- From: Alex Danilo <alex@abbra.com>
- Date: Wed, 09 Nov 2011 16:22:55 +1100
- To: Rik Cabanier <cabanier@gmail.com>
- Cc: www-svg <www-svg@w3.org>, public-fx@w3.org
Hi Rik, --Original Message--: > > >>a. split up the spec in 2 sections: Porter-Duff & Blending. > >Agreed, it separates the two concepts properly. > >>Porter-Duff are compositing primitives that describes how 2 images (src+dst) can be merged. > >Here, I'd agree with David Baron's comment and change the names to 'source' and 'dest' in >line with CSS spec. readability. > >That sounds fine. > > > >>Blending describes how the top image will 'blend' with its underlying colors. The result of this is a new blended image. So far, we assume that after blending, this image is composited with Porter-Duff src-over. > >No it doesn't. > >The SVG compositing spec does. >Some of the blending modes talk about doing 'src-over' or 'dst-over' depending on the color, but I believe that's a bug. That is a bug for sure. >If the blending was designed to be compatible with Adobe's model, src-over IS implied. >If you look at basic compositing formula in the PDF reference manual (https://www.adobe.com/content/dam/Adobe/en/devnet/pdf/pdfs/PDF32000_2008.pdf section 11.3.3), you will see that it is using 'src-over'. I am intimately knowledgable with those functions and yes PDF is using src-over. But there's no reason to limit it to just that. > >Blending describes how the colour channels mix. It is independent of the P-D operators. >The diagram in the existing spec. attempts to describe that. i.e. the one that has a square >with 4 sections - one multi-coloured, one blue, one yellow and one white. > >Blending applies only to the multi-colour area whilst P-D manages how the different >'regions' combine. There is no reason that a blending mode can't apply to a different >P-D operator. > >>I am tempted to split the spec, but keep the comp-op keyword the same for both PD and blending. > >I think this is a mistake. We should split them. > >For example, I have two circles as part of a Venn diagram and I want to apply a blend >to their intersection - I can P-D 'src-in' the objects and apply comp-op="overlay" or similar. >The result of that is an area which has the 'overlay' applied to just the intersection of >the objects. > >I can't remember if 'Shake' was able to do that, but it did handle P-D and blending IIRC. > >>This does imply that you won't be able to do xor or src-in with blended content. Does anyone believe that this is a use case? > >Yes it's a use case. I think you'll find that sort of thing used in high-end video editing etc, > > >OK. Unless anyone objects, let's make them 2 separate properties. It is cleaner that way. > >The 'comp-op' keyword will only apply to the PD blend modes. 'src-over' will be the default. >The 'blend' keyword will specify what blending mode to use. 'Normal' will be the default. In ASV the blend keyword was 'adobe-blending-mode' and it handles all the examples in the spec dealing with blending if you go: s/comp-op/adobe-blending-mode/g in a text editor. So, I'd suggest 'blend-mode' or 'blending-mode' may be nicer. Alex >Rik > > > >
Received on Wednesday, 9 November 2011 05:23:38 UTC