[Qgis-developer] Addition to QgsRenderContext

[Magnus Homann]

Is it OK to add transparency setting into the render context? This would make it much easier to
cache point symbols with transparency.

Current contents:

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     /**Painter for rendering operations*/
     QPainter* mPainter;

     /**For transformation between coordinate systems. Can be 0 if on-the-fly reprojection is not used*/
     QgsCoordinateTransform* mCoordTransform;

     /**True if vertex markers for editing should be drawn*/
     bool mDrawEditingInformation;

     QgsRectangle mExtent;

     /**If true then no rendered vector elements should be cached as image*/
     bool mForceVectorOutput;

     QgsMapToPixel mMapToPixel;

     /**True if the rendering has been canceled*/
     bool mRenderingStopped;

     /**Factor to scale line widths and point marker sizes*/
     double mScaleFactor;

     /**Factor to scale rasters*/
     double mRasterScaleFactor;

     /**Map scale*/
     double mRendererScale;
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