Implement tiles synchronization

When a tiledPage is painted, we want to avoid updating the base
layer. GLWebViewState and WebView.cpp are now refcounting the
base layer, delaying updating the base layer we use to paint
until we are done with a full tile paint.

bug:3224744
Change-Id: Ica2b8f1db146a1e059fc0735dc53107fc40da07a

1 files changed, 28 insertions, 2 deletions

diff --git a/WebCore/platform/graphics/android/BaseLayerAndroid.cpp b/WebCore/platform/graphics/android/BaseLayerAndroid.cpp
index 1e7e209..57a53ab 100644
--- a/WebCore/platform/graphics/android/BaseLayerAndroid.cpp
+++ b/WebCore/platform/graphics/android/BaseLayerAndroid.cpp
@@ -174,6 +174,10 @@ bool BaseLayerAndroid::drawBasePictureInGL(SkRect& viewport, float scale)
         nextTiledPage->prepare(goingDown, goingLeft, viewportTileBounds);
     }
 
+    bool zooming = false;
+    if (m_glWebViewState->scaleRequestState() != GLWebViewState::kNoScaleRequest)
+        zooming = true;
+
     float transparency = 1;
     bool doSwap = false;
 
@@ -209,8 +213,30 @@ bool BaseLayerAndroid::drawBasePictureInGL(SkRect& viewport, float scale)
     TiledPage* tiledPage = m_glWebViewState->frontPage();
     tiledPage->setScale(m_glWebViewState->currentScale());
     const SkIRect& preZoomBounds = m_glWebViewState->preZoomBounds();
-    tiledPage->prepare(goingDown, goingLeft, preZoomBounds);
-    tiledPage->draw(transparency, preZoomBounds);
+
+    TiledPage* nextTiledPage = m_glWebViewState->backPage();
+
+    // We are now using an hybrid model -- during zooming or scrolling,
+    // we will display the current tiledPage even if some tiles are
+    // out of date. When standing still on the other hand, we wait until
+    // the back page is ready before swapping the pages, ensuring that the
+    // displayed content is in sync.
+    if (!zooming && !m_glWebViewState->moving()) {
+        if (!tiledPage->ready(preZoomBounds)) {
+            nextTiledPage->setScale(m_glWebViewState->currentScale());
+            nextTiledPage->prepare(goingDown, goingLeft, preZoomBounds);
+        }
+        if (nextTiledPage->ready(preZoomBounds)) {
+            nextTiledPage->draw(transparency, preZoomBounds);
+            doSwap = true;
+        } else {
+            tiledPage->draw(transparency, preZoomBounds);
+        }
+    } else {
+        // Ask for the tiles and draw -- tiles may be out of date.
+        tiledPage->prepare(goingDown, goingLeft, preZoomBounds);
+        tiledPage->draw(transparency, preZoomBounds);
+    }
 
     bool ret = false;
     if (m_glWebViewState->scaleRequestState() != GLWebViewState::kNoScaleRequest