#2033: Moving g.pnmcomp to lib/display to improve render performance of wxGUI
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Reporter: huhabla | Owner: grass-dev@…
Type: enhancement | Status: new
Priority: major | Milestone: 7.0.0
Component: wxGUI | Version: svn-trunk
Keywords: display, Python, multiprocessing | Platform: All
Cpu: All |
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Comment(by glynn):
Replying to [comment:6 huhabla]:
> It seems to me that creating raw bmp images without mmap enabled shows
the best performance for the PNG and Cairo driver. Maybe i did something
wrong, but the use of mmap shows no obvious benefit?
Using mmap() in the driver is probably not that significant in this
context.
It's more useful when GRASS_PNG_READ=TRUE, the resolution is high, and the
rendering is simple and/or limited to a portion of the image. In that
situation, mmap() eliminates the read() as well as the write(), and only
the modified portion needs to be read and written.
Another area where it matters is with e.g. wximgview.py (and its
predecessors), as it's safe to read a BMP image which is being modified
using mmap(), whereas doing the same thing to a file which is being
written out with write() runs the risk reading a truncated file.
Other than that, the performance difference between using mmap() and
read() on the read side boils down to mmap() avoiding a memcpy(). The
extent to which that matters depends upon what else you're doing with the
data. For wxGUI, it's probably a drop in the ocean.
> Any suggestions to improve the benchmark? Does my setup produce
reasonable results?
There isn't anything I'd particularly take issue with. However:
1. With the cairo driver, BMP files use pre-multiplied alpha (because
that's what cairo uses internally), whereas PPM/PGM output includes an un-
multiplication step. So depending upon your perspective, the cairodriver
benchmarks are rigged against PPM or in favour of BMP.
2. Producing separate results for PPM with g.pnmcomp and PPM with PIL
would provide a clearer comparison between the two compositing options and
the various formats.
--
Ticket URL: <http://trac.osgeo.org/grass/ticket/2033#comment:7>
GRASS GIS <http://grass.osgeo.org>
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