Allow frames with overflow:hidden scroll in slow scrolling path when scaled up

Source/core/page/FrameView.cpp

Index: Source/core/page/FrameView.cpp
diff --git a/Source/core/page/FrameView.cpp b/Source/core/page/FrameView.cpp
index a369ca46cebbc67fa6798531fedb145f5e0c648e..f7d5d41b8d1afe413268633602238af08f70116d 100644
--- a/Source/core/page/FrameView.cpp
+++ b/Source/core/page/FrameView.cpp
@@ -222,6 +222,9 @@ PassRefPtr<FrameView> FrameView::create(Frame* frame, const IntSize& initialSize
 
 FrameView::~FrameView()
 {
+    // Avoid scrollbar updates during destruction.
+    setProhibitsScrolling(true);
+
     if (m_postLayoutTasksTimer.isActive()) {
         m_postLayoutTasksTimer.stop();
         m_actionScheduler->clear();
@@ -502,17 +505,6 @@ void FrameView::setCanHaveScrollbars(bool canHaveScrollbars)
     ScrollView::setCanHaveScrollbars(canHaveScrollbars);
 }
 
-void FrameView::updateCanHaveScrollbars()
-{
-    ScrollbarMode hMode;
-    ScrollbarMode vMode;
-    scrollbarModes(hMode, vMode);
-    if (hMode == ScrollbarAlwaysOff && vMode == ScrollbarAlwaysOff)
-        setCanHaveScrollbars(false);
-    else
-        setCanHaveScrollbars(true);
-}
-
 PassRefPtr<Scrollbar> FrameView::createScrollbar(ScrollbarOrientation orientation)
 {
     if (Settings* settings = m_frame->settings()) {
@@ -575,9 +567,20 @@ void FrameView::adjustViewSize()
     ASSERT(m_frame->view() == this);
 
     const IntRect rect = renderView->documentRect();
-    const IntSize& size = rect.size();
+    IntSize size = rect.size();
+
+    // For originally unscrollable content, may still allow scrolling in case that the page
+    // is scaled up, but only allow scrolling around the layout size, not the whole content size.
+    ScrollbarMode hMode;
+    ScrollbarMode vMode;
+    calculateScrollbarModesForLayout(hMode, vMode, RulesFromWebContent);
+    if (hMode == ScrollbarAlwaysOff)
+        size.setWidth(layoutWidth());
+    if (vMode == ScrollbarAlwaysOff)
+        size.setHeight(layoutHeight());

[Xianzhu, 2013/05/03 20:52:41]

Change 1: let contentsSize() be the layout size if the content is not supposed
to be scrollable when not scaled.

This ensures that the overflowed contents won't be scrolled in. For
ScrollableArea, the layout size is actually the scrollable content size in the
case.

Just verified that this also fixes the scroll range issue for overflow:hidden in
the fast path.

+
     ScrollView::setScrollOrigin(IntPoint(-rect.x(), -rect.y()), !m_frame->document()->printing(), size == contentsSize());
-    
+
     setContentsSize(size);
 }
 
@@ -673,7 +676,7 @@ void FrameView::calculateScrollbarModesForLayout(ScrollbarMode& hMode, Scrollbar
         return;
     }  
     
-    if (m_canHaveScrollbars || strategy == RulesFromWebContentOnly) {
+    if (m_canHaveScrollbars || !(strategy & RulesFromClient)) {
         hMode = ScrollbarAuto;
         // Seamless documents begin with heights of 0; we special case that here
         // to correctly render documents that don't need scrollbars.
@@ -681,10 +684,11 @@ void FrameView::calculateScrollbarModesForLayout(ScrollbarMode& hMode, Scrollbar
         bool isSeamlessDocument = frame() && frame()->document() && frame()->document()->shouldDisplaySeamlesslyWithParent();
         vMode = (isSeamlessDocument && !fullVisibleSize.height()) ? ScrollbarAlwaysOff : ScrollbarAuto;
     } else {
+        // The client disallows scrolling of this frame.
         hMode = ScrollbarAlwaysOff;
         vMode = ScrollbarAlwaysOff;
     }
-    
+
     if (!m_layoutRoot) {
         Document* document = m_frame->document();
         Node* documentElement = document->documentElement();
@@ -702,7 +706,18 @@ void FrameView::calculateScrollbarModesForLayout(ScrollbarMode& hMode, Scrollbar
             }
         } else if (rootRenderer)
             applyOverflowToViewport(rootRenderer, hMode, vMode);
-    }    
+    }
+
+    if (visibleContentScaleFactor() > 1 && (strategy & RulesFromVisibleContentScaleFactor)) {
+        // When the page is scaled up, for pages originally not allowed to scroll,
+        // the viewport may become smaller than its originally not-scrollable contents.
+        // Should allow scrolling to so that the user can pan around to see all the contents
+        // when the page is not scaled.
+        if (hMode == ScrollbarAlwaysOff)
+            hMode = ScrollbarAuto;
+        if (vMode == ScrollbarAlwaysOff)
+            vMode = ScrollbarAuto;
+    }

[Xianzhu, 2013/05/03 20:52:41]

Change 2: Allow scrolling of originally not-scrollable frames if the frame is
scaled up, by forcing the scrollbar mode to ScrollbarAuto.

 }
 
 void FrameView::updateCompositingLayersAfterStyleChange()
@@ -2610,6 +2625,7 @@ bool FrameView::isScrollable()
     // 2) display:none or visibility:hidden set to self or inherited.
     // 3) overflow{-x,-y}: hidden;
     // 4) scrolling: no;
+    // 5) visibleContentScaleFactor
 
     // Covers #1
     IntSize contentsSize = this->contentsSize();
@@ -2622,10 +2638,11 @@ bool FrameView::isScrollable()
     if (owner && (!owner->renderer() || !owner->renderer()->visibleToHitTesting()))
         return false;
 
-    // Cover #3 and #4.
+    // Cover #3, #4 and #5.
     ScrollbarMode horizontalMode;
     ScrollbarMode verticalMode;
-    calculateScrollbarModesForLayout(horizontalMode, verticalMode, RulesFromWebContentOnly);
+    calculateScrollbarModesForLayout(horizontalMode, verticalMode,
+            static_cast<ScrollbarModesCalculationStrategy>(RulesFromWebContent | RulesFromVisibleContentScaleFactor));

[Xianzhu, 2013/05/03 20:52:41]

This is not the key change, just to let isScrollable() return the actual
scrollable status.

     if (horizontalMode == ScrollbarAlwaysOff && verticalMode == ScrollbarAlwaysOff)
         return false;