[Android WebView] Implement Ubercomp for Render Thread support

android_webview/browser/parent_output_surface.cc

+// Copyright 2014 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 "android_webview/browser/parent_output_surface.h"
+
+#include "cc/output/output_surface_client.h"
+#include "gpu/command_buffer/client/gles2_interface.h"
+
+namespace android_webview {
+
+ParentOutputSurface::ParentOutputSurface(
+    scoped_refptr<cc::ContextProvider> context_provider)
+    : cc::OutputSurface(context_provider), weak_factory_(this) {
+  capabilities_.draw_and_swap_full_viewport_every_frame = true;
+}
+
+ParentOutputSurface::~ParentOutputSurface() {
+}
+
+bool ParentOutputSurface::BindToClient(cc::OutputSurfaceClient* client) {
+  bool result = cc::OutputSurface::BindToClient(client);
+  if (result)
+    UpdateClientBeforeDraw();

[danakj, 2014/05/20 21:50:02]

why? you call SetDrawConstraints before every Composite() already

+  return result;
+}
+
+void ParentOutputSurface::SwapBuffers(cc::CompositorFrame* frame) {
+  context_provider_->ContextGL()->ShallowFlushCHROMIUM();

[danakj, 2014/05/20 21:50:02]

why?

[boliu, 2014/05/21 01:33:26]

This is the "synchronous" behavior of parent compositor. This will flush all the
GL of this draw from the command buffer before returning.

And this reminds me, we don't need the flush in child compositor swap for
ubercomp.

+  client_->DidSwapBuffers();
+}
+
+base::WeakPtr<ParentOutputSurface> ParentOutputSurface::GetWeakPtr() {
+  return weak_factory_.GetWeakPtr();

[no sievers, 2014/05/20 20:48:26]

Any chance we can avoid the need for WeakPtr?

[boliu, 2014/05/21 01:33:26]

It's really only needed for the DCHECK for the UpdateClientBeforeDraw dance.
Refactored using DidBeginMainFrame and got rid of it.

+}
+
+void ParentOutputSurface::SetDrawConstraints(const gfx::Size& surface_size,
+                                             const gfx::Rect& clip) {
+  surface_size_ = surface_size;
+  clip_ = clip;
+  if (client_)

[danakj, 2014/05/20 21:50:02]

How would you get here with a null client, on the first Composite()? Maybe we
can solve that without needing to do this UpdateClientBeforeDraw in two places..

If you update the OutputSurface state in DidBeginMainFrame(), that will happen
inside Composite() after it has set up the OutputSurface. (You could make a
cc_unittest to verify this and ensure we don't break that.) Then you'd need to
store the viewport/clip on the HardwareRenderer to use them there, but you
wouldn't need to deal with this in both BindToClient and here, and check for
client_ being null and stuff. Less branches!

[boliu, 2014/05/21 01:33:26]

Done. Thanks for the suggestion :D

+    UpdateClientBeforeDraw();
+}
+
+void ParentOutputSurface::UpdateClientBeforeDraw() {
+  SetNeedsRedrawRect(gfx::Rect(surface_size_));
+  gfx::Transform identity;
+  gfx::Rect empty;
+  SetExternalDrawConstraints(identity, empty, clip_, true);
+}
+
+}  // namespace android_webview