Pixel snap SVG's root border box to local transform [spv2]

third_party/WebKit/Source/core/paint/SVGRootPainter.h

 // 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.
 
 #ifndef SVGRootPainter_h
 #define SVGRootPainter_h
 
 #include "wtf/Allocator.h"
 
 namespace blink {
 
 struct PaintInfo;
+class AffineTransform;
+class IntRect;
 class LayoutPoint;
 class LayoutSVGRoot;
 
 class SVGRootPainter {
     STACK_ALLOCATED();
 public:
     SVGRootPainter(const LayoutSVGRoot& layoutSVGRoot) : m_layoutSVGRoot(layoutSVGRoot) { }
 
     void paint(const PaintInfo&, const LayoutPoint&);
 
+    // Convert from container offsets (html/LayoutUnits) to our snapped local SVG transform space.

[chrishtr, 2016/07/06 17:50:58]

pixelSnapped?

[pdr., 2016/07/06 18:33:44]

I wonder if we can start moving away from "pixel snapped" because we're really
not snapping to pixels in blink. For consistency with pixelSnappedIntRect, I can
see an argument for switching this to pixelSnapedPaintOffsetToBorderBox though.
WDUT?

[trchen, 2016/07/06 19:00:21]

Now I think of it, it is not really "snapped paint offset", the return value is
not even an offset. Perhaps stretchToSnappedBorderBoxFromUnsnapped or something
alike.

To be more precise, we are not snapping to physical pixels but CSS/DOM pixels. I
don't think "pixel snapped" is particularly wrong, but we do need a strong
signal to distinguish "layout snapping" and "raster snapping".

The comments here could be more verbose though. This transform here is specific
to SVG root, and deserves more explanation. Perhaps something like:

The embedded SVG document use unsnapped viewport box to layout, while SVG root's
border box ultimately gets snapped during paint. A translate/scale transform is
applied to compensate the difference.

[pdr., 2016/07/06 20:23:27]

I updated the name to be "transformToPixelSnappedBorderBox" and wrote a slightly
tweaked version of your comment.

PTAL

+    AffineTransform snappedPaintOffsetToBorderBox(const LayoutPoint& paintOffset) const;
+
 private:
+    IntRect pixelSnappedSize(const LayoutPoint& paintOffset) const;
+
     const LayoutSVGRoot& m_layoutSVGRoot;
 };
 
 } // namespace blink
 
 #endif // SVGRootPainter_h