Add infrastructure for partial layouts

Source/core/page/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 161 matching lines @@
     , m_isTrackingRepaints(false)
     , m_shouldUpdateWhileOffscreen(true)
     , m_deferSetNeedsLayouts(0)
     , m_setNeedsLayoutWasDeferred(false)
     , m_scrollCorner(0)
     , m_shouldAutoSize(false)
     , m_inAutoSize(false)
     , m_didRunAutosize(false)
     , m_hasSoftwareFilters(false)
     , m_visibleContentScaleFactor(1)
+    , m_shouldStopPartialLayout(false)
+    , m_stopLayoutAtRenderer(0)
 {
     init();
 
     // FIXME: Can m_frame ever be null here?
     if (!m_frame)
         return;
 
     Page* page = m_frame->page();
     if (!page)
         return;
@@ skipping 649 matching lines @@
 void FrameView::layout(bool allowSubtree)
 {
     // We should never layout a Document which is not in a Frame.
     ASSERT(m_frame);
     ASSERT(m_frame->view() == this);
     ASSERT(m_frame->page());
 
     if (m_inLayout)
         return;
 
+    ASSERT(!shouldStopPartialLayout());
+
     TRACE_EVENT0("webkit", "FrameView::layout");
     TRACE_EVENT_SCOPED_SAMPLING_STATE("Blink", "Layout");
 
     // Protect the view from being deleted during layout (in recalcStyle)
     RefPtr<FrameView> protector(this);
 
     // Every scroll that happens during layout is programmatic.
     TemporaryChange<bool> changeInProgrammaticScroll(m_inProgrammaticScroll, true);
 
     m_layoutTimer.stop();
@@ skipping 117 matching lines @@
                     else if (rootRenderer && rootRenderer->stretchesToViewport())
                         rootRenderer->setChildNeedsLayout();
                 }
             }
         }
 
         layer = rootForThisLayout->enclosingLayer();
 
         m_actionScheduler->pause();
 
+        // Text Autosizing requires two-pass layout which is incompatible with partial layout. If
+        // enabled, only do partial layout for the second layout.
+        // FIXME (crbug.com/256657): Do not do two layouts for text autosizing.
+        RenderObject* delayPartialLayoutForRenderer = 0;
+        if (m_frame->settings() && m_frame->settings()->textAutosizingEnabled()) {

[eseidel, 2013/08/20 21:00:39]

You don't need all this if you add a "m_disablePartialLayoutCount" and just
increment it for the first layout when textAutosigingEnabled is true.

// We need to disable partial layouts for the first layout if we might
// end up doing two-pass layout for autosizing.
PartialLayoutDisabler disabler(m_frame->settings()->textAutosizingEnabled());

[pdr., 2013/08/26 05:50:40]

Done.

+            delayPartialLayoutForRenderer = m_stopLayoutAtRenderer;
+            m_stopLayoutAtRenderer = 0;
+        }
+
         {
             bool disableLayoutState = false;
             if (inSubtreeLayout) {
                 RenderView* view = rootForThisLayout->view();
                 disableLayoutState = view->shouldDisableLayoutStateForSubtree(rootForThisLayout);
                 view->pushLayoutState(rootForThisLayout);
             }
             LayoutStateDisabler layoutStateDisabler(disableLayoutState ? rootForThisLayout->view() : 0);
 
             m_inLayout = true;
             beginDeferredRepaints();
             forceLayoutParentViewIfNeeded();
             rootForThisLayout->layout();
 
+            // If text autosizing is enabled, do a partial layout for the second layout.
+            if (delayPartialLayoutForRenderer) {
+                ASSERT(!shouldStopPartialLayout());
+                m_stopLayoutAtRenderer = delayPartialLayoutForRenderer;
+            }
             bool autosized = document->textAutosizer()->processSubtree(rootForThisLayout);
             if (autosized && rootForThisLayout->needsLayout()) {
                 TRACE_EVENT0("webkit", "2nd layout due to Text Autosizing");
                 rootForThisLayout->layout();
             }
 
             endDeferredRepaints();
             m_inLayout = false;
 
             if (inSubtreeLayout)
                 rootForThisLayout->view()->popLayoutState(rootForThisLayout);
         }
         m_layoutRoot = 0;
     } // Reset m_layoutSchedulingEnabled to its previous value.
 
+    // Reset partial layout state post-layout and exit here if a partial layout was done.
+    if (shouldStopPartialLayout()) {
+        resetPartialLayoutState();
+        return;
+    }
+    resetPartialLayoutState();

[eseidel, 2013/08/20 21:00:39]

Shouldn't the original caller drive this?

[pdr., 2013/08/26 05:50:40]

Fixing this was enlightening. resetPartialLayoutState() was masking a bug.

We disable overlay scrollbars when running tests (for cross-platform
consistency). Because non-overlay scrollbars cause a second layout through
adjustViewSize(), I've added a PartialLayoutDisabler for the primary layout. In
the common case, the first ("primary?") layout will early-out if scrollbars are
present, so we should still have a nice speed win.

I've also changed this so the original caller
(partialUpdateLayoutIgnorePendingStylesheets) is now the one to call reset().

I've added two tests to prove this works.

+
     bool neededFullRepaint = m_doFullRepaint;
 
     if (!inSubtreeLayout && !toRenderView(rootForThisLayout)->printing())
         adjustViewSize();
 
     m_doFullRepaint = neededFullRepaint;
 
     // Now update the positions of all layers.
     beginDeferredRepaints();
     if (m_doFullRepaint)
@@ skipping 63 matching lines @@
     // however m_inLayout is not set for most of this function, so none of our RELEASE_ASSERTS
     // in Frame/Page will fire. One of the post-layout tasks is disconnecting the Frame from
     // the page in fast/frames/crash-remove-iframe-during-object-beforeload-2.html
     // necessitating this check here.
     ASSERT(frame());
     // ASSERT(frame()->page());
     if (frame() && frame()->page())
         frame()->page()->chrome().client()->layoutUpdated(frame());
 }
 
+#ifndef NDEBUG
+void FrameView::checkPartialLayoutAllowed()
+{
+    RenderObject* renderer = m_stopLayoutAtRenderer;
+    while (renderer) {

[esprehn, 2013/08/23 20:47:27]

This could be a for() loop :)

[pdr., 2013/08/26 05:50:40]

This function was useful for checking my logic in writing this patch, but it's
no longer all that useful (it's redundant since we do this check in
Document::partialUpdateLayoutIgnorePendingStylesheets). I've removed this for
now.

+        ASSERT(renderer->supportsPartialLayout());
+        renderer = renderer->parent();
+    }
+}
+#endif
+
 RenderBox* FrameView::embeddedContentBox() const
 {
     RenderView* renderView = this->renderView();
     if (!renderView)
         return 0;
 
     RenderObject* firstChild = renderView->firstChild();
     if (!firstChild || !firstChild->isBox())
         return 0;
 
@@ skipping 2234 matching lines @@
 }
 
 AXObjectCache* FrameView::axObjectCache() const
 {
     if (frame() && frame()->document())
         return frame()->document()->existingAXObjectCache();
     return 0;
 }
 
 } // namespace WebCore