsCommit();
 }
 
-void TextureLayer::SetPremultipliedAlpha(bool premultiplied_alpha) {
-  if (premultiplied_alpha_.Read(*this) == premultiplied_alpha)
-    return;
-  premultiplied_alpha_.Write(*this) = premultiplied_alpha;
-  SetNeedsCommit();
-}
-
 void TextureLayer::SetBlendBackgroundColor(bool blend) {
   if (blend_background_color_.Read(*this) == blend)
     return;
@@ -206,7 +198,6 @@ void TextureLayer::PushDirtyPropertiesTo(
     TextureLayerImpl* texture_layer = static_cast<TextureLayerImpl*>(layer);
     texture_layer->SetUVTopLeft(uv_top_left_.Read(*this));
     texture_layer->SetUVBottomRight(uv_bottom_right_.Read(*this));
-    texture_layer->SetPremultipliedAlpha(premultiplied_alpha_.Read(*this));
     texture_layer->SetBlendBackgroundColor(blend_background_color_.Read(*this));
     texture_layer->SetForceTextureToOpaque(
         force_texture_to_opaque_.Read(*this));

cc/layers/texture_layer.h

@@ -97,10 +97,6 @@ class CC_EXPORT TextureLayer : public Layer {
   // Sets a UV transform to be used at draw time. Defaults to (0, 0) and (1, 1).
   void SetUV(const gfx::PointF& top_left, const gfx::PointF& bottom_right);
 
-  // Sets whether the alpha channel is premultiplied or unpremultiplied.
-  // Defaults to true.
-  void SetPremultipliedAlpha(bool premultiplied_alpha);
-
   // Sets whether the texture should be blended with the background color
   // at draw time. Defaults to false.
   void SetBlendBackgroundColor(bool blend);
@@ -153,7 +149,6 @@ class CC_EXPORT TextureLayer : public Layer {
   ProtectedSequenceReadable<gfx::PointF> uv_top_left_;
   ProtectedSequenceReadable<gfx::PointF> uv_bottom_right_;
   // [bottom left, top left, top right, bottom right]
-  ProtectedSequenceReadable<bool> premultiplied_alpha_;
   ProtectedSequenceReadable<bool> blend_background_color_;
   ProtectedSequenceReadable<bool> force_texture_to_opaque_;
 

cc/layers/texture_layer_impl.cc

@@ -53,7 +53,6 @@ void TextureLayerImpl::PushPropertiesTo(LayerImpl* layer) {
   TextureLayerImpl* texture_layer = static_cast<TextureLayerImpl*>(layer);
   texture_layer->SetUVTopLeft(uv_top_left_);
   texture_layer->SetUVBottomRight(uv_bottom_right_);
-  texture_layer->SetPremultipliedAlpha(premultiplied_alpha_);
   texture_layer->SetBlendBackgroundColor(blend_background_color_);
   texture_layer->SetForceTextureToOpaque(force_texture_to_opaque_);
   if (needs_set_resource_push_) {
@@ -101,11 +100,6 @@ bool TextureLayerImpl::WillDraw(
             transferable_resource_.resource_source));
       }
 
-      // NOTE: We must perform any updates to `transferable_resource_` *before*
-      // exporting it to the resource provider, as that copies the resource into
-      // a new instance that is what is transferred across processes.
-      transferable_resource_.alpha_type =
-          premultiplied_alpha_ ? kPremul_SkAlphaType : kUnpremul_SkAlphaType;
       resource_id_ = resource_provider->ImportResource(
           transferable_resource_,
           /* impl_thread_release_callback= */ viz::ReleaseCallback(),
@@ -194,10 +188,6 @@ gfx::ContentColorUsage TextureLayerImpl::GetContentColorUsage() const {
   return transferable_resource_.color_space.GetContentColorUsage();
 }
 
-void TextureLayerImpl::SetPremultipliedAlpha(bool premultiplied_alpha) {
-  premultiplied_alpha_ = premultiplied_alpha;
-}
-
 void TextureLayerImpl::SetBlendBackgroundColor(bool blend) {
   blend_background_color_ = blend;
 }

cc/layers/texture_layer_impl.h

@@ -52,7 +52,6 @@ class CC_EXPORT TextureLayerImpl : public LayerImpl {
   // must explicitly invalidate if they intend to cause a visible change in the
   // layer's output.
   void SetTextureId(unsigned id);
-  void SetPremultipliedAlpha(bool premultiplied_alpha);
   void SetBlendBackgroundColor(bool blend);
   void SetForceTextureToOpaque(bool opaque);
   void SetUVTopLeft(const gfx::PointF& top_left);
@@ -70,7 +69,6 @@ class CC_EXPORT TextureLayerImpl : public LayerImpl {
   static bool MayEvictResourceInBackground(
       viz::TransferableResource::ResourceSource source);
 
