Make ResponderEventPlugin work with DOM renderer (not in working state)

src/renderers/shared/event/eventPlugins/PanResponder.js

@@ -0,0 +1,361 @@
+/**
+ * @providesModule PanResponder
+ */
+
+"use strict";
+
+var TouchHistoryMath = require('TouchHistoryMath');
+
+var currentCentroidXOfTouchesChangedAfter =
+  TouchHistoryMath.currentCentroidXOfTouchesChangedAfter;
+var currentCentroidYOfTouchesChangedAfter =
+  TouchHistoryMath.currentCentroidYOfTouchesChangedAfter;
+var previousCentroidXOfTouchesChangedAfter =
+  TouchHistoryMath.previousCentroidXOfTouchesChangedAfter;
+var previousCentroidYOfTouchesChangedAfter =
+  TouchHistoryMath.previousCentroidYOfTouchesChangedAfter;
+var currentCentroidX = TouchHistoryMath.currentCentroidX;
+var currentCentroidY = TouchHistoryMath.currentCentroidY;
+
+/**
+ * `PanResponder` reconciles several touches into a single gesture. It makes
+ * single-touch gestures resilient to extra touches, and can be used to
+ * recognize simple multi-touch gestures.
+ *
+ * It provides a predictable wrapper of the responder handlers provided by the
+ * [gesture responder system](/react-native/docs/gesture-responder-system.html).
+ * For each handler, it provides a new `gestureState` object alongside the
+ * normal event.
+ *
+ * A `gestureState` object has the following:
+ *
+ *  - `stateID` - ID of the gestureState- persisted as long as there at least
+ *     one touch on screen
+ *  - `moveX` - the latest screen coordinates of the recently-moved touch
+ *  - `moveY` - the latest screen coordinates of the recently-moved touch
+ *  - `x0` - the screen coordinates of the responder grant
+ *  - `y0` - the screen coordinates of the responder grant
+ *  - `dx` - accumulated distance of the gesture since the touch started
+ *  - `dy` - accumulated distance of the gesture since the touch started
+ *  - `vx` - current velocity of the gesture
+ *  - `vy` - current velocity of the gesture
+ *  - `numberActiveTouches` - Number of touches currently on screeen
+ *
+ * ### Basic Usage
+ *
+ * ```
+ *   componentWillMount: function() {
+ *     this._panGesture = PanResponder.create({
+ *       // Ask to be the responder:
+ *       onStartShouldSetPanResponder: (evt, gestureState) => true,
+ *       onStartShouldSetPanResponderCapture: (evt, gestureState) => true,
+ *       onMoveShouldSetPanResponder: (evt, gestureState) => true,
+ *       onMoveShouldSetPanResponderCapture: (evt, gestureState) => true,
+ *
+ *       onPanResponderGrant: (evt, gestureState) => {
+ *         // The guesture has started. Show visual feedback so the user knows
+ *         // what is happening!
+ *
+ *         // gestureState.{x,y}0 will be set to zero now
+ *       },
+ *       onPanResponderMove: (evt, gestureState) => {
+ *         // The most recent move distance is gestureState.move{X,Y}
+ *
+ *         // The accumulated gesture distance since becoming responder is
+ *         // gestureState.d{x,y}
+ *       },
+ *       onPanResponderTerminationRequest: (evt, gestureState) => true,
+ *       onPanResponderRelease: (evt, gestureState) => {
+ *         // The user has released all touches while this view is the
+ *         // responder. This typically means a gesture has succeeded
+ *       },
+ *       onPanResponderTerminate: (evt, gestureState) => {
+ *         // Another component has become the responder, so this gesture
+ *         // should be cancelled
+ *       },
+ *       onShouldBlockNativeResponder: (evt, gestureState) => {
+ *         // Returns whether this component should block native components from becoming the JS
+ *         // responder. Returns true by default. Is currently only supported on android.
