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Re: Updated Summary of Discussions about FX work items

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Thu, 30 Jun 2011 17:40:22 -0700
Message-ID: <BANLkTin=0tdsFnUUqv2gZRuxN3MTQy89sp+HbBpg=bdbStR+Dg@mail.gmail.com>
To: Alex Danilo <alex@abbra.com>
Cc: Vincent Hardy <vhardy@adobe.com>, Erik Dahlstrom <ed@opera.com>, "public-svg-wg@w3.org" <public-svg-wg@w3.org>
On Thu, Jun 30, 2011 at 4:24 PM, Alex Danilo <alex@abbra.com> wrote:
> However,  there's been a large thread on www-style that I've stayed away from that
> relates to the angles used for CSS gradients.
>
> CSS3 gradients is specifying 0 degrees to be vertical, i'e. poiting up along the Y axis.
> Their rationale is that it's like a compass.
>
> SVG uses the X-axis as 0 degrees, like in maths, architectural drawing and many other
> things.
>
> The angle concept in CSS gradients is incompatible with SVG's model so perhaps someone
> who is in both domains can point this out to them.

The decision to use bearing angles (0deg is up, positive is CW) was
based on overwhelming preference for it expressed in a poll of authors
which got about 100 responses.

Where precisely are angles used in SVG?  So far I've found the following:

1. glyph-orientation-*
2. rotate
3. translate (the rotate() and skew*() commands)
4. azimuth
5. elevation
6. orient
7. d (the elliptical arc commands)

In 1-3 and 6-7, the angle indicates a CW rotation, not a direction.
This is compatible with angles in linear-gradient().

In 4 and 5, the angle indicates a direction.  4 indicates a CW
rotation from the x axis, which is slightly incompatible with angles
in linear-gradient().  5 indicates a rotation from the plane of the
screen toward the viewer, which can't be compared with angles in
linear-gradient().

~TJ
Received on Friday, 1 July 2011 00:41:09 UTC

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