RE: [css-compositing] some proposals

Hi Rik,

From: Rik Cabanier [mailto:cabanier@gmail.com]
Sent: Monday, 21 November 2011 3:50 PM
To: Cyril Concolato
Cc: www-svg; public-fx@w3.org; Alex Danilo (alex@abbra.com)
Subject: Re: [css-compositing] some proposals


On Sun, Nov 20, 2011 at 4:29 PM, Cyril Concolato <Cyril.Concolato@cisra.canon.com.au<mailto:Cyril.Concolato@cisra.canon.com.au>> wrote:
Hi Rik, Alex,

Just to make sure I understand the proposal. What would happen if you apply the 'dst-atop' compositing operator with partially transparent objects together with say a 'plus' blending operator. I understand that the 'plus' would only apply on the intersection but I'm not sure about the maths. Would you compose the equations, in which order? It doesn't look like you can consider that the result of the (alpha-)compositing becomes the source (or destination) of the (color-compositing) blending ,does it?

No, blending/color-compositing happens first, followed by alpha-compositing.
[Cyril] How can you do the blending/color-compositing on the intersection of the two objects if you haven't done alpha-compositing? You might not even have an intersection if you apply xor for instance. Anyway, I think the two operations should actually happen at the same time. I'm just trying to see what would be the result of applying both 'dst-atop' and 'plus' because both take care of opacity.

Cyril
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