Bug 721100 - After panning, tap area is offset at wrong place. r=pcwalton

When rendering with an offset for MultiTileLayer, the tile origin was moved
to compensate, but this lead to there being a mismatch between Gecko's
displayport origin and the one recorded on the Java side.

Instead of altering the origin, allow setting a render offset on MultiTileLayer
instead, so the origin remains correct.

mobile/android/base/gfx/GeckoSoftwareLayerClient.java

@@ -292,9 +292,7 @@ public class GeckoSoftwareLayerClient extends LayerClient implements GeckoEventL
 
         LayerController controller = getLayerController();
         PointF displayportOrigin = mGeckoViewport.getDisplayportOrigin();
-        Point tileOrigin = PointUtils.round(displayportOrigin);
-        tileOrigin.offset(-mRenderOffset.x, -mRenderOffset.y);
-        mTileLayer.setOrigin(tileOrigin);
+        mTileLayer.setOrigin(PointUtils.round(displayportOrigin));
         mTileLayer.setResolution(mGeckoViewport.getZoomFactor());
 
         if (onlyUpdatePageSize) {
@@ -323,6 +321,7 @@ public class GeckoSoftwareLayerClient extends LayerClient implements GeckoEventL
                     Rect rect = new Rect(x, y, x + width, y + height);
                     rect.offset(mRenderOffset.x, mRenderOffset.y);
                     ((MultiTileLayer)mTileLayer).invalidate(rect);
+                    ((MultiTileLayer)mTileLayer).setRenderOffset(mRenderOffset);
                 }
             } finally {
                 endTransaction(mTileLayer);

mobile/android/base/gfx/MultiTileLayer.java

@@ -67,6 +67,7 @@ public class MultiTileLayer extends Layer {
     private IntSize mBufferSize;
     private Region mDirtyRegion;
     private Region mValidRegion;
+    private Point mRenderOffset;
     private final LinkedList<SubTile> mTiles;
     private final HashMap<Long, SubTile> mPositionHash;
 
@@ -78,6 +79,7 @@ public class MultiTileLayer extends Layer {
         mBufferSize = new IntSize(0, 0);
         mDirtyRegion = new Region();
         mValidRegion = new Region();
+        mRenderOffset = new Point();
         mTiles = new LinkedList<SubTile>();
         mPositionHash = new HashMap<Long, SubTile>();
     }
@@ -160,6 +162,12 @@ public class MultiTileLayer extends Layer {
         return new Long((((long)point.x) << 32) | point.y);
     }
 
+    private Point getOffsetOrigin() {
+        Point origin = new Point(getOrigin());
+        origin.offset(-mRenderOffset.x, -mRenderOffset.y);
+        return origin;
+    }
+
     /**
      * Performs the necessary functions to update the specified properties of
      * a sub-tile.
@@ -172,7 +180,7 @@ public class MultiTileLayer extends Layer {
                 // buffer. This is done as SingleTileLayer always updates the
                 // entire width, regardless of the dirty-rect's width, and so
                 // can override existing data.
-                Point origin = getOrigin();
+                Point origin = getOffsetOrigin();
                 Rect validRect = tile.getValidTextureArea();
                 validRect.offset(tileOrigin.x - origin.x, tileOrigin.y - origin.y);
                 Region validRegion = new Region(validRect);
@@ -226,9 +234,9 @@ public class MultiTileLayer extends Layer {
         }
 
         // Check that we're capable of updating from this origin.
-        Point origin = getOrigin();
+        Point origin = getOffsetOrigin();
         if ((origin.x % mTileSize.width) != 0 || (origin.y % mTileSize.height) != 0) {
-            Log.e(LOGTAG, "MultiTileLayer doesn't support non tile-aligned origins! (" +
+            Log.e(LOGTAG, "MultiTileLayer doesn't support non tile-aligned buffers! (" +
                   origin.x + ", " + origin.y + ")");
             return true;
         }
@@ -395,6 +403,10 @@ public class MultiTileLayer extends Layer {
         }
     }
 
+    public void setRenderOffset(Point offset) {
+        mRenderOffset.set(offset.x, offset.y);
+    }
+
     /**
      * Invalidates all sub-tiles. This should be called if the source backing
      * this layer has changed. This method is only valid inside a transaction.