[Qgis-developer] Rendering with transparency -- slow

[Christoph Spoerri]

Hi there,

I diagrammed the data model currently used by the lib_refactoring branch. 
While trying to understand the interaction of the classes and their purpose, 
I saw that some classes share similar functions (e.g. nextFeature in layer 
and provider classes), at the same time some classes could be further 
refactored. 

So, I went ahead and created a proposed data model, the way I would have 
designed it. The idea behind the model is that we have two main classes:

- QgsDataSet: used for data manipulation on a feature level (e.g. adding, 
deleting, etc.), used in QgsMapLayer for rendering. This class would contains 
methods such as nextFeature(), deleteFeature(), updateGeometry(), 
createPyramid(), etc.

- QgsDataProvider: used for data manipulation on a dataset level, e.g. 
copy/deleting an entire dataset, format conversion, select subset of 
features, etc.

The QgsMapLayer classe(s) would only be used for rendering purposes, and 
methods such as nextFeature, etc would be remove from the class.


Please let me know what you think. If folks think this approach makes sense, I 
would be happy to continue developing the model and post my progress for 
comments on the wiki site.

cheers,
Christoph
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