[QGIS-trac] Re: [Quantum GIS] #2832: rule-based renderer in symbology-ng should show rules in legend

[Quantum GIS]

#2832: rule-based renderer in symbology-ng should show rules in legend
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   Reporter:  nirvn                             |              Owner:  wonder       
       Type:  patch                             |             Status:  new          
   Priority:  major: does not work as expected  |          Milestone:  Version 1.6.0
  Component:  Symbology                         |            Version:  Trunk        
   Keywords:                                    |   Platform_version:               
   Platform:  All                               |           Must_fix:  No           
Status_info:  0                                 |  
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Comment(by mayeulk):

 Thank you wonder for putting it in the trunk!
 Here are some thoughts about how to deal with the symbol levels.
 IMHO, here are many examples where symbol levels are needed (and with the
 only workaround of having tens of layers).
 I cannot think of many examples where using several symbols (hence many
 matched rules) is absolutely required; even less examples where multiple
 matched rules AND symbol levels together are required ; for those examples
 (for instance: rule A and B), if we use the full patch
 rule_based_renderer.diff, there is the easy workaround of creating one
 rule C with (C <=> (A and B)) and putting it before A and B.
 Anyway, thinking of how to deal with combining symbol levels and multiple-
 matched rules will be easier if we can test rule based rendering with
 symbol levels. I am precisely working on this. I have just made my own
 build (based on 14481) by completely the patch in r14404 (including symbol
 levels).
 The first obvious needed feature would be to reorder the rules (change the
 priority order).
 Then, next to the "use symbol levels" check box, a warning should say that
 if symbol levels are activated, only the first matched rule will be
 applied. Then qgsrulebasedrendererv2.cpp should be modified to return
 "mCurrentSymbol" if symbol levels are not activated, and only the first
 matching rule if they are.
 Finally, symbol levels are saved in memory when closing the dialog box,
 but they are not saved to the file yet and this would need to be fixed.
 I'm working on rendering  openstreetmap data in a customized way with
 filters based directly on the full-length OSM tags (but I cannot save my
 changes because of the above).

 Should we have the changes suggested here, users will be able to choose
 between multiple matched rules and symbol levels. We will then have use
 cases to think about where to go next. What do you think?

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Ticket URL: <http://trac.osgeo.org/qgis/ticket/2832#comment:8>
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