[Qgis-developer] Render speed

Tim Sutton tim at linfiniti.com
Thu Jan 10 05:29:19 EST 2008


Other things we could to the list (though they may be out there in

 - prevent unneccessary rerendering of a scene by using composition
management (no idea if this is viable with QGraphicsScene though)
 - prerendering off screen areas in a background thread
 - composit each layer to screen as it is rendered
 - go trough all rendering loops and move as much if..then...foo logic
to outside of the loop - for exmple pre-create all brushes and pens
before the loop and then just select the appropriate one from the
brushes and pens collection during render loops.
 - get people like Frank Warmerdam to review main render loops to see
if are accessing data in most efficient way possible

and my final tougue in cheek option:

 - dont permit canvas size greater then 100x100px and issue each user
with a large magnifying glass

About three years ago a colleague and I would regularly test render
performance of QGIS by comparing rendering the same datasets (vector
and raster) against ArcView and ArcMap on the same (dual boot
machine). QGIS did pretty well then with the exception of being slower
at rendering large vector scenes when zoomed out. This is a useful
metric to use since these apps are the standards against which many
users will measure how fast QGIIS is. I no longer have access to Arc*
apps but Im sure there are obliging users out there who can help.

I will be more than happy to write some benchmarking unit tests too..



2008/1/10, Albert Cervera Areny <albert at sedifa.com>:
> >
> > - possibility to cancel long rendering operations (as described by Martin)
> > - a faster attribute table based on model/view (as described by Tim)
> > - caching of WMS tiles for fast panning actions by WMS provider
> Indeed, caching should be done for all backends, GML is very slow, and others
> could see a performance boost too, acording to previous discussions. Not
> volunteering right now, though ;)
> > - parallel rendering of layers on multicore processors
> > - on-the-fly generalisation of complex geometries (only upon user request!)
> >
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Tim Sutton
QGIS Project Steering Committee Member - Release  Manager
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