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Re: [css-transforms] Object Bounding Box units and transformations on gradients, patterns, and masks

From: Dirk Schulze <dschulze@adobe.com>
Date: Tue, 31 Mar 2015 05:11:27 +0000
To: Amelia Bellamy-Royds <amelia.bellamy.royds@gmail.com>
CC: "public-fx@w3.org" <public-fx@w3.org>, www-svg <www-svg@w3.org>
Message-ID: <0745014E-8CD1-4B68-9A34-123EFE15F472@adobe.com>

On Mar 30, 2015, at 11:13 PM, Amelia Bellamy-Royds <amelia.bellamy.royds@gmail.com<mailto:amelia.bellamy.royds@gmail.com>> wrote:

In the CSS transforms module, the section "User Coordinate space" has the following statement:

In particular the patternUnits<http://www.w3.org/TR/2011/REC-SVG11-20110816/pservers.html#PatternElementPatternUnitsAttribute>, gradientUnits<http://www.w3.org/TR/2011/REC-SVG11-20110816/pservers.html#LinearGradientElementGradientUnitsAttribute> and maskUnits<http://www.w3.org/TR/2011/REC-SVG11-20110816/masking.html#MaskElementMaskUnitsAttribute> attributes don’t affect the user coordinate system used for transformations [SVG11]<http://dev.w3.org/csswg/css-transforms-1/#biblio-svg11>.


  *   last published working draft http://www.w3.org/TR/2013/WD-css-transforms-1-20131126/#svg-user-coordinate-space

  *   current editor's draft http://dev.w3.org/csswg/css-transforms-1/#svg-user-coordinate-space

Although the draft spec references SVG 1.1, this would be a breaking change from current SVG behavior.  The SVG definition used for gradientTransform and patternTransform is as follows:

 This additional transformation matrix is post-multiplied to (i.e., inserted to the right of) any previously defined transformations, including the implicit transformation necessary to convert from object bounding box units<http://www.w3.org/TR/SVG11/coords.html#ObjectBoundingBox> to user space.


  *   http://www.w3.org/TR/SVG11/pservers.html#LinearGradientElementGradientTransformAttribute

  *   http://www.w3.org/TR/SVG11/pservers.html#PatternElementPatternTransformAttribute

Unless there is an overwhelming reason to change this, I would recommend that the CSS transforms text be updated to state the transformation applies in the user coordinate system in effect for the element's contents, including any implicit transformations created by patternUnits, gradientUnits, or maskUnits.

This sounds reasonable. Could you please file the issue on Bugzilla so that we keep track of it?




Received on Tuesday, 31 March 2015 05:12:00 UTC

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