+ *         return true;
+ *       },
+ *     });
+ *   },
+ *
+ *   render: function() {
+ *     return (
+ *       <View {...this._panResponder.panHandlers} />
+ *     );
+ *   },
+ *
+ * ```
+ *
+ * ### Working Example
+ *
+ * To see it in action, try the
+ * [PanResponder example in UIExplorer](https://github.com/facebook/react-native/blob/master/Examples/UIExplorer/ResponderExample.js)
+ */
+
+var PanResponder = {
+
+  /**
+   *
+   * A graphical explanation of the touch data flow:
+   *
+   * +----------------------------+             +--------------------------------+
+   * | ResponderTouchHistoryStore |             |TouchHistoryMath                |
+   * +----------------------------+             +----------+---------------------+
+   * |Global store of touchHistory|             |Allocation-less math util       |
+   * |including activeness, start |             |on touch history (centroids     |
+   * |position, prev/cur position.|             |and multitouch movement etc)    |
+   * |                            |             |                                |
+   * +----^-----------------------+             +----^---------------------------+
+   *      |                                          |
+   *      | (records relevant history                |
+   *      |  of touches relevant for                 |
+   *      |  implementing higher level               |
+   *      |  gestures)                               |
+   *      |                                          |
+   * +----+-----------------------+             +----|---------------------------+
+   * | ResponderEventPlugin       |             |    |   Your App/Component      |
+   * +----------------------------+             +----|---------------------------+
+   * |Negotiates which view gets  | Low level   |    |             High level    |
+   * |onResponderMove events.     | events w/   |  +-+-------+     events w/     |
+   * |Also records history into   | touchHistory|  |   Pan   |     multitouch +  |
+   * |ResponderTouchHistoryStore. +---------------->Responder+-----> accumulative|
+   * +----------------------------+ attached to |  |         |     distance and  |
+   *                                 each event |  +---------+     velocity.     |
+   *                                            |                                |
+   *                                            |                                |
+   *                                            +--------------------------------+
+   *
+   *
+   *
+   * Gesture that calculates cumulative movement over time in a way that just
+   * "does the right thing" for multiple touches. The "right thing" is very
+   * nuanced. When moving two touches in opposite directions, the cumulative
+   * distance is zero in each dimension. When two touches move in parallel five
+   * pixels in the same direction, the cumulative distance is five, not ten. If
+   * two touches start, one moves five in a direction, then stops and the other
+   * touch moves fives in the same direction, the cumulative distance is ten.
+   *
+   * This logic requires a kind of processing of time "clusters" of touch events
+   * so that two touch moves that essentially occur in parallel but move every
+   * other frame respectively, are considered part of the same movement.
+   *
+   * Explanation of some of the non-obvious fields:
+   *
+   * - moveX/moveY: If no move event has been observed, then `(moveX, moveY)` is
+   *   invalid. If a move event has been observed, `(moveX, moveY)` is the
+   *   centroid of the most recently moved "cluster" of active touches.
+   *   (Currently all move have the same timeStamp, but later we should add some
+   *   threshold for what is considered to be "moving"). If a palm is
+   *   accidentally counted as a touch, but a finger is moving greatly, the palm
+   *   will move slightly, but we only want to count the single moving touch.
+   * - x0/y0: Centroid location (non-cumulative) at the time of becoming
+   *   responder.
+   * - dx/dy: Cumulative touch distance - not the same thing as sum of each touch
+   *   distance. Accounts for touch moves that are clustered together in time,
+   *   moving the same direction. Only valid when currently responder (otherwise,
+   *   it only represents the drag distance below the threshold).
+   * - vx/vy: Velocity.
+   */
+
+  _initializeGestureState: function(gestureState) {
+    gestureState.moveX = 0;
+    gestureState.moveY = 0;
+    gestureState.x0 = 0;
+    gestureState.y0 = 0;
+    gestureState.dx = 0;
+    gestureState.dy = 0;
+    gestureState.vx = 0;
+    gestureState.vy = 0;
+    gestureState.numberActiveTouches = 0;
+    // All `gestureState` accounts for timeStamps up until:
+    gestureState._accountsForMovesUpTo = 0;
+  },
+
+  /**
+   * This is nuanced and is necessary. It is incorrect to continuously take all
+   * active *and* recently moved touches, find the centroid, and track how that
+   * result changes over time. Instead, we must take all recently moved
+   * touches, and calculate how the centroid has changed just for those
+   * recently moved touches, and append that change to an accumulator. This is
+   * to (at least) handle the case where the user is moving three fingers, and
+   * then one of the fingers stops but the other two continue.
