Bug 1141127 - When inside a slop area around the first touchstart, prevent touchmove events from going to content. r=botond

gfx/layers/apz/src/InputBlockState.cpp

@@ -103,9 +103,7 @@ CancelableBlockState::SetContentResponse(bool aPreventDefault)
   }
   TBS_LOG("%p got content response %d with timer expired %d\n",
     this, aPreventDefault, mContentResponseTimerExpired);
-  if (!mContentResponseTimerExpired) {
+  mPreventDefault = aPreventDefault;
-    mPreventDefault = aPreventDefault;
-  }
   mContentResponded = true;
   return true;
 }
@@ -625,6 +623,7 @@ TouchBlockState::TouchBlockState(const RefPtr<AsyncPanZoomController>& aTargetAp
   , mAllowedTouchBehaviorSet(false)
   , mDuringFastFling(false)
   , mSingleTapOccurred(false)
+  , mInSlop(false)
   , mTouchCounter(aCounter)
 {
   TBS_LOG("Creating %p\n", this);
@@ -831,5 +830,33 @@ TouchBlockState::TouchActionAllowsPanningXY() const
       && (flags & AllowedTouchBehavior::VERTICAL_PAN);
 }
 
+bool
+TouchBlockState::UpdateSlopState(const MultiTouchInput& aInput)
+{
+  if (aInput.mType == MultiTouchInput::MULTITOUCH_START) {
+    // this is by definition the first event in this block. If it's the first
+    // touch, then we enter a slop state.
+    mInSlop = (aInput.mTouches.Length() == 1);
+    if (mInSlop) {
+      mSlopOrigin = aInput.mTouches[0].mScreenPoint;
+      TBS_LOG("%p entering slop with origin %s\n", this, Stringify(mSlopOrigin).c_str());
+    }
+    return false;
+  }
+  if (mInSlop) {
+    bool stayInSlop = (aInput.mType == MultiTouchInput::MULTITOUCH_MOVE) &&
+        (aInput.mTouches.Length() == 1) &&
+        ((aInput.mTouches[0].mScreenPoint - mSlopOrigin).Length() <
+            AsyncPanZoomController::GetTouchStartTolerance());
+    if (!stayInSlop) {
+      // we're out of the slop zone, and will stay out for the remainder of
+      // this block
+      TBS_LOG("%p exiting slop\n", this);
+      mInSlop = false;
+    }
+  }
+  return mInSlop;
+}
+
 } // namespace layers
 } // namespace mozilla

gfx/layers/apz/src/InputBlockState.h

@@ -430,6 +430,16 @@ public:
   bool TouchActionAllowsPanningY() const;
   bool TouchActionAllowsPanningXY() const;
 
+  /**
+   * Notifies the input block of an incoming touch event so that the block can
+   * update its internal slop state. "Slop" refers to the area around the
+   * initial touchstart where we drop touchmove events so that content doesn't
+   * see them.
+   * @return true iff the provided event is a touchmove in the slop area and
+   *         so should not be sent to content.
+   */
+  bool UpdateSlopState(const MultiTouchInput& aInput);
+
   bool HasEvents() const override;
   void DropEvents() override;
   void HandleEvents() override;
@@ -442,6 +452,8 @@ private:
   bool mAllowedTouchBehaviorSet;
   bool mDuringFastFling;
   bool mSingleTapOccurred;
+  bool mInSlop;
+  ScreenIntPoint mSlopOrigin;
   nsTArray<MultiTouchInput> mEvents;
   // A reference to the InputQueue's touch counter
   TouchCounter& mTouchCounter;

gfx/layers/apz/src/InputQueue.cpp

@@ -160,7 +160,12 @@ InputQueue::ReceiveTouchInput(const RefPtr<AsyncPanZoomController>& aTarget,
     INPQ_LOG("dropping event due to block %p being in fast motion\n", block);
     result = nsEventStatus_eConsumeNoDefault;
   } else if (target && target->ArePointerEventsConsumable(block, aEvent.AsMultiTouchInput().mTouches.Length())) {
-    result = nsEventStatus_eConsumeDoDefault;
+    if (block->UpdateSlopState(aEvent.AsMultiTouchInput())) {
+      INPQ_LOG("dropping event due to block %p being in slop\n", block);
+      result = nsEventStatus_eConsumeNoDefault;
+    } else {
+      result = nsEventStatus_eConsumeDoDefault;
+    }
   }
   if (!MaybeHandleCurrentBlock(block, aEvent)) {
     block->AddEvent(aEvent.AsMultiTouchInput());