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RE: Filters spec: CSS vs SVG

From: David Dailey <ddailey@zoominternet.net>
Date: Fri, 6 May 2011 20:51:10 -0400
To: "'Rik Cabanier'" <cabanier@gmail.com>, "'Dean Jackson'" <dino@apple.com>
Cc: "'Chris Lilley'" <chris@w3.org>, "'Erik Dahlstrom'" <ed@opera.com>, <public-fx@w3.org>, "'www-svg'" <www-svg@w3.org>, "'Jon Frost'" <jonfrost2020@gmail.com>
Message-ID: <001c01cc0c50$dc065020$9412f060$@net>
If Rik's summary here is consistent with what other folks are saying, then
I'm happy, and the urgency of my previous message can be deleted!





From: www-svg-request@w3.org [mailto:www-svg-request@w3.org] On Behalf Of
Rik Cabanier
Sent: Friday, May 06, 2011 8:39 PM
To: Dean Jackson
Cc: Chris Lilley; Erik Dahlstrom; public-fx@w3.org; www-svg
Subject: Re: Filters spec: CSS vs SVG


Thanks for the clarification Dean!

In summary:

- we will have 1 spec for both SVG and CSS

- CSS might have features that don't apply to SVG. The spec needs to call
this out.

- Likewise SVG might have features that don't apply to CSS.

- We should NOT remove existing SVG features (unless everyone agrees that
they aren't necessary and are unused)


With this in mind, I'll reword my original list:

- remove section 6, the filter effects region

- mark backgound-image and background-alpha as applying only to SVG content.
Revisit when CSS compositing is defined.

- mark section on the enable-background keyword as applying only to SVG
content. Revisit when CSS compositing is defined.

- change default behavior of an unknown filter to 'ignore' instead of the
'null filter'

- remove filters that create an image and move them to the image-values spec
(ie feTurbulence) for CSS. Leave SVG behavior intact

- mark the feComposite filter as only applying to SVG. A future CSS/SVG
compositing spec can address this better.


On Fri, May 6, 2011 at 12:12 PM, Dean Jackson <dino@apple.com> wrote:


On 06/05/2011, at 8:15 AM, Rik Cabanier wrote:

Hi Chris,


these were just the changes that have been discussed on the FX mailing list.

In the start of this thread, I said that I wasn't aware that this was
intended to be a replacement for SVG filters.


I personally don't think that this should be the case and I'm fairly sure
that Dean didn't intend this either. 


My understanding was, and still is, that the Filters specification is
supposed to cover both the SVG and CSS use cases - ie. it is a replacement
for the SVG filters module.


The CSS parts were intended to be additions that could be described in SVG.
Whether or not an implementation actually uses SVG filters is a detail left
up to them. Also, the CSS part was intended to be less powerful than SVG
filters - that's where the "dropping" of features comes from. They are just
not available in CSS, giving the implementation the option to never
implement them.


It did get slightly confusing when the suggestion to drop enable-background
from SVG filters came up. It seems most implementors are happy with this. My
comment was that it was fine to remove it, but since there is content out
there that uses it (eg. Adobe Illustrator output) then we probably should
mark it as deprecated for a while before complete removal.



Enable-background is important for the SVG compositing spec. 

Unless we want to simplify SVG blending (which I'm not opposed to), it is


The CSS filter spec just took the general approach of the SVG filter specfor
simplicity. If possible, we should not change behavior of overlapping
functionality but it should be OK to remove or add keywords.


At the moment I don't think there is anything in the CSS part that requires
a change in the SVG part. At least nothing that implies removal of SVG


I expect in the future we'll be tempted to add more effects - these should
be added to both CSS and SVG. If an effect is not appropriate in CSS, it's
ok for it to be SVG-only. SVG is always the way to do the more complex


[Aside: If we start thinking of this spec as CSS vs Markup filters, rather
than CSS vs SVG, it might be helpful. There is only a little bit of actual
SVG in Filters]


Can you elaborate on what you mean with 'CSS vs Markup'?





For now, the filter spec is supposed to be as simple as possible both for
implementors and web designers.

This means:

- easy syntax for basic filters. More complicated filters can be done using
a subset of SVG filter. The reason for their use is that they were already
well defined.

- no access to the background or blending for ease of implementation

- no enable-background. This concept does not exist in the HTML.

- no section support. HTML generally is not a fixed layout so 'sections'
don't make much sense.


I agree that IF this is a replacemet spec, we need to thread more lightly...




On Thu, May 5, 2011 at 5:01 AM, Chris Lilley <chris@w3.org> wrote:

On Wednesday, May 4, 2011, 11:29:45 PM, Rik wrote:

RC> Thank Erik!I didn't know that this was a replacement for the current

RC> So far, I think these are the following proposed changes:
RC> - remove section 6, the filter effects region
RC>  - remove backgound-image and background-alpha
RC> - remove section on the enable-background keyword
RC> - change default behavior of an unknown filter to 'ignore' instead of
the 'null filter'
RC>  - remove filters that create an image and move them to the
RC> image-values spec (ie feTurbulence)
RC> - remove the feComposite filter and replace with the CSS/SVG compositing

Given that your first sentence quoted above makes clear that you understand
that this is a replacement spec that covers both HTML/CSS as well as SVG
(and SVG/CSS) usage - please provide an analysis of the impact of such
*radical* changes to existing on existing uses of SVG filters.



Received on Saturday, 7 May 2011 00:51:41 UTC

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