+   *
+   * This is very different than taking all of the recently moved touches and
+   * storing their centroid as `dx/dy`. For correctness, we must *accumulate
+   * changes* in the centroid of recently moved touches.
+   *
+   * There is also some nuance with how we handle multiple moved touches in a
+   * single event. With the way `ReactNativeEventEmitter` dispatches touches as
+   * individual events, multiple touches generate two 'move' events, each of
+   * them triggering `onResponderMove`. But with the way `PanResponder` works,
+   * all of the gesture inference is performed on the first dispatch, since it
+   * looks at all of the touches (even the ones for which there hasn't been a
+   * native dispatch yet). Therefore, `PanResponder` does not call
+   * `onResponderMove` passed the first dispatch. This diverges from the
+   * typical responder callback pattern (without using `PanResponder`), but
+   * avoids more dispatches than necessary.
+   */
+  _updateGestureStateOnMove: function(gestureState, touchHistory) {
+    gestureState.numberActiveTouches = touchHistory.numberActiveTouches;
+    gestureState.moveX = currentCentroidXOfTouchesChangedAfter(
+      touchHistory,
+      gestureState._accountsForMovesUpTo
+    );
+    gestureState.moveY = currentCentroidYOfTouchesChangedAfter(
+      touchHistory,
+      gestureState._accountsForMovesUpTo
+    );
+    var movedAfter = gestureState._accountsForMovesUpTo;
+    var prevX = previousCentroidXOfTouchesChangedAfter(touchHistory, movedAfter);
+    var x = currentCentroidXOfTouchesChangedAfter(touchHistory, movedAfter);
+    var prevY = previousCentroidYOfTouchesChangedAfter(touchHistory, movedAfter);
+    var y = currentCentroidYOfTouchesChangedAfter(touchHistory, movedAfter);
+    var nextDX = gestureState.dx + (x - prevX);
+    var nextDY = gestureState.dy + (y - prevY);
+
+    // TODO: This must be filtered intelligently.
+    var dt =
+      (touchHistory.mostRecentTimeStamp - gestureState._accountsForMovesUpTo);
+    gestureState.vx = (nextDX - gestureState.dx) / dt;
+    gestureState.vy = (nextDY - gestureState.dy) / dt;
+
+    gestureState.dx = nextDX;
+    gestureState.dy = nextDY;
+    gestureState._accountsForMovesUpTo = touchHistory.mostRecentTimeStamp;
+  },
+
+  /**
+   * @param {object} config Enhanced versions of all of the responder callbacks
+   * that provide not only the typical `ResponderSyntheticEvent`, but also the
+   * `PanResponder` gesture state.  Simply replace the word `Responder` with
+   * `PanResponder` in each of the typical `onResponder*` callbacks. For
+   * example, the `config` object would look like:
+   *
+   *  - `onMoveShouldSetPanResponder: (e, gestureState) => {...}`
+   *  - `onMoveShouldSetPanResponderCapture: (e, gestureState) => {...}`
+   *  - `onStartShouldSetPanResponder: (e, gestureState) => {...}`
+   *  - `onStartShouldSetPanResponderCapture: (e, gestureState) => {...}`
+   *  - `onPanResponderReject: (e, gestureState) => {...}`
+   *  - `onPanResponderGrant: (e, gestureState) => {...}`
+   *  - `onPanResponderStart: (e, gestureState) => {...}`
+   *  - `onPanResponderEnd: (e, gestureState) => {...}`
+   *  - `onPanResponderRelease: (e, gestureState) => {...}`
+   *  - `onPanResponderMove: (e, gestureState) => {...}`
+   *  - `onPanResponderTerminate: (e, gestureState) => {...}`
+   *  - `onPanResponderTerminationRequest: (e, gestureState) => {...}`
+   *  - 'onShouldBlockNativeResponder: (e, gestureState) => {...}'
+   *
+   *  In general, for events that have capture equivalents, we update the
+   *  gestureState once in the capture phase and can use it in the bubble phase
+   *  as well.
+   *
+   *  Be careful with onStartShould* callbacks. They only reflect updated
+   *  `gestureState` for start/end events that bubble/capture to the Node.
+   *  Once the node is the responder, you can rely on every start/end event
+   *  being processed by the gesture and `gestureState` being updated
+   *  accordingly. (numberActiveTouches) may not be totally accurate unless you
+   *  are the responder.
