Re: Image variants or sets and addressing fragments (fMAP, fcTL, fdAT, aPAL)

"Matthias B." <[email protected]>:
> 
> In order for your suggested features to be useful on the web, there
> would have to be corresponding CSS selectors and/or DOM objects. Are
> you in contact with the relevant W3C groups? I don't think there's any
> point in the PNG/MNG group making the first step here without any
> support from the major players on the web.

As a matter of fact, I am indeed in contact with the CSS WG and WhatWG (for
different matters), but nothing of what I'm proposing here requires any changes
in or additions to CSS, DOM, JS, HTML, ... or even URL
<https://url.spec.whatwg.org/>. Wherever image resources are referenced by URL,
fragment identifiers are already supported transparently, i.e. it's the job of
the image renderer to deal with that information. Except for Microsoft, all
major browser vendors are now supporting APNG <http://caniuse.com/#feat=apng>
and thus `fdAT` and `fcTL` are already widely implemented. Only `fMAP` is
entirely new (and needs some work). `aPLT` is much like `sPLT` syntax-wise, but
has different semantics and implications. Nevertheless, the new sprite stack and
palette manipulation features I'm proposing are designed to have useful fallback
behavior. Sprite maps, which are already widely used, have no good fallback or
addressing interface, but CSS requiring spatial Media Fragments support for
`image()` notation <https://drafts.csswg.org/css-images-4/#image-fragments>
makes them much more useful on the web. 

    background-image: url('swirl.png'); /* old UAs */
    background-image: image('sprites.png#xywh=10,30,60,20'); /* new UAs */

That being said, now would be the perfect time to get a note or example
regarding named subimages in PNG added to css-images which would certainly
improve the adoption rate (once approved as an extension by the PNG Group).

> For anything that's not the web, private chunks are the way to go.

Everything ends up on the web (or at least in browsers) nowadays.

JFTR, I'm trying to get all of this added to PNG proper, because I think it's
well in scope, but if that fails I will take it to APNG, which will hopefully
move to a location with defined specification process soon (e.g. WhatWG).

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