Minimize tearing for fixed element in single surface mode

bug:5683630

Change-Id: I43f738f2649a79b4ad7865ed27375c07195fa9b9

3 files changed, 21 insertions, 6 deletions

diff --git a/Source/WebCore/platform/graphics/android/layers/BaseLayerAndroid.cpp b/Source/WebCore/platform/graphics/android/layers/BaseLayerAndroid.cpp
index f03a140..511261e 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 18f65c7..bca1614 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 cd26356..fbd0aa5 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();