[SVG] Transform animation leaves traces of text behind.

Source/core/rendering/PaintInfo.h

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 67 matching lines @@
     bool shouldPaintWithinRoot(const RenderObject* renderer) const
     {
         return !paintingRoot || paintingRoot == renderer;
     }
 
     bool forceBlackText() const { return paintBehavior & PaintBehaviorForceBlackText; }
 
     bool skipRootBackground() const { return paintBehavior & PaintBehaviorSkipRootBackground; }
     bool paintRootBackgroundOnly() const { return paintBehavior & PaintBehaviorRootBackgroundOnly; }
 
     void applyTransform(const AffineTransform& localToAncestorTransform, bool identityStatusUnknown = true)

[Stephen Chennney, 2014/03/19 12:11:05]

What code uses this? I'm worried that this patch is introducing a relatively
expensive operation (isInvertible) that is then immediately repeated inside
AffineTransform::inverse(). If it's just SVG, then fine. But if this is used a
lot then I think we need to add "inverseMapRect" to AffineTransform to avoid the
extra call.

[Erik Dahlström (inactive), 2014/03/19 14:00:10]

All of the users of the PaintInfo.applyTransform method I found were in svg,
everyone outside svg uses TransformationMatrix / TransformState AFAICT. 

Note that there was already one place that checked isInvertible (for
non-scaling-stroke), but it wasn't using this particular method just the same
call-pattern (AffineTransform.inverse().mapRect()).

     {
         if (identityStatusUnknown && localToAncestorTransform.isIdentity())
             return;
 
         context->concatCTM(localToAncestorTransform);
 
         if (rect == infiniteRect())
             return;
 
-        rect = localToAncestorTransform.inverse().mapRect(rect);
+        if (localToAncestorTransform.isInvertible())
+            rect = localToAncestorTransform.inverse().mapRect(rect);
+        else
+            rect.setSize(IntSize(0, 0));
     }
 
     static IntRect infiniteRect() { return IntRect(LayoutRect::infiniteRect()); }
     const RenderLayerModelObject* paintContainer() const { return m_paintContainer; }
 
     ListHashSet<RenderInline*>* outlineObjects() { return m_outlineObjects; }
     void setOutlineObjects(ListHashSet<RenderInline*>* objects) { m_outlineObjects = objects; }
 
     // FIXME: Introduce setters/getters at some point. Requires a lot of changes throughout rendering/.
     GraphicsContext* context;
     IntRect rect;
     PaintPhase phase;
     PaintBehavior paintBehavior;
     RenderObject* paintingRoot; // used to draw just one element and its visual kids
     OverlapTestRequestMap* overlapTestRequests;
 
 private:
 
     const RenderLayerModelObject* m_paintContainer; // the layer object that originates the current painting
     ListHashSet<RenderInline*>* m_outlineObjects; // used to list outlines that should be painted by a block with inline children
 };
 
 } // namespace WebCore
 
 #endif // PaintInfo_h