Minimize tearing for fixed element in single surface mode

bug:5683630

Change-Id: I43f738f2649a79b4ad7865ed27375c07195fa9b9

6 files changed, 28 insertions, 12 deletions

diff --git a/Source/WebCore/platform/graphics/android/GLWebViewState.h b/Source/WebCore/platform/graphics/android/GLWebViewState.h
index b643405d6..c2094ffe6 100644
--- a/Source/WebCore/platform/graphics/android/GLWebViewState.h
+++ b/Source/WebCore/platform/graphics/android/GLWebViewState.h
@@ -196,6 +196,8 @@ public:
 
     float scale() { return m_scale; }
 
+    // Currently, we only use 3 modes : kAllTextures, kClippedTextures and
+    // kSingleSurfaceRendering ( for every mode > kClippedTextures ) .
     enum LayersRenderingMode {
         kAllTextures              = 0, // all layers are drawn with textures fully covering them
         kClippedTextures          = 1, // all layers are drawn, but their textures will be clipped
@@ -206,6 +208,7 @@ public:
     };
 
     LayersRenderingMode layersRenderingMode() { return m_layersRenderingMode; }
+    bool isSingleSurfaceRenderingMode() { return m_layersRenderingMode == kSingleSurfaceRendering; }
     void scrollLayer(int layerId, int x, int y);
 
 private:
diff --git a/Source/WebCore/platform/graphics/android/layers/BaseLayerAndroid.cpp b/Source/WebCore/platform/graphics/android/layers/BaseLayerAndroid.cpp
index f03a1404b..511261ebf 100644
--- a/Source/WebCore/platform/graphics/android/layers/BaseLayerAndroid.cpp
+++ b/Source/WebCore/platform/graphics/android/layers/BaseLayerAndroid.cpp
@@ -86,8 +86,20 @@ void BaseLayerAndroid::updatePositionsRecursive(const SkRect& visibleContentRect
     FloatRect clip(0, 0, getWidth(), getHeight());
 
     bool forcePositionCalculation = !m_positionsCalculated;
-    float scale = state() ? state()->scale() : 1.0f;
-    updateGLPositionsAndScale(ident, clip, 1, scale, forcePositionCalculation);
+    float scale = 1.0f;
+    // To minimize tearing in single surface mode, don't update the fixed element
+    // when scrolling. The fixed element will move incorrectly when scrolling,
+    // but its position will be corrected after scrolling.
+    bool disableFixedElemUpdate = false;
+    GLWebViewState* webViewState = state();
+    if (webViewState) {
+        scale = webViewState->scale();
+        disableFixedElemUpdate = webViewState->isScrolling()
+                                 && webViewState->isSingleSurfaceRenderingMode();
+    }
+    updateGLPositionsAndScale(ident, clip, 1, scale, forcePositionCalculation,
+                              disableFixedElemUpdate);
+
     m_positionsCalculated = true;
 }
 
diff --git a/Source/WebCore/platform/graphics/android/layers/LayerAndroid.cpp b/Source/WebCore/platform/graphics/android/layers/LayerAndroid.cpp
index 18f65c7c3..bca1614ee 100644
--- a/Source/WebCore/platform/graphics/android/layers/LayerAndroid.cpp
+++ b/Source/WebCore/platform/graphics/android/layers/LayerAndroid.cpp
@@ -461,13 +461,14 @@ void LayerAndroid::updateLocalGLPositionsAndScale(const TransformationMatrix& pa
 
 void LayerAndroid::updateGLPositionsAndScale(const TransformationMatrix& parentMatrix,
                                              const FloatRect& clipping, float opacity,
-                                             float scale, bool forceCalculation)
+                                             float scale, bool forceCalculation,
+                                             bool disableFixedElemUpdate)
 {
     // constantly recalculate the draw transform of layers that may require it (and their children)
     forceCalculation |= isPositionFixed()
         || contentIsScrollable()
         || (m_animations.size() != 0);
-
+    forceCalculation &= !(disableFixedElemUpdate && isPositionFixed());
     if (forceCalculation)
         updateLocalGLPositionsAndScale(parentMatrix, clipping, opacity, scale);
 
