[filter-effects] Blending without compositing


The SVG WG resolved at the F2F in Tokyo this summer that <feBlend> in Filter Effects should support blending without compositing. This shall avoid double compositing as it can happen in combination with BackgroundImage today. [1]

We did have some difficulties to define the exact way to disable compositing. There are two different proposal so far:

1) Support all compositing operators on <feBlend>

The idea is that we actually do not disable compositing but allow the author to use a different compositing operator. The ‘mode’ attribute could be extended to support compositing modes as well:

<blending> = [normal | multiply | screen | darken | lighten] || [over | in | out | atop | xor]

which could look like this:

<feBlend mode=“screen atop” in2=“BackgroundImage” />

(The compositing values could be replaced by the keywords used by Canvas.)

2) Create new attribute ‘compositing'

SVG does not support boolean attributes yet. Therefore the attribute ‘compositing' would need values like ‘composite’/’no-compositing’ or simply ‘true’/‘false’.

With this attribute the compositing step can just be omitted completely or switched to source-over compositing following the formulas from CSS Compositing and Blending.

Any preferences?


[1] http://dev.w3.org/fxtf/filters/#issue-9d31c6c7

Received on Friday, 6 December 2013 13:17:00 UTC