Compute scroll limits correctly

 Bug: 6563848

Change-Id: I167487fab64c97b6c4ec7f1b14639415ce15e26f

3 files changed, 31 insertions, 17 deletions

diff --git a/Source/WebCore/platform/graphics/android/GraphicsLayerAndroid.cpp b/Source/WebCore/platform/graphics/android/GraphicsLayerAndroid.cpp
index 5207ace..e34125c 100644
--- a/Source/WebCore/platform/graphics/android/GraphicsLayerAndroid.cpp
+++ b/Source/WebCore/platform/graphics/android/GraphicsLayerAndroid.cpp
@@ -670,6 +670,14 @@ void GraphicsLayerAndroid::updateScrollOffset() {
     askForSync();
 }
 
+static void setScrollLimits(ScrollableLayerAndroid* scrollableLayer, RenderLayer* renderLayer)
+{
+    RenderBox* box = renderLayer->renderBox();
+    scrollableLayer->setScrollLimits(0, 0,
+            renderLayer->scrollWidth() - box->clientWidth(),
+            renderLayer->scrollHeight() - box->clientHeight());
+}
+
 bool GraphicsLayerAndroid::repaint()
 {
     ALOGV("(%x) repaint(), gPaused(%d) m_needsRepaint(%d) m_haveContents(%d) ",
@@ -730,7 +738,7 @@ bool GraphicsLayerAndroid::repaint()
             // for the contents to be in the correct position.
             m_foregroundLayer->setPosition(-x, -y);
             // Set the scrollable bounds of the layer.
-            static_cast<ScrollableLayerAndroid*>(m_foregroundLayer)->setScrollLimits(-x, -y, m_size.width(), m_size.height());
+            setScrollLimits(static_cast<ScrollableLayerAndroid*>(m_foregroundLayer), layer);
 
             // Invalidate the entire layer for now, as webkit will only send the
             // setNeedsDisplayInRect() for the visible (clipped) scrollable area,
@@ -788,8 +796,7 @@ bool GraphicsLayerAndroid::repaint()
             // limits based on the view size.
             if (m_contentLayer->isIFrameContent()) {
                 FrameView* view = layer->renderer()->frame()->view();
-                static_cast<IFrameContentLayerAndroid*>(m_contentLayer)->setScrollLimits(
-                    m_position.x(), m_position.y(), view->layoutWidth(), view->layoutHeight());
+                setScrollLimits(static_cast<ScrollableLayerAndroid*>(m_contentLayer), layer);
                 ALOGV("setScrollLimits(%.2f, %.2f, w: %d h: %d) layer %d, frame scroll position is %d, %d",
                       m_position.x(), m_position.y(), view->layoutWidth(), view->layoutHeight(),
                       m_contentLayer->uniqueId(), view->scrollX(), view->scrollY());
diff --git a/Source/WebCore/platform/graphics/android/layers/ScrollableLayerAndroid.cpp b/Source/WebCore/platform/graphics/android/layers/ScrollableLayerAndroid.cpp
index 1178103..c29ab2d 100644
--- a/Source/WebCore/platform/graphics/android/layers/ScrollableLayerAndroid.cpp
+++ b/Source/WebCore/platform/graphics/android/layers/ScrollableLayerAndroid.cpp
@@ -29,21 +29,31 @@ bool ScrollableLayerAndroid::scrollTo(int x, int y)
 
 void ScrollableLayerAndroid::getScrollBounds(IntRect* out) const
 {
-    const SkPoint& pos = getPosition();
-    out->setX(m_scrollLimits.fLeft - pos.fX);
-    out->setY(m_scrollLimits.fTop - pos.fY);
-    out->setWidth(getSize().width() - m_scrollLimits.width());
-    out->setHeight(getSize().height() - m_scrollLimits.height());
+    out->setX(m_scrollLimits.fLeft);
+    out->setY(m_scrollLimits.fTop);
+    out->setWidth(m_scrollLimits.width());
+    out->setHeight(m_scrollLimits.height());
 }
 
 void ScrollableLayerAndroid::getScrollRect(SkIRect* out) const
 {
-    const SkPoint& pos = getPosition();
-    out->fLeft = m_scrollLimits.fLeft - pos.fX + getScrollOffset().x();
-    out->fTop = m_scrollLimits.fTop - pos.fY + getScrollOffset().y();
+    out->fLeft = getScrollOffset().x();
+    out->fTop = getScrollOffset().y();
 
-    out->fRight = getSize().width() - m_scrollLimits.width();
-    out->fBottom = getSize().height() - m_scrollLimits.height();
+    out->fRight = m_scrollLimits.width();
+    out->fBottom = m_scrollLimits.height();
+}
+
+void ScrollableLayerAndroid::setScrollLimits(float minX, float minY,
+                                             float maxX, float maxY)
+{
+    if (minX < 0) minX = 0;
+    if (minY < 0) minY = 0;
+    if (maxX < 0) maxX = 0;
+    if (maxY < 0) maxY = 0;
+    if (minX > maxX) minX = maxX;
+    if (minY > maxY) minY = maxY;
+    m_scrollLimits.set(minX, minY, minX + maxX, minY + maxY);
 }
 
 bool ScrollableLayerAndroid::scrollRectIntoView(const SkIRect& rect)
diff --git a/Source/WebCore/platform/graphics/android/layers/ScrollableLayerAndroid.h b/Source/WebCore/platform/graphics/android/layers/ScrollableLayerAndroid.h
index 430f053..b3c828f 100644
--- a/Source/WebCore/platform/graphics/android/layers/ScrollableLayerAndroid.h
+++ b/Source/WebCore/platform/graphics/android/layers/ScrollableLayerAndroid.h
@@ -54,10 +54,7 @@ public:
     // fBottom = maxScrollY
     virtual void getScrollRect(SkIRect*) const;
 
-    void setScrollLimits(float x, float y, float width, float height)
-    {
-        m_scrollLimits.set(x, y, x + width, y + height);
-    }
+    void setScrollLimits(float minX, float minY, float maxX, float maxY);
 
     // Given a rect in the layer, scrolls to bring the rect into view. Uses a
     // lazy approach, whereby we scroll as little as possible to bring the