- From: Rik Cabanier <cabanier@gmail.com>
- Date: Tue, 8 Nov 2011 21:03:25 -0800
- To: Alex Danilo <alex@abbra.com>
- Cc: www-svg <www-svg@w3.org>, public-fx@w3.org
- Message-ID: <CAGN7qDD3PZKAZvZAYTKKk3T1C+pCSFVQov=59ucoA5=JZHLtDQ@mail.gmail.com>
> > > >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. 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'. > > 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. Rik
Received on Wednesday, 9 November 2011 05:04:06 UTC