Bug 1181703 - Allow re-entering the panning state if a second finger is tapped while panning with one finger. r=botond

--HG--
extra : commitid : GdPNUwhizt3

gfx/layers/apz/src/AsyncPanZoomController.cpp

@@ -1337,10 +1337,18 @@ nsEventStatus AsyncPanZoomController::OnTouchEnd(const MultiTouchInput& aEvent)
     // that were not big enough to trigger scrolling. Clear that out.
     mX.SetVelocity(0);
     mY.SetVelocity(0);
-    // It's possible we may be overscrolled if the user tapped during a
-    // previous overscroll pan. Make sure to snap back in this situation.
-    if (!SnapBackIfOverscrolled()) {
-      SetState(NOTHING);
+    APZC_LOG("%p still has %u touch points active\n", this,
+        CurrentTouchBlock()->GetActiveTouchCount());
+    // In cases where the user is panning, then taps the second finger without
+    // entering a pinch, we will arrive here when the second finger is lifted.
+    // However the first finger is still down so we want to remain in state
+    // TOUCHING.
+    if (CurrentTouchBlock()->GetActiveTouchCount() == 0) {
+      // It's possible we may be overscrolled if the user tapped during a
+      // previous overscroll pan. Make sure to snap back in this situation.
+      if (!SnapBackIfOverscrolled()) {
+        SetState(NOTHING);
+      }
     }
     return nsEventStatus_eIgnore;
 

gfx/layers/apz/src/InputBlockState.cpp

@@ -861,5 +861,11 @@ TouchBlockState::UpdateSlopState(const MultiTouchInput& aInput,
   return mInSlop;
 }
 
+uint32_t
+TouchBlockState::GetActiveTouchCount() const
+{
+  return mTouchCounter.GetActiveTouchCount();
+}
+
 } // namespace layers
 } // namespace mozilla

gfx/layers/apz/src/InputBlockState.h

@@ -442,6 +442,11 @@ public:
   bool UpdateSlopState(const MultiTouchInput& aInput,
                        bool aApzcCanConsumeEvents);
 
+  /**
+   * Returns the number of touch points currently active.
+   */
+  uint32_t GetActiveTouchCount() const;
+
   bool HasEvents() const override;
   void DropEvents() override;
   void HandleEvents() override;