Bug 1059023 - Do not compose layer hidden under the opaque layer. r=mattwoodrow

widget/gonk/HwcComposer2D.cpp

@@ -397,17 +397,21 @@ HwcComposer2D::PrepareLayerList(Layer* aLayer,
     // OK!  We can compose this layer with hwc.
     int current = mList ? mList->numHwLayers : 0;
 
-    // Do not compose any layer below full-screen Opaque layer
-    // Note: It can be generalized to non-fullscreen Opaque layers.
     bool isOpaque = (opacity == 0xFF) && (aLayer->GetContentFlags() & Layer::CONTENT_OPAQUE);
     if (current && isOpaque) {
-        nsIntRect displayRect = nsIntRect(displayFrame.left, displayFrame.top,
-            displayFrame.right - displayFrame.left, displayFrame.bottom - displayFrame.top);
+        nsIntRect displayRect = HwcUtils::HwcToIntRect(displayFrame);
         if (displayRect.Contains(mScreenRect)) {
-            // In z-order, all previous layers are below
-            // the current layer. We can ignore them now.
+            // In z-order, all previous layers are below current layer
+            // Do not compose any layer below full-screen opaque layer
             mList->numHwLayers = current = 0;
             mHwcLayerMap.Clear();
+        } else {
+            nsIntRect rect = HwcUtils::HwcToIntRect(mList->hwLayers[current-1].displayFrame);
+            if (displayRect.Contains(rect)) {
+                // Do not compose layer hidden under the opaque layer
+                mHwcLayerMap.RemoveElementAt(current-1);
+                current = --mList->numHwLayers;
+            }
         }
     }
 

widget/gonk/HwcUtils.cpp

@@ -146,4 +146,10 @@ HwcUtils::CalculateClipRect(const gfx::Matrix& transform,
     return true;
 }
 
+nsIntRect
+HwcUtils::HwcToIntRect(hwc_rect_t aRect) {
+    return nsIntRect(aRect.left, aRect.top, aRect.right - aRect.left,
+                aRect.bottom - aRect.top);
+}
+
 } // namespace mozilla

widget/gonk/HwcUtils.h

@@ -118,6 +118,9 @@ static bool PrepareLayerRects(nsIntRect aVisible, const gfx::Matrix& aTransform,
                               hwc_rect_t* aSourceCrop,
                               hwc_rect_t* aVisibleRegionScreen);
 
+/* Converts hwc_rect_t to nsIntRect */
+static nsIntRect HwcToIntRect(hwc_rect_t aRect);
+
 };
 
 } // namespace mozilla