+   */
+  create: function(config) {
+    var gestureState = {
+      // Useful for debugging
+      stateID: Math.random(),
+    };
+    PanResponder._initializeGestureState(gestureState);
+    var panHandlers = {
+      onStartShouldSetResponder: function(e) {
+        return config.onStartShouldSetPanResponder === undefined ? false :
+          config.onStartShouldSetPanResponder(e, gestureState);
+      },
+      onMoveShouldSetResponder: function(e) {
+        return config.onMoveShouldSetPanResponder === undefined ? false :
+          config.onMoveShouldSetPanResponder(e, gestureState);
+      },
+      onStartShouldSetResponderCapture: function(e) {
+        // TODO: Actually, we should reinitialize the state any time
+        // touches.length increases from 0 active to > 0 active.
+        if (e.nativeEvent.touches.length === 1) {
+          PanResponder._initializeGestureState(gestureState);
+        }
+        gestureState.numberActiveTouches = e.touchHistory.numberActiveTouches;
+        return config.onStartShouldSetPanResponderCapture !== undefined ?
+          config.onStartShouldSetPanResponderCapture(e, gestureState) : false;
+      },
+
+      onMoveShouldSetResponderCapture: function(e) {
+        var touchHistory = e.touchHistory;
+        // Responder system incorrectly dispatches should* to current responder
+        // Filter out any touch moves past the first one - we would have
+        // already processed multi-touch geometry during the first event.
+        if (gestureState._accountsForMovesUpTo === touchHistory.mostRecentTimeStamp) {
+          return false;
+        }
+        PanResponder._updateGestureStateOnMove(gestureState, touchHistory);
+        return config.onMoveShouldSetResponderCapture ?
+          config.onMoveShouldSetPanResponderCapture(e, gestureState) : false;
+      },
+
+      onResponderGrant: function(e) {
+        gestureState.x0 = currentCentroidX(e.touchHistory);
+        gestureState.y0 = currentCentroidY(e.touchHistory);
+        gestureState.dx = 0;
+        gestureState.dy = 0;
+        config.onPanResponderGrant && config.onPanResponderGrant(e, gestureState);
+        // TODO: t7467124 investigate if this can be removed
+        return config.onShouldBlockNativeResponder === undefined ? true :
+          config.onShouldBlockNativeResponder();
+      },
+
+      onResponderReject: function(e) {
+        config.onPanResponderReject && config.onPanResponderReject(e, gestureState);
+      },
+
+      onResponderRelease: function(e) {
+        config.onPanResponderRelease && config.onPanResponderRelease(e, gestureState);
+        PanResponder._initializeGestureState(gestureState);
+      },
+
+      onResponderStart: function(e) {
+        var touchHistory = e.touchHistory;
+        gestureState.numberActiveTouches = touchHistory.numberActiveTouches;
+        config.onPanResponderStart && config.onPanResponderStart(e, gestureState);
+      },
+
+      onResponderMove: function(e) {
+        var touchHistory = e.touchHistory;
+        // Guard against the dispatch of two touch moves when there are two
+        // simultaneously changed touches.
+        if (gestureState._accountsForMovesUpTo === touchHistory.mostRecentTimeStamp) {
+          return;
+        }
+        // Filter out any touch moves past the first one - we would have
+        // already processed multi-touch geometry during the first event.
+        PanResponder._updateGestureStateOnMove(gestureState, touchHistory);
+        config.onPanResponderMove && config.onPanResponderMove(e, gestureState);
+      },
+
+      onResponderEnd: function(e) {
+        var touchHistory = e.touchHistory;
+        gestureState.numberActiveTouches = touchHistory.numberActiveTouches;
+        config.onPanResponderEnd && config.onPanResponderEnd(e, gestureState);
+      },
+
+      onResponderTerminate: function(e) {
+        config.onPanResponderTerminate &&
+          config.onPanResponderTerminate(e, gestureState);
+        PanResponder._initializeGestureState(gestureState);
+      },
+
+      onResponderTerminationRequest: function(e) {
+        return config.onPanResponderTerminationRequest === undefined ? true :
+          config.onPanResponderTerminationRequest(e, gestureState);
+      },
+    };
+    return {panHandlers: panHandlers};
+  },
+};
+
+module.exports = PanResponder;