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const DIRECTION_LEFT = [-1, 0]
const DIRECTION_RIGHT = [1, 0]
const DIRECTION_UP = [0, -1]
const DIRECTION_DOWN = [0, 1]
// const DISTANCE_MIN = 1
// const isSwipeEvent = e => (e.touches.length === 1)
// const isSwipeEventEnd = e => (e.changedTouches.length === 1)
// const isScaleEvent = e => (e.targetTouches.length === 2)
// const isScaleEventEnd = e => (e.targetTouches.length === 1)
const deltaCoord = (oldCoord, newCoord) => [newCoord[0] - oldCoord[0], newCoord[1] - oldCoord[1]]
// const vectorMinus = (a, b) => a.map((k, n) => k - b[n])
// const vectorAdd = (a, b) => a.map((k, n) => k + b[n])
// const avgCoord = (coords) => [...coords].reduce(vectorAdd, [0, 0]).map(d => d / coords.length)
const touchCoord = touch => [touch.screenX, touch.screenY]
const touchEventCoord = e => touchCoord(e.touches[0])
const pointerEventCoord = e => [e.clientX, e.clientY]
const vectorLength = v => Math.sqrt(v[0] * v[0] + v[1] * v[1])
const perpendicular = v => [v[1], -v[0]]
const dotProduct = (v1, v2) => v1[0] * v2[0] + v1[1] * v2[1]
// const numProduct = (num, v) => v.map(k => num * k)
const project = (v1, v2) => {
const scalar = (dotProduct(v1, v2) / dotProduct(v2, v2))
return [scalar * v2[0], scalar * v2[1]]
}
// direction: either use the constants above or an arbitrary 2d vector.
// threshold: how many Px to move from touch origin before checking if the
// callback should be called.
// divergentTolerance: a scalar for much of divergent direction we tolerate when
// above threshold. for example, with 1.0 we only call the callback if
// divergent component of delta is < 1.0 * direction component of delta.
const swipeGesture = (direction, onSwipe, threshold = 30, perpendicularTolerance = 1.0) => {
return {
direction,
onSwipe,
threshold,
perpendicularTolerance,
_startPos: [0, 0],
_swiping: false
}
}
const beginSwipe = (event, gesture) => {
gesture._startPos = touchEventCoord(event)
gesture._swiping = true
}
const updateSwipe = (event, gesture) => {
if (!gesture._swiping) return
// movement too small
const delta = deltaCoord(gesture._startPos, touchEventCoord(event))
if (vectorLength(delta) < gesture.threshold) return
// movement is opposite from direction
if (dotProduct(delta, gesture.direction) < 0) return
// movement perpendicular to direction is too much
const towardsDir = project(delta, gesture.direction)
const perpendicularDir = perpendicular(gesture.direction)
const towardsPerpendicular = project(delta, perpendicularDir)
if (
vectorLength(towardsDir) * gesture.perpendicularTolerance <
vectorLength(towardsPerpendicular)
) return
gesture.onSwipe()
gesture._swiping = false
}
class SwipeAndClickGesture {
// swipePreviewCallback(offsets: Array[Number])
// offsets: the offset vector which the underlying component should move, from the starting position
// swipeEndCallback(sign: 0|-1|1)
// sign: if the swipe does not meet the threshold, 0
// if the swipe meets the threshold in the positive direction, 1
// if the swipe meets the threshold in the negative direction, -1
constructor ({
direction,
// swipeStartCallback
swipePreviewCallback,
swipeEndCallback,
swipeCancelCallback,
swipelessClickCallback,
threshold = 30, perpendicularTolerance = 1.0
}) {
const nop = () => { console.log('Warning: Not implemented') }
this.direction = direction
this.swipePreviewCallback = swipePreviewCallback || nop
this.swipeEndCallback = swipeEndCallback || nop
this.swipeCancelCallback = swipeCancelCallback || nop
this.swipelessClickCallback = swipelessClickCallback || nop
this.threshold = threshold
this.perpendicularTolerance = perpendicularTolerance
this._reset()
}
_reset () {
this._startPos = [0, 0]
this._pointerId = -1
this._swiping = false
this._swiped = false
}
start (event) {
console.log('start() called', event)
this._startPos = pointerEventCoord(event)
this._pointerId = event.pointerId
console.log('start pos:', this._startPos)
this._swiping = true
this._swiped = false
}
move (event) {
if (this._swiping && this._pointerId === event.pointerId) {
this._swiped = true
const coord = pointerEventCoord(event)
const delta = deltaCoord(this._startPos, coord)
this.swipePreviewCallback(delta)
}
}
cancel (event) {
if (!this._swiping || this._pointerId !== event.pointerId) {
return
}
this.swipeCancelCallback()
}
end (event) {
if (!this._swiping) {
console.log('not swiping')
return
}
if (this._pointerId !== event.pointerId) {
console.log('pointer id does not match')
return
}
this._swiping = false
console.log('end: is swipe event')
// movement too small
const coord = pointerEventCoord(event)
const delta = deltaCoord(this._startPos, coord)
const sign = (() => {
if (vectorLength(delta) < this.threshold) {
return 0
}
// movement is opposite from direction
const isPositive = dotProduct(delta, this.direction) > 0
// movement perpendicular to direction is too much
const towardsDir = project(delta, this.direction)
const perpendicularDir = perpendicular(this.direction)
const towardsPerpendicular = project(delta, perpendicularDir)
if (
vectorLength(towardsDir) * this.perpendicularTolerance <
vectorLength(towardsPerpendicular)
) {
return 0
}
return isPositive ? 1 : -1
})()
if (this._swiped) {
this.swipeEndCallback(sign)
} else {
this.swipelessClickCallback()
}
this._reset()
}
}
const GestureService = {
DIRECTION_LEFT,
DIRECTION_RIGHT,
DIRECTION_UP,
DIRECTION_DOWN,
swipeGesture,
beginSwipe,
updateSwipe,
SwipeAndClickGesture
}
export default GestureService
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