362 lines
17 KiB
JavaScript
362 lines
17 KiB
JavaScript
/**
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* @providesModule PanResponder
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*/
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"use strict";
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var TouchHistoryMath = require('TouchHistoryMath');
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var currentCentroidXOfTouchesChangedAfter =
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TouchHistoryMath.currentCentroidXOfTouchesChangedAfter;
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var currentCentroidYOfTouchesChangedAfter =
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TouchHistoryMath.currentCentroidYOfTouchesChangedAfter;
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var previousCentroidXOfTouchesChangedAfter =
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TouchHistoryMath.previousCentroidXOfTouchesChangedAfter;
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var previousCentroidYOfTouchesChangedAfter =
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TouchHistoryMath.previousCentroidYOfTouchesChangedAfter;
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var currentCentroidX = TouchHistoryMath.currentCentroidX;
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var currentCentroidY = TouchHistoryMath.currentCentroidY;
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/**
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* `PanResponder` reconciles several touches into a single gesture. It makes
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* single-touch gestures resilient to extra touches, and can be used to
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* recognize simple multi-touch gestures.
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*
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* It provides a predictable wrapper of the responder handlers provided by the
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* [gesture responder system](/react-native/docs/gesture-responder-system.html).
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* For each handler, it provides a new `gestureState` object alongside the
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* normal event.
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*
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* A `gestureState` object has the following:
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*
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* - `stateID` - ID of the gestureState- persisted as long as there at least
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* one touch on screen
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* - `moveX` - the latest screen coordinates of the recently-moved touch
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* - `moveY` - the latest screen coordinates of the recently-moved touch
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* - `x0` - the screen coordinates of the responder grant
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* - `y0` - the screen coordinates of the responder grant
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* - `dx` - accumulated distance of the gesture since the touch started
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* - `dy` - accumulated distance of the gesture since the touch started
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* - `vx` - current velocity of the gesture
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* - `vy` - current velocity of the gesture
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* - `numberActiveTouches` - Number of touches currently on screeen
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*
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* ### Basic Usage
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*
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* ```
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* componentWillMount: function() {
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* this._panResponder = PanResponder.create({
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* // Ask to be the responder:
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* onStartShouldSetPanResponder: (evt, gestureState) => true,
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* onStartShouldSetPanResponderCapture: (evt, gestureState) => true,
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* onMoveShouldSetPanResponder: (evt, gestureState) => true,
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* onMoveShouldSetPanResponderCapture: (evt, gestureState) => true,
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*
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* onPanResponderGrant: (evt, gestureState) => {
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* // The guesture has started. Show visual feedback so the user knows
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* // what is happening!
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*
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* // gestureState.{x,y}0 will be set to zero now
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* },
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* onPanResponderMove: (evt, gestureState) => {
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* // The most recent move distance is gestureState.move{X,Y}
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*
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* // The accumulated gesture distance since becoming responder is
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* // gestureState.d{x,y}
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* },
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* onPanResponderTerminationRequest: (evt, gestureState) => true,
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* onPanResponderRelease: (evt, gestureState) => {
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* // The user has released all touches while this view is the
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* // responder. This typically means a gesture has succeeded
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* },
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* onPanResponderTerminate: (evt, gestureState) => {
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* // Another component has become the responder, so this gesture
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* // should be cancelled
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* },
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* onShouldBlockNativeResponder: (evt, gestureState) => {
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* // Returns whether this component should block native components from becoming the JS
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* // responder. Returns true by default. Is currently only supported on android.
