void Axis::EndOverscrollAnimation() {
ParentLayerCoord overscroll = GetOverscroll();
mFirstOverscrollAnimationSample = 0;
mLastOverscrollPeak = 0;
mOverscrollScale = 1.0f;
mOverscroll = overscroll;
}
float Axis::GetExcess() {
switch (GetOverscroll()) {
case OVERSCROLL_MINUS: return GetOrigin() - GetPageStart();
case OVERSCROLL_PLUS: return GetCompositionEnd() - GetPageEnd();
case OVERSCROLL_BOTH: return (GetCompositionEnd() - GetPageEnd()) +
(GetPageStart() - GetOrigin());
default: return 0;
}
}
ParentLayerCoord Axis::ApplyResistance(ParentLayerCoord aRequestedOverscroll) const {
// 'resistanceFactor' is a value between 0 and 1, which:
// - tends to 1 as the existing overscroll tends to 0
// - tends to 0 as the existing overscroll tends to the composition length
// The actual overscroll is the requested overscroll multiplied by this
// factor; this should prevent overscrolling by more than the composition
// length.
float resistanceFactor = 1 - fabsf(GetOverscroll()) / GetCompositionLength();
return resistanceFactor < 0 ? ParentLayerCoord(0) : aRequestedOverscroll * resistanceFactor;
}
ParentLayerCoord Axis::ApplyResistance(ParentLayerCoord aRequestedOverscroll) const {
// 'resistanceFactor' is a value between 0 and 1/16, which:
// - tends to 1/16 as the existing overscroll tends to 0
// - tends to 0 as the existing overscroll tends to the composition length
// The actual overscroll is the requested overscroll multiplied by this
// factor.
float resistanceFactor = (1 - fabsf(GetOverscroll()) / GetCompositionLength()) / 16;
float result = resistanceFactor < 0 ? ParentLayerCoord(0) : aRequestedOverscroll * resistanceFactor;
result = clamped(result, -8.0f, 8.0f);
return result;
}
void Axis::StopSamplingOverscrollAnimation() {
ParentLayerCoord overscroll = GetOverscroll();
ClearOverscroll();
mOverscroll = overscroll;
}
