Prepare tiles in reverse draw order

bug:5335634

By preparing tiles in the reverse of draw order, tiles on top are given textures
first and less likely to be missing.

Change-Id: Idafde3e0789e24459bba2db150081969810a0021

3 files changed, 28 insertions, 4 deletions

diff --git a/Source/WebCore/platform/graphics/android/BaseLayerAndroid.cpp b/Source/WebCore/platform/graphics/android/BaseLayerAndroid.cpp
index 1fa69f8..1d22cf9 100644
--- a/Source/WebCore/platform/graphics/android/BaseLayerAndroid.cpp
+++ b/Source/WebCore/platform/graphics/android/BaseLayerAndroid.cpp
@@ -281,6 +281,7 @@ bool BaseLayerAndroid::drawGL(double currentTime, LayerAndroid* compositedRoot,
         // Clean up GL textures for video layer.
         TilesManager::instance()->videoLayerManager()->deleteUnusedTextures();
 
+        compositedRoot->prepare(m_glWebViewState);
         if (compositedRoot->drawGL(m_glWebViewState, matrix))
             needsRedraw = true;
         else if (!animsRunning)
diff --git a/Source/WebCore/platform/graphics/android/LayerAndroid.cpp b/Source/WebCore/platform/graphics/android/LayerAndroid.cpp
index 48dcaaa..17e466f 100644
--- a/Source/WebCore/platform/graphics/android/LayerAndroid.cpp
+++ b/Source/WebCore/platform/graphics/android/LayerAndroid.cpp
@@ -793,6 +793,26 @@ void LayerAndroid::clearDirtyRegion()
     m_dirtyRegion.setEmpty();
 }
 
+void LayerAndroid::prepare(GLWebViewState* glWebViewState)
+{
+    int count = this->countChildren();
+    if (count > 0) {
+        Vector <LayerAndroid*> sublayers;
+        for (int i = 0; i < count; i++)
+            sublayers.append(this->getChild(i));
+
+        // now we sort for the transparency
+        std::stable_sort(sublayers.begin(), sublayers.end(), compareLayerZ);
+
+        // iterate in reverse so top layers get textures first
+        for (int i = count-1; i >= 0; i--)
+            sublayers[i]->prepare(glWebViewState);
+    }
+
+    if (m_texture)
+        m_texture->prepare(glWebViewState);
+}
+
 bool LayerAndroid::drawGL(GLWebViewState* glWebViewState, SkMatrix& matrix)
 {
     TilesManager::instance()->shader()->clip(m_clippingRect);
@@ -801,10 +821,8 @@ bool LayerAndroid::drawGL(GLWebViewState* glWebViewState, SkMatrix& matrix)
 
     bool askPaint = false;
 
-    if (m_texture) {
-        m_texture->prepare(glWebViewState);
+    if (m_texture)
         askPaint |= m_texture->draw();
-    }
 
     // When the layer is dirty, the UI thread should be notified to redraw.
     askPaint |= drawChildrenGL(glWebViewState, matrix);
@@ -817,7 +835,6 @@ bool LayerAndroid::drawGL(GLWebViewState* glWebViewState, SkMatrix& matrix)
     return askPaint;
 }
 
-
 bool LayerAndroid::drawChildrenGL(GLWebViewState* glWebViewState, SkMatrix& matrix)
 {
     bool askPaint = false;
diff --git a/Source/WebCore/platform/graphics/android/LayerAndroid.h b/Source/WebCore/platform/graphics/android/LayerAndroid.h
index 7192aaf..6aca993 100644
--- a/Source/WebCore/platform/graphics/android/LayerAndroid.h
+++ b/Source/WebCore/platform/graphics/android/LayerAndroid.h
@@ -121,8 +121,14 @@ public:
     void showLayer(int indent);
 
     float getScale() { return m_scale; }
+
+    // draw layer and its children via Z, pre-order traversal
     virtual bool drawGL(GLWebViewState*, SkMatrix&);
     bool drawChildrenGL(GLWebViewState*, SkMatrix&);
+
+    // prepare layer and its children via reverse-Z, post-order traversal
+    void prepare(GLWebViewState*);
+
     void updateGLPositionsAndScale(const TransformationMatrix& parentMatrix,
                                    const FloatRect& clip, float opacity, float scale);
     void setDrawOpacity(float opacity) { m_drawOpacity = opacity; }