Bug 1140578 - Prevent resampling moves across non-move touch events. r=mchang

widget/gonk/GeckoTouchDispatcher.cpp

@@ -64,6 +64,7 @@ GeckoTouchDispatcher::GetInstance()
 GeckoTouchDispatcher::GeckoTouchDispatcher()
   : mTouchQueueLock("GeckoTouchDispatcher::mTouchQueueLock")
   , mHavePendingTouchMoves(false)
+  , mInflightNonMoveEvents(0)
   , mTouchEventsFiltered(false)
 {
   // Since GeckoTouchDispatcher is initialized when input is initialized
@@ -112,6 +113,16 @@ GeckoTouchDispatcher::NotifyTouch(MultiTouchInput& aTouch, TimeStamp aEventTime)
 
   if (aTouch.mType == MultiTouchInput::MULTITOUCH_MOVE) {
     MutexAutoLock lock(mTouchQueueLock);
+    if (mInflightNonMoveEvents > 0) {
+      // If we have any pending non-move events, we shouldn't resample the
+      // move events because we might end up dispatching events out of order.
+      // Instead, fall back to a non-resampling in-order dispatch until we're
+      // done processing the non-move events.
+      layers::APZThreadUtils::RunOnControllerThread(NewRunnableMethod(
+        this, &GeckoTouchDispatcher::DispatchTouchEvent, aTouch));
+      return;
+    }
+
     mTouchMoveEvents.push_back(aTouch);
     mHavePendingTouchMoves = true;
     if (mResamplingEnabled) {
@@ -121,8 +132,32 @@ GeckoTouchDispatcher::NotifyTouch(MultiTouchInput& aTouch, TimeStamp aEventTime)
     layers::APZThreadUtils::RunOnControllerThread(NewRunnableMethod(
       this, &GeckoTouchDispatcher::DispatchTouchMoveEvents, TimeStamp::Now()));
   } else {
+    if (mResamplingEnabled) {
+      MutexAutoLock lock(mTouchQueueLock);
+      mInflightNonMoveEvents++;
+    }
     layers::APZThreadUtils::RunOnControllerThread(NewRunnableMethod(
-      this, &GeckoTouchDispatcher::DispatchTouchEvent, aTouch));
+      this, &GeckoTouchDispatcher::DispatchTouchNonMoveEvent, aTouch));
+  }
+}
+
+void
+GeckoTouchDispatcher::DispatchTouchNonMoveEvent(MultiTouchInput aInput)
+{
+  layers::APZThreadUtils::AssertOnControllerThread();
+
+  if (mResamplingEnabled) {
+    // Flush pending touch move events, if there are any
+    // (DispatchTouchMoveEvents will check the mHavePendingTouchMoves flag and
+    // bail out if there's nothing to be done).
+    NotifyVsync(TimeStamp::Now());
+  }
+  DispatchTouchEvent(aInput);
+
+  if (mResamplingEnabled) {
+    MutexAutoLock lock(mTouchQueueLock);
+    mInflightNonMoveEvents--;
+    MOZ_ASSERT(mInflightNonMoveEvents >= 0);
   }
 }
 

widget/gonk/GeckoTouchDispatcher.h

@@ -49,6 +49,7 @@ public:
   static GeckoTouchDispatcher* GetInstance();
   void NotifyTouch(MultiTouchInput& aTouch, TimeStamp aEventTime);
   void DispatchTouchEvent(MultiTouchInput aMultiTouch);
+  void DispatchTouchNonMoveEvent(MultiTouchInput aInput);
   void DispatchTouchMoveEvents(TimeStamp aVsyncTime);
   void NotifyVsync(TimeStamp aVsyncTimestamp);
   void SetCompositorVsyncObserver(layers::CompositorVsyncObserver* aObserver);
@@ -65,6 +66,7 @@ private:
   Mutex mTouchQueueLock;
   std::vector<MultiTouchInput> mTouchMoveEvents;
   bool mHavePendingTouchMoves;
+  int mInflightNonMoveEvents;
   // end stuff protected by mTouchQueueLock
 
   bool mResamplingEnabled;