Run smooth scroll animations on the compositor when possible

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

Index: third_party/WebKit/Source/platform/scroll/ScrollAnimator.cpp
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollAnimator.cpp b/third_party/WebKit/Source/platform/scroll/ScrollAnimator.cpp
index c3b47315630a09445668430e1400f374fa7d5225..a7fb64b8ffc490b41ffdd4b3cca7192fe8a02213 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollAnimator.cpp
+++ b/third_party/WebKit/Source/platform/scroll/ScrollAnimator.cpp
@@ -32,12 +32,13 @@
 #include "platform/scroll/ScrollAnimator.h"
 
 #include "platform/TraceEvent.h"
+#include "platform/graphics/GraphicsLayer.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"
-#include <algorithm>
 
 namespace blink {
 
@@ -50,21 +51,22 @@ PassOwnPtrWillBeRawPtr<ScrollAnimatorBase> ScrollAnimatorBase::create(Scrollable
 
 ScrollAnimator::ScrollAnimator(ScrollableArea* scrollableArea, WTF::TimeFunction timeFunction)
     : ScrollAnimatorBase(scrollableArea)
+    , m_lastTickTime(0.0)
     , m_timeFunction(timeFunction)
 {
 }
 
 ScrollAnimator::~ScrollAnimator()
 {
-    cancelAnimations();
 }
 
 FloatPoint ScrollAnimator::desiredTargetPosition() const
 {
-    return m_animationCurve ? FloatPoint(m_animationCurve->targetValue()) : currentPosition();
+    return m_animationCurve ? m_targetOffset : currentPosition();
 }
 
-float ScrollAnimator::computeDeltaToConsume(ScrollbarOrientation orientation, float pixelDelta) const
+float ScrollAnimator::computeDeltaToConsume(
+    ScrollbarOrientation orientation, float pixelDelta) const
 {
     FloatPoint pos = desiredTargetPosition();
     float currentPos = (orientation == HorizontalScrollbar) ? pos.x() : pos.y();
@@ -72,7 +74,16 @@ float ScrollAnimator::computeDeltaToConsume(ScrollbarOrientation orientation, fl
     return (currentPos == newPos) ? 0.0f : (newPos - currentPos);
 }
 
-ScrollResultOneDimensional ScrollAnimator::userScroll(ScrollbarOrientation orientation, ScrollGranularity granularity, float step, float delta)
+void ScrollAnimator::resetAnimationState()
+{
+    ScrollAnimatorCompositorCoordinator::resetAnimationState();
+    if (m_animationCurve)
+        m_animationCurve.clear();
+    m_startTime = 0.0;
+}
+
+ScrollResultOneDimensional ScrollAnimator::userScroll(
+    ScrollbarOrientation orientation, ScrollGranularity granularity, float step, float delta)
 {
     if (!m_scrollableArea->scrollAnimatorEnabled())
         return ScrollAnimatorBase::userScroll(orientation, granularity, step, delta);
@@ -83,14 +94,33 @@ ScrollResultOneDimensional ScrollAnimator::userScroll(ScrollbarOrientation orien
         return ScrollAnimatorBase::userScroll(orientation, granularity, step, delta);
 
     float usedPixelDelta = computeDeltaToConsume(orientation, step * delta);
-    FloatPoint pixelDelta = (orientation == VerticalScrollbar ? FloatPoint(0, usedPixelDelta) : FloatPoint(usedPixelDelta, 0));
+    FloatPoint pixelDelta = (orientation == VerticalScrollbar
+        ? FloatPoint(0, usedPixelDelta) : FloatPoint(usedPixelDelta, 0));
 
     FloatPoint targetPos = desiredTargetPosition();
     targetPos.moveBy(pixelDelta);
 
     if (m_animationCurve) {
-        if (!(targetPos - m_animationCurve->targetValue()).isZero())
-            m_animationCurve->updateTarget(m_timeFunction() - m_startTime, targetPos);
+        if ((targetPos - m_targetOffset).isZero()) {
+            // Report unused delta only if there is no animation running. See
+            // comment below regarding scroll latching.
+            return ScrollResultOneDimensional(/* didScroll */ true, /* unusedScrollDelta */ 0);
+        }
+
+        m_targetOffset = targetPos;
+        ASSERT(m_runState == RunState::RunningOnMainThread
+            || m_runState == RunState::RunningOnCompositor
+            || m_runState == RunState::RunningOnCompositorButNeedsUpdate);
+
+        if (m_runState == RunState::RunningOnCompositor
+            || m_runState == RunState::RunningOnCompositorButNeedsUpdate) {
+            m_runState = RunState::RunningOnCompositorButNeedsUpdate;
+            return ScrollResultOneDimensional(/* didScroll */ true, /* unusedScrollDelta */ 0);
+        }
+
+        // Running on the main thread, simply update the target offset instead
+        // of sending to the compositor.
+        m_animationCurve->updateTarget(m_timeFunction() - m_startTime, targetPos);
         return ScrollResultOneDimensional(/* didScroll */ true, /* unusedScrollDelta */ 0);
     }
 
@@ -101,16 +131,17 @@ ScrollResultOneDimensional ScrollAnimator::userScroll(ScrollbarOrientation orien
         return ScrollResultOneDimensional(/* didScroll */ false, delta);
     }
 
