Bug 704575 - Union dirty rects instead of painting all of them. r=kats

In bug #703821 we disabled the squashing of multiple draw events, as it caused
corruption due to the dirty rects being ignored. Re-enable it, and union the
dirty rectangles to avoid this corruption.

widget/src/android/nsAppShell.cpp

@@ -214,7 +214,7 @@ nsAppShell::ProcessNextNativeEvent(bool mayWait)
     {
         MutexAutoLock lock(mCondLock);
 
-        curEvent = GetNextEvent();
+        curEvent = PopNextEvent();
         if (!curEvent && mayWait) {
             // hmm, should we really hardcode this 10s?
 #if defined(DEBUG_ANDROID_EVENTS)
@@ -229,7 +229,7 @@ nsAppShell::ProcessNextNativeEvent(bool mayWait)
             mQueueCond.Wait();
 #endif
 
-            curEvent = GetNextEvent();
+            curEvent = PopNextEvent();
         }
     }
 
@@ -244,10 +244,7 @@ nsAppShell::ProcessNextNativeEvent(bool mayWait)
         int curType = curEvent->Type();
         int nextType = nextEvent->Type();
 
-        // Do not skip draw events if the Java compositor is in use, since the Java compositor
-        // updates only the rect that changed - thus we will lose updates.
-#ifndef MOZ_JAVA_COMPOSITOR
-        while (nextType == AndroidGeckoEvent::DRAW &&
+        while (nextType == AndroidGeckoEvent::DRAW && mLastDrawEvent &&
                mNumDraws > 1)
         {
             // skip this draw, since there's a later one already in the queue.. this will let us
@@ -256,7 +253,27 @@ nsAppShell::ProcessNextNativeEvent(bool mayWait)
             // and end up with just
             //   MOVE DRAW
             // when we process all the events.
-            RemoveNextEvent();
+
+            // Combine the next draw event's rect with the last one in the queue
+            const nsIntRect& nextRect = nextEvent->Rect();
+            const nsIntRect& lastRect = mLastDrawEvent->Rect();
+            int combinedArea = (lastRect.width * lastRect.height) +
+                               (nextRect.width * nextRect.height);
+
+            nsIntRect combinedRect = lastRect.Union(nextRect);
+            mLastDrawEvent->Init(AndroidGeckoEvent::DRAW, combinedRect);
+
+            // XXX We may want to consider using regions instead of rectangles.
+            //     Print an error if we're upload a lot more than we would
+            //     if we handled this as two separate events.
+            int boundsArea = combinedRect.width * combinedRect.height;
+            if (boundsArea > combinedArea * 8)
+                ALOG("nsAppShell::ProcessNextNativeEvent: "
+                     "Area of bounds greatly exceeds combined area: %d > %d",
+                     boundsArea, combinedArea);
+
+            // Remove the next draw event
+            PopNextEvent();
             delete nextEvent;
 
 #if defined(DEBUG_ANDROID_EVENTS)
@@ -266,7 +283,6 @@ nsAppShell::ProcessNextNativeEvent(bool mayWait)
             nextEvent = PeekNextEvent();
             nextType = nextEvent->Type();
         }
-#endif
 
         // If the next type of event isn't the same as the current type,
         // we don't coalesce.
@@ -285,8 +301,7 @@ nsAppShell::ProcessNextNativeEvent(bool mayWait)
         ALOG("# Removing % 2d event", curType);
 #endif
 
-        RemoveNextEvent();
-        curEvent = nextEvent;
+        curEvent = PopNextEvent();
         nextEvent = PeekNextEvent();
     }
 
@@ -438,7 +453,7 @@ nsAppShell::ResendLastResizeEvent(nsWindow* aDest) {
 }
 
 AndroidGeckoEvent*
-nsAppShell::GetNextEvent()
+nsAppShell::PopNextEvent()
 {
     AndroidGeckoEvent *ae = nsnull;
     MutexAutoLock lock(mQueueLock);
@@ -446,7 +461,8 @@ nsAppShell::GetNextEvent()
         ae = mEventQueue[0];
         mEventQueue.RemoveElementAt(0);
         if (ae->Type() == AndroidGeckoEvent::DRAW) {
-            mNumDraws--;
+            if (--mNumDraws == 0)
+                mLastDrawEvent = nsnull;
         }
     }
 
@@ -488,25 +504,12 @@ nsAppShell::PostEvent(AndroidGeckoEvent *ae)
 
         if (ae->Type() == AndroidGeckoEvent::DRAW) {
             mNumDraws++;
+            mLastDrawEvent = ae;
         }
     }
     NotifyNativeEvent();
 }
 
-void
-nsAppShell::RemoveNextEvent()
-{
-    AndroidGeckoEvent *ae = nsnull;
-    MutexAutoLock lock(mQueueLock);
-    if (mEventQueue.Length()) {
-        ae = mEventQueue[0];
-        mEventQueue.RemoveElementAt(0);
-        if (ae->Type() == AndroidGeckoEvent::DRAW) {
-            mNumDraws--;
-        }
-    }
-}
-
 void
 nsAppShell::OnResume()
 {

widget/src/android/nsAppShell.h

@@ -76,7 +76,6 @@ public:
     virtual bool ProcessNextNativeEvent(bool mayWait);
 
     void PostEvent(mozilla::AndroidGeckoEvent *event);
-    void RemoveNextEvent();
     void OnResume();
 
     nsresult AddObserver(const nsAString &aObserverKey, nsIObserver *aObserver);
@@ -93,10 +92,11 @@ protected:
     Mutex mCondLock;
     CondVar mQueueCond;
     int mNumDraws;
+    mozilla::AndroidGeckoEvent *mLastDrawEvent;
     nsTArray<mozilla::AndroidGeckoEvent *> mEventQueue;
     nsInterfaceHashtable<nsStringHashKey, nsIObserver> mObserversHash;
 
-    mozilla::AndroidGeckoEvent *GetNextEvent();
+    mozilla::AndroidGeckoEvent *PopNextEvent();
     mozilla::AndroidGeckoEvent *PeekNextEvent();
 };