[Qgis-developer] Transparency: group versus layer transparency/opacity

[Andreas Neumann]

Hi QGIS developers,

For QGIS 1.3 (or whatever the successor is called) I would like to discuss
whether we can add group transparency in addition to the regular layer
transparency.

This is a concept available in SVG. The difference is that with group
opacity/transparency, the layers in the group are rendered first
individually (with or without opacity) and then the transparency is added
on the intermediate rendering result of the group as a whole.

The difference is clearly seen if you have layers in a group where
polygons of different layers overlap. You don't want opacity on the
individual layers (since this would change colors), but you want to be
able to set the opacity on the parent group, for being able to have a
background base map shine through.

Here are two links on the topic:
http://www.w3.org/TR/SVG/masking.html#ObjectAndGroupOpacityProperties
and
http://labs.trolltech.com/blogs/2009/04/23/layered-rendering-part-2-it-helps-solve-many-problems/

Maybe something to discuss at the Vienna meeting?

Should I file a feature request?

Thanks,
Andreas


-- 
Andreas Neumann
http://www.carto.net/neumann/
http://www.svgopen.org/