-    m_animationCurve = adoptPtr(Platform::current()->compositorSupport()->createScrollOffsetAnimationCurve(
-        targetPos,
-        WebCompositorAnimationCurve::TimingFunctionTypeEaseInOut,
-        WebScrollOffsetAnimationCurve::ScrollDurationConstant));
-
-    m_animationCurve->setInitialValue(currentPosition());
+    m_targetOffset = targetPos;
     m_startTime = m_timeFunction();
 
     scrollableArea()->registerForAnimation();
-    animationTimerFired();
+    if (!m_scrollableArea->scheduleAnimation()) {
+        scrollToOffsetWithoutAnimation(targetPos);
+        resetAnimationState();
+        return ScrollResultOneDimensional(/* didScroll */ true, /* unusedScrollDelta */ 0);
+    }
+
+    m_runState = RunState::WaitingToSendToCompositor;
     return ScrollResultOneDimensional(/* didScroll */ true, /* unusedScrollDelta */ 0);
 }
 
@@ -119,34 +150,23 @@ void ScrollAnimator::scrollToOffsetWithoutAnimation(const FloatPoint& offset)
     m_currentPosX = offset.x();
     m_currentPosY = offset.y();
 
-    cancelAnimations();
+    resetAnimationState();
     notifyPositionChanged();
 }
 
-void ScrollAnimator::cancelAnimations()
+void ScrollAnimator::tickAnimation(double monotonicTime)
 {
-    if (m_animationCurve)
-        m_animationCurve.clear();
-}
+    m_lastTickTime = monotonicTime;
 
-void ScrollAnimator::serviceScrollAnimations()
-{
-    if (hasRunningAnimation())
-        animationTimerFired();
-}
+    if (m_runState != RunState::RunningOnMainThread)
+        return;
 
-bool ScrollAnimator::hasRunningAnimation() const
-{
-    return m_animationCurve;
-}
-
-void ScrollAnimator::animationTimerFired()
-{
-    TRACE_EVENT0("blink", "ScrollAnimator::animationTimerFired");
-    double elapsedTime = m_timeFunction() - m_startTime;
+    TRACE_EVENT0("blink", "ScrollAnimator::tickAnimation");
+    double elapsedTime = monotonicTime - m_startTime;
 
     bool isFinished = (elapsedTime > m_animationCurve->duration());
-    FloatPoint offset = isFinished ? m_animationCurve->targetValue() : m_animationCurve->getValue(elapsedTime);
+    FloatPoint offset = isFinished ? m_animationCurve->targetValue()
+        : m_animationCurve->getValue(elapsedTime);
 
     offset = FloatPoint(m_scrollableArea->clampScrollPosition(offset));
 
@@ -154,7 +174,7 @@ void ScrollAnimator::animationTimerFired()
     m_currentPosY = offset.y();
 
     if (isFinished)
-        m_animationCurve.clear();
+        resetAnimationState();
     else
         scrollableArea()->scheduleAnimation();
 
@@ -162,6 +182,105 @@ void ScrollAnimator::animationTimerFired()
     notifyPositionChanged();
 }
 
+void ScrollAnimator::updateCompositorAnimations()
+{
+    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) {
+            resetAnimationState();
+            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();
+
+            m_compositorAnimationId = 0;
+            m_compositorAnimationGroupId = 0;
+
+            m_animationCurve->updateTarget(m_lastTickTime - m_startTime,
+                m_targetOffset);
+            m_runState = RunState::WaitingToSendToCompositor;
+        }
+
+        if (!m_animationCurve) {
+            m_animationCurve = adoptPtr(Platform::current()->compositorSupport()
+                ->createScrollOffsetAnimationCurve(
+                    m_targetOffset,
+                    WebCompositorAnimationCurve::TimingFunctionTypeEaseInOut,
+                    WebScrollOffsetAnimationCurve::ScrollDurationConstant));
+            m_animationCurve->setInitialValue(currentPosition());
+        }
+
+        bool sentToCompositor = false;
+        if (GraphicsLayer* layer = m_scrollableArea->layerForScrolling()) {
+            ASSERT(layer->scrollableArea() == m_scrollableArea);
+            if (!layer->platformLayer()->shouldScrollOnMainThread()) {
+                OwnPtr<WebCompositorAnimation> animation = adoptPtr(
+                    Platform::current()->compositorSupport()->createAnimation(
+                        *m_animationCurve,
+                        WebCompositorAnimation::TargetPropertyScrollOffset));
+                // Being here means that either there is an animation that needs
+                // to be sent to the compositor, or an animation that needs to
+                // be updated (a new scroll event before the previous animation
+                // is finished). In either case, the start time is when the
+                // first animation was initiated. This re-targets the animation
+                // using the current time on main thread.
+                animation->setStartTime(m_startTime);
+
+                int animationId = animation->id();
+                int animationGroupId = animation->group();
+
+                sentToCompositor = addAnimation(animation.release());
+                if (sentToCompositor) {
+                    m_runState = RunState::RunningOnCompositor;
+                    m_compositorAnimationId = animationId;
+                    m_compositorAnimationGroupId = animationGroupId;
+                }
+            }
+        }
+
+        if (!sentToCompositor) {
+            m_runState = RunState::RunningOnMainThread;
+            if (!m_scrollableArea->scheduleAnimation()) {
+                scrollToOffsetWithoutAnimation(m_targetOffset);
+                resetAnimationState();
+            }
+        }
+    }
+}
+
+void ScrollAnimator::notifyCompositorAnimationFinished(int groupId)
+{
+    ScrollAnimatorCompositorCoordinator::compositorAnimationFinished(groupId);
+}
+
+void ScrollAnimator::cancelAnimation()
+{
+    ScrollAnimatorCompositorCoordinator::cancelAnimation();
+}
+
+void ScrollAnimator::layerForCompositedScrollingDidChange(
+    WebCompositorAnimationTimeline* timeline)
+{
+    reattachCompositorPlayerIfNeeded(timeline);
+}
+
 DEFINE_TRACE(ScrollAnimator)
 {
     ScrollAnimatorBase::trace(visitor);