[Bf-committers] import_obj.py - Reimplementation

CoDEmanX codemanx at gmx.de
Thu Jan 3 17:58:24 CET 2013

OBJ import can take quite some time and use a lot memory, but only if 
you use splitting ("keep vert order" imports way faster). Is there 
something else causing the bad performance?

Multiprocessing would be great, for splitting it might work. But 
probably not for any code that calls bpy api functions...

C/C++ importer: This year's GSoC project "FBX importer" wasn't actually 
about FBX, but assimp integration (= C/C++ importers for FBX, OBJ etc.). 
There are builds available at graphicall.org. However, I'd keep the 
python addons in trunk.

Python + Lib: Why improve performance of a python script if a C/C++ 
importer is available (assimp) and faster than the script will ever be? 
In addition, I/O scripts should be kept simple IMO, so that scripters 
can learn from them for their own addons.

If there are any simple python hacks to improve performance, they should 
be applied of course.

Am 03.01.2013 03:16, schrieb Isaac Lenton:
> Hi
> A few days ago I was using Blender's import_obj.py script to import a few
> rather bulky OBJ files into blender (200MB and above).  On my little system
> it takes about 2 minutes for every file.  I have been looking into improving
> this script with simple optimisation, splitting the work amongst multiple
> workers and changing the amount of memory the script uses.  Some of these
> methods are successful, but the results are only minor.  I did manage to
> reduce the loading time of the 200MB file to 1 minute 40 seconds.
> Although a quicker method for importing my data into Blender would be to
> use another format, I quite like the OBJ format and I am "in the mood" for
> optimising.
> In order to significantly improve the speed of Blender's OBJ importer I can
> see a couple of options:
>      - Implement the importer straight in C/C++ and build into Blender.
>          I think this option is probably undesirable considering it takes
>          away one of the really nice things about Blender's add-ons (the
>          add-on part!).
>      - Keep the implementation in pure python.
>          Also, in my opinion, undesirable.  The Python is great, but it can
>          slither only so fast.  (Also, what are your opinions on using Python's
>          multiprocessing module in import scripts?)
>      - Keep the python script but implement the most expensive methods in
>          a C dynamic library.  This option will keep the interface to the
>          exporter exactly the same, the module will still be able to be
>          imported using pythons `import` and Blender will not even notice
>          the difference.  The library would be placed in the same directory
>          as the script (scripts/addons/io_scene_obj) and the script would
>          simply add the line `from . import TheNewLibrary` at the start.
>          Downside: using plain C and python can be painful (but fun).
>      - Keep the python script but implement the most expensive methods in
>          a boost::python C++ dynamic library.  Same as above.
>          Downside: Boost::Python libraries have a big overhead.
> I find for my own code, when size is not important, I prefer the last option.
> I am interested to hear any opinions on the above ideas, and any ideas anyone
> may have on generally improving the speed of Blender's importers.  Are any
> of these options Blender compatible (as in, could they be included in the
> official release)?
> Thanks,
> Isaac Lenton
> (ilent2)
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