Run CSSOM smooth scroll animations on the compositor when possible

Source/platform/scroll/ProgrammaticScrollAnimator.cpp

Index: Source/platform/scroll/ProgrammaticScrollAnimator.cpp
diff --git a/Source/platform/scroll/ProgrammaticScrollAnimator.cpp b/Source/platform/scroll/ProgrammaticScrollAnimator.cpp
index 574018064f1a97aeb528ca6e7a317ae5dec6e2aa..7b2332936a21758aa06070ec8d54633bc147ff9b 100644
--- a/Source/platform/scroll/ProgrammaticScrollAnimator.cpp
+++ b/Source/platform/scroll/ProgrammaticScrollAnimator.cpp
@@ -6,8 +6,10 @@
 #include "platform/scroll/ProgrammaticScrollAnimator.h"
 
 #include "platform/geometry/IntPoint.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 "public/platform/WebScrollOffsetAnimationCurve.h"
 
@@ -21,6 +23,9 @@ PassOwnPtr<ProgrammaticScrollAnimator> ProgrammaticScrollAnimator::create(Scroll
 ProgrammaticScrollAnimator::ProgrammaticScrollAnimator(ScrollableArea* scrollableArea)
     : m_scrollableArea(scrollableArea)
     , m_startTime(0.0)
+    , m_runState(RunState::Idle)
+    , m_compositorAnimationId(0)
+    , m_compositorAnimationGroupId(0)
 {
 }
 
@@ -32,6 +37,9 @@ void ProgrammaticScrollAnimator::resetAnimationState()
 {
     m_animationCurve.clear();
     m_startTime = 0.0;
+    m_runState = RunState::Idle;
+    m_compositorAnimationId = 0;
+    m_compositorAnimationGroupId = 0;
 }
 
 void ProgrammaticScrollAnimator::animateToOffset(FloatPoint offset)
@@ -46,35 +54,134 @@ void ProgrammaticScrollAnimator::animateToOffset(FloatPoint offset)
         resetAnimationState();
         m_scrollableArea->notifyScrollPositionChanged(IntPoint(offset.x(), offset.y()));
     }
+    m_runState = RunState::WaitingToSendToCompositor;
 }
 
 void ProgrammaticScrollAnimator::cancelAnimation()
 {
-    resetAnimationState();
+    switch (m_runState) {
+    case RunState::Idle:
+    case RunState::WaitingToCancelOnCompositor:
+        break;
+    case RunState::WaitingToSendToCompositor:
+        if (m_compositorAnimationId) {
+            // We still have a previous animation running on the compositor.
+            m_runState = RunState::WaitingToCancelOnCompositor;
+        } else {
+            resetAnimationState();
+        }
+        break;
+    case RunState::RunningOnMainThread:
+        resetAnimationState();
+        break;
+    case RunState::RunningOnCompositor:
+        m_runState = RunState::WaitingToCancelOnCompositor;
+
+        // Get serviced the next time compositor updates are allowed.
+        m_scrollableArea->registerForAnimation();
+    }
 }
 
 void ProgrammaticScrollAnimator::tickAnimation(double monotonicTime)
 {
-    if (m_animationCurve) {
-        if (!m_startTime)
-            m_startTime = monotonicTime;
-        double elapsedTime = monotonicTime - m_startTime;
-        bool isFinished = (elapsedTime > m_animationCurve->duration());
-        FloatPoint offset = m_animationCurve->getValue(elapsedTime);
-        m_scrollableArea->notifyScrollPositionChanged(IntPoint(offset.x(), offset.y()));
+    if (m_runState != RunState::RunningOnMainThread)
+        return;
 
-        if (isFinished) {
-            resetAnimationState();
-        } else if (!m_scrollableArea->scheduleAnimation()) {
-            m_scrollableArea->notifyScrollPositionChanged(IntPoint(m_targetOffset.x(), m_targetOffset.y()));
+    if (!m_startTime)
+        m_startTime = monotonicTime;
+    double elapsedTime = monotonicTime - m_startTime;
+    bool isFinished = (elapsedTime > m_animationCurve->duration());
+    FloatPoint offset = m_animationCurve->getValue(elapsedTime);
+    m_scrollableArea->notifyScrollPositionChanged(IntPoint(offset.x(), offset.y()));
+
+    if (isFinished) {
+        resetAnimationState();
+    } else if (!m_scrollableArea->scheduleAnimation()) {
+        m_scrollableArea->notifyScrollPositionChanged(IntPoint(m_targetOffset.x(), m_targetOffset.y()));
+        resetAnimationState();
+    }
+}
+
+bool ProgrammaticScrollAnimator::hasAnimationThatRequiresService() const
+{
+    switch (m_runState) {
+    case RunState::Idle:
+    case RunState::RunningOnCompositor:
+        return false;
+    case RunState::WaitingToSendToCompositor:
+    case RunState::RunningOnMainThread:
+    case RunState::WaitingToCancelOnCompositor:
+        return true;
+    }
+    ASSERT_NOT_REACHED();
+    return false;
+}
+
+void ProgrammaticScrollAnimator::updateCompositorAnimations()
+{
+    if (m_compositorAnimationId && m_runState != RunState::RunningOnCompositor) {
+        // 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);
+        if (GraphicsLayer* layer = m_scrollableArea->layerForScrolling())
+            layer->removeAnimation(m_compositorAnimationId);
+        m_compositorAnimationId = 0;
+        m_compositorAnimationGroupId = 0;
+        if (m_runState == RunState::WaitingToCancelOnCompositor) {
             resetAnimationState();
+            return;
+        }
+    }
+
+    if (m_runState == RunState::WaitingToSendToCompositor) {
+        bool sentToCompositor = false;
+
+        if (GraphicsLayer* layer = m_scrollableArea->layerForScrolling()) {
+            if (!layer->platformLayer()->shouldScrollOnMainThread()) {
+                OwnPtr<WebCompositorAnimation> animation = adoptPtr(Platform::current()->compositorSupport()->createAnimation(*m_animationCurve, WebCompositorAnimation::TargetPropertyScrollOffset));
+
+                int animationId = animation->id();
+                int animationGroupId = animation->group();
+                if (m_scrollableArea->layerForScrolling()->addAnimation(animation.release())) {
+                    sentToCompositor = true;
+                    m_runState = RunState::RunningOnCompositor;
+                    m_compositorAnimationId = animationId;
+                    m_compositorAnimationGroupId = animationGroupId;
+                }
+            }
+        }
+
+        if (!sentToCompositor) {
+            m_runState = RunState::RunningOnMainThread;
+            if (!m_scrollableArea->scheduleAnimation()) {
+                m_scrollableArea->notifyScrollPositionChanged(IntPoint(m_targetOffset.x(), m_targetOffset.y()));
+                resetAnimationState();
+            }
         }
     }
 }
 
-bool ProgrammaticScrollAnimator::hasRunningAnimation() const
+void ProgrammaticScrollAnimator::notifyCompositorAnimationFinished(int groupId)
 {
-    return !!m_animationCurve;
+    if (m_compositorAnimationGroupId != groupId)
+        return;
+
+    m_compositorAnimationId = 0;
+    m_compositorAnimationGroupId = 0;
+
+    switch (m_runState) {
+    case RunState::Idle:
+    case RunState::RunningOnMainThread:
+        ASSERT_NOT_REACHED();
+        break;
+    case RunState::WaitingToSendToCompositor:
+        break;
+    case RunState::RunningOnCompositor:
+    case RunState::WaitingToCancelOnCompositor:
+        resetAnimationState();
+    }
 }
 
 } // namespace blink