[QGIS-trac] [Quantum GIS] #1898: Group Transparency/Opacity for Legend Groups

[Quantum GIS]

#1898: Group Transparency/Opacity for Legend Groups
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   Reporter:  neumann                           |              Owner:  nobody       
       Type:  enhancement                       |             Status:  new          
   Priority:  major: does not work as expected  |          Milestone:  Version 1.3.0
  Component:  Symbology                         |            Version:  HEAD         
   Keywords:                                    |   Platform_version:               
   Platform:  Debian                            |           Must_fix:  No           
Status_info:  0                                 |  
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 It would be nice if we could have group transparency (on groups of
 layers). This is a concept available in SVG (and potentially other
 technologies). 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/

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Ticket URL: <https://trac.osgeo.org/qgis/ticket/1898>
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