/* static */ DeltaValues
WheelTransaction::AccelerateWheelDelta(WidgetWheelEvent* aEvent,
bool aAllowScrollSpeedOverride)
{
DeltaValues result(aEvent);
// Don't accelerate the delta values if the event isn't line scrolling.
if (aEvent->deltaMode != nsIDOMWheelEvent::DOM_DELTA_LINE) {
return result;
}
if (aAllowScrollSpeedOverride) {
result = OverrideSystemScrollSpeed(aEvent);
}
// Accelerate by the sScrollSeriesCounter
int32_t start = GetAccelerationStart();
if (start >= 0 && sScrollSeriesCounter >= start) {
int32_t factor = GetAccelerationFactor();
if (factor > 0) {
result.deltaX = ComputeAcceleratedWheelDelta(result.deltaX, factor);
result.deltaY = ComputeAcceleratedWheelDelta(result.deltaY, factor);
}
}
return result;
}
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;
}
