3 files changed, 24 insertions, 4 deletions
diff --git a/WebCore/platform/ScrollView.cpp b/WebCore/platform/ScrollView.cpp
index 8c4b115..d59d10a 100644
--- a/WebCore/platform/ScrollView.cpp
+++ b/WebCore/platform/ScrollView.cpp
@@ -713,10 +713,16 @@ void ScrollView::frameRectsChanged()
 void ScrollView::repaintContentRectangle(const IntRect& rect, bool now)
 {
     IntRect visibleContent = visibleContentRect();
+#ifdef ANDROID_CAPTURE_OFFSCREEN_PAINTS
+    IntRect fullVis = visibleContent;
+#endif
     visibleContent.intersect(rect);
+#ifdef ANDROID_CAPTURE_OFFSCREEN_PAINTS
+    if (rect != visibleContent)
+        platformOffscreenContentRectangle(fullVis, rect);
+#endif
     if (visibleContent.isEmpty())
         return;
-
     if (platformWidget()) {
         platformRepaintContentRectangle(visibleContent, now);
         return;
diff --git a/WebCore/platform/ScrollView.h b/WebCore/platform/ScrollView.h
index ef3d03d..2da6829 100644
--- a/WebCore/platform/ScrollView.h
+++ b/WebCore/platform/ScrollView.h
@@ -334,7 +334,9 @@ private:
 public:
     bool platformProhibitsScrolling();
 #ifdef ANDROID_CAPTURE_OFFSCREEN_PAINTS
-    void platformOffscreenContentRectangle(const IntRect& );
+    // capture parts of rect not contained by vis
+    void platformOffscreenContentRectangle(const IntRect& vis,
+        const IntRect& rect);
 #endif
 #endif
 }; // class ScrollView
diff --git a/WebCore/platform/android/ScrollViewAndroid.cpp b/WebCore/platform/android/ScrollViewAndroid.cpp
index 274c04f..9149deb 100644
--- a/WebCore/platform/android/ScrollViewAndroid.cpp
+++ b/WebCore/platform/android/ScrollViewAndroid.cpp
@@ -30,6 +30,7 @@
 #include "FloatRect.h"
 #include "FrameView.h"
 #include "IntRect.h"
+#include "SkRegion.h"
 #include "WebCoreFrameBridge.h"
 #include "WebCoreViewBridge.h"
 #include "WebViewCore.h"
@@ -96,9 +97,20 @@ void ScrollView::platformRepaintContentRectangle(const IntRect &rect, bool now)
 }
 
 #ifdef ANDROID_CAPTURE_OFFSCREEN_PAINTS
-void ScrollView::platformOffscreenContentRectangle(const IntRect& rect)
+/*
+    Compute the offscreen parts of the drawn rectangle by subtracting
+    vis from rect. This can compute up to four rectangular slices.
+*/
+void ScrollView::platformOffscreenContentRectangle(const IntRect& vis,
+    const IntRect& rect)
 {
-    android::WebViewCore::getWebViewCore(this)->offInvalidate(rect);
+    SkRegion rectRgn = SkRegion(rect);
+    rectRgn.op(vis, SkRegion::kDifference_Op);
+    SkRegion::Iterator iter(rectRgn);
+    for (; !iter.done(); iter.next()) {
+        const SkIRect& diff = iter.rect();
+        android::WebViewCore::getWebViewCore(this)->offInvalidate(diff);
+    }
 }
 #endif