Re: [PyOpenGL-Users] Difficulty accessing glCreateShader

[Gijs <in...@bs...>]

Mohan wrote:
> Hi Mike,
>
> Thank you very much for the (very quick!) reply. Changing the code to refer 
> to
>
>    glCreateShader = OpenGL.GL.glCreateShader 
>
> etc. solved that problem. Unfortunately, there is still an error, namely
>
>    ValueError: glShaderSource requires 2 arguments (shaderObj, string), 
> received 4:
>     (2L, 1, <cparam 'P' (0187bd28)>, <cparam 'P' (0187bd78)>)
>  
> (I have kept the
>
>    glShaderSource.argtypes = [c_int, c_int, POINTER(c_char_p), 
> POINTER(c_int)]
>
> in the source.)
>
> In another post on a very similar problem (pyopengl-Bugs-1878648), you wrote
>
>> I'm guessing what's
> happening is that you are on Win32, and that at the point where you import
> the module, there's no glShaderSource function. As a result the wrappers
> were not being created. Later, when you tried to call them, the
> null-function wrapper was able to resolve the function and tried to call it
> directly.<
>
> Is there a workaround for this? I had a look at the example you mentioned 
> in that post, and it references glShaderSourceARB rather than 
> glShaderSource. I can switch to ARB extensions if need be, but I'd like to 
> understand why the straightforward 2.0 approach isn't working, i.e. why 
> there's no glShaderSource function when the module is imported.
>
> It sounds like I might be asking for help in an inappropriate place, in 
> that I'm not really using the functionality of PyOpenGL. (I am very 
> grateful for the previous assistance!) Would you happen to know of a more 
> appropriate mailing list or forum?
>
> Thanks again,
> Mohan
>
> PS. My mail client is misbehaving -- I've waited half an hour to avoid 
> double posts, but in case something went wrong I'm very sorry!
Hello Mohan,

I fooled around with these kinds of problems quite a bit and the best
way to make it work without too much work, is to switch all your OpenGL
code to their ARB equivalents. Best thing is that it makes it portable
across platforms as well. If you use the ARB function calls instead of
the "normal" ones, Windows, Mac OS X and Linux usually works 99% of the
time (not including driver differences).

I'm not completely clear on the problem, but it has something to do with
how/when the functions are bound to their OpenGL functions. Windows
binds them later on, while Mac OS X and Linux bind them earlier (from
what I've seen so far). Maybe Windows binds them when you call the Glut
init functions, but I'm sure Mike can give you a better answer regarding
the problem.

Regards, Gijs