Emit hover pointer events on Android

Summary: Changelog: [Internal] - Add logic to handle hover events, experimental

Reviewed By: vincentriemer

Differential Revision: D35116525

fbshipit-source-id: e47a94b5f04c14caadc08ad37e4d80adc1affc15

ReactAndroid/src/main/java/com/facebook/react/ReactRootView.java

@@ -261,6 +261,12 @@ public class ReactRootView extends FrameLayout implements RootView, ReactRoot {
     return super.onInterceptTouchEvent(ev);
   }
 
+  @Override
+  public boolean onInterceptHoverEvent(MotionEvent ev) {
+    dispatchJSPointerEvent(ev);
+    return super.onInterceptHoverEvent(ev);
+  }
+
   @Override
   public boolean onTouchEvent(MotionEvent ev) {
     if (shouldDispatchJSTouchEvent(ev)) {
@@ -273,6 +279,12 @@ public class ReactRootView extends FrameLayout implements RootView, ReactRoot {
     return true;
   }
 
+  @Override
+  public boolean onHoverEvent(MotionEvent ev) {
+    dispatchJSPointerEvent(ev);
+    return super.onHoverEvent(ev);
+  }
+
   @Override
   protected void dispatchDraw(Canvas canvas) {
     try {

ReactAndroid/src/main/java/com/facebook/react/uimanager/JSPointerDispatcher.java

@@ -18,6 +18,8 @@ import com.facebook.react.uimanager.events.PointerEvent;
 import com.facebook.react.uimanager.events.PointerEventHelper;
 import com.facebook.react.uimanager.events.TouchEvent;
 import com.facebook.react.uimanager.events.TouchEventCoalescingKeyHelper;
+import java.util.Collections;
+import java.util.List;
 
 /**
  * JSPointerDispatcher handles dispatching pointer events to JS from RootViews. If you implement
@@ -34,6 +36,13 @@ public class JSPointerDispatcher {
   private final TouchEventCoalescingKeyHelper mTouchEventCoalescingKeyHelper =
       new TouchEventCoalescingKeyHelper();
 
+  private static final float ONMOVE_EPSILON = 1f;
+
+  // Set globally for hover interactions, referenced for coalescing hover events
+  private long mHoverInteractionKey = TouchEvent.UNSET;
+  private List<Integer> mLastHitState = Collections.emptyList();
+  private final float[] mLastEventCoordinates = new float[2];
+
   public JSPointerDispatcher(ViewGroup viewGroup) {
     mRootViewGroup = viewGroup;
   }
@@ -71,6 +80,18 @@ public class JSPointerDispatcher {
     int action = motionEvent.getActionMasked();
     int targetTag = findTargetTagAndSetCoordinates(motionEvent);
 
+    if (supportsHover) {
+      if (action == MotionEvent.ACTION_HOVER_MOVE) {
+        handleHoverEvent(motionEvent, eventDispatcher, surfaceId);
+        return;
+      }
+
+      // Ignore hover enter/exit because it's handled in `handleHoverEvent`
+      if (action == MotionEvent.ACTION_HOVER_EXIT || action == MotionEvent.ACTION_HOVER_ENTER) {
+        return;
+      }
+    }
+
     // First down pointer
     if (action == MotionEvent.ACTION_DOWN) {
 
@@ -161,6 +182,101 @@ public class JSPointerDispatcher {
         ev.getX(), ev.getY(), mRootViewGroup, mTargetCoordinates, null);
   }
 
