Move overscroll bounce to impl thread

content/renderer/input/input_scroll_elasticity_controller.cc

Index: content/renderer/input/input_scroll_elasticity_controller.cc
diff --git a/content/renderer/input/input_scroll_elasticity_controller.cc b/content/renderer/input/input_scroll_elasticity_controller.cc
new file mode 100644
index 0000000000000000000000000000000000000000..c89419d55c1e7ad97f4976d2bde1e0ae6aa3123c
--- /dev/null
+++ b/content/renderer/input/input_scroll_elasticity_controller.cc
@@ -0,0 +1,397 @@
+#include "content/renderer/input/input_scroll_elasticity_controller.h"
+
+namespace content {
+
+static const float scrollVelocityZeroingTimeout = 0.10f;
+static const float rubberbandDirectionLockStretchRatio = 1;
+static const float rubberbandMinimumRequiredDeltaBeforeStretch = 10;
+
+static const float rubberbandStiffness = 20;
+static const float rubberbandAmplitude = 0.31f;
+static const float rubberbandPeriod = 1.6f;
+
+static float elasticDeltaForTimeDelta(float initialPosition, float initialVelocity, float elapsedTime)
+{
+    float amplitude = rubberbandAmplitude;
+    float period = rubberbandPeriod;
+    float criticalDampeningFactor = expf((-elapsedTime * rubberbandStiffness) / period);
+
+    return (initialPosition + (-initialVelocity * elapsedTime * amplitude)) * criticalDampeningFactor;
+}
+
+static float elasticDeltaForReboundDelta(float delta)
+{
+    float stiffness = std::max(rubberbandStiffness, 1.0f);
+    return delta / stiffness;
+}
+
+static float reboundDeltaForElasticDelta(float delta)
+{
+    return delta * rubberbandStiffness;
+}
+
+static float scrollWheelMultiplier()
+{
+    static float multiplier = -1;
+    if (multiplier < 0) {
+        // XXX
+        // multiplier = [[NSUserDefaults standardUserDefaults] floatForKey:@"NSScrollWheelMultiplier"];
+        if (multiplier <= 0)
+            multiplier = 1;
+    }
+    return multiplier;
+}
+
+InputScrollElasticityController::InputScrollElasticityController(cc::ScrollElasticityControllerClient* client)
+    : m_client(client)
+    , m_inScrollGesture(false)
+    , m_hasScrolled(false)
+    , m_momentumScrollInProgress(false)
+    , m_ignoreMomentumScrolls(false)
+    , m_snapRubberbandTimerIsActive(false) { }
+
+InputScrollElasticityController::~InputScrollElasticityController() { }
+
+void InputScrollElasticityController::WillShutdown() {
+  m_client = NULL;
+}
+
+void InputScrollElasticityController::Animate(base::TimeTicks time) {
+  snapRubberBandTimerFired();
+}
+
+bool InputScrollElasticityController::handleWheelEvent(const blink::WebMouseWheelEvent& wheelEvent)
+{
+    if (wheelEvent.phase == blink::WebMouseWheelEvent::PhaseMayBegin)
+        return false;
+
+    if (wheelEvent.phase == blink::WebMouseWheelEvent::PhaseBegan) {
+        m_inScrollGesture = true;
+        m_hasScrolled = false;
+        m_momentumScrollInProgress = false;
+        m_ignoreMomentumScrolls = false;
+        m_lastMomentumScrollTimestamp = base::Time();
+        m_momentumVelocity = gfx::Vector2dF();
+
+        gfx::Vector2dF stretchAmount = m_client->stretchAmount();
+        m_stretchScrollForce.set_x(reboundDeltaForElasticDelta(stretchAmount.x()));
+        m_stretchScrollForce.set_y(reboundDeltaForElasticDelta(stretchAmount.y()));
+        m_overflowScrollDelta = gfx::Vector2dF();
+
+        stopSnapRubberbandTimer();
+
+        // TODO(erikchen): Use the commented out line once Chromium uses the return value correctly.
+        // crbug.com/375512
+        // return shouldHandleEvent(wheelEvent);
+
+        // This logic is incorrect, since diagonal wheel events are not consumed.
