speed of raster repainting

[Bernhard Reiter]

On Fri, Dec 31, 2004 at 01:27:19AM -0500, Russell Nelson wrote:
> I notice that raster repainting is fairly slow.  The raster needs to
> be repainted whenever the layer order is changed or layer visibility
> changes.  The time seems to be evenly split between ProjectRasterFile(),
> and wxImageFromStream().  There is some room for improvement there, I
> think.  ProjectRasterFile seems to be returning a BMP file, whereas it
> could return a wxImage.  That would make the raster repaint twice as
> fast.  Also, it could keep a cache of projected data, so if all the
> parameters to ProjectRasterFile are the same, it would return the same
> projected data.
> 
> Mapviewer only displays UTM maps, so it doesn't have to deal with
> changing the projection.  Still, keeping an internal cache of tiles as
> pixmaps, ready for drawing, lets me repaint 16 200x200 pixmaps at
> least ten times per second.

Having a nive cache system is a long standing wish,
we did not want to do premature optimisation, this is why we do not
have it in there yet. 

I also believe that caching projected data will help a lot with
raster and other data. 
Did you do any profiling, because that would be evidence that we
are slow because of this and saves us one step. :)

Also feel free to hack up some optimisation.
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