Re: [filter-effects] feBlend filter

Hi Tav,

On Thu, May 30, 2013 at 1:49 AM, Tavmjong Bah <tavmjong@free.fr> wrote:

> On Wed, 2013-05-29 at 13:52 -0700, Rik Cabanier wrote:
>
> There is a perhaps a more obvious example at:
>
> http://tavmjong.free.fr/INKSCAPE/MANUAL/html/Filters-Compositing.html


yes, this is the "double counting background" issue that is mentioned on
that page.


>
>
> I don't know where the comment in the text about this problem being
> fixed in SVG 1.2 came from. I can't find anything in the that spec about
> it.
>

Maybe they were thinking of the SVG compositing spec?


>
> A cleaned up SVG file of this example is attached. The example renders
> as expected in Opera, Batik, srvg, and Inkscape, but not in Firefox or
> Chrome.
>

Your example fixes the issue with alpha in the backdrop by matting with
white.
However. as I showed in my example yesterday, the problem also happens when
you have alpha in the source and I haven't looked into how that can be
fixed with the current spec.


>
> I think that this is an important enough flaw in SVG 1.1 that breaking
> backwards compatibility may be warranted.
>

Maybe we can add special handling when you use background image in feBlend?
It's ugly but wouldn't break site that use feBlend to blend with
intermediate surfaces.