Perform glReadPixels with PBOs in the gpu, if PBOs are available.

gpu/command_buffer/service/feature_info.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/feature_info.h"
 
 #include <set>
 
 #include "base/command_line.h"
 #include "base/strings/string_number_conversions.h"
@@ skipping 99 matching lines @@
       angle_pack_reverse_row_order(false),
       arb_texture_rectangle(false),
       angle_instanced_arrays(false),
       occlusion_query_boolean(false),
       use_arb_occlusion_query2_for_occlusion_query_boolean(false),
       use_arb_occlusion_query_for_occlusion_query_boolean(false),
       native_vertex_array_object(false),
       enable_shader_name_hashing(false),
       enable_samplers(false),
       ext_draw_buffers(false),
-      ext_frag_depth(false) {
+      ext_frag_depth(false),
+      use_async_readpixels(false) {
 }
 
 FeatureInfo::Workarounds::Workarounds() :
 #define GPU_OP(type, name) name(false),
     GPU_DRIVER_BUG_WORKAROUNDS(GPU_OP)
 #undef GPU_OP
     max_texture_size(0),
     max_cube_map_texture_size(0) {
 }
 
@@ skipping 485 matching lines @@
          ++i) {
       validators_.g_l_state.AddValue(i);
     }
   }
 
   if (extensions.Contains("GL_EXT_frag_depth") || gfx::HasDesktopGLFeatures()) {
     AddExtensionString("GL_EXT_frag_depth");
     feature_flags_.ext_frag_depth = true;
   }
 
+  bool ui_gl_fence_works =
+      extensions.Contains("GL_NV_fence") ||
+      extensions.Contains("GL_ARB_sync");
+
+  if (ui_gl_fence_works &&
+      extensions.Contains("GL_ARB_pixel_buffer_object") &&
+      !workarounds_.disable_async_readpixels) {
+    feature_flags_.use_async_readpixels = true;
+  }
+
   if (!disallowed_features_.swap_buffer_complete_callback)
     AddExtensionString("GL_CHROMIUM_swapbuffers_complete_callback");
 
   bool is_es3 = false;
   const char* str = reinterpret_cast<const char*>(glGetString(GL_VERSION));
   if (str) {
     std::string lstr(StringToLowerASCII(std::string(str)));
     is_es3 = (lstr.substr(0, 12) == "opengl es 3.");
   }
 
   if (is_es3 || extensions.Contains("GL_ARB_sampler_objects")) {
     feature_flags_.enable_samplers = true;
     // TODO(dsinclair): Add AddExtensionString("GL_CHROMIUM_sampler_objects")
     // when available.
   }
 }
 
 void FeatureInfo::AddExtensionString(const std::string& str) {
   if (extensions_.find(str) == std::string::npos) {
     extensions_ += (extensions_.empty() ? "" : " ") + str;
   }
 }
 
 FeatureInfo::~FeatureInfo() {
 }
 
 }  // namespace gles2
 }  // namespace gpu