exo: Handle cross-fade animations properly.

components/exo/buffer.cc

 // Copyright 2015 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 "components/exo/buffer.h"
 
 #include <GLES2/gl2.h>
 #include <GLES2/gl2ext.h>
 #include <GLES2/gl2extchromium.h>
 #include <stdint.h>
@@ skipping 351 matching lines @@
       query_type_(query_type),
       use_zero_copy_(use_zero_copy),
       is_overlay_candidate_(is_overlay_candidate),
       use_count_(0) {}
 
 Buffer::~Buffer() {}
 
 std::unique_ptr<cc::SingleReleaseCallback> Buffer::ProduceTextureMailbox(
     cc::TextureMailbox* texture_mailbox,
     bool secure_output_only,
-    bool lost_context) {
-  DLOG_IF(WARNING, use_count_)
+    bool non_client_usage) {
+  // Non-client usage can only be allowed when the client is no allowed to

[Daniele Castagna, 2016/06/06 02:47:53]

no allow? no longer allowed? not allowed?

[reveman, 2016/06/06 03:17:36]

not allowed, fixed.

+  // use the buffer. If the buffer has been released to the client then it
+  // can no longer be used as the client might be writing to it.
+  if (non_client_usage && !use_count_)
+    return nullptr;
+
+  DLOG_IF(WARNING, use_count_ && !non_client_usage)

[Daniele Castagna, 2016/06/06 02:47:53]

I'd avoid the double negation of !non if possible.

[reveman, 2016/06/06 03:17:36]

done

       << "Producing a texture mailbox for a buffer that has not been released";
 
   // Some clients think that they can reuse a buffer before it's released by
   // performing a fast blit into the buffer. This behavior is bad as it prevents
   // the client from knowing when the buffer is actually released (e.g. the
   // release notification for the previous use of buffer can arrive after the
   // buffer has been reused). We stop running the release callback when this
   // type of behavior is detected as having the buffer always be busy will
   // result in fewer drawing artifacts.
-  if (use_count_ && !lost_context)
+  if (use_count_ && !non_client_usage)
     release_callback_.Reset();
 
   // Increment the use count for this buffer.
   ++use_count_;
 
   // If textures are lost, destroy them to ensure that we create new ones below.
   if (contents_texture_ && contents_texture_->IsLost())
     contents_texture_.reset();
   if (texture_ && texture_->IsLost())
     texture_.reset();
@@ skipping 95 matching lines @@
 }
 
 void Buffer::ReleaseContentsTexture(std::unique_ptr<Texture> texture) {
   TRACE_EVENT0("exo", "Buffer::ReleaseContentsTexture");
 
   contents_texture_ = std::move(texture);
   Release();
 }
 
 }  // namespace exo