Separate prefetching TileGrid from front/back

Can now draw all available tiles while preparing new zoom level

bug:5690291
Change-Id: Ic08acc59e052d6b05d282329eed2cc526cb8f2f3

2 files changed, 29 insertions, 16 deletions

diff --git a/Source/WebCore/platform/graphics/android/rendering/SurfaceBacking.cpp b/Source/WebCore/platform/graphics/android/rendering/SurfaceBacking.cpp
index 7c8f570..b8d751c 100644
--- a/Source/WebCore/platform/graphics/android/rendering/SurfaceBacking.cpp
+++ b/Source/WebCore/platform/graphics/android/rendering/SurfaceBacking.cpp
@@ -42,6 +42,7 @@ SurfaceBacking::SurfaceBacking(bool isBaseSurface)
 {
     m_frontTexture = new TileGrid(isBaseSurface);
     m_backTexture = new TileGrid(isBaseSurface);
+    m_lowResTexture = new TileGrid(isBaseSurface);
     m_scale = -1;
     m_futureScale = -1;
     m_zooming = false;
@@ -51,6 +52,7 @@ SurfaceBacking::~SurfaceBacking()
 {
     delete m_frontTexture;
     delete m_backTexture;
+    delete m_lowResTexture;
 }
 
 void SurfaceBacking::prepareGL(GLWebViewState* state, bool allowZoom,
@@ -70,6 +72,9 @@ void SurfaceBacking::prepareGL(GLWebViewState* state, bool allowZoom,
         m_futureScale = scale;
         m_zoomUpdateTime = WTF::currentTime() + SurfaceBacking::s_zoomUpdateDelay;
         m_zooming = true;
+
+        // release back texture's TileTextures, so they can be reused immediately
+        m_backTexture->discardTextures();
     }
 
     bool useExpandPrefetch = aggressiveRendering;
@@ -77,39 +82,43 @@ void SurfaceBacking::prepareGL(GLWebViewState* state, bool allowZoom,
           this, scale, m_scale, m_futureScale, m_zooming,
           m_frontTexture, m_backTexture);
 
-    if (!m_zooming) {
-        m_frontTexture->prepareGL(state, m_scale,
-                                  prepareArea, unclippedArea, painter, false, useExpandPrefetch);
-        if (aggressiveRendering) {
-            // prepare the back tiled texture to render content in low res
-            float lowResPrefetchScale = m_scale * LOW_RES_PREFETCH_SCALE_MODIFIER;
-            m_backTexture->prepareGL(state, lowResPrefetchScale,
-                                     prepareArea, unclippedArea, painter, true, useExpandPrefetch);
-            m_backTexture->swapTiles();
-        }
-    } else if (m_zoomUpdateTime < WTF::currentTime()) {
+    if (m_zooming && (m_zoomUpdateTime < WTF::currentTime())) {
         m_backTexture->prepareGL(state, m_futureScale,
-                                 prepareArea, unclippedArea, painter, false, useExpandPrefetch);
+                                 prepareArea, unclippedArea, painter, false, false);
         if (m_backTexture->isReady()) {
             // zooming completed, swap the textures and new front tiles
             swapTileGrids();
 
             m_frontTexture->swapTiles();
             m_backTexture->discardTextures();
+            m_lowResTexture->discardTextures();
 
             m_scale = m_futureScale;
             m_zooming = false;
         }
     }
+
+    if (!m_zooming) {
+        m_frontTexture->prepareGL(state, m_scale,
+                                  prepareArea, unclippedArea, painter, false, useExpandPrefetch);
+        if (aggressiveRendering) {
+            // prepare low res content
+            float lowResPrefetchScale = m_scale * LOW_RES_PREFETCH_SCALE_MODIFIER;
+            m_lowResTexture->prepareGL(state, lowResPrefetchScale,
+                                       prepareArea, unclippedArea, painter,
+                                       true, useExpandPrefetch);
+            m_lowResTexture->swapTiles();
+        }
+    }
 }
 
 void SurfaceBacking::drawGL(const IntRect& visibleArea, float opacity,
                             const TransformationMatrix* transform,
                             bool aggressiveRendering, const Color* background)
 {
-    // draw low res prefetch page, if needed
-    if (aggressiveRendering && !m_zooming && m_frontTexture->isMissingContent())
-        m_backTexture->drawGL(visibleArea, opacity, transform);
+    // draw low res prefetch page if zooming or front texture missing content
+    if (aggressiveRendering && isMissingContent())
+        m_lowResTexture->drawGL(visibleArea, opacity, transform);
 
     m_frontTexture->drawGL(visibleArea, opacity, transform, background);
 }
@@ -118,12 +127,14 @@ void SurfaceBacking::markAsDirty(const SkRegion& dirtyArea)
 {
     m_backTexture->markAsDirty(dirtyArea);
     m_frontTexture->markAsDirty(dirtyArea);
+    m_lowResTexture->markAsDirty(dirtyArea);
 }
 
 void SurfaceBacking::swapTiles()
 {
     m_backTexture->swapTiles();
     m_frontTexture->swapTiles();
+    m_lowResTexture->swapTiles();
 }
 
 void SurfaceBacking::computeTexturesAmount(TexturesResult* result, LayerAndroid* layer)
diff --git a/Source/WebCore/platform/graphics/android/rendering/SurfaceBacking.h b/Source/WebCore/platform/graphics/android/rendering/SurfaceBacking.h
index ec01dbe..bbac9b5 100644
--- a/Source/WebCore/platform/graphics/android/rendering/SurfaceBacking.h
+++ b/Source/WebCore/platform/graphics/android/rendering/SurfaceBacking.h
@@ -61,7 +61,7 @@ public:
 
     bool isMissingContent()
     {
-        return !m_zooming && m_frontTexture->isMissingContent();
+        return m_zooming || m_frontTexture->isMissingContent();
     }
 
     int nbTextures(IntRect& area, float scale)
@@ -80,6 +80,8 @@ private:
 
     TileGrid* m_frontTexture;
     TileGrid* m_backTexture;
+    TileGrid* m_lowResTexture;
+
     float m_scale;
     float m_futureScale;
     double m_zoomUpdateTime;