Re: [PyOpenGL-Devel] pyopengl and pypy

[Mike C. F. <mcf...@vr...>]

On 10-11-26 07:54 PM, rndblnch wrote:
> hello,
>
> i'm trying to make my pyopengl(3.0.1)-based code run with pypy (1.4).
> i ran into some issues:
> 1) the use of ctypes.pythonapi (for PyString_AsString in arrays/strings.py and
> PyBuffer_FromMemory in arrays/vbo.py)
> 2) an "AttributeError: type object 'ArrayDatatype' has no attribute
> '_CData_input'", trackback:
> ...
>   File "/Users/Shared/src/pypy-1.4-osx/site-packages/OpenGL/latebind.py", line
> 45, in __call__
>     return self._finalCall( *args, **named )
>   File "/Users/Shared/src/pypy-1.4-osx/site-packages/OpenGL/wrapper.py", line
> 784, in wrapperCall
>     result = self.wrappedOperation( *cArguments )
>   File
> "/Users/Shared/src/pypy-1.4-osx/site-packages/OpenGL/platform/baseplatform.py",
> line 335, in __call__
>     return self( *args, **named )
>   File "/Users/Shared/src/pypy-1.4-osx/lib_pypy/_ctypes/function.py", line 166,
> in __call__
>     argtypes, argsandobjs = self._wrap_args(argtypes, args)
>   File "/Users/Shared/src/pypy-1.4-osx/lib_pypy/_ctypes/function.py", line 281,
> in _wrap_args
>     wrapped = argtype._CData_input(arg)
> AttributeError: type object 'ArrayDatatype' has no attribute '_CData_input'
>
> i guess that for 1) it should be possible to write pure ctypes/python
> replacements for the needed functions (any hints welcome :)
> for 2) i didn't manage to understand enough the relationship between pyopengl
> and ctypes to get any clue about what's going on.
>
> anybody with some experience with/interested by such issues?
>   
I'm definitely interested, but have very little time these days to play
with PyOpenGL.

There's a lot of machinery in PyOpenGL that produces the ctypes
array-wrapper functionality (in the OpenGL/arrays package for the most
part), but in the end, it's just doing standard ctypes calls about 95%
of the time.  Every once in a rare while I had to use an undocumented
implementation feature of ctypes, but I don't think that's the problem
here.  _CData_input looks to be something pypy-specific which would be
the equivalent of the from_param method on CPython ctypes?  I'm guessing
the pypy implementation assumes an inheritance relationship among all
data-types and that _CData_input is a method on their _CData class.  For
whatever reason, the subclasses of ctypes.POINTER( <constant-type> ) are
not picking up that method.

For the first issue, those are going to require some reworking, in
essence those are "C" implemented code that happens to use Python/ctypes
as the implementation language and makes assumptions about the
data-storage for the objects (e.g. that a string is internally a
contiguous series of bytes, which is *not necessarily* true in PyPy). 
We'd need to find a mechanism in PyPy that would give us that direct
memory-pointer access to be able to use it.  Note: a compacting garbage
collector (or anything else that can move memory locations) will cause
problems there, so we may need to find a way to signal PyPy not to move
a given object, and to use contiguous data-arrays for their storage.

HTH,
Mike

-- 
________________________________________________
  Mike C. Fletcher
  Designer, VR Plumber, Coder
  http://www.vrplumber.com
  http://blog.vrplumber.com