Unify Android Webview and Chrome's fling

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 b9336d6119a230f9ccef7ac87c39bad71015c35d..91110c1be67e60d83c0c42c471b96fe1b68d042c 100644
--- a/android_webview/browser/browser_view_renderer.cc
+++ b/android_webview/browser/browser_view_renderer.cc
@@ -414,6 +414,12 @@ void BrowserViewRenderer::OnDetachedFromWindow() {
   UpdateCompositorIsActive();
 }
 
+void BrowserViewRenderer::OnComputeScroll(base::TimeTicks animation_time) {
+  if (pending_fling_animation_.is_null())
+    return;
+  FlushPendingScrollAnimation(animation_time);
+}
+
 void BrowserViewRenderer::ReleaseHardware() {
   DCHECK(hardware_enabled_);
   ReturnUnusedResource(shared_renderer_state_.PassUncommittedFrameOnUI());
@@ -550,8 +556,8 @@ gfx::Vector2dF BrowserViewRenderer::GetTotalRootLayerScrollOffset() {
   return scroll_offset_dip_;
 }
 
-bool BrowserViewRenderer::IsExternalFlingActive() const {
-  return client_->IsFlingActive();
+bool BrowserViewRenderer::IsExternalScrollActive() const {
+  return client_->IsSmoothScrollingActive();
 }
 
 void BrowserViewRenderer::UpdateRootLayerState(
@@ -605,6 +611,12 @@ BrowserViewRenderer::RootLayerStateAsValue(
   return state;
 }
 
+void BrowserViewRenderer::SetNeedsAnimateScroll(
+    const AnimationCallback& scroll_animation) {
+  pending_fling_animation_ = scroll_animation;
+  client_->PostInvalidate();

[boliu, 2015/05/29 19:42:47]

Conceptually this feels wrong. What does "SetNeedAnimate" have to do with
invalidates? You are waiting for OnComputeScroll, and PostInvalidate is for
OnDraws.

Have we considered moving driving animations to the animate step? Is that how
chrome works, etc? How does this work before this CL?

And more practically, does this need to be integrated into
PostInvalidateWithFallback? ie pending_fling_animation_.is_null() will be one
more state that controls whether fallback ticks should be scheduled or
cancelled.

[hush (inactive), 2015/06/05 21:47:21]

We've discussed this in person.
The fling animation is driven by "computeScroll" call which is an Android view
api. And we have to hook fling with it because there are applications (Inbox for
example) that rely on that fact to overide computeScroll to nothing to achieve
their own custom fling.
computeScroll is called within View#updateDisplayListIfDirty, which is during
the draw step, instead of animation step, from the choreorgrapher's point of
view.

I will update description about how this works before and after this CL. Sorry
for the short description there..
I think you mean when pending_fling_animation_ is not null, there is no point in
rescheduling fallback ticks because there is definitely a PostInvalidate in
flight. I will do it.

+}
+
 void BrowserViewRenderer::DidOverscroll(gfx::Vector2dF accumulated_overscroll,
                                         gfx::Vector2dF latest_overscroll_delta,
                                         gfx::Vector2dF current_fling_velocity) {
@@ -617,7 +629,11 @@ void BrowserViewRenderer::DidOverscroll(gfx::Vector2dF accumulated_overscroll,
       scaled_overscroll_delta + overscroll_rounding_error_);
   overscroll_rounding_error_ =
       scaled_overscroll_delta - rounded_overscroll_delta;
-  client_->DidOverscroll(rounded_overscroll_delta);
+

[boliu, 2015/05/29 19:42:47]

nit: blank lines

[hush (inactive), 2015/06/05 21:47:21]

Done.

+  gfx::Vector2dF fling_velocity_pixels =
+      gfx::ScaleVector2d(current_fling_velocity, physical_pixel_scale);
+
+  client_->DidOverscroll(rounded_overscroll_delta, fling_velocity_pixels);
 }
 
 void BrowserViewRenderer::PostInvalidate() {
@@ -694,6 +710,16 @@ void BrowserViewRenderer::ForceFakeCompositeSW() {
   CompositeSW(&canvas);
 }
 
+void BrowserViewRenderer::FlushPendingScrollAnimation(

[boliu, 2015/05/29 19:42:47]

There is only one call site. Just inline this?

[hush (inactive), 2015/06/05 21:47:21]

Done.

+    base::TimeTicks animation_time) {
+  TRACE_EVENT0("android_webview",
+               "BrowserViewRenderer::FlushPendingScrollAnimation");
+  DCHECK(!pending_fling_animation_.is_null());
+  AnimationCallback animation = pending_fling_animation_;
+  pending_fling_animation_.Reset();
+  animation.Run(animation_time);
+}
+
 bool BrowserViewRenderer::CompositeSW(SkCanvas* canvas) {
   DCHECK(compositor_);
   CancelFallbackTick();