Don't submit empty frames in android webview

android_webview/browser/surfaces_instance.cc

 // Copyright 2016 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/surfaces_instance.h"
 
 #include <algorithm>
 #include <utility>
 
 #include "android_webview/browser/aw_gl_surface.h"
 #include "android_webview/browser/aw_render_thread_context_provider.h"
 #include "android_webview/browser/deferred_gpu_command_service.h"
 #include "android_webview/browser/parent_output_surface.h"
 #include "base/memory/ptr_util.h"
 #include "cc/output/renderer_settings.h"
 #include "cc/output/texture_mailbox_deleter.h"
+#include "cc/quads/solid_color_draw_quad.h"
 #include "cc/quads/surface_draw_quad.h"
 #include "cc/scheduler/begin_frame_source.h"
 #include "cc/surfaces/compositor_frame_sink_support.h"
 #include "cc/surfaces/display.h"
 #include "cc/surfaces/display_scheduler.h"
 #include "cc/surfaces/local_surface_id_allocator.h"
 #include "cc/surfaces/surface_manager.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/geometry/size.h"
 #include "ui/gfx/transform.h"
@@ skipping 106 matching lines @@
                        gfx::Rect(quad_state->quad_layer_rect), child_id,
                        cc::SurfaceDrawQuadType::PRIMARY, nullptr);
 
   cc::CompositorFrame frame;
   // We draw synchronously, so acknowledge a manual BeginFrame.
   frame.metadata.begin_frame_ack =
       cc::BeginFrameAck::CreateManualAckWithDamage();
   frame.render_pass_list.push_back(std::move(render_pass));
   frame.metadata.referenced_surfaces = child_ids_;
 
-  if (!root_id_.is_valid()) {
+  if (!root_id_.is_valid() || frame_size != surface_size_) {
     root_id_ = local_surface_id_allocator_->GenerateId();
+    surface_size_ = frame_size;
     display_->SetLocalSurfaceId(root_id_, 1.f);
   }
   support_->SubmitCompositorFrame(root_id_, std::move(frame));
 
   display_->Resize(viewport);
   display_->DrawAndSwap();
 }
 
 void SurfacesInstance::AddChildId(const cc::SurfaceId& child_id) {
   DCHECK(std::find(child_ids_.begin(), child_ids_.end(), child_id) ==
          child_ids_.end());
   child_ids_.push_back(child_id);
   if (root_id_.is_valid())
     SetEmptyRootFrame();
 }
 
 void SurfacesInstance::RemoveChildId(const cc::SurfaceId& child_id) {
   auto itr = std::find(child_ids_.begin(), child_ids_.end(), child_id);
   DCHECK(itr != child_ids_.end());
   child_ids_.erase(itr);
   if (root_id_.is_valid())
     SetEmptyRootFrame();
 }
 
 void SurfacesInstance::SetEmptyRootFrame() {

[boliu, 2017/05/04 17:08:00]

rename the method name and variable names please, since it's no longer empty.
should reflect that this sets a frame that does not refer to any other surface
ids

[Saman Sami, 2017/05/04 21:38:46]

Done.

+  if (!root_id_.is_valid())

[boliu, 2017/05/04 17:08:00]

this should be a DCHECK it looks like? every call to this method already have
this check

[Saman Sami, 2017/05/04 21:38:46]

Done.

+    return;
+  std::unique_ptr<cc::RenderPass> render_pass = cc::RenderPass::Create();
+  cc::SharedQuadState* quad_state =
+      render_pass->CreateAndAppendSharedQuadState();
+  gfx::Rect rect(surface_size_);
+  cc::SolidColorDrawQuad* solid_quad =
+      render_pass->CreateAndAppendDrawQuad<cc::SolidColorDrawQuad>();
+  solid_quad->SetNew(quad_state, rect, rect, SK_ColorBLACK, false);
   cc::CompositorFrame empty_frame;
+  empty_frame.render_pass_list.push_back(std::move(render_pass));
   // We draw synchronously, so acknowledge a manual BeginFrame.
   empty_frame.metadata.begin_frame_ack =
       cc::BeginFrameAck::CreateManualAckWithDamage();
   empty_frame.metadata.referenced_surfaces = child_ids_;
   support_->SubmitCompositorFrame(root_id_, std::move(empty_frame));
 }
 
 void SurfacesInstance::DidReceiveCompositorFrameAck(
     const cc::ReturnedResourceArray& resources) {
   ReclaimResources(resources);
 }
 
 void SurfacesInstance::OnBeginFrame(const cc::BeginFrameArgs& args) {}
 
 void SurfacesInstance::WillDrawSurface(
     const cc::LocalSurfaceId& local_surface_id,
     const gfx::Rect& damage_rect) {}
 
 void SurfacesInstance::ReclaimResources(
     const cc::ReturnedResourceArray& resources) {
   // Root surface should have no resources to return.
   CHECK(resources.empty());
 }
 
 }  // namespace android_webview