Optimize repaint on FrameView resize

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 865 matching lines @@
 
     Document* document = m_frame->document();
     bool inSubtreeLayout = isSubtreeLayout();
     RenderObject* rootForThisLayout = inSubtreeLayout ? m_layoutSubtreeRoot : document->renderer();
     if (!rootForThisLayout) {
         // FIXME: Do we need to set m_size here?
         ASSERT_NOT_REACHED();
         return;
     }
 
-    bool shouldDoFullLayout = false;
     FontCachePurgePreventer fontCachePurgePreventer;
     RenderLayer* layer;
     {
         TemporaryChange<bool> changeSchedulingEnabled(m_layoutSchedulingEnabled, false);
 
         m_nestedLayoutCount++;
         if (!inSubtreeLayout) {
             Document* document = m_frame->document();
             Node* body = document->body();
             if (body && body->renderer()) {
                 if (isHTMLFrameSetElement(*body)) {
                     body->renderer()->setChildNeedsLayout();
                 } else if (isHTMLBodyElement(*body)) {
                     if (!m_firstLayout && m_size.height() != layoutSize().height() && body->renderer()->enclosingBox()->stretchesToViewport())
                         body->renderer()->setChildNeedsLayout();
                 }
             }
         }
         updateCounters();
         autoSizeIfEnabled();
 
         ScrollbarMode hMode;
         ScrollbarMode vMode;
         calculateScrollbarModesForLayoutAndSetViewportRenderer(hMode, vMode);
 
-        shouldDoFullLayout = !inSubtreeLayout && (m_firstLayout || toRenderView(rootForThisLayout)->document().printing());
+        bool shouldDoFullRepaint = !inSubtreeLayout && (m_firstLayout || toRenderView(rootForThisLayout)->document().printing());
 
         if (!inSubtreeLayout) {
             // Now set our scrollbar state for the layout.
             ScrollbarMode currentHMode = horizontalScrollbarMode();
             ScrollbarMode currentVMode = verticalScrollbarMode();
 
             if (m_firstLayout) {
                 setScrollbarsSuppressed(true);
 
                 m_firstLayout = false;
@@ skipping 12 matching lines @@
                 setScrollbarsSuppressed(false, true);
             } else if (hMode != currentHMode || vMode != currentVMode) {
                 setScrollbarModes(hMode, vMode);
             }
 
             LayoutSize oldSize = m_size;
 
             m_size = LayoutSize(layoutSize().width(), layoutSize().height());
 
             if (oldSize != m_size) {
-                shouldDoFullLayout = true;
+                // It's hard to predict here which of full repaint or per-descendant repaint costs less.
+                // For vertical writing mode or width change, it's more likely that per-descendant repaint
+                // eventually turns out to be full repaint but with the cost to handle layout states and
+                // discrete repaint rects, so marking full repaint here is more likely to cost less.
+                // For height only changes, per-descendant repaint is more likely to avoid unnecessary
+                // full repaints.
+                if (!renderView()->style()->isHorizontalWritingMode() || oldSize.width() != m_size.width())
+                    shouldDoFullRepaint = true;
+
                 if (!m_firstLayout) {
                     RenderBox* rootRenderer = document->documentElement() ? document->documentElement()->renderBox() : 0;
                     RenderBox* bodyRenderer = rootRenderer && document->body() ? document->body()->renderBox() : 0;
                     if (bodyRenderer && bodyRenderer->stretchesToViewport())
                         bodyRenderer->setChildNeedsLayout();
                     else if (rootRenderer && rootRenderer->stretchesToViewport())
                         rootRenderer->setChildNeedsLayout();
                 }
             }
         }
 
         layer = rootForThisLayout->enclosingLayer();
 
         // We need to set m_doFullRepaint before triggering layout as RenderObject::checkForRepaint
         // checks the boolean to disable local repaints.
-        m_doFullRepaint |= shouldDoFullLayout;
+        m_doFullRepaint |= shouldDoFullRepaint;
 
         performLayout(rootForThisLayout, inSubtreeLayout);
 
         m_layoutSubtreeRoot = 0;
     } // Reset m_layoutSchedulingEnabled to its previous value.
 
     if (!inSubtreeLayout && !toRenderView(rootForThisLayout)->document().printing())
         adjustViewSize();
 
     layer->updateLayerPositionsAfterLayout(renderView()->layer(), updateLayerPositionFlags(layer, inSubtreeLayout, m_doFullRepaint));
@@ skipping 791 matching lines @@
         repaintRect.move(-scrollOffset());
         m_trackedRepaintRects.append(repaintRect);
     }
 
     ScrollView::repaintContentRectangle(r);
 }
 
 void FrameView::contentsResized()
 {
     ScrollView::contentsResized();
-    setNeedsLayout();
+    if (RenderView* renderView = this->renderView()) {
+        // Don't directly repaint layer in setNeedsLayout. We'll handle repaint in layout().
+        renderView->setNeedsLayout(MarkContainingBlockChain, 0, DontRepaintLayer);
+    }
 }
 
 void FrameView::scrollbarExistenceDidChange()
 {
     // We check to make sure the view is attached to a frame() as this method can
     // be triggered before the view is attached by LocalFrame::createView(...) setting
     // various values such as setScrollBarModes(...) for example.  An ASSERT is
     // triggered when a view is layout before being attached to a frame().
     if (!frame().view())
         return;
@@ skipping 1459 matching lines @@
 void FrameView::willRemoveScrollbar(Scrollbar* scrollbar, ScrollbarOrientation orientation)
 {
     ScrollableArea::willRemoveScrollbar(scrollbar, orientation);
     if (AXObjectCache* cache = axObjectCache()) {
         cache->remove(scrollbar);
         cache->handleScrollbarUpdate(this);
     }
 }
 
 } // namespace WebCore