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Re: SVG Tiny 1.2 CR2006-08-10: 9.2 rect element with rounded corners

From: Andreas Neumann <neumann@karto.baug.ethz.ch>
Date: Mon, 28 Aug 2006 12:21:53 +0200
Message-ID: <44F2C3C1.3010903@karto.baug.ethz.ch>
To: "Dr. Olaf Hoffmann" <Dr.O.Hoffmann@gmx.de>, www-svg@w3.org

Hello,

Thank you for your review! We also agree that it is useful to describe 
in detail how stroking of basic shapes work, to ensure interoperability. 
We discussed this issue last week and decided to change the text 
slightly to explain the elliptical arcs different, without relying on 
wording of the elliptical arc command of the path specification in the 
SVG1.1. full profile.

SVG 1.2 Tiny is supposed to be a standalone core profile that should not 
rely on features existing only in the full profile.

Here is the proposal:

--------------

Old wording:

perform an absolute elliptical arc operation to coordinate (x+rx,y),
where the effective values for the rx and ry attributes on the 'rect'
element converted to user space are used as the rx and ry attributes on
the elliptical arc command, respectively, the x-axis-rotation is set to
zero, the large-arc-flag is set to zero, and the sweep-flag is set to one

New proposed wording:

perform an absolute elliptical arc operation to coordinate (x+rx,y),
where the effective values for the rx and ry attributes on the 'rect'
element converted to user space are used as the semimajor and semiminor
axis, respectively, zero x-axis-rotation, a clockwise sweep direction
and choosing the smaller arc sweep.

---------------

Note that I believe that terms like "semimajor and semiminor axis", 
"x-axis-rotation", "sweep direction" and "small arc sweep" are general 
terms in computer graphics, not specific to the SVG 1.1 full path 
specification.

As a result of the elliptical arc we can't refer to an SVG path anymore 
but rather refer to an "outline" (not linked to the path chapter).

old wording:
... that produces the same result as if the following path were
specified ....

new wording:
... that produces the same result as if the following outline were
specified ...


I hope that this slightly new text addresses the issue without having to 
rely on specific wording of the SVG 1.1 full specification.

Andreas


Dr. Olaf Hoffmann wrote:

>Hello,
>
>while I'm starting to create some documents as examples and 
>test cases for SVG Tiny 1.2 I discovered unfortunately a minor 
>formal or logical problem with the definition of the rect element.
>
>It is specified:
>"A 'rect' element, taking its rounded corners into account, 
>must be rendered in a way that produces the same result as if 
>the following path were specified instead:
>....
>perform an absolute elliptical arc operation to coordinate (x+rx,y), 
>where the effective values for the rx and ry attributes on the 'rect' 
>element converted to user space are used as the rx and ry attributes 
>on the elliptical arc command, respectively, the x-axis-rotation is 
>set to zero, the large-arc-flag is set to zero, and the sweep-flag 
>is set to one
>....
>the elliptical arc commands
>...."
>
>For this it is referenced to the path chapter of SVG Tiny 1.2.
>Of course, this chapter does not describe elliptical arc 
>operations or commands, because they are not part of 
>SVG Tiny 1.2, therefore it is not possible to specify a
>rectangle with rounded corners as a SVG Tiny path.
>It is very useful to have this representation as a path 
>for example to determine how stroke-dasharray has to be rendered
>correctly, but the link to the path chapter is misleading for 
>readers, it would be more helpful to have a link to the path chapter
>of SVG 1.1, which contains path commands for elliptical arcs
>and the description of parameters like x-axis-rotation, large-arc-flag 
>and sweep-flag, which are not understandable with the SVG Tiny 1.2
>CR alone.
>
>Best wishes
>
>
>  
>


-- 
----------------------------------------------
Andreas Neumann
Institute of Cartography
ETH Zurich
Wolfgang-Paulistrasse 15
CH-8093  Zurich, Switzerland

Phone: ++41-44-633 3031, Fax: ++41-44-633 1153
e-mail: neumann@karto.baug.ethz.ch
www: http://www.carto.net/neumann/
SVG.Open: http://www.svgopen.org/
Carto.net: http://www.carto.net/
Received on Monday, 28 August 2006 10:21:59 GMT

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