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* return true;
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* },
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* });
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* },
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*
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* render: function() {
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* return (
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* <View {...this._panResponder.panHandlers} />
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* );
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* },
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*
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* ```
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*
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* ### Working Example
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*
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* To see it in action, try the
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* [PanResponder example in UIExplorer](https://github.com/facebook/react-native/blob/master/Examples/UIExplorer/PanResponderExample.js)
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*/
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var PanResponder = {
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/**
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*
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* A graphical explanation of the touch data flow:
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*
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* +----------------------------+ +--------------------------------+
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* | ResponderTouchHistoryStore | |TouchHistoryMath |
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* +----------------------------+ +----------+---------------------+
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* |Global store of touchHistory| |Allocation-less math util |
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* |including activeness, start | |on touch history (centroids |
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* |position, prev/cur position.| |and multitouch movement etc) |
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* | | | |
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* +----^-----------------------+ +----^---------------------------+
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* | |
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* | (records relevant history |
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* | of touches relevant for |
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* | implementing higher level |
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* | gestures) |
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* | |
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* +----+-----------------------+ +----|---------------------------+
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* | ResponderEventPlugin | | | Your App/Component |
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* +----------------------------+ +----|---------------------------+
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* |Negotiates which view gets | Low level | | High level |
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* |onResponderMove events. | events w/ | +-+-------+ events w/ |
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* |Also records history into | touchHistory| | Pan | multitouch + |
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* |ResponderTouchHistoryStore. +---------------->Responder+-----> accumulative|
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* +----------------------------+ attached to | | | distance and |
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* each event | +---------+ velocity. |
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* | |
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* | |
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* +--------------------------------+
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*
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*
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*
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* Gesture that calculates cumulative movement over time in a way that just
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* "does the right thing" for multiple touches. The "right thing" is very
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* nuanced. When moving two touches in opposite directions, the cumulative
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* distance is zero in each dimension. When two touches move in parallel five
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* pixels in the same direction, the cumulative distance is five, not ten. If
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* two touches start, one moves five in a direction, then stops and the other
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* touch moves fives in the same direction, the cumulative distance is ten.
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*
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* This logic requires a kind of processing of time "clusters" of touch events
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* so that two touch moves that essentially occur in parallel but move every
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* other frame respectively, are considered part of the same movement.
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*
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* Explanation of some of the non-obvious fields:
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*
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* - moveX/moveY: If no move event has been observed, then `(moveX, moveY)` is
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* invalid. If a move event has been observed, `(moveX, moveY)` is the
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* centroid of the most recently moved "cluster" of active touches.
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* (Currently all move have the same timeStamp, but later we should add some
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* threshold for what is considered to be "moving"). If a palm is
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* accidentally counted as a touch, but a finger is moving greatly, the palm
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* will move slightly, but we only want to count the single moving touch.
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* - x0/y0: Centroid location (non-cumulative) at the time of becoming
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* responder.
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* - dx/dy: Cumulative touch distance - not the same thing as sum of each touch
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* distance. Accounts for touch moves that are clustered together in time,
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* moving the same direction. Only valid when currently responder (otherwise,
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* it only represents the drag distance below the threshold).
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* - vx/vy: Velocity.
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*/
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_initializeGestureState: function(gestureState) {
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gestureState.moveX = 0;
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gestureState.moveY = 0;
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gestureState.x0 = 0;
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gestureState.y0 = 0;
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gestureState.dx = 0;
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gestureState.dy = 0;
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gestureState.vx = 0;
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gestureState.vy = 0;
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gestureState.numberActiveTouches = 0;
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// All `gestureState` accounts for timeStamps up until:
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gestureState._accountsForMovesUpTo = 0;
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},
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/**
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* This is nuanced and is necessary. It is incorrect to continuously take all
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* active *and* recently moved touches, find the centroid, and track how that
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* result changes over time. Instead, we must take all recently moved
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* touches, and calculate how the centroid has changed just for those
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* recently moved touches, and append that change to an accumulator. This is
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* to (at least) handle the case where the user is moving three fingers, and
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* then one of the fingers stops but the other two continue.
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*
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* This is very different than taking all of the recently moved touches and
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* storing their centroid as `dx/dy`. For correctness, we must *accumulate
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* changes* in the centroid of recently moved touches.
