Hi, 2010/12/1 renaud blanch <rndblnch@gmail.com>
i'm trying to make some pyopengl [0] -based code [1] run on top of pypy. this is partially successful, but i need some advice to progress further. pyopengl 3.x makes use of ctypes to provide the opengl binding, and it works out of the box for simple functions (those that do not takes c-pointer to buffers of data as arguments). for the rest, the first issue is that pyopengl use two functions from the ctypes.pythonapi lib, namely PyString_AsString and PyBuffer_FromMemory. any advice on how to replace those functions to make them compatible with pypy?
Mike Fletcher (pyopengl author) gave me some hints about that point:
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.
Don't worry, with PyPy's ctypes you'll never get the address of a moving object. c_char_p makes a non-moving copy of the string. But IMO the call to pythonapi.PyString_AsString could be removed in OpenGL/arrays/strings.py: def dataPointer(value): return ctypes.cast(ctypes.c_char_p(value), ctypes.c_void_p).value I don't know about the other function, though. -- Amaury Forgeot d'Arc