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RE: SVG 2 rendering model

From: Leonard Rosenthol <lrosenth@adobe.com>
Date: Thu, 2 Aug 2012 17:54:05 -0700
To: Rik Cabanier <cabanier@adobe.com>, Nikos Andronikos <nikos.andronikos@cisra.canon.com.au>, "public-svg-wg@w3.org" <public-svg-wg@w3.org>
Message-ID: <D23D6B9E57D654429A9AB6918CACEAA9C563EF85A8@NAMBX02.corp.adobe.com>
In the case of a non-isolated transparency group, no buffer is required.   And in fact, it may actually be WRONG to use one, since you may well be blending the wrong colors in the wrong order depending on what's in the group.

Leonard

-----Original Message-----
From: Rik Cabanier 
Sent: Thursday, August 02, 2012 4:25 PM
To: Leonard Rosenthol; Nikos Andronikos; public-svg-wg@w3.org
Subject: RE: SVG 2 rendering model

An implementor always has to do this anyway.
The only difference is if the bitmap is filled with transparent black (= isolated) or the backdrop (=non-isolated)

In PDF, this information comes from the bbox in the transparency group. Regardless of isolation, the buffer is created. (See 11.4.3 in the PDF spec)

Rik

> -----Original Message-----
> From: Leonard Rosenthol
> Sent: Thursday, August 02, 2012 1:09 PM
> To: Rik Cabanier; Nikos Andronikos; public-svg-wg@w3.org
> Subject: Re: SVG 2 rendering model
> 
> On 8/2/12 3:34 PM, "Rik Cabanier" <cabanier@adobe.com> wrote:
> 
> >Hi Leonard,
> >
> >> The problem with making isolated the default is that it will impact 
> >> performance for all of the normal cases.
> >Isolated is faster since you don't have to composite all the group to 
> >get the background.
> 
> But you DO have to create an "offscreen buffer", composite the entire
> group into that, and then blit the entire "offscreen" back.   So you're
> clearly using more memory and time than simply putting bits into the 
> existing buffer.
> 
> 
> >The compositing spec specifies the order in which filters and 
> >compositing happens.
> >The filters spec should say if the stacking group it creates is 
> >isolated or not. I believe people don't want it to be isolated (and 
> >can post some examples if needed)
> 
> But how would you apply a filter to a group that has already been 
> blended into the background?  The result is certainly going to be 
> different - which may be good or bad.
> 
> I would think that given a group with a filter applied to it, you have 
> to make that specific group isolated, apply the filter, and only then 
> blend it to the background.
> 
> Leonard
Received on Friday, 3 August 2012 00:54:35 GMT

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