Move TouchHistoryMath from React Repo to React Native

Summary:
This hasn't been used by React core for a while. It's unclear why it was in the first place.

We can move it back next to the Panresponder.

facebook/react#12557

Reviewed By: sophiebits

Differential Revision: D7529949

fbshipit-source-id: ef9892cfa8d2d6768da216b81befabe02795a245

Author: sebmarkbage

Libraries/Interaction/TouchHistoryMath.js

@@ -0,0 +1,151 @@
+/**
+ * Copyright (c) 2016-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+const TouchHistoryMath = {
+  /**
+   * This code is optimized and not intended to look beautiful. This allows
+   * computing of touch centroids that have moved after `touchesChangedAfter`
+   * timeStamp. You can compute the current centroid involving all touches
+   * moves after `touchesChangedAfter`, or you can compute the previous
+   * centroid of all touches that were moved after `touchesChangedAfter`.
+   *
+   * @param {TouchHistoryMath} touchHistory Standard Responder touch track
+   * data.
+   * @param {number} touchesChangedAfter timeStamp after which moved touches
+   * are considered "actively moving" - not just "active".
+   * @param {boolean} isXAxis Consider `x` dimension vs. `y` dimension.
+   * @param {boolean} ofCurrent Compute current centroid for actively moving
+   * touches vs. previous centroid of now actively moving touches.
+   * @return {number} value of centroid in specified dimension.
+   */
+  centroidDimension: function(
+    touchHistory,
+    touchesChangedAfter,
+    isXAxis,
+    ofCurrent,
+  ) {
+    const touchBank = touchHistory.touchBank;
+    let total = 0;
+    let count = 0;
+
+    const oneTouchData =
+      touchHistory.numberActiveTouches === 1
+        ? touchHistory.touchBank[touchHistory.indexOfSingleActiveTouch]
+        : null;
+
+    if (oneTouchData !== null) {
+      if (
+        oneTouchData.touchActive &&
+        oneTouchData.currentTimeStamp > touchesChangedAfter
+      ) {
+        total +=
+          ofCurrent && isXAxis
+            ? oneTouchData.currentPageX
+            : ofCurrent && !isXAxis
+              ? oneTouchData.currentPageY
+              : !ofCurrent && isXAxis
+                ? oneTouchData.previousPageX
+                : oneTouchData.previousPageY;
+        count = 1;
+      }
+    } else {
+      for (let i = 0; i < touchBank.length; i++) {
+        const touchTrack = touchBank[i];
+        if (
+          touchTrack !== null &&
+          touchTrack !== undefined &&
+          touchTrack.touchActive &&
+          touchTrack.currentTimeStamp >= touchesChangedAfter
+        ) {
+          let toAdd; // Yuck, program temporarily in invalid state.
+          if (ofCurrent && isXAxis) {
+            toAdd = touchTrack.currentPageX;
+          } else if (ofCurrent && !isXAxis) {
+            toAdd = touchTrack.currentPageY;
+          } else if (!ofCurrent && isXAxis) {
+            toAdd = touchTrack.previousPageX;
+          } else {
+            toAdd = touchTrack.previousPageY;
+          }
+          total += toAdd;
+          count++;
+        }
+      }
+    }
+    return count > 0 ? total / count : TouchHistoryMath.noCentroid;
+  },
+
+  currentCentroidXOfTouchesChangedAfter: function(
+    touchHistory,
+    touchesChangedAfter,
+  ) {
+    return TouchHistoryMath.centroidDimension(
+      touchHistory,
+      touchesChangedAfter,
+      true, // isXAxis
+      true, // ofCurrent
+    );
+  },
+
+  currentCentroidYOfTouchesChangedAfter: function(
+    touchHistory,
+    touchesChangedAfter,
+  ) {
+    return TouchHistoryMath.centroidDimension(
+      touchHistory,
+      touchesChangedAfter,
+      false, // isXAxis
+      true, // ofCurrent
+    );
+  },
+
+  previousCentroidXOfTouchesChangedAfter: function(
+    touchHistory,
+    touchesChangedAfter,
+  ) {
+    return TouchHistoryMath.centroidDimension(
+      touchHistory,
+      touchesChangedAfter,
+      true, // isXAxis
+      false, // ofCurrent
+    );
+  },
+
+  previousCentroidYOfTouchesChangedAfter: function(
+    touchHistory,
+    touchesChangedAfter,
+  ) {
+    return TouchHistoryMath.centroidDimension(
+      touchHistory,
+      touchesChangedAfter,
+      false, // isXAxis
+      false, // ofCurrent
+    );
+  },
+
+  currentCentroidX: function(touchHistory) {
+    return TouchHistoryMath.centroidDimension(
+      touchHistory,
+      0, // touchesChangedAfter
+      true, // isXAxis
+      true, // ofCurrent
+    );
+  },
+
+  currentCentroidY: function(touchHistory) {
+    return TouchHistoryMath.centroidDimension(
+      touchHistory,
+      0, // touchesChangedAfter
+      false, // isXAxis
+      true, // ofCurrent
+    );
+  },
+
+  noCentroid: -1,
+};
+
+module.exports = TouchHistoryMath;