@@ -498,7 +499,9 @@ void LayerAndroid::updateGLPositionsAndScale(const TransformationMatrix& parentM
         childMatrix.translate(-getSize().width() * 0.5f, -getSize().height() * 0.5f);
     }
     for (int i = 0; i < countChildren(); i++)
-        this->getChild(i)->updateGLPositionsAndScale(childMatrix, drawClip(), opacity, scale, forceCalculation);
+        this->getChild(i)->updateGLPositionsAndScale(childMatrix, drawClip(),
+                                                     opacity, scale, forceCalculation,
+                                                     disableFixedElemUpdate);
 }
 
 bool LayerAndroid::visible() {
diff --git a/Source/WebCore/platform/graphics/android/layers/LayerAndroid.h b/Source/WebCore/platform/graphics/android/layers/LayerAndroid.h
index cd2635656..fbd0aa5c4 100644
--- a/Source/WebCore/platform/graphics/android/layers/LayerAndroid.h
+++ b/Source/WebCore/platform/graphics/android/layers/LayerAndroid.h
@@ -156,7 +156,7 @@ public:
 
     void updateGLPositionsAndScale(const TransformationMatrix& parentMatrix,
                                    const FloatRect& clip, float opacity, float scale,
-                                   bool forceCalculations);
+                                   bool forceCalculations, bool disableFixedElemUpdate);
     void setDrawOpacity(float opacity) { m_drawOpacity = opacity; }
     float drawOpacity() { return m_drawOpacity; }
     bool visible();
diff --git a/Source/WebCore/platform/graphics/android/rendering/Surface.cpp b/Source/WebCore/platform/graphics/android/rendering/Surface.cpp
index 94b7b6e47..176e86e5a 100644
--- a/Source/WebCore/platform/graphics/android/rendering/Surface.cpp
+++ b/Source/WebCore/platform/graphics/android/rendering/Surface.cpp
@@ -370,7 +370,7 @@ bool Surface::paint(SkCanvas* canvas)
         // In single surface mode, draw layer content onto the base layer
         if (isBase()
             && getFirstLayer()->countChildren()
-            && getFirstLayer()->state()->layersRenderingMode() > GLWebViewState::kClippedTextures) {
+            && getFirstLayer()->state()->isSingleSurfaceRenderingMode()) {
             for (int i = 0; i < getFirstLayer()->countChildren(); i++)
                 getFirstLayer()->getChild(i)->drawCanvas(canvas, true, Layer::FlattenedLayers);
         }
diff --git a/Source/WebCore/platform/graphics/android/rendering/SurfaceCollection.cpp b/Source/WebCore/platform/graphics/android/rendering/SurfaceCollection.cpp
index 83b81a16c..e09486904 100644
--- a/Source/WebCore/platform/graphics/android/rendering/SurfaceCollection.cpp
+++ b/Source/WebCore/platform/graphics/android/rendering/SurfaceCollection.cpp
@@ -86,8 +86,7 @@ void SurfaceCollection::prepareGL(const SkRect& visibleContentRect, bool tryToFa
 {
     TRACE_METHOD();
     updateLayerPositions(visibleContentRect);
-    bool layerTilesDisabled = m_compositedRoot->state()->layersRenderingMode()
-        > GLWebViewState::kClippedTextures;
+    bool layerTilesDisabled = m_compositedRoot->state()->isSingleSurfaceRenderingMode();
     if (!layerTilesDisabled) {
         for (unsigned int i = 0; tryToFastBlit && i < m_surfaces.size(); i++)
             tryToFastBlit &= m_surfaces[i]->canUpdateWithBlit();
@@ -114,8 +113,7 @@ bool SurfaceCollection::drawGL(const SkRect& visibleContentRect)
 
     bool needsRedraw = false;
     updateLayerPositions(visibleContentRect);
-    bool layerTilesDisabled = m_compositedRoot->state()->layersRenderingMode()
-        > GLWebViewState::kClippedTextures;
+    bool layerTilesDisabled = m_compositedRoot->state()->isSingleSurfaceRenderingMode();
 
     // create a duplicate vector of surfaces, sorted by z value
     Vector <Surface*> surfaces;
@@ -151,7 +149,7 @@ void SurfaceCollection::addFrameworkInvals()
 bool SurfaceCollection::isReady()
 {
     // Override layer readiness check for single surface mode
-    if (m_compositedRoot->state()->layersRenderingMode() > GLWebViewState::kClippedTextures) {
+    if (m_compositedRoot->state()->isSingleSurfaceRenderingMode()) {
         // TODO: single surface mode should be properly double buffered
         return true;
     }