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[Bug 28385] New: Follow current SVG behavior for transforms interaction with object bounding box units

From: <bugzilla@jessica.w3.org>
Date: Tue, 31 Mar 2015 17:40:16 +0000
To: public-css-bugzilla@w3.org
Message-ID: <bug-28385-5148@http.www.w3.org/Bugs/Public/>
https://www.w3.org/Bugs/Public/show_bug.cgi?id=28385

            Bug ID: 28385
           Summary: Follow current SVG behavior for transforms interaction
                    with object bounding box units
           Product: CSS
           Version: unspecified
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Transforms
          Assignee: smfr@me.com
          Reporter: amelia.bellamy.royds@gmail.com
        QA Contact: public-css-bugzilla@w3.org
                CC: ayg@aryeh.name, cmarrin@apple.com, dino@apple.com,
                    dschulze@adobe.com, eoconnor@apple.com, smfr@me.com

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

> In particular the patternUnits, gradientUnits and maskUnits 
> attributes don’t affect the user coordinate system used for
> transformations [SVG11].

Links:
- 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 to user space.

Links:
-
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 text is a duplicate of a note sent to the email list:
https://lists.w3.org/Archives/Public/public-fx/2015JanMar/0136.html )

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