[Thuban-list] displaying raster is very slow

[Jonathan Coles]

2005/6/29, Jan-Oliver Wagner <jan at intevation.de>:
> in fact Thuban has so far not undergone performance tuning
> for raster. There is probably lots of opportunities
> to make it run faster.
> 
> IIRC Jonathan did something in this area, but it might
> only work with wxWidget 2.5/2.6 ... ?

The work that I did earlier in the year was about supporting different
kinds of transparency. Alpha blending requires wxWidgets >= 2.5.3.
There is some more limited transparency support that uses a bitmap to
represent which pixels should be on or off. That works under ealier
versions of wxWidgets as well as later versions.

Off the top of my head, I can think of three areas that might be
affecting the speed:

1) The warping of the source image to fit the projection. This code is
essentially just calls to the GDAL library, which is seperate from
Thuban.

2) If any form of transparency is enabled, especially the bitmapping form, then
this could be taking a while for a large image.

3) The image drawing code of wxWidgets, but I've been drawing large
images (i.e. those that cover a large number of physical pixels) and
haven't noticed this to be a problem.

The easiest thing to try is to turn off transparency on the image
layer. If that improves performance then that's the source of the
problem. Using alpha blending may also improve the speed over bitmap
transparency because a lot of tedious computation isn't necessary.
Remember, however, that alpha blending is only supported under
wxWidgets >= 2.5.3.

Hope that helps,

--jonathan

-- 
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Jonathan Coles                               http://www.jpcoles.com
jonathan at jpcoles.com
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