Fix smooth scroll jump when switching scroll handling between MT and CC

third_party/WebKit/Source/platform/scroll/ScrollAnimator.cpp

 /*
  * Copyright (c) 2011, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 14 matching lines @@
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "platform/scroll/ScrollAnimator.h"
 
 #include "platform/TraceEvent.h"
 #include "platform/graphics/GraphicsLayer.h"
+#include "platform/scroll/MainThreadScrollingReason.h"
 #include "platform/scroll/ScrollableArea.h"
 #include "public/platform/Platform.h"
 #include "public/platform/WebCompositorAnimation.h"
 #include "public/platform/WebCompositorSupport.h"
 #include "wtf/CurrentTime.h"
 #include "wtf/PassRefPtr.h"
 
 namespace blink {
 
+WebLayer* toWebLayer(blink::GraphicsLayer* layer)

[jbroman, 2016/02/10 20:36:37]

Please make this a static function or enclose it in an anonymous namespace. It's
not advertised in the header, and it could conceivably collide with another
function sharing this name.

Also, this is in the blink namespace, so please remove the blink:: namespace
qualification.

[ymalik, 2016/02/10 21:57:58]

Done. Thanks!

+{
+    return layer ? layer->platformLayer() : nullptr;
+}
+
 PassOwnPtrWillBeRawPtr<ScrollAnimatorBase> ScrollAnimatorBase::create(ScrollableArea* scrollableArea)
 {
     if (scrollableArea && scrollableArea->scrollAnimatorEnabled())
         return adoptPtrWillBeNoop(new ScrollAnimator(scrollableArea));
     return adoptPtrWillBeNoop(new ScrollAnimatorBase(scrollableArea));
 }
 
 ScrollAnimator::ScrollAnimator(ScrollableArea* scrollableArea, WTF::TimeFunction timeFunction)
     : ScrollAnimatorBase(scrollableArea)
     , m_timeFunction(timeFunction)
@@ skipping 128 matching lines @@
 
     if (isFinished)
         m_runState = RunState::PostAnimationCleanup;
     else
         scrollableArea()->scheduleAnimation();
 
     TRACE_EVENT0("blink", "ScrollAnimator::notifyPositionChanged");
     notifyPositionChanged();
 }
 
+void ScrollAnimator::postAnimationCleanupAndReset()
+{
+    // Remove the temporary main thread scrolling reason that was added while
+    // main thread had scheduled an animation.
+    removeMainThreadScrollingReason();
+
+    resetAnimationState();
+}
+
 void ScrollAnimator::updateCompositorAnimations()
 {
-    if (m_runState == RunState::PostAnimationCleanup)
-        return resetAnimationState();
+    if (m_runState == RunState::PostAnimationCleanup) {
+        postAnimationCleanupAndReset();
+        return;
+    }
 
     if (m_compositorAnimationId && m_runState != RunState::RunningOnCompositor
         && m_runState != RunState::RunningOnCompositorButNeedsUpdate) {
         // If the current run state is WaitingToSendToCompositor but we have a
         // non-zero compositor animation id, there's a currently running
         // compositor animation that needs to be removed here before the new
         // animation is added below.
         ASSERT(m_runState == RunState::WaitingToCancelOnCompositor
             || m_runState == RunState::WaitingToSendToCompositor);
 
         abortAnimation();
 
         m_compositorAnimationId = 0;
         m_compositorAnimationGroupId = 0;
         if (m_runState == RunState::WaitingToCancelOnCompositor) {
-            return resetAnimationState();
+            postAnimationCleanupAndReset();
+            return;
         }
     }
 
     if (m_runState == RunState::WaitingToSendToCompositor
         || m_runState == RunState::RunningOnCompositorButNeedsUpdate) {
         if (m_runState == RunState::RunningOnCompositorButNeedsUpdate) {
             // Abort the running animation before a new one with an updated
             // target is added.
             abortAnimation();
 
@@ skipping 34 matching lines @@
             int animationGroupId = animation->group();
 
             sentToCompositor = addAnimation(animation.release());
             if (sentToCompositor) {
                 m_runState = RunState::RunningOnCompositor;
                 m_compositorAnimationId = animationId;
                 m_compositorAnimationGroupId = animationGroupId;
             }
         }
 
+        bool runningOnMainThread = false;
         if (!sentToCompositor) {
-            if (registerAndScheduleAnimation())
+            runningOnMainThread = registerAndScheduleAnimation();
+            if (runningOnMainThread)
                 m_runState = RunState::RunningOnMainThread;
         }
+
+        // Main thread should deal with the scroll animations it started.
+        if (sentToCompositor || runningOnMainThread)
+            addMainThreadScrollingReason();
+        else
+            removeMainThreadScrollingReason();
     }
 }
 
+void ScrollAnimator::addMainThreadScrollingReason()
+{
+    if (WebLayer* scrollLayer = toWebLayer(scrollableArea()->layerForScrolling())) {
+        scrollLayer->addMainThreadScrollingReasons(
+            MainThreadScrollingReason::kAnimatingScollOnMainThread);
+    }
+}
+
+void ScrollAnimator::removeMainThreadScrollingReason()
+{
+    if (WebLayer* scrollLayer = toWebLayer(scrollableArea()->layerForScrolling())) {
+        scrollLayer->clearMainThreadScrollingReasons(
+            MainThreadScrollingReason::kAnimatingScollOnMainThread);
+    }
+}
+
 void ScrollAnimator::notifyCompositorAnimationAborted(int groupId)
 {
     // An animation aborted by the compositor is treated as a finished
     // animation.
     ScrollAnimatorCompositorCoordinator::compositorAnimationFinished(groupId);
 }
 
 void ScrollAnimator::notifyCompositorAnimationFinished(int groupId)
 {
     ScrollAnimatorCompositorCoordinator::compositorAnimationFinished(groupId);
 }
 
 void ScrollAnimator::cancelAnimation()
 {
     ScrollAnimatorCompositorCoordinator::cancelAnimation();
 }
 
 void ScrollAnimator::layerForCompositedScrollingDidChange(
     WebCompositorAnimationTimeline* timeline)
 {
-    reattachCompositorPlayerIfNeeded(timeline);
+    if (reattachCompositorPlayerIfNeeded(timeline) && m_animationCurve)
+        addMainThreadScrollingReason();
 }
 
 bool ScrollAnimator::registerAndScheduleAnimation()
 {
     scrollableArea()->registerForAnimation();
     if (!m_scrollableArea->scheduleAnimation()) {
         scrollToOffsetWithoutAnimation(m_targetOffset);
         resetAnimationState();
         return false;
     }
     return true;
 }
 
 DEFINE_TRACE(ScrollAnimator)
 {
     ScrollAnimatorBase::trace(visitor);
 }
 
 } // namespace blink