float Axis::AdjustDisplacement(float aDisplacement, float& aOverscrollAmountOut,
bool aScrollingDisabled) {
if (mAxisLocked) {
aOverscrollAmountOut = 0;
return 0;
}
if (aScrollingDisabled) {
// Scrolling is disabled on this axis, stop scrolling.
aOverscrollAmountOut = aDisplacement;
return 0;
}
float displacement = aDisplacement;
// If this displacement will cause an overscroll, throttle it. Can potentially
// bring it to 0 even if the velocity is high.
if (DisplacementWillOverscroll(displacement) != OVERSCROLL_NONE) {
// No need to have a velocity along this axis anymore; it won't take us
// anywhere, so we're just spinning needlessly.
mVelocity = 0.0f;
aOverscrollAmountOut = DisplacementWillOverscrollAmount(displacement);
displacement -= aOverscrollAmountOut;
}
return displacement;
}
bool Axis::AdjustDisplacement(CSSCoord aDisplacement,
CSSCoord& aDisplacementOut,
CSSCoord& aOverscrollAmountOut)
{
if (mAxisLocked) {
aOverscrollAmountOut = 0;
aDisplacementOut = 0;
return false;
}
CSSCoord displacement = aDisplacement;
// First consume any overscroll in the opposite direction along this axis.
CSSCoord consumedOverscroll = 0;
if (mOverscroll > 0 && aDisplacement < 0) {
consumedOverscroll = std::min(mOverscroll, -aDisplacement);
} else if (mOverscroll < 0 && aDisplacement > 0) {
consumedOverscroll = 0.f - std::min(-mOverscroll, aDisplacement);
}
mOverscroll -= consumedOverscroll;
displacement += consumedOverscroll;
// Split the requested displacement into an allowed displacement that does
// not overscroll, and an overscroll amount.
if (DisplacementWillOverscroll(displacement) != OVERSCROLL_NONE) {
// No need to have a velocity along this axis anymore; it won't take us
// anywhere, so we're just spinning needlessly.
mVelocity = 0.0f;
aOverscrollAmountOut = DisplacementWillOverscrollAmount(displacement);
displacement -= aOverscrollAmountOut;
}
aDisplacementOut = displacement;
return fabsf(consumedOverscroll) > EPSILON;
}
float Axis::DisplacementWillOverscrollAmount(int32_t aDisplacement) {
switch (DisplacementWillOverscroll(aDisplacement)) {
case OVERSCROLL_MINUS: return (GetOrigin() + aDisplacement) - GetPageStart();
case OVERSCROLL_PLUS: return (GetCompositionEnd() + aDisplacement) - GetPageEnd();
// Don't handle overscrolled in both directions; a displacement can't cause
// this, it must have already been zoomed out too far.
default: return 0;
}
}
float Axis::GetDisplacementForDuration(float aScale, const TimeDuration& aDelta) {
if (fabsf(mVelocity) < gVelocityThreshold) {
mAcceleration = 0;
}
float accelerationFactor = GetAccelerationFactor();
float displacement = mVelocity * aScale * aDelta.ToMilliseconds() * accelerationFactor;
// If this displacement will cause an overscroll, throttle it. Can potentially
// bring it to 0 even if the velocity is high.
if (DisplacementWillOverscroll(displacement) != OVERSCROLL_NONE) {
// No need to have a velocity along this axis anymore; it won't take us
// anywhere, so we're just spinning needlessly.
mVelocity = 0.0f;
mAcceleration = 0;
displacement -= DisplacementWillOverscrollAmount(displacement);
}
return displacement;
}
