what does prototype say about the function?

use OpenGL;
print prototype("OpenGL::glColor3f"), "\n";
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When the module is compiled, a OpenGL.c file is generated, can you post the code for the function wrapper?

Also, how is the function registered in the interpreter? Look for a cv = newXS("OpenGL::glColor3f", ...) statement probably followed by sv_setpv((SV*)cv, "$$$") to set the prototype