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*
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* There is also some nuance with how we handle multiple moved touches in a
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* single event. With the way `ReactNativeEventEmitter` dispatches touches as
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* individual events, multiple touches generate two 'move' events, each of
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* them triggering `onResponderMove`. But with the way `PanResponder` works,
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* all of the gesture inference is performed on the first dispatch, since it
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* looks at all of the touches (even the ones for which there hasn't been a
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* native dispatch yet). Therefore, `PanResponder` does not call
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* `onResponderMove` passed the first dispatch. This diverges from the
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* typical responder callback pattern (without using `PanResponder`), but
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* avoids more dispatches than necessary.
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*/
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_updateGestureStateOnMove: function(gestureState, touchHistory) {
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gestureState.numberActiveTouches = touchHistory.numberActiveTouches;
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gestureState.moveX = currentCentroidXOfTouchesChangedAfter(
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touchHistory,
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gestureState._accountsForMovesUpTo
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);
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gestureState.moveY = currentCentroidYOfTouchesChangedAfter(
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touchHistory,
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gestureState._accountsForMovesUpTo
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);
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var movedAfter = gestureState._accountsForMovesUpTo;
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var prevX = previousCentroidXOfTouchesChangedAfter(touchHistory, movedAfter);
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var x = currentCentroidXOfTouchesChangedAfter(touchHistory, movedAfter);
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var prevY = previousCentroidYOfTouchesChangedAfter(touchHistory, movedAfter);
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var y = currentCentroidYOfTouchesChangedAfter(touchHistory, movedAfter);
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var nextDX = gestureState.dx + (x - prevX);
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var nextDY = gestureState.dy + (y - prevY);
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// TODO: This must be filtered intelligently.
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var dt =
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(touchHistory.mostRecentTimeStamp - gestureState._accountsForMovesUpTo);
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gestureState.vx = (nextDX - gestureState.dx) / dt;
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gestureState.vy = (nextDY - gestureState.dy) / dt;
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gestureState.dx = nextDX;
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gestureState.dy = nextDY;
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gestureState._accountsForMovesUpTo = touchHistory.mostRecentTimeStamp;
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},
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/**
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* @param {object} config Enhanced versions of all of the responder callbacks
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* that provide not only the typical `ResponderSyntheticEvent`, but also the
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* `PanResponder` gesture state. Simply replace the word `Responder` with
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* `PanResponder` in each of the typical `onResponder*` callbacks. For
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* example, the `config` object would look like:
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*
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* - `onMoveShouldSetPanResponder: (e, gestureState) => {...}`
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* - `onMoveShouldSetPanResponderCapture: (e, gestureState) => {...}`
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* - `onStartShouldSetPanResponder: (e, gestureState) => {...}`
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* - `onStartShouldSetPanResponderCapture: (e, gestureState) => {...}`
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* - `onPanResponderReject: (e, gestureState) => {...}`
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* - `onPanResponderGrant: (e, gestureState) => {...}`
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* - `onPanResponderStart: (e, gestureState) => {...}`
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* - `onPanResponderEnd: (e, gestureState) => {...}`
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* - `onPanResponderRelease: (e, gestureState) => {...}`
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* - `onPanResponderMove: (e, gestureState) => {...}`
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* - `onPanResponderTerminate: (e, gestureState) => {...}`
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* - `onPanResponderTerminationRequest: (e, gestureState) => {...}`
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* - `onShouldBlockNativeResponder: (e, gestureState) => {...}`
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*
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* In general, for events that have capture equivalents, we update the
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* gestureState once in the capture phase and can use it in the bubble phase
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* as well.
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*
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* Be careful with onStartShould* callbacks. They only reflect updated
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* `gestureState` for start/end events that bubble/capture to the Node.
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* Once the node is the responder, you can rely on every start/end event
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* being processed by the gesture and `gestureState` being updated
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* accordingly. (numberActiveTouches) may not be totally accurate unless you
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* are the responder.
