Fix partial painting with render pipeline throttling

third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/paint/PaintLayerPainter.h"
 
+#include "core/frame/FrameView.h"
 #include "core/frame/Settings.h"
 #include "core/layout/ClipPathOperation.h"
 #include "core/layout/LayoutBlock.h"
 #include "core/layout/LayoutFrame.h"
 #include "core/layout/LayoutView.h"
 #include "core/layout/svg/LayoutSVGResourceClipper.h"
 #include "core/page/Page.h"
 #include "core/paint/FilterPainter.h"
 #include "core/paint/LayerClipRecorder.h"
 #include "core/paint/LayerFixedPositionRecorder.h"
@@ skipping 56 matching lines @@
     }
 
     // Non self-painting layers without self-painting descendants don't need to be painted as their
     // layoutObject() should properly paint itself.
     if (!m_paintLayer.isSelfPaintingLayer() && !m_paintLayer.hasSelfPaintingLayerDescendant())
         return FullyPainted;
 
     if (shouldSuppressPaintingLayer(&m_paintLayer))
         return FullyPainted;
 
-    // TODO(skyostil): Unify this early-out logic with subsequence caching.
-    if (m_paintLayer.layoutObject()->isLayoutPart() && toLayoutPart(m_paintLayer.layoutObject())->isThrottledFrameView())
-        return FullyPainted;
-
     // If this layer is totally invisible then there is nothing to paint.
     if (!m_paintLayer.layoutObject()->opacity() && !m_paintLayer.layoutObject()->hasBackdropFilter())
         return FullyPainted;
 
     if (m_paintLayer.paintsWithTransparency(paintingInfo.globalPaintFlags()))
         paintFlags |= PaintLayerHaveTransparency;
 
     LayerFixedPositionRecorder fixedPositionRecorder(context, *m_paintLayer.layoutObject());
 
     // PaintLayerAppliedTransform is used in LayoutReplica, to avoid applying the transform twice.
@@ skipping 165 matching lines @@
     bool shouldPaintOutline = isSelfPaintingLayer && !isPaintingOverlayScrollbars
         && ((isPaintingScrollingContent && isPaintingCompositedBackground)
         || (!isPaintingScrollingContent && isPaintingCompositedForeground));
     bool shouldPaintContent = m_paintLayer.hasVisibleContent() && isSelfPaintingLayer && !isPaintingOverlayScrollbars;
 
     PaintResult result = FullyPainted;
 
     if (paintFlags & PaintLayerPaintingRootBackgroundOnly && !m_paintLayer.layoutObject()->isLayoutView() && !m_paintLayer.layoutObject()->isDocumentElement())
         return result;
 
-    // TODO(skyostil): Unify this early-out logic with subsequence caching.
-    if (m_paintLayer.layoutObject()->isLayoutPart() && toLayoutPart(m_paintLayer.layoutObject())->isThrottledFrameView())
-        return FullyPainted;
+    if (m_paintLayer.layoutObject()->isLayoutView() && toLayoutView(m_paintLayer.layoutObject())->frameView()->shouldThrottleRendering()) {
+        // Make sure we re-record any cached subsequence when this layer becomes
+        // unthrottled again.
+        result = MayBeClippedByPaintDirtyRect;
+        m_paintLayer.setPreviousPaintResult(result);
+        return result;

[chrishtr, 2016/01/20 17:08:11]

I think you need to call m_paintLayer.setPreviousPaintResult(result) before
returning here. Does that fix your current bug?

[Sami, 2016/01/20 18:06:42]

Hmm, isn't that what I'm doing on line 273 or did I miss something?-)

[Sami, 2016/01/20 18:10:09]

And to be clear the other part of the bugfix is this line here:
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...

[Xianzhu, 2016/01/20 18:31:12]

I think we need to clear m_paintLayer's other previousXXX states to avoid them
happening to be the same as the new ones once the FrameView becomes
non-throttled.

[Sami, 2016/01/20 18:49:31]

Good point. Looks like it should be sufficient to reset previousPaintDirtyRect?
(or instead ensure needsRepaint is set if we decide to do that instead.)

[Xianzhu, 2016/01/20 18:51:03]

needsRepaint should be suffice.

+    }
 
     // Ensure our lists are up-to-date.
     m_paintLayer.stackingNode()->updateLayerListsIfNeeded();
 
     LayoutSize subpixelAccumulation = m_paintLayer.compositingState() == PaintsIntoOwnBacking ? m_paintLayer.subpixelAccumulation() : paintingInfoArg.subPixelAccumulation;
     ShouldRespectOverflowClip respectOverflowClip = shouldRespectOverflowClip(paintFlags, m_paintLayer.layoutObject());
 
     Optional<SubsequenceRecorder> subsequenceRecorder;
     if (shouldCreateSubsequence(m_paintLayer, context, paintingInfoArg, paintFlags)) {
         if (!shouldRepaintSubsequence(m_paintLayer, paintingInfoArg, respectOverflowClip, subpixelAccumulation)
@@ skipping 456 matching lines @@
     if (!m_paintLayer.containsDirtyOverlayScrollbars())
         return;
 
     PaintLayerPaintingInfo paintingInfo(&m_paintLayer, LayoutRect(enclosingIntRect(damageRect)), paintFlags, LayoutSize(), paintingRoot);
     paintLayer(context, paintingInfo, PaintLayerPaintingOverlayScrollbars);
 
     m_paintLayer.setContainsDirtyOverlayScrollbars(false);
 }
 
 } // namespace blink