// TODO Keep static memory references to all arrays used in _tickUpdateTranslation
function _tickUpdateTranslation(timestamp) {
var dt = (timestamp - (_tickUpdateTranslation.lastTimestamp || timestamp))
_tickUpdateTranslation.lastTimestamp = timestamp
// if (dt >= 20) { log("SLOW FRAME") }
var excess = _boundsExcess(bouncingOffset)
if (touch.isTouching) {
var positionByDrag = [
touch.bouncingScrollAtStart[X] + touch.offset[X],
touch.bouncingScrollAtStart[Y] + touch.offset[Y]
]
var excess = _boundsExcess(positionByDrag)
boundedOffset[X] = positionByDrag[X] - excess[X]
boundedOffset[Y] = positionByDrag[Y] - excess[Y]
if (_isOutOfBounds(excess)) {
// While dragging out of bounds, the excess drag has a halved effect on bouncingOffset
_updateTranslation(
boundedOffset[X] + excess[X] / OUT_OF_BOUNDS_DRAG_DIVIDER,
boundedOffset[Y] + excess[Y] / OUT_OF_BOUNDS_DRAG_DIVIDER
)
} else {
_updateTranslation(positionByDrag[X], positionByDrag[Y])
}
} else if (_isFloating() || _isOutOfBounds(excess)) {
var distance = tags.pos.abs(excess)
var deceleration = clip(60 / dt, 0, 1) * DECELERATION_RATE
if (excess[Y]) {
if (excess[Y] * velocity[Y] <= 0) {
// Outside bounds, moving back in
if (distance[Y] < 0.5 && velocity[Y] < 0.01) {
// Close the remaining little gap at once
bouncingOffset[Y] -= excess[Y]
velocity[Y] = 0
} else {
velocity[Y] = -excess[Y] * BOUNCE_BACK_VELOCITY_BY_DISTANCE
}
} else {
// Outside bounds, still moving out
velocity[Y] -= excess[Y] * OUT_OF_BOUNDS_SLOWDOWN_RATE / dt
}
}
velocity[X] *= deceleration
velocity[Y] *= deceleration
var positionByVelocity = [
bouncingOffset[X] + velocity[X] * dt,
bouncingOffset[Y] + velocity[Y] * dt,
]
_updateTranslation(positionByVelocity[X], positionByVelocity[Y])
var excess = _boundsExcess(positionByVelocity)
boundedOffset[X] = positionByVelocity[X] - excess[X]
boundedOffset[Y] = positionByVelocity[Y] - excess[Y]
}
// Cut off early, the last fraction of velocity doesn't have much impact on movement
var bouncingScrollExcess = _boundsExcess(bouncingOffset)
if (velocity[Y] && Math.abs(velocity[Y]) < VELOCITY_CUTOFF && !_isOutOfBounds(bouncingScrollExcess)) {
velocity[Y] = 0
}
if (touch.isTouching || _isFloating() || _isOutOfBounds(bouncingScrollExcess)) {
// keep animating as long as user is actively touching or the view has a velocity or the view is bouncing
requestAnimationFrame(_tickUpdateTranslation)
} else {
_tickUpdateTranslation.lastTimestamp = null
}
}
function _startRequestingAnimationFrames() {
if (_tickUpdateTranslation.lastTimestamp) { return }
requestAnimationFrame(_tickUpdateTranslation)
}