optimizing layout performance when only transform3d matrix changed by

Source/core/rendering/style/RenderStyleConstants.h

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2003, 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 38 matching lines @@
 // (2) StyleDifferenceRecompositeLayer - The layer needs its position and transform updated, but no repaint.
 // (3) StyleDifferenceRepaint - The object just needs to be repainted.
 // (4) StyleDifferenceRepaintIfTextOrColorChange - The object needs to be repainted if it contains text or properties dependent on color (e.g., border or outline).
 // (5) StyleDifferenceRepaintLayer - The layer and its descendant layers needs to be repainted.
 // (6) StyleDifferenceLayoutPositionedMovementOnly - Only the position of this positioned object has been updated.
 // (7) StyleDifferenceSimplifiedLayout - Only overflow needs to be recomputed.
 // (8) StyleDifferenceSimplifiedLayoutAndPositionedMovement - Both positioned movement and simplified layout updates are required.
 // (9) StyleDifferenceLayout - A full layout is required.
 enum StyleDifference {
     StyleDifferenceEqual,
+    StyleDifferenceMinRecompositeLayer,
     StyleDifferenceRecompositeLayer,

[Ian Vollick, 2014/03/18 11:59:16]

Rather than adding "MinRecompositeLayer", could we make
StyleDifferenceRecompositeLayer mean what you intend here, and we could rename
the old enumerator to StyleDifferenceUpdateCompositingLayers to more accurately
indicate that more work will be done?

     StyleDifferenceRepaint,
     StyleDifferenceRepaintIfTextOrColorChange,
     StyleDifferenceRepaintLayer,
     StyleDifferenceLayoutPositionedMovementOnly,
     StyleDifferenceSimplifiedLayout,
     StyleDifferenceSimplifiedLayoutAndPositionedMovement,
     StyleDifferenceLayout
 };
 
 // When some style properties change, different amounts of work have to be done depending on
 // context (e.g. whether the property is changing on an element which has a compositing layer).
 // A simple StyleDifference does not provide enough information so we return a bit mask of
 // StyleDifferenceContextSensitiveProperties from RenderStyle::diff() too.
 enum StyleDifferenceContextSensitiveProperty {
     ContextSensitivePropertyNone = 0,
     ContextSensitivePropertyTransform = (1 << 0),
     ContextSensitivePropertyOpacity = (1 << 1),
-    ContextSensitivePropertyFilter = (1 << 2)
+    ContextSensitivePropertyFilter = (1 << 2),
+    ContextSensitivePropertyTransform3D = (1 << 3)

[Ian Vollick, 2014/03/18 11:59:16]

I thought that transform, opacity and filter were supposed to be precisely that
set of properties that could be modified without affecting layout. Perhaps we
don't need a new enumerator here, and instead, we could check to see if the
style change for these properties could possibly affect compositing reasons, and
if not, we could use StyleDifferenceRecompositeLayer.

[yaojie.yan, 2014/03/20 07:43:19]

Yes, I will address them in the following up patches.
On 2014/03/18 11:59:16, Ian Vollick wrote:

+
 };
 
 // Static pseudo styles. Dynamic ones are produced on the fly.
 enum PseudoId {
     // The order must be NOP ID, public IDs, and then internal IDs.
     // If you add or remove a public ID, you must update _pseudoBits in RenderStyle.
     NOPSEUDO, FIRST_LINE, FIRST_LETTER, BEFORE, AFTER, BACKDROP, SELECTION, FIRST_LINE_INHERITED, SCROLLBAR,
     // Internal IDs follow:
     SCROLLBAR_THUMB, SCROLLBAR_BUTTON, SCROLLBAR_TRACK, SCROLLBAR_TRACK_PIECE, SCROLLBAR_CORNER, RESIZER, INPUT_LIST_BUTTON,
     // Special values follow:
@@ skipping 465 matching lines @@
 // Reasonable maximum to prevent insane font sizes from causing crashes on some platforms (such as Windows).
 static const float maximumAllowedFontSize = 1000000.0f;
 
 enum TextIndentLine { TextIndentFirstLine, TextIndentEachLine };
 
 enum LayoutBox { BoxMissing = 0, MarginBox, BorderBox, PaddingBox, ContentBox };
 
 } // namespace WebCore
 
 #endif // RenderStyleConstants_h