+  // called on hover_move motion events only
+  private void handleHoverEvent(
+      MotionEvent motionEvent, EventDispatcher eventDispatcher, int surfaceId) {
+
+    int action = motionEvent.getActionMasked();
+    if (action != MotionEvent.ACTION_HOVER_MOVE) {
+      return;
+    }
+
+    float x = motionEvent.getX();
+    float y = motionEvent.getY();
+
+    boolean qualifiedMove =
+        (Math.abs(mLastEventCoordinates[0] - x) > ONMOVE_EPSILON
+            || Math.abs(mLastEventCoordinates[1] - y) > ONMOVE_EPSILON);
+
+    // Early exit
+    if (!qualifiedMove) {
+      return;
+    }
+
+    // Set the interaction key if unset, to be used as a coalescing key for hover interactions
+    if (mHoverInteractionKey < 0) {
+      mHoverInteractionKey = motionEvent.getEventTime();
+      mTouchEventCoalescingKeyHelper.addCoalescingKey(mHoverInteractionKey);
+    }
+
+    List<Integer> currHitState =
+        TouchTargetHelper.findTargetPathAndCoordinatesForTouch(
+            x, y, mRootViewGroup, mTargetCoordinates);
+
+    // If child is handling, eliminate target tags under handling child
+    if (mChildHandlingNativeGesture > 0) {
+      int index = currHitState.indexOf(mChildHandlingNativeGesture);
+      if (index > 0) {
+        currHitState.subList(0, index).clear();
+      }
+    }
+
+    int targetTag = currHitState.size() > 0 ? currHitState.get(0) : -1;
+    // If targetTag is empty, we should bail?
+    if (targetTag == -1) {
+      return;
+    }
+
+    // hitState is list ordered from inner child -> parent tag
+    // Traverse hitState back-to-front to find the first divergence with mLastHitState
+    // FIXME: this may generate incorrect events when view collapsing changes the hierarchy
+    int firstDivergentIndex = 0;
+    while (firstDivergentIndex < Math.min(currHitState.size(), mLastHitState.size())
+        && currHitState
+            .get(currHitState.size() - 1 - firstDivergentIndex)
+            .equals(mLastHitState.get(mLastHitState.size() - 1 - firstDivergentIndex))) {
+      firstDivergentIndex++;
+    }
+
+    boolean hasDiverged = firstDivergentIndex < Math.max(currHitState.size(), mLastHitState.size());
+
+    // Fire all relevant enter events
+    if (hasDiverged) {
+      // If something has changed in either enter/exit, let's start a new coalescing key
+      mTouchEventCoalescingKeyHelper.incrementCoalescingKey(mHoverInteractionKey);
+
+      List<Integer> enterTargetTags =
+          currHitState.subList(0, currHitState.size() - firstDivergentIndex);
+      if (enterTargetTags.size() > 0) {
+        for (Integer enterTargetTag : enterTargetTags) {
+          eventDispatcher.dispatchEvent(
+              PointerEvent.obtain(
+                  PointerEventHelper.POINTER_ENTER, surfaceId, enterTargetTag, motionEvent));
+        }
+      }
+
+      // Fire all relevant exit events
+      List<Integer> exitTargetTags =
+          mLastHitState.subList(0, mLastHitState.size() - firstDivergentIndex);
+      if (exitTargetTags.size() > 0) {
+        for (Integer exitTargetTag : exitTargetTags) {
+          eventDispatcher.dispatchEvent(
+              PointerEvent.obtain(
+                  PointerEventHelper.POINTER_LEAVE, surfaceId, exitTargetTag, motionEvent));
+        }
+      }
+    }
+
+    int coalescingKey = mTouchEventCoalescingKeyHelper.getCoalescingKey(mHoverInteractionKey);
+    eventDispatcher.dispatchEvent(
+        PointerEvent.obtain(
+            PointerEventHelper.POINTER_MOVE, surfaceId, targetTag, motionEvent, coalescingKey));
+
+    mLastHitState = currHitState;
+    mLastEventCoordinates[0] = x;
+    mLastEventCoordinates[1] = y;
+  }
+
   private void dispatchCancelEvent(
       int targetTag, MotionEvent motionEvent, EventDispatcher eventDispatcher) {
     // This means the gesture has already ended, via some other CANCEL or UP event. This is not

ReactAndroid/src/main/java/com/facebook/react/views/modal/ReactModalHostView.java

@@ -539,6 +539,22 @@ public class ReactModalHostView extends ViewGroup
       return true;
     }
 
+    @Override
+    public boolean onInterceptHoverEvent(MotionEvent event) {
+      if (mJSPointerDispatcher != null) {
+        mJSPointerDispatcher.handleMotionEvent(event, mEventDispatcher);
+      }
+      return super.onHoverEvent(event);
+    }
+
+    @Override
+    public boolean onHoverEvent(MotionEvent event) {
+      if (mJSPointerDispatcher != null) {
+        mJSPointerDispatcher.handleMotionEvent(event, mEventDispatcher);
+      }
+      return super.onHoverEvent(event);
+    }
+
     @Override
     public void onChildStartedNativeGesture(MotionEvent ev) {
       this.onChildStartedNativeGesture(null, ev);