sync compositor: Signal async frame on IO thread

android_webview/browser/browser_view_renderer.cc

Index: android_webview/browser/browser_view_renderer.cc
diff --git a/android_webview/browser/browser_view_renderer.cc b/android_webview/browser/browser_view_renderer.cc
index 1f0d849e1e5b60719b9b133bb0cca61acf518678..14165922ae0a3986a5dca49b4687047a66086a2c 100644
--- a/android_webview/browser/browser_view_renderer.cc
+++ b/android_webview/browser/browser_view_renderer.cc
@@ -109,7 +109,8 @@ BrowserViewRenderer::BrowserViewRenderer(
       max_page_scale_factor_(0.f),
       on_new_picture_enable_(false),
       clear_view_(false),
-      offscreen_pre_raster_(false) {}
+      offscreen_pre_raster_(false),
+      first_sync_frame_(false) {}
 
 BrowserViewRenderer::~BrowserViewRenderer() {
   DCHECK(compositor_map_.empty());
@@ -232,20 +233,24 @@ bool BrowserViewRenderer::OnDrawHardware() {
   gfx::Rect viewport_rect_for_tile_priority =
       ComputeViewportRectForTilePriority();
 
-  if (async_on_draw_hardware_) {
-    compositor_->DemandDrawHwAsync(size_, viewport_rect_for_tile_priority,
-                                   transform_for_tile_priority);
-    return current_compositor_frame_consumer_->HasFrameOnUI();
+  scoped_refptr<content::SynchronousCompositor::FrameFuture> future; // Async.
+  content::SynchronousCompositor::Frame frame; // Sync.
+  bool async = async_on_draw_hardware_ && first_sync_frame_;

[dcheng, 2016/10/21 06:42:56]

This might be worth a comment: it's not clear to me why async should be true if
|first_sync_frame_| is true.

[boliu, 2016/10/21 15:15:32]

renamed this to "allow_async_draw_" and added a comment to the header where
there was already a TODO to remove it

+  if (async) {
+    future = compositor_->DemandDrawHwAsync(
+        size_, viewport_rect_for_tile_priority, transform_for_tile_priority);
+  } else {
+    frame = compositor_->DemandDrawHw(size_, viewport_rect_for_tile_priority,
+                                      transform_for_tile_priority);
   }
 
-  content::SynchronousCompositor::Frame frame = compositor_->DemandDrawHw(
-      size_, viewport_rect_for_tile_priority, transform_for_tile_priority);
-  if (!frame.frame) {
+  if (!frame.frame && !future) {

[dcheng, 2016/10/21 06:42:56]

Maybe a comment that documents what this means would be helpful too, though
maybe it's obvious to someone more familiar with the compositor.

[boliu, 2016/10/21 15:15:32]

yeah should generally be clear to compositor folks I think, compositor can
choose to not produce a new frame if it thinks the nothing has changed since the
previous frame

in chrome where things are async, it just doesn't send anything back to the
browser, in webview, the way we implemented it is don't return a frame

     TRACE_EVENT_INSTANT0("android_webview", "NoNewFrame",
                          TRACE_EVENT_SCOPE_THREAD);
     return current_compositor_frame_consumer_->HasFrameOnUI();
   }
 
+  first_sync_frame_ = true;
   std::unique_ptr<ChildFrame> child_frame = base::MakeUnique<ChildFrame>(
       frame.compositor_frame_sink_id, std::move(frame.frame), compositor_id_,
       viewport_rect_for_tile_priority.IsEmpty(), transform_for_tile_priority,
@@ -254,29 +259,10 @@ bool BrowserViewRenderer::OnDrawHardware() {
   ReturnUnusedResource(
       current_compositor_frame_consumer_->PassUncommittedFrameOnUI());
   current_compositor_frame_consumer_->SetFrameOnUI(std::move(child_frame),
-                                                   nullptr);
-
+                                                   future);

[dcheng, 2016/10/21 06:42:56]

Nit: std::move(future)

[boliu, 2016/10/21 15:15:32]

Done.

   return true;
 }
 
-void BrowserViewRenderer::OnDrawHardwareProcessFrameFuture(
-    const scoped_refptr<content::SynchronousCompositor::FrameFuture>&
-        frame_future) {
-  gfx::Transform transform_for_tile_priority =
-      external_draw_constraints_.transform;
-  gfx::Rect viewport_rect_for_tile_priority =
-      ComputeViewportRectForTilePriority();
-
-  ReturnUnusedResource(
-      current_compositor_frame_consumer_->PassUncommittedFrameOnUI());
-  current_compositor_frame_consumer_->SetFrameOnUI(
-      base::MakeUnique<ChildFrame>(
-          0, nullptr, compositor_id_, viewport_rect_for_tile_priority.IsEmpty(),
-          transform_for_tile_priority, offscreen_pre_raster_,
-          external_draw_constraints_.is_layer),
-      frame_future);
-}
-
 gfx::Rect BrowserViewRenderer::ComputeViewportRectForTilePriority() {
   // If the WebView is on a layer, WebView does not know what transform is
   // applied onto the layer so global visible rect does not make sense here.