75 lines
2.2 KiB
JavaScript
75 lines
2.2 KiB
JavaScript
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const DIRECTION_LEFT = [-1, 0]
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const DIRECTION_RIGHT = [1, 0]
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const DIRECTION_UP = [0, -1]
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const DIRECTION_DOWN = [0, 1]
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const deltaCoord = (oldCoord, newCoord) => [newCoord[0] - oldCoord[0], newCoord[1] - oldCoord[1]]
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const touchEventCoord = e => ([e.touches[0].screenX, e.touches[0].screenY])
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const vectorLength = v => Math.sqrt(v[0] * v[0] + v[1] * v[1])
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const perpendicular = v => [v[1], -v[0]]
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const dotProduct = (v1, v2) => v1[0] * v2[0] + v1[1] * v2[1]
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const project = (v1, v2) => {
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const scalar = (dotProduct(v1, v2) / dotProduct(v2, v2))
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return [scalar * v2[0], scalar * v2[1]]
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}
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// direction: either use the constants above or an arbitrary 2d vector.
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// threshold: how many Px to move from touch origin before checking if the
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// callback should be called.
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// divergentTolerance: a scalar for much of divergent direction we tolerate when
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// above threshold. for example, with 1.0 we only call the callback if
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// divergent component of delta is < 1.0 * direction component of delta.
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const swipeGesture = (direction, onSwipe, threshold = 30, perpendicularTolerance = 1.0) => {
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return {
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direction,
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onSwipe,
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threshold,
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perpendicularTolerance,
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_startPos: [0, 0],
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_swiping: false
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}
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}
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const beginSwipe = (event, gesture) => {
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gesture._startPos = touchEventCoord(event)
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gesture._swiping = true
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}
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const updateSwipe = (event, gesture) => {
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if (!gesture._swiping) return
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// movement too small
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const delta = deltaCoord(gesture._startPos, touchEventCoord(event))
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if (vectorLength(delta) < gesture.threshold) return
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// movement is opposite from direction
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if (dotProduct(delta, gesture.direction) < 0) return
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// movement perpendicular to direction is too much
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const towardsDir = project(delta, gesture.direction)
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const perpendicularDir = perpendicular(gesture.direction)
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const towardsPerpendicular = project(delta, perpendicularDir)
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if (
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vectorLength(towardsDir) * gesture.perpendicularTolerance <
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vectorLength(towardsPerpendicular)
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) return
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gesture.onSwipe()
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gesture._swiping = false
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}
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const GestureService = {
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DIRECTION_LEFT,
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DIRECTION_RIGHT,
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DIRECTION_UP,
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DIRECTION_DOWN,
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swipeGesture,
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beginSwipe,
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updateSwipe
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}
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export default GestureService
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