+        if (m_client->pinnedInDirection(gfx::Vector2dF(-wheelEvent.deltaX, 0))) {
+            if (wheelEvent.deltaX > 0 && !wheelEvent.canRubberbandLeft)
+                return false;
+            if (wheelEvent.deltaX < 0 && !wheelEvent.canRubberbandRight)
+                return false;
+        }
+
+        return true;
+    }
+
+    if (wheelEvent.phase == blink::WebMouseWheelEvent::PhaseEnded || wheelEvent.phase == blink::WebMouseWheelEvent::PhaseCancelled) {
+        snapRubberBand();
+        return m_hasScrolled;
+    }
+
+    bool isMomentumScrollEvent = (wheelEvent.momentumPhase != blink::WebMouseWheelEvent::PhaseNone);
+    if (m_ignoreMomentumScrolls && (isMomentumScrollEvent || m_snapRubberbandTimerIsActive)) {
+        if (wheelEvent.momentumPhase == blink::WebMouseWheelEvent::PhaseEnded) {
+            m_ignoreMomentumScrolls = false;
+            return true;
+        }
+        return false;
+    }
+
+    if (!shouldHandleEvent(wheelEvent))
+        return false;
+
+    float deltaX = m_overflowScrollDelta.x() - wheelEvent.deltaX;
+    float deltaY = m_overflowScrollDelta.y() - wheelEvent.deltaY;
+    float eventCoalescedDeltaX = -wheelEvent.deltaX;
+    float eventCoalescedDeltaY = -wheelEvent.deltaY;
+
+    // Reset overflow values because we may decide to remove delta at various points and put it into overflow.
+    m_overflowScrollDelta = gfx::Vector2dF();
+
+    gfx::Vector2dF stretchAmount = m_client->stretchAmount();
+    bool isVerticallyStretched = stretchAmount.y();
+    bool isHorizontallyStretched = stretchAmount.x();
+
+    // Slightly prefer scrolling vertically by applying the = case to deltaY
+    if (fabsf(deltaY) >= fabsf(deltaX))
+        deltaX = 0;
+    else
+        deltaY = 0;
+
+    bool shouldStretch = false;
+
+    blink::WebMouseWheelEvent::Phase momentumPhase = wheelEvent.momentumPhase;
+
+    // If we are starting momentum scrolling then do some setup.
+    if (!m_momentumScrollInProgress && (momentumPhase == blink::WebMouseWheelEvent::PhaseBegan || momentumPhase == blink::WebMouseWheelEvent::PhaseChanged)) {
+        m_momentumScrollInProgress = true;
+        // Start the snap rubber band timer if it's not running. This is needed to
+        // snap back from the over scroll caused by momentum events.
+        if (!m_snapRubberbandTimerIsActive && m_startTime == base::Time())
+            snapRubberBand();
+    }
+
+    // XXX
+    base::Time wheelEventTimestamp = base::Time::Now();
+    float timeDelta = (wheelEventTimestamp - m_lastMomentumScrollTimestamp).InSecondsF();
+    if (m_inScrollGesture || m_momentumScrollInProgress) {
+        if (m_lastMomentumScrollTimestamp != base::Time() && timeDelta > 0 && timeDelta < scrollVelocityZeroingTimeout) {
+            m_momentumVelocity.set_x(eventCoalescedDeltaX / (float)timeDelta);
+            m_momentumVelocity.set_y(eventCoalescedDeltaY / (float)timeDelta);
+            m_lastMomentumScrollTimestamp = wheelEventTimestamp;
+        } else {
+            m_lastMomentumScrollTimestamp = wheelEventTimestamp;
+            m_momentumVelocity = gfx::Vector2dF();
+        }
+
+        if (isVerticallyStretched) {
+            if (!isHorizontallyStretched && m_client->pinnedInDirection(gfx::Vector2dF(deltaX, 0))) {
+                // Stretching only in the vertical.
+                if (deltaY != 0 && (fabsf(deltaX / deltaY) < rubberbandDirectionLockStretchRatio))
+                    deltaX = 0;
+                else if (fabsf(deltaX) < rubberbandMinimumRequiredDeltaBeforeStretch) {
+                    m_overflowScrollDelta.set_x(m_overflowScrollDelta.x() + deltaX);
+                    deltaX = 0;
+                } else
+                    m_overflowScrollDelta.set_x(m_overflowScrollDelta.x() + deltaX);
+            }
+        } else if (isHorizontallyStretched) {
+            // Stretching only in the horizontal.
+            if (m_client->pinnedInDirection(gfx::Vector2dF(0, deltaY))) {
+                if (deltaX != 0 && (fabsf(deltaY / deltaX) < rubberbandDirectionLockStretchRatio))
+                    deltaY = 0;
+                else if (fabsf(deltaY) < rubberbandMinimumRequiredDeltaBeforeStretch) {
+                    m_overflowScrollDelta.set_y(m_overflowScrollDelta.y() + deltaY);
+                    deltaY = 0;
+                } else
+                    m_overflowScrollDelta.set_y(m_overflowScrollDelta.y() + deltaY);
+            }
+        } else {
+            // Not stretching at all yet.
