Enable asynchronous glReadPixels on Windows.

gpu/command_buffer/service/gles2_cmd_decoder.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 "gpu/command_buffer/service/gles2_cmd_decoder.h"
 
 #include <stdio.h>
 
 #include <algorithm>
 #include <list>
@@ skipping 7532 matching lines @@
 
   if (buffer != 0) {
     glBindBuffer(GL_PIXEL_PACK_BUFFER_ARB, buffer);
     void* data;
     if (features().map_buffer_range) {
       data = glMapBufferRange(
           GL_PIXEL_PACK_BUFFER_ARB, 0, pixels_size, GL_MAP_READ_BIT);
     } else {
       data = glMapBuffer(GL_PIXEL_PACK_BUFFER_ARB, GL_READ_ONLY);
     }
-    memcpy(pixels, data, pixels_size);
+    if (data)

[piman, 2014/11/11 22:54:31]

In which case should data be NULL?
Should we raise GL_OUT_OF_MEMORY, or lose the context if that's the case?

Silently failing seems bad.

+      memcpy(pixels, data, pixels_size);
     // GL_PIXEL_PACK_BUFFER_ARB is currently unused, so we don't
     // have to restore the state.
     glUnmapBuffer(GL_PIXEL_PACK_BUFFER_ARB);
     glBindBuffer(GL_PIXEL_PACK_BUFFER_ARB, 0);
     glDeleteBuffersARB(1, &buffer);
+    if (!data)
+      return;
   }
 
   if (result != NULL) {
     *result = true;
   }
 
   GLenum read_format = GetBoundReadFrameBufferInternalFormat();
   uint32 channels_exist = GLES2Util::GetChannelsForFormat(read_format);
   if ((channels_exist & 0x0008) == 0 &&
       workarounds().clear_alpha_in_readpixels) {
@@ skipping 175 matching lines @@
         glReadPixels(
             read_x, ry, read_width, 1, format, type, dst + dest_row_offset);
       }
       dst += padded_row_size;
     }
   } else {
     if (async && features().use_async_readpixels) {
       GLuint buffer = 0;
       glGenBuffersARB(1, &buffer);
       glBindBuffer(GL_PIXEL_PACK_BUFFER_ARB, buffer);
-      glBufferData(GL_PIXEL_PACK_BUFFER_ARB, pixels_size, NULL, GL_STREAM_READ);
+      // For ANGLE client version 2, GL_STREAM_READ is not available.
+      const GLenum usage_hint =
+          features().is_angle ? GL_STATIC_DRAW : GL_STREAM_READ;
+      glBufferData(GL_PIXEL_PACK_BUFFER_ARB, pixels_size, NULL, usage_hint);
       GLenum error = glGetError();
       if (error == GL_NO_ERROR) {
         glReadPixels(x, y, width, height, format, type, 0);
         pending_readpixel_fences_.push(linked_ptr<FenceCallback>(
             new FenceCallback()));
         WaitForReadPixels(base::Bind(
             &GLES2DecoderImpl::FinishReadPixels,
             base::internal::SupportsWeakPtrBase::StaticAsWeakPtr
             <GLES2DecoderImpl>(this),
             c, buffer));
@@ skipping 3697 matching lines @@
   }
 }
 
 // Include the auto-generated part of this file. We split this because it means
 // we can easily edit the non-auto generated parts right here in this file
 // instead of having to edit some template or the code generator.
 #include "gpu/command_buffer/service/gles2_cmd_decoder_autogen.h"
 
 }  // namespace gles2
 }  // namespace gpu