Add compositor support for half-float RGBA buffers and textures

cc/output/gl_renderer.cc

 // Copyright 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/output/gl_renderer.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 411 matching lines @@
     auto* cache_controller = context_provider->CacheController();
     cache_controller->ClientBecameNotVisible(std::move(context_visibility_));
   }
 }
 
 bool GLRenderer::CanPartialSwap() {
   auto* context_provider = output_surface_->context_provider();
   return context_provider->ContextCapabilities().post_sub_buffer;
 }
 
+ResourceFormat GLRenderer::BackbufferFormat() const {
+  // TODO(ccameron): If we are targeting high bit depth or HDR, we should use
+  // RGBA_F16 here.
+  return resource_provider_->best_texture_format();
+}
+
 void GLRenderer::DidChangeVisibility() {
   if (visible_) {
     output_surface_->EnsureBackbuffer();
   } else {
     TRACE_EVENT0("cc", "GLRenderer::DidChangeVisibility dropping resources");
     ReleaseRenderPassTextures();
     output_surface_->DiscardBackbuffer();
   }
 
   PrepareGeometry(NO_BINDING);
@@ skipping 458 matching lines @@
 }
 
 std::unique_ptr<ScopedResource> GLRenderer::GetBackdropTexture(
     DrawingFrame* frame,
     const gfx::Rect& bounding_rect) {
   std::unique_ptr<ScopedResource> device_background_texture =
       ScopedResource::Create(resource_provider_);
   // CopyTexImage2D fails when called on a texture having immutable storage.
   device_background_texture->Allocate(
       bounding_rect.size(), ResourceProvider::TEXTURE_HINT_DEFAULT,
-      resource_provider_->best_texture_format(), frame->device_color_space);
+      BackbufferFormat(), frame->device_color_space);
   {
     ResourceProvider::ScopedWriteLockGL lock(
         resource_provider_, device_background_texture->id(), false);
     GetFramebufferTexture(lock.texture_id(), bounding_rect);
   }
   return device_background_texture;
 }
 
 sk_sp<SkImage> GLRenderer::ApplyBackgroundFilters(
     const RenderPassDrawQuad* quad,
@@ skipping 2661 matching lines @@
     return;
 
   // Report GPU overdraw as a percentage of |max_result|.
   TRACE_COUNTER1(
       TRACE_DISABLED_BY_DEFAULT("cc.debug.overdraw"), "GPU Overdraw",
       (std::accumulate(overdraw->begin(), overdraw->end(), 0) * 100) /
           max_result);
 }
 
 }  // namespace cc