+            if (m_client->pinnedInDirection(gfx::Vector2dF(deltaX, deltaY))) {
+                if (fabsf(deltaY) >= fabsf(deltaX)) {
+                    if (fabsf(deltaX) < rubberbandMinimumRequiredDeltaBeforeStretch) {
+                        m_overflowScrollDelta.set_x(m_overflowScrollDelta.x() + deltaX);
+                        deltaX = 0;
+                    } else
+                        m_overflowScrollDelta.set_x(m_overflowScrollDelta.x() + deltaX);
+                }
+                shouldStretch = true;
+            }
+        }
+    }
+
+    if (deltaX != 0 || deltaY != 0) {
+        m_hasScrolled = true;
+        if (!(shouldStretch || isVerticallyStretched || isHorizontallyStretched)) {
+            if (deltaY != 0) {
+                deltaY *= scrollWheelMultiplier();
+                m_client->immediateScrollBy(gfx::Vector2dF(0, deltaY));
+            }
+            if (deltaX != 0) {
+                deltaX *= scrollWheelMultiplier();
+                m_client->immediateScrollBy(gfx::Vector2dF(deltaX, 0));
+            }
+        } else {
+            if (!m_client->allowsHorizontalStretching()) {
+                deltaX = 0;
+                eventCoalescedDeltaX = 0;
+            } else if ((deltaX != 0) && !isHorizontallyStretched && !m_client->pinnedInDirection(gfx::Vector2dF(deltaX, 0))) {
+                deltaX *= scrollWheelMultiplier();
+
+                m_client->immediateScrollByWithoutContentEdgeConstraints(gfx::Vector2dF(deltaX, 0));
+                deltaX = 0;
+            }
+
+            if (!m_client->allowsVerticalStretching()) {
+                deltaY = 0;
+                eventCoalescedDeltaY = 0;
+            } else if ((deltaY != 0) && !isVerticallyStretched && !m_client->pinnedInDirection(gfx::Vector2dF(0, deltaY))) {
+                deltaY *= scrollWheelMultiplier();
+
+                m_client->immediateScrollByWithoutContentEdgeConstraints(gfx::Vector2dF(0, deltaY));
+                deltaY = 0;
+            }
+
+            gfx::Vector2dF stretchAmount = m_client->stretchAmount();
+
+            if (m_momentumScrollInProgress) {
+                if ((m_client->pinnedInDirection(gfx::Vector2dF(eventCoalescedDeltaX, eventCoalescedDeltaY)) || (fabsf(eventCoalescedDeltaX) + fabsf(eventCoalescedDeltaY) <= 0)) && m_lastMomentumScrollTimestamp != base::Time()) {
+                    m_ignoreMomentumScrolls = true;
+                    m_momentumScrollInProgress = false;
+                    snapRubberBand();
+                }
+            }
+
+            m_stretchScrollForce.set_x(m_stretchScrollForce.x() + deltaX);
+            m_stretchScrollForce.set_y(m_stretchScrollForce.y() + deltaY);
+
+            gfx::Vector2dF dampedDelta(ceilf(elasticDeltaForReboundDelta(m_stretchScrollForce.x())), ceilf(elasticDeltaForReboundDelta(m_stretchScrollForce.y())));
+
+            m_client->immediateScrollByWithoutContentEdgeConstraints(dampedDelta - stretchAmount);
+        }
+    }
+
+    if (m_momentumScrollInProgress && momentumPhase == blink::WebMouseWheelEvent::PhaseEnded) {
+        m_momentumScrollInProgress = false;
+        m_ignoreMomentumScrolls = false;
+        m_lastMomentumScrollTimestamp = base::Time();
+    }
+
+    return true;
+}
+
+static inline float roundTowardZero(float num)
+{
+    return num > 0 ? ceilf(num - 0.5f) : floorf(num + 0.5f);
+}
+
+static inline float roundToDevicePixelTowardZero(float num)
+{
+    float roundedNum = roundf(num);
+    if (fabs(num - roundedNum) < 0.125)
+        num = roundedNum;
+
+    return roundTowardZero(num);
+}
+
+void InputScrollElasticityController::snapRubberBandTimerFired()
+{
+    if (!m_momentumScrollInProgress || m_ignoreMomentumScrolls) {
+        float timeDelta = (base::Time::Now() - m_startTime).InSecondsF();
+
+        if (m_startStretch == gfx::Vector2dF()) {
+            m_startStretch = m_client->stretchAmount();
+            if (m_startStretch == gfx::Vector2dF()) {
+                stopSnapRubberbandTimer();
+
+                m_stretchScrollForce = gfx::Vector2dF();
+                m_startTime = base::Time();
+                m_origOrigin = gfx::Vector2dF();
+                m_origVelocity = gfx::Vector2dF();
+                return;
+            }
+