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*/
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create: function(config) {
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var gestureState = {
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// Useful for debugging
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stateID: Math.random(),
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};
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PanResponder._initializeGestureState(gestureState);
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var panHandlers = {
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onStartShouldSetResponder: function(e) {
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return config.onStartShouldSetPanResponder === undefined ? false :
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config.onStartShouldSetPanResponder(e, gestureState);
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},
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onMoveShouldSetResponder: function(e) {
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return config.onMoveShouldSetPanResponder === undefined ? false :
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config.onMoveShouldSetPanResponder(e, gestureState);
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},
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onStartShouldSetResponderCapture: function(e) {
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// TODO: Actually, we should reinitialize the state any time
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// touches.length increases from 0 active to > 0 active.
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if (e.nativeEvent.touches.length === 1) {
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PanResponder._initializeGestureState(gestureState);
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}
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gestureState.numberActiveTouches = e.touchHistory.numberActiveTouches;
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return config.onStartShouldSetPanResponderCapture !== undefined ?
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config.onStartShouldSetPanResponderCapture(e, gestureState) : false;
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},
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onMoveShouldSetResponderCapture: function(e) {
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var touchHistory = e.touchHistory;
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// Responder system incorrectly dispatches should* to current responder
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// Filter out any touch moves past the first one - we would have
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// already processed multi-touch geometry during the first event.
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if (gestureState._accountsForMovesUpTo === touchHistory.mostRecentTimeStamp) {
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return false;
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}
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PanResponder._updateGestureStateOnMove(gestureState, touchHistory);
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return config.onMoveShouldSetPanResponderCapture ?
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config.onMoveShouldSetPanResponderCapture(e, gestureState) : false;
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},
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onResponderGrant: function(e) {
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gestureState.x0 = currentCentroidX(e.touchHistory);
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gestureState.y0 = currentCentroidY(e.touchHistory);
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gestureState.dx = 0;
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gestureState.dy = 0;
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config.onPanResponderGrant && config.onPanResponderGrant(e, gestureState);
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// TODO: t7467124 investigate if this can be removed
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return config.onShouldBlockNativeResponder === undefined ? true :
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config.onShouldBlockNativeResponder();
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},
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onResponderReject: function(e) {
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config.onPanResponderReject && config.onPanResponderReject(e, gestureState);
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},
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onResponderRelease: function(e) {
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config.onPanResponderRelease && config.onPanResponderRelease(e, gestureState);
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PanResponder._initializeGestureState(gestureState);
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},
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onResponderStart: function(e) {
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var touchHistory = e.touchHistory;
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gestureState.numberActiveTouches = touchHistory.numberActiveTouches;
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config.onPanResponderStart && config.onPanResponderStart(e, gestureState);
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},
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onResponderMove: function(e) {
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var touchHistory = e.touchHistory;
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// Guard against the dispatch of two touch moves when there are two
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// simultaneously changed touches.
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if (gestureState._accountsForMovesUpTo === touchHistory.mostRecentTimeStamp) {
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return;
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}
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// Filter out any touch moves past the first one - we would have
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// already processed multi-touch geometry during the first event.
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PanResponder._updateGestureStateOnMove(gestureState, touchHistory);
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config.onPanResponderMove && config.onPanResponderMove(e, gestureState);
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},
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onResponderEnd: function(e) {
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var touchHistory = e.touchHistory;
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gestureState.numberActiveTouches = touchHistory.numberActiveTouches;
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config.onPanResponderEnd && config.onPanResponderEnd(e, gestureState);
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},
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onResponderTerminate: function(e) {
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config.onPanResponderTerminate &&
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config.onPanResponderTerminate(e, gestureState);
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PanResponder._initializeGestureState(gestureState);
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},
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onResponderTerminationRequest: function(e) {
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return config.onPanResponderTerminationRequest === undefined ? true :
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config.onPanResponderTerminationRequest(e, gestureState);
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},
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};
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return {panHandlers: panHandlers};
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},
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};
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module.exports = PanResponder;
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