[Qgis-developer] Ellipse renderer

[Marco Hugentobler]

Hi QGIS devs

Recently, I was writing a symbollayer to render ellipse shapes (and also 
rectangles, triangles, crosses by specifying width and height). Moreover, the 
symbol layer allows to set all parameters (width, height, colors, rotation, 
outline with) from data fields, in mm or map units. 

The code is contained in my github clone int the branch 
'data_defined_symbollayer'. To give it a try, you can do the following:

git add remote add mhugent git://github.com/mhugent/Quantum-GIS.git
git checkout --track mhugent/data_defined_symbollayer

The reason it's in a branch is that data defined rendering in symbol layers 
needed some API changes. They are quite small:

- A pointer to the rendered QgsFeature* has been added to 
QgsSymbolV2RenderContext (such that the symbollayer has the possibility to 
check the data defined attribute values)

- A symbollayer has the possibility to specify which attribute fields it needs 
for rendering (by default, QgsSymbolLayerV2::usedAttributes returns an empty 
set).

- The symbollayer widgets receive a pointer to their vector layer. Normal 
symbol layer widgets don't use it, the widgets of  data defined symbol layers 
get the available fields through that pointer.

At first, I tried to achieve the data defined layer without API change by 
creating a new subclass of  QgsFeatureRendererV2 (as discussed with Martin in 
Lisbon. However, it turned out this approach would need a lot of duplication 
to provide graduated / unique / rule based classification and to provide a 
seamless  integration with the existing symbology(ng).

What do you think?

Regards,
Marco   

-- 
Dr. Marco Hugentobler
Sourcepole -  Linux & Open Source Solutions
Churerstrasse 22, CH-8808 Pfäffikon SZ, Switzerland
marco.hugentobler at sourcepole.ch http://www.sourcepole.ch
Technical Advisor QGIS Project Steering Committee