+            m_origOrigin = m_client->absoluteScrollPosition() - m_startStretch;
+            m_origVelocity = m_momentumVelocity;
+
+            // Just like normal scrolling, prefer vertical rubberbanding
+            if (fabsf(m_origVelocity.y()) >= fabsf(m_origVelocity.x()))
+                m_origVelocity.set_x(0);
+
+            // Don't rubber-band horizontally if it's not possible to scroll horizontally
+            if (!m_client->canScrollHorizontally())
+                m_origVelocity.set_x(0);
+
+            // Don't rubber-band vertically if it's not possible to scroll vertically
+            if (!m_client->canScrollVertically())
+                m_origVelocity.set_y(0);
+        }
+
+        gfx::Vector2dF delta(roundToDevicePixelTowardZero(elasticDeltaForTimeDelta(m_startStretch.x(), -m_origVelocity.x(), (float)timeDelta)),
+                         roundToDevicePixelTowardZero(elasticDeltaForTimeDelta(m_startStretch.y(), -m_origVelocity.y(), (float)timeDelta)));
+
+        if (fabs(delta.x()) >= 1 || fabs(delta.y()) >= 1) {
+            m_client->immediateScrollByWithoutContentEdgeConstraints(gfx::Vector2dF(delta.x(), delta.y()) - m_client->stretchAmount());
+
+            gfx::Vector2dF newStretch = m_client->stretchAmount();
+
+            m_stretchScrollForce.set_x(reboundDeltaForElasticDelta(newStretch.x()));
+            m_stretchScrollForce.set_y(reboundDeltaForElasticDelta(newStretch.y()));
+        } else {
+            m_client->adjustScrollPositionToBoundsIfNecessary();
+
+            stopSnapRubberbandTimer();
+            m_stretchScrollForce = gfx::Vector2dF();
+            m_startTime = base::Time();
+            m_startStretch = gfx::Vector2dF();
+            m_origOrigin = gfx::Vector2dF();
+            m_origVelocity = gfx::Vector2dF();
+        }
+    } else {
+        m_startTime = base::Time::Now();
+        m_startStretch = gfx::Vector2dF();
+    }
+}
+
+bool InputScrollElasticityController::isRubberBandInProgress() const
+{
+    if (!m_inScrollGesture && !m_momentumScrollInProgress && !m_snapRubberbandTimerIsActive)
+        return false;
+
+    return !m_client->stretchAmount().IsZero();
+}
+
+void InputScrollElasticityController::stopSnapRubberbandTimer()
+{
+    m_client->stopSnapRubberbandTimer();
+    m_snapRubberbandTimerIsActive = false;
+}
+
+void InputScrollElasticityController::snapRubberBand()
+{
+    float timeDelta = (base::Time::Now() - m_lastMomentumScrollTimestamp).InSecondsF();
+    if (m_lastMomentumScrollTimestamp != base::Time() && timeDelta >= scrollVelocityZeroingTimeout)
+        m_momentumVelocity = gfx::Vector2dF();
+
+    m_inScrollGesture = false;
+
+    if (m_snapRubberbandTimerIsActive)
+        return;
+
+    m_startStretch = gfx::Vector2dF();
+    m_origOrigin = gfx::Vector2dF();
+    m_origVelocity = gfx::Vector2dF();
+
+    // If there's no momentum scroll or stretch amount, no need to start the timer.
+    if (!m_momentumScrollInProgress && m_client->stretchAmount() == gfx::Vector2dF()) {
+        m_startTime = base::Time();
+        m_stretchScrollForce = gfx::Vector2dF();
+        return;
+    }
+
+    m_startTime = base::Time::Now();
+    m_client->startSnapRubberbandTimer();
+    m_snapRubberbandTimerIsActive = true;
+}
+
+bool InputScrollElasticityController::shouldHandleEvent(const blink::WebMouseWheelEvent& wheelEvent)
+{
+    // Once any scrolling has happened, all future events should be handled.
+    if (m_hasScrolled)
+        return true;
+
+    // The event can't cause scrolling to start if its delta is 0.
+    if (wheelEvent.deltaX == 0 && wheelEvent.deltaY == 0)
+        return false;
+
+    // If the client isn't pinned, then the event is guaranteed to cause scrolling.
+    if (!m_client->pinnedInDirection(gfx::Vector2dF(-wheelEvent.deltaX, 0)))
+        return true;
+
+    // If the event is pinned, then the client can't scroll, but it might rubber band.
+    // Check if the event allows rubber banding.
+    if (wheelEvent.deltaY == 0) {
+        if (wheelEvent.deltaX > 0 && !wheelEvent.canRubberbandLeft)
+            return false;
+        if (wheelEvent.deltaX < 0 && !wheelEvent.canRubberbandRight)
+            return false;
+    }
+
+    // The event is going to either cause scrolling or rubber banding.
+    return true;
+}
+
+}  // namespace content