Adjust event location when two-finger dragging in TouchExplorer

To scroll on the screen when using TalkBack, a user need to dragging two
finger pointers. If the dragging pointer are closer that a given distance
we use the location of the primary one. Otherwise, we should adjust the
event location to take the middle between the two finger pointers.

Bug: 126354276
Test: atest TouchExplorerTest
Change-Id: I9e95ccec964d7930498febdd02731b94826fbb7b

services/accessibility/java/com/android/server/accessibility/TouchExplorer.java

@@ -703,12 +703,17 @@ private void handleMotionEventStateDragging(MotionEvent event, int policyFlags)
                             final float secondPtrX = event.getX(1);
                             final float secondPtrY = event.getY(1);
 
-                            final float deltaX = firstPtrX - secondPtrX;
-                            final float deltaY = firstPtrY - secondPtrY;
+                            final int pointerIndex = event.findPointerIndex(mDraggingPointerId);
+                            final float deltaX =
+                                    (pointerIndex == 0) ? (secondPtrX - firstPtrX)
+                                            : (firstPtrX - secondPtrX);
+                            final float deltaY =
+                                    (pointerIndex == 0) ? (secondPtrY - firstPtrY)
+                                            : (firstPtrY - secondPtrY);
                             final double distance = Math.hypot(deltaX, deltaY);
 
                             if (distance > mScaledMinPointerDistanceToUseMiddleLocation) {
-                                event.setLocation(deltaX / 2, deltaY / 2);
+                                event.offsetLocation(deltaX / 2, deltaY / 2);
                             }
 
                             // If still dragging send a drag event.