-  bool premultiplied_alpha() const { return premultiplied_alpha_; }
   bool blend_background_color() const { return blend_background_color_; }
   bool force_texture_to_opaque() const { return force_texture_to_opaque_; }
   bool needs_set_resource_push() const { return needs_set_resource_push_; }
@@ -89,7 +87,6 @@ class CC_EXPORT TextureLayerImpl : public LayerImpl {
   void FreeTransferableResource();
   void OnResourceEvicted();
 
-  bool premultiplied_alpha_ = true;
   bool blend_background_color_ = false;
   bool force_texture_to_opaque_ = false;
 

cc/layers/texture_layer_unittest.cc

@@ -259,7 +259,6 @@ TEST_F(TextureLayerTest, CheckPropertyChangeCausesCorrectBehavior) {
                                      ));
   EXPECT_SET_NEEDS_COMMIT(1, test_layer->SetUV(gfx::PointF(0.25f, 0.25f),
                                                gfx::PointF(0.75f, 0.75f)));
-  EXPECT_SET_NEEDS_COMMIT(1, test_layer->SetPremultipliedAlpha(false));
   EXPECT_SET_NEEDS_COMMIT(1, test_layer->SetBlendBackgroundColor(true));
 }
 

cc/mojo_embedder/viz_layer_context.cc

@@ -555,7 +555,6 @@ void SerializeTextureLayerExtra(TextureLayerImpl& layer,
                                 viz::mojom::TextureLayerExtraPtr& extra,
                                 viz::ClientResourceProvider& resource_provider,
                                 viz::RasterContextProvider& context_provider) {
-  extra->premultiplied_alpha = layer.premultiplied_alpha();
   extra->blend_background_color = layer.blend_background_color();
   extra->force_texture_to_opaque = layer.force_texture_to_opaque();
   extra->uv_top_left = layer.uv_top_left();

components/viz/service/layers/layer_context_impl.cc

@@ -436,7 +436,6 @@ void UpdateMirrorLayerExtra(const mojom::MirrorLayerExtraPtr& extra,
 
 void UpdateTextureLayerExtra(const mojom::TextureLayerExtraPtr& extra,
                              cc::TextureLayerImpl& layer) {
-  layer.SetPremultipliedAlpha(extra->premultiplied_alpha);
   layer.SetBlendBackgroundColor(extra->blend_background_color);
   layer.SetForceTextureToOpaque(extra->force_texture_to_opaque);
   layer.SetUVTopLeft(extra->uv_top_left);

services/viz/public/mojom/compositing/layer.mojom

@@ -85,7 +85,6 @@ struct SurfaceLayerExtra {
 // Extra fields in a cc::TextureLayerImpl that has been added to a tree or
 // modified in some interesting way since a prior tree update.
 struct TextureLayerExtra {
-  bool premultiplied_alpha;
   bool blend_background_color;
   bool force_texture_to_opaque;
   gfx.mojom.PointF uv_top_left;

third_party/blink/renderer/platform/graphics/gpu/drawing_buffer.cc

@@ -481,6 +481,14 @@ bool DrawingBuffer::PrepareTransferableResource(
     }
   }
 
+  // If staging_texture_ exists, then premultiplication
+  // has already been handled via CopySubTextureCHROMIUM.
+  // TODO(crbug.com/410591523): Always set this field when not using
+  // `staging_texture_` under a killswitch.
+  if (!staging_texture_ && requested_alpha_type_ == kUnpremul_SkAlphaType) {
+    out_resource->alpha_type = requested_alpha_type_;
+  }
+
   return true;
 }
 
@@ -1213,12 +1221,6 @@ cc::Layer* DrawingBuffer::CcLayer() {
     layer_->SetContentsOpaque(requested_alpha_type_ == kOpaque_SkAlphaType);
     layer_->SetBlendBackgroundColor(requested_alpha_type_ !=
                                     kOpaque_SkAlphaType);
-
-    // If staging_texture_ exists, then premultiplication
-    // has already been handled via CopySubTextureCHROMIUM.
-    if (!staging_texture_ && requested_alpha_type_ == kUnpremul_SkAlphaType) {
-      layer_->SetPremultipliedAlpha(false);
-    }
   }
 
   return layer_.get();