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

content/common/gpu/client/gl_helper.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/common/gpu/client/gl_helper.h"
 
 #include <queue>
 #include <string>
 
 #include "base/bind.h"
@@ skipping 175 matching lines @@
     Request(const gfx::Size& size_,
             int32 bytes_per_row_,
             int32 row_stride_bytes_,
             unsigned char* pixels_,
             const base::Callback<void(bool)>& callback_)
         : size(size_),
           bytes_per_row(bytes_per_row_),
           row_stride_bytes(row_stride_bytes_),
           pixels(pixels_),
           callback(callback_),
-          buffer(0) {
+          buffer(0),
+          query(0) {
     }
 
     gfx::Size size;
     int bytes_per_row;
     int row_stride_bytes;
     unsigned char* pixels;
     base::Callback<void(bool)> callback;
     GLuint buffer;
+    WebKit::WebGLId query;
   };
 
   // A readback pipeline that also converts the data to YUV before
   // reading it back.
   class ReadbackYUVImpl : public ReadbackYUVInterface {
    public:
     ReadbackYUVImpl(WebGraphicsContext3D* context,
                     CopyTextureToImpl* copy_impl,
                     GLHelperScaling* scaler_impl,
                     GLHelper::ScalerQuality quality,
@@ skipping 160 matching lines @@
   request->buffer = context_->createBuffer();
   context_->bindBuffer(GL_PIXEL_PACK_TRANSFER_BUFFER_CHROMIUM,
                        request->buffer);
   context_->bufferData(GL_PIXEL_PACK_TRANSFER_BUFFER_CHROMIUM,
                        4 * dst_size.GetArea(),
                        NULL,
                        GL_STREAM_READ);
 
   context_->readPixels(0, 0, dst_size.width(), dst_size.height(),
                        GL_RGBA, GL_UNSIGNED_BYTE, NULL);
+  request->query = context_->createQueryEXT();
+  context_->beginQueryEXT(GL_ASYNC_PIXEL_TRANSFERS_COMPLETED_CHROMIUM,
+                          request->query);
   context_->bindBuffer(GL_PIXEL_PACK_TRANSFER_BUFFER_CHROMIUM, 0);
-  cc::SyncPointHelper::SignalSyncPoint(
+  cc::SyncPointHelper::SignalQuery(
       context_,
-      context_->insertSyncPoint(),
+      request->query,
       base::Bind(&CopyTextureToImpl::ReadbackDone, AsWeakPtr(), request));

[piman, 2013/06/17 19:55:06]

It is weird that you call signalQuery between begin and end. glGetQueryObject
would return GL_INVALID_OPERATION, and I think it would make sense that
SignalQuery behaves the same, as it's somewhat undefined what the behavior
should be.

[hubbe, 2013/06/25 20:02:51]

Done.

+  context_->endQueryEXT(GL_ASYNC_PIXEL_TRANSFERS_COMPLETED_CHROMIUM);
 }
 
 
 void GLHelper::CopyTextureToImpl::CropScaleReadbackAndCleanTexture(
     WebGLId src_texture,
     const gfx::Size& src_size,
     const gfx::Rect& src_subrect,
     const gfx::Size& dst_size,
     unsigned char* out,
     const base::Callback<void(bool)>& callback,
@@ skipping 91 matching lines @@
       context_->unmapBufferCHROMIUM(GL_PIXEL_PACK_TRANSFER_BUFFER_CHROMIUM);
     }
     context_->bindBuffer(GL_PIXEL_PACK_TRANSFER_BUFFER_CHROMIUM, 0);
   }
 
   FinishRequest(request, result);
 }
 
 void GLHelper::CopyTextureToImpl::FinishRequest(Request* request,
                                                 bool result) {
+  TRACE_EVENT0("mirror", "GLHelper::CopyTextureToImpl::FinishRequest");
   DCHECK(request_queue_.front() == request);
   request_queue_.pop();
   request->callback.Run(result);
   ScopedFlush flush(context_);
+  if (request->query != 0) {
+    context_->deleteQueryEXT(request->query);
+    request->query = 0;
+  }
   if (request->buffer != 0) {
     context_->deleteBuffer(request->buffer);
     request->buffer = 0;
   }
   delete request;
 }
 
 void GLHelper::CopyTextureToImpl::CancelRequests() {
   while (!request_queue_.empty()) {
     Request* request = request_queue_.front();
@@ skipping 445 matching lines @@
       quality,
       src_size,
       src_subrect,
       dst_size,
       dst_subrect,
       flip_vertically,
       use_mrt);
 }
 
 }  // namespace content