OGL Crash

[Robert Lunnon]

I have a problem with OGL , during initialisation I have a segfault occurring 
in the following code segment, note that I have instrumented the code


XVisualInfo *X11DRV_setup_opengl_visual( Display *display )
{
    XVisualInfo *visual = NULL;
    /* In order to support OpenGL or D3D, we require a double-buffered visual 
and stencil buffer support, */
fprintf(stderr,"setup visual\n");
    int dblBuf[] = {GLX_RGBA,GLX_DEPTH_SIZE, 16, GLX_STENCIL_SIZE, 8, 
GLX_DOUBLEBUFFER, None};
    if (!has_opengl()) return NULL;
fprintf(stderr,"Choosing Visual display=%p DefaultScreen=%p 
dblBuf=%p\n",display, DefaultScreen(display), dblBuf);
    wine_tsx11_lock();
************************Crash Occurs in the following line
    visual = pglXChooseVisual(display, DefaultScreen(display), dblBuf);
    wine_tsx11_unlock();
fprintf(stderr,"Visual is %d\n",visual);


Output is 
setup visual
Choosing Visual display=81ad320 DefaultScreen=0 dblBuf=7fd1ef70
Handling exception at EIP 7f0434b7 accessing 2a0
wine: Unhandled page fault on read access to 0x000002a0 at address 7f0434b7 
(thread 0009), starting debugger...
Can't attach process 8: error 5

I suspect the problem is DefaultScreen returning 0
Anyone know where this is defined ?