float ScrollAnimator::computeDeltaToConsume(
ScrollbarOrientation orientation, float pixelDelta) const
{
FloatPoint pos = desiredTargetPosition();
float currentPos = (orientation == HorizontalScrollbar) ? pos.x() : pos.y();
float newPos = clampScrollPosition(orientation, currentPos + pixelDelta);
return (currentPos == newPos) ? 0.0f : (newPos - currentPos);
}
ScrollResultOneDimensional ScrollAnimator::userScroll(
ScrollbarOrientation orientation, ScrollGranularity granularity, float step, float delta)
{
if (!m_scrollableArea->scrollAnimatorEnabled())
return ScrollAnimatorBase::userScroll(orientation, granularity, step, delta);
TRACE_EVENT0("blink", "ScrollAnimator::scroll");
if (granularity == ScrollByPrecisePixel)
return ScrollAnimatorBase::userScroll(orientation, granularity, step, delta);
float usedPixelDelta = computeDeltaToConsume(orientation, step * delta);
FloatPoint pixelDelta = (orientation == VerticalScrollbar
? FloatPoint(0, usedPixelDelta) : FloatPoint(usedPixelDelta, 0));
FloatPoint targetPos = desiredTargetPosition();
targetPos.moveBy(pixelDelta);
if (m_animationCurve) {
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) {
if (registerAndScheduleAnimation())
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);
}
if ((targetPos - currentPosition()).isZero()) {
// Report unused delta only if there is no animation and we are not
// starting one. This ensures we latch for the duration of the
// animation rather than animating multiple scrollers at the same time.
return ScrollResultOneDimensional(/* didScroll */ false, delta);
}
m_targetOffset = targetPos;
m_startTime = m_timeFunction();
if (registerAndScheduleAnimation())
m_runState = RunState::WaitingToSendToCompositor;
return ScrollResultOneDimensional(/* didScroll */ true, /* unusedScrollDelta */ 0);
}
