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RE: [svg2] radialGradient @fr constraints

From: David Dailey <ddailey@zoominternet.net>
Date: Wed, 29 Aug 2012 06:32:01 -0400
To: "'Erik Dahlstrom'" <ed@opera.com>, <www-svg@w3.org>
Message-ID: <002a01cd85d1$869652b0$93c2f810$@net>
Fwiw, the example at http://srufaculty.sru.edu/david.dailey/svg/newstuff/gradient11c.svg
(that is now many years old and appears in more than one book) is rendered in ways that I consider proper in only Chrome and ASV. Opera makes it too grainy; Safari doesn't reflect gradients; FF refuses to differentiate between fx and cx (and even crashed for me thrice this morning while running it for a while!); IE9 doesn't reflect the gradients beyond the horizon (and they seem to have dropped animation from the graphical web).

HTML had the opportunity, in 2007, to have canvas follow SVG's syntax for radial gradients. Some people even advised as much. Reversing the role of leadership here would seem silly. Apple, despite, its recent victories in the wars*, should not have so unilateral a role in defining graphics for the web.

Regards
David

*There was a reason the policy of mutually assured destruction worked. 
-----Original Message-----
From: Erik Dahlstrom [mailto:ed@opera.com] 
Sent: Wednesday, August 29, 2012 4:33 AM
To: www-svg@w3.org
Subject: [svg2] radialGradient @fr constraints

Some issues regarding the added 'fr' attribute on radialGradient:

a) Should 'fr' be allowed to be negative? (this is disallowed in <canvas>). What should happen if it is?
b) Should we still keep the constraint[1] to move the focal point inside the other circle? <canvas> doesn't do this. What the spec currently defines means some kinds of conical gradients aren't possible to do with <radialGradient>.
c) Related to b): the case where the focal point is outside the other circle, but the focal radius makes the two circles intersect, how should that be handled?

Proposal:
a) disallow negative values for 'fr', and let these cases fallback to the lacuna value '0%'.
b) remove the constraint and handle it the same as in <canvas>, noting that this may break some existing content. If we do this way it doesn't matter how the two circles are positioned relative to one another, so it addresses c) as well.


[1] https://svgwg.org/svg2-draft/pservers.html#RadialGradientNotes
--
Erik Dahlstrom, Core Technology Developer, Opera Software Co-Chair, W3C SVG Working Group Personal blog: http://my.opera.com/macdev_ed
Received on Wednesday, 29 August 2012 10:32:38 GMT

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