Bug 775463: Implement tolerance in double tap detection r=cjones

gfx/layers/ipc/AsyncPanZoomController.cpp

@@ -24,6 +24,8 @@ using namespace mozilla::css;
 namespace mozilla {
 namespace layers {
 
+const float AsyncPanZoomController::TOUCH_START_TOLERANCE = 1.0f/16.0f;
+
 static const float EPSILON = 0.0001;
 
 /**
@@ -275,8 +277,8 @@ nsEventStatus AsyncPanZoomController::OnTouchMove(const MultiTouchInput& aEvent)
       return nsEventStatus_eIgnore;
 
     case TOUCHING: {
-      float panThreshold = 1.0f/2.0f * mDPI;
       UpdateWithTouchAtDevicePoint(aEvent);
+      float panThreshold = TOUCH_START_TOLERANCE * mDPI;
       if (PanDistance() < panThreshold) {
         return nsEventStatus_eIgnore;
       }
@@ -723,6 +725,10 @@ void AsyncPanZoomController::SetDPI(int aDPI) {
   mDPI = aDPI;
 }
 
+int AsyncPanZoomController::GetDPI() {
+  return mDPI;
+}
+
 void AsyncPanZoomController::ScheduleComposite() {
   if (mCompositorParent) {
     mCompositorParent->ScheduleRenderOnCompositorThread();

gfx/layers/ipc/AsyncPanZoomController.h

@@ -57,6 +57,14 @@ public:
     USE_GESTURE_DETECTOR
   };
 
+  /**
+   * Constant describing the tolerance in distance we use, multiplied by the
+   * device DPI, before we start panning the screen. This is to prevent us from
+   * accidentally processing taps as touch moves, and from very short/accidental
+   * touches moving the screen.
+   */
+  static const float TOUCH_START_TOLERANCE;
+
   AsyncPanZoomController(GeckoContentController* aController,
                          GestureBehavior aGestures = DEFAULT_GESTURES);
   ~AsyncPanZoomController();
@@ -179,6 +187,12 @@ public:
    */
   void SetDPI(int aDPI);
 
+  /**
+   * Gets the DPI of the device for use outside the panning and zooming logic.
+   * It defaults to 72 if not set using SetDPI() at any point.
+   */
+  int GetDPI();
+
 protected:
   /**
    * Helper method for touches beginning. Sets everything up for panning and any

gfx/layers/ipc/GestureEventListener.cpp

@@ -63,6 +63,7 @@ nsEventStatus GestureEventListener::HandleInputEvent(const InputData& aEvent)
     size_t length = mTouches.Length();
     if (length == 1) {
       mTapStartTime = event.mTime;
+      mTouchStartPosition = event.mTouches[0].mScreenPoint;
       if (mState == GESTURE_NONE) {
         mState = GESTURE_WAITING_SINGLE_TAP;
       }
@@ -74,9 +75,14 @@ nsEventStatus GestureEventListener::HandleInputEvent(const InputData& aEvent)
     break;
   }
   case MultiTouchInput::MULTITOUCH_MOVE: {
-    // If we move at all, just bail out of the tap. We need to change this so
-    // that there's some tolerance in the future.
-    HandleTapCancel(event);
+    // If we move too much, bail out of the tap.
+    nsIntPoint touch = (nsIntPoint&)event.mTouches[0].mScreenPoint;
+    if (mTouches.Length() == 1 &&
+        NS_hypot(mTouchStartPosition.x - touch.x, mTouchStartPosition.y - touch.y) >
+          mAsyncPanZoomController->GetDPI() * AsyncPanZoomController::TOUCH_START_TOLERANCE)
+    {
+      HandleTapCancel(event);
+    }
 
     bool foundAlreadyExistingTouch = false;
     for (size_t i = 0; i < mTouches.Length(); i++) {

gfx/layers/ipc/GestureEventListener.h

@@ -1,7 +1,4 @@
-/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set sw=4 ts=8 et tw=80 : */
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */ /* vim: set sw=4 ts=8 et tw=80 : */ /* This Source Code Form is subject to the terms of the Mozilla Public * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #ifndef mozilla_layers_GestureEventListener_h
@@ -170,6 +167,13 @@ protected:
    * we can cancel it if a double tap actually comes in.
    */
   CancelableTask *mDoubleTapTimeoutTask;
+
+  /**
+   * Position of the last touch starting. This is only valid during an attempt
+   * to determine if a touch is a tap. This means that it is used in both the
+   * "GESTURE_WAITING_SINGLE_TAP" and "GESTURE_WAITING_DOUBLE_TAP" states.
+   */
+  nsIntPoint mTouchStartPosition;
 };
 
 }