Fixed Inconsistent behaviour of custom-scrollbar

Source/core/frame/FrameView.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 3281 matching lines @@
         int clientWidth = visibleWidth();
         IntRect oldRect(m_horizontalScrollbar->frameRect());
         IntRect hBarRect((shouldPlaceVerticalScrollbarOnLeft() && m_verticalScrollbar) ? m_verticalScrollbar->width() : 0,
             height() - m_horizontalScrollbar->height(),
             width() - (m_verticalScrollbar ? m_verticalScrollbar->width() : 0),
             m_horizontalScrollbar->height());
         m_horizontalScrollbar->setFrameRect(adjustScrollbarRectForResizer(hBarRect, m_horizontalScrollbar.get()));
         if (!m_scrollbarsSuppressed && oldRect != m_horizontalScrollbar->frameRect())
             m_horizontalScrollbar->invalidate();
 
+        oldRect = m_horizontalScrollbar->frameRect();
+
         if (m_scrollbarsSuppressed)
             m_horizontalScrollbar->setSuppressInvalidation(true);
         m_horizontalScrollbar->setEnabled(contentsWidth() > clientWidth);
         m_horizontalScrollbar->setProportion(clientWidth, contentsWidth());
         m_horizontalScrollbar->offsetDidChange();
         if (m_scrollbarsSuppressed)
             m_horizontalScrollbar->setSuppressInvalidation(false);
+
+        if (!m_scrollbarsSuppressed && oldRect != m_horizontalScrollbar->frameRect() && m_horizontalScrollbar->isCustomScrollbar()) {
+            IntRect hBarRect((shouldPlaceVerticalScrollbarOnLeft() && m_verticalScrollbar) ? m_verticalScrollbar->width() : 0,
+                height() - m_horizontalScrollbar->height(),
+                width() - (m_verticalScrollbar ? m_verticalScrollbar->width() : 0),
+                m_horizontalScrollbar->height());
+            m_horizontalScrollbar->setFrameRect(adjustScrollbarRectForResizer(hBarRect, m_horizontalScrollbar.get()));
+            if (oldRect.height() != m_horizontalScrollbar->frameRect().height())
+                scrollbarExistenceDidChange();

[esprehn, 2014/10/29 06:43:50]

What behavior are you trying to trigger here? The existence didn't change when
the height changes, this doesn't seem like the right call.

[MuVen, 2014/10/29 09:39:59]

Upon zooming in, customScrollbar style scales by scaleFactor. When
SetEnabled is called, updateScrollbarParts will be called with in the SetEnabled
function, which triggers RenderScrollbar::updateScrollbarPart. In this API
RenderStyle of the scrollbar is calculated (which is multiplied by scale factor)
and the style is set to the RenderScrollbar at the end of the API.When you move
back to updateScrollbarParts, it checks for the scrollbar thickness, if the
thickness is changed it sets the  
box->setChildNeedsLayout(); scrollbarExistenceDidChange(will be invoked if
thickness of the scrollbar is changed) call will relayout if
box->setChildNeedsLayout is set. If Layout is not triggered, Assert 
ASSERT(!rootForThisLayout->needsLayout()); will be invoked in FrameView::layout
function.

+            m_horizontalScrollbar->invalidate();
+        }
     }
 
     if (m_verticalScrollbar) {
         int clientHeight = visibleHeight();
         IntRect oldRect(m_verticalScrollbar->frameRect());
         IntRect vBarRect(shouldPlaceVerticalScrollbarOnLeft() ? 0 : (width() - m_verticalScrollbar->width()),
             0,
             m_verticalScrollbar->width(),
             height() - (m_horizontalScrollbar ? m_horizontalScrollbar->height() : 0));
         m_verticalScrollbar->setFrameRect(adjustScrollbarRectForResizer(vBarRect, m_verticalScrollbar.get()));
         if (!m_scrollbarsSuppressed && oldRect != m_verticalScrollbar->frameRect())
             m_verticalScrollbar->invalidate();
 
+        oldRect = m_verticalScrollbar->frameRect();
+
         if (m_scrollbarsSuppressed)
             m_verticalScrollbar->setSuppressInvalidation(true);
         m_verticalScrollbar->setEnabled(contentsHeight() > clientHeight);
         m_verticalScrollbar->setProportion(clientHeight, contentsHeight());
         m_verticalScrollbar->offsetDidChange();
         if (m_scrollbarsSuppressed)
             m_verticalScrollbar->setSuppressInvalidation(false);
+
+        if (!m_scrollbarsSuppressed && oldRect != m_verticalScrollbar->frameRect() && m_verticalScrollbar->isCustomScrollbar()) {
+            IntRect vBarRect(shouldPlaceVerticalScrollbarOnLeft() ? 0 : (width() - m_verticalScrollbar->width()),
+                0,
+                m_verticalScrollbar->width(),
+                height() - (m_horizontalScrollbar ? m_horizontalScrollbar->height() : 0));
+            m_verticalScrollbar->setFrameRect(adjustScrollbarRectForResizer(vBarRect, m_verticalScrollbar.get()));
+            if (oldRect.width() != m_verticalScrollbar->frameRect().width())
+                scrollbarExistenceDidChange();
+            m_verticalScrollbar->invalidate();
+        }

[rwlbuis, 2014/10/28 14:59:03]

I see a repeated code pattern, meaning a shared function could be made, but it
probably is not needed for this fix...

     }
 }
 
 IntRect FrameView::adjustScrollbarRectForResizer(const IntRect& rect, Scrollbar* scrollbar)
 {
     // Get our window resizer rect and see if we overlap. Adjust to avoid the overlap
     // if necessary.
     IntRect adjustedRect(rect);
     bool overlapsResizer = false;
     if (!rect.isEmpty() && !windowResizerRect().isEmpty()) {
@@ skipping 579 matching lines @@
         return;
 
     ScrollableArea::setScrollOrigin(origin);
 
     // Update if the scroll origin changes, since our position will be different if the content size did not change.
     if (updatePositionAtAll && updatePositionSynchronously)
         updateScrollbars(scrollOffsetDouble());
 }
 
 } // namespace blink