Improve transition between opaque and translucent compositor views.

content/browser/renderer_host/compositor_impl_android.cc

 // Copyright (c) 2012 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 "content/browser/renderer_host/compositor_impl_android.h"
 
 #include <android/bitmap.h>
 #include <android/native_window_jni.h>
 #include <stdint.h>
 #include <unordered_set>
@@ skipping 114 matching lines @@
   if (has_transparent_background) {
     attributes.alpha_size = 8;
   } else if (base::SysInfo::IsLowEndDevice()) {
     // In this case we prefer to use RGB565 format instead of RGBA8888 if
     // possible.
     // TODO(danakj): GpuCommandBufferStub constructor checks for alpha == 0 in
     // order to enable 565, but it should avoid using 565 when -1s are
     // specified
     // (IOW check that a <= 0 && rgb > 0 && rgb <= 565) then alpha should be
     // -1.
+    // TODO(liberato): This condition is memorized in ComositorView.java, to
+    // avoid using two surfaces temporarily during alpha <-> no alpha
+    // transitions.  If these mismatch, then we risk a power regression if the
+    // SurfaceView is not marked as eOpaque (FORMAT_OPAQUE), and we have an
+    // EGL surface with an alpha channel.  SurfaceFlinger needs at least one of
+    // those hints to optimize out alpha blending.
     attributes.alpha_size = 0;
     attributes.red_size = 5;
     attributes.green_size = 6;
     attributes.blue_size = 5;
   }
 
   return attributes;
 }
 
 class AndroidOutputSurface : public cc::OutputSurface {
@@ skipping 588 matching lines @@
 
 cc::FrameSinkId CompositorImpl::GetFrameSinkId() {
   return frame_sink_id_;
 }
 
 bool CompositorImpl::HavePendingReadbacks() {
   return !readback_layer_tree_->children().empty();
 }
 
 }  // namespace content