Implement client side PBOs for glReadPixel

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 6927 matching lines @@
   }
   typedef cmds::ReadPixels::Result Result;
   uint32 pixels_size;
   if (!GLES2Util::ComputeImageDataSizes(
       width, height, format, type, state_.pack_alignment, &pixels_size,
       NULL, NULL)) {
     return error::kOutOfBounds;
   }
   void* pixels = GetSharedMemoryAs<void*>(
       c.pixels_shm_id, c.pixels_shm_offset, pixels_size);
-  Result* result = GetSharedMemoryAs<Result*>(
+  if (!pixels) {
+    return error::kOutOfBounds;
+  }
+  Result* result = NULL;
+  if (c.result_shm_id != 0) {
+    result = GetSharedMemoryAs<Result*>(
         c.result_shm_id, c.result_shm_offset, sizeof(*result));
-  if (!pixels || !result) {
-    return error::kOutOfBounds;
+    if (!result) {
+      return error::kOutOfBounds;
+    }
   }
 
   if (!validators_->read_pixel_format.IsValid(format)) {
     LOCAL_SET_GL_ERROR_INVALID_ENUM("glReadPixels", format, "format");
     return error::kNoError;
   }
   if (!validators_->pixel_type.IsValid(type)) {
     LOCAL_SET_GL_ERROR_INVALID_ENUM("glReadPixels", type, "type");
     return error::kNoError;
   }
@@ skipping 60 matching lines @@
         glReadPixels(
             read_x, ry, read_width, 1, format, type, dst + dest_row_offset);
       }
       dst += padded_row_size;
     }
   } else {
     glReadPixels(x, y, width, height, format, type, pixels);
   }
   GLenum error = LOCAL_PEEK_GL_ERROR("glReadPixels");
   if (error == GL_NO_ERROR) {
-    *result = true;
+    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) {
       // Set the alpha to 255 because some drivers are buggy in this regard.
       uint32 temp_size;
 
       uint32 unpadded_row_size;
       uint32 padded_row_size;
@@ skipping 3410 matching lines @@
   return error::kNoError;
 }
 
 // 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