Sort surface drawing order by Z value

bug:6275189
Change-Id: Ib9cabadb77777244c6ef707c32ce53db3ebf3181

2 files changed, 19 insertions, 2 deletions

diff --git a/Source/WebCore/platform/graphics/android/rendering/Surface.h b/Source/WebCore/platform/graphics/android/rendering/Surface.h
index 27c997e..756fabd 100644
--- a/Source/WebCore/platform/graphics/android/rendering/Surface.h
+++ b/Source/WebCore/platform/graphics/android/rendering/Surface.h
@@ -56,7 +56,7 @@ public:
 
     void computeTexturesAmount(TexturesResult* result);
 
-    LayerAndroid* getFirstLayer() { return m_layers[0]; }
+    LayerAndroid* getFirstLayer() const { return m_layers[0]; }
     bool needsTexture() { return m_needsTexture; }
     bool hasText() { return m_hasText; }
     bool isBase();
diff --git a/Source/WebCore/platform/graphics/android/rendering/SurfaceCollection.cpp b/Source/WebCore/platform/graphics/android/rendering/SurfaceCollection.cpp
index 0bbaf91..cd5ceef 100644
--- a/Source/WebCore/platform/graphics/android/rendering/SurfaceCollection.cpp
+++ b/Source/WebCore/platform/graphics/android/rendering/SurfaceCollection.cpp
@@ -95,6 +95,15 @@ void SurfaceCollection::prepareGL(const SkRect& visibleRect)
         m_surfaces[i]->prepareGL(layerTilesDisabled);
 }
 
+static inline bool compareSurfaceZ(const Surface* a, const Surface* b)
+{
+    const LayerAndroid* la = a->getFirstLayer();
+    const LayerAndroid* lb = b->getFirstLayer();
+
+    // swap drawing order if zValue suggests it AND the layers are in the same stacking context
+    return (la->zValue() > lb->zValue()) && (la->getParent() == lb->getParent());
+}
+
 bool SurfaceCollection::drawGL(const SkRect& visibleRect)
 {
 #ifdef DEBUG_COUNT
@@ -105,8 +114,16 @@ bool SurfaceCollection::drawGL(const SkRect& visibleRect)
     updateLayerPositions(visibleRect);
     bool layerTilesDisabled = m_compositedRoot->state()->layersRenderingMode()
         > GLWebViewState::kClippedTextures;
+
+    // create a duplicate vector of surfaces, sorted by z value
+    Vector <Surface*> surfaces;
+    for (unsigned int i = 0; i < m_surfaces.size(); i++)
+        surfaces.append(m_surfaces[i]);
+    std::stable_sort(surfaces.begin()+1, surfaces.end(), compareSurfaceZ);
+
+    // draw the sorted vector
     for (unsigned int i = 0; i < m_surfaces.size(); i++)
-        needsRedraw |= m_surfaces[i]->drawGL(layerTilesDisabled);
+        needsRedraw |= surfaces[i]->drawGL(layerTilesDisabled);
 
     return needsRedraw;
 }