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Re: First draft of the blending and compositing spec

From: Jeremie Patonnier <jeremie.patonnier@gmail.com>
Date: Thu, 31 May 2012 20:20:18 +0200
Message-ID: <CAEi838nYqciRqxt4R=W+0ULosGb1iobECEMkA-OMCnvgUb31Ew@mail.gmail.com>
To: Rik Cabanier <cabanier@gmail.com>
Cc: public-fx@w3.org

I took the time to read this draft and I wish to thank you to push such a
proposal. As an author, I dream of such feature available in the browser :D

Here are some thought about the draft. I'm not an expert in compositing and
blending but I felt smart by reading this spec it's amazingly clear and
understandable. Still, I saw things that puzzled me so here are they :

4.2 : This part really needs an example
4.3 : You say "knockout group" but the property is "knock-out". why are you
using a dash for the property and not for the designation?

I found unclear the way each element, inside the knockout group, is
prioritized to determine which element knock-out which other one. It looks
like it depend of the z-index of each element but it's not clearly stated.
It could also be interpreted as dependent of the source code flow. In the
end I presume it depend of the paint order define by each browser. The
"knock-out" property definition does not really help much more here.

5 : Even if it's "standard" to use the word destination when we are talking
about Porter Duff stuff, it make the spec harder to read and understand.
IMO it could be easier to chose a word ("backdrop" or "destination"
whatever you prefer) and remain consistent all along the spec. It will
avoid confusion.

I'm not an expert in compositing so, I do not understand what the 4 pixel
subregions mean and the spec does not really help to understand this. As a
consequence, the example looks wired and it's unclear to me why each pixel
subregion is 25% in the example. I think it needs some clarification (at
least for dumb author like me).

5.1.13 : A visual example will be helpful to understand the math

8.1 : This section make some reference about HTML elements. What about SVG
ones? Is it planed to have something about compositing and blending fill
and stroke independently?

8.2.1 : When using the alpha-compositing property, how do we know what the
destination is? Is it the whole background page?

"Elements will always composite with ‘clip-to-self’ set to ‘true’." this
sentence let think that there is some kind of "clip-to-self" property
available that could be turned off. Is it possible to rephrase this? Maybe
: "Elements will composite as their 'clip-to-self' behavior is always
considered enabled"

8.2.3 I should miss something : "For an individual layer ‘isolation’ is
always ‘isolate’." What a "layer" is?

8.2.4: IMO "knock-out: knock-out;" looks a bit awkward. Because it's a
yep/nope property, could we imagine something like this : the "knock-out"
value become the "enabled" value and the "preserve" value become the "none"
value. I really think it make things clearer for author :

div { knock-out: enabled; }
div ( knock-out: none; }

I think both really speak for themselves with those values :)

8.3.7 : I think there is a need to be able to do that in SVG with the
stroke independent than the fill. Unfortunately, I do not have relevant use
case to provide at the moment.

I hope it will help

Best regards
Web : http://jeremie.patonnier.net
Twitter : @JeremiePat <http://twitter.com/JeremiePat>

2012/5/10 Rik Cabanier <cabanier@gmail.com>

> All,
> during yesterday FX meeting, some people voiced concern with the lack of
> context of the 'enable-background' [1] and 'isolate' [2] properties.
> I've added some annotations and would like feedback to see if it clarifies
> their usage.
> Thanks!
>    Rik
> [1]
> https://dvcs.w3.org/hg/FXTF/rawfile/tip/compositing/index.html#comp-enable-background
> [2]
> https://dvcs.w3.org/hg/FXTF/rawfile/tip/compositing/index.html#enable-background
> On Thu, May 3, 2012 at 10:20 PM, Rik Cabanier <cabanier@gmail.com> wrote:
>> All,
>> Nikos and I have created a first pass at a compositing and blending spec
>> and posted it here:
>> https://dvcs.w3.org/hg/FXTF/rawfile/tip/compositing/index.html
>> The section on compositing needs more depth, but I think the blending and
>> specification section are ready for a first review.
>> We will present this during next week's FX face-to-face meeting along
>> with some prototype implementations.
>> Let us know what you think.
>> Thanks!
>>    Rik Cabanier
>>    Adobe Systems, Inc
Received on Thursday, 31 May 2012 18:21:08 UTC

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