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RE: [svg2] radialGradient @fr constraints

From: David Dailey <ddailey@zoominternet.net>
Date: Wed, 29 Aug 2012 15:04:16 -0400
To: "'Erik Dahlstrom'" <ed@opera.com>, <www-svg@w3.org>
Message-ID: <004601cd8619$162b6720$42823560$@net>
Yes, I think that is the issue. I've simplified my example to get rid of the animation and to include only one gradient:

The different browsers' behavior is shown at http://cs.sru.edu/~ddailey/svg/gradientscreen.jpg

ASV and Chrome agree with me. (I hold the opinion since it is the coolest effect, and isn't that what reflected radial gradients are largely all about anyhow?)

Using a pair of these gradients overlaid with opacity provides a very nice animated effect when combined with feDisplacement to give water effects, with the activity beyond the horizon providing a somewhat realistic impression of fractal reflection.  


-----Original Message-----
From: Erik Dahlstrom [mailto:ed@opera.com] 
Sent: Wednesday, August 29, 2012 7:51 AM
To: www-svg@w3.org
Subject: Re: [svg2] radialGradient @fr constraints

Hi David,
You mean the condition displayed in figure 8 here, https://svgwg.org/svg2-draft/pservers.html#RadialGradientNotes right?

The discussion and rationale for that addition can be found here:

[[ Summary of the issue: when the focal point is on the circle edge, with repeat, then the distance between the first and last stop for the repeating colors is 0 and the (SVG1.1) spec. does not define what should happen. ]]

On Wed, 29 Aug 2012 12:32:01 +0200, David Dailey <ddailey@zoominternet.net> wrote:

> 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

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 19:04:48 UTC

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