GemMan? (and by association, gemwin) disables alpha testing, alpha blending, culling, and lighting. Lighting defaults to two sided, with GL_COLOR_MATERIAL enabled. The viewport is set to:

 float xDivy = (float)m_width / (float)m_height;

 glMatrixMode(GL_PROJECTION);

 glLoadIdentity();

 glFrustum(-xDivy, xDivy, -1.0, 1.0, 1.0, 20.0);

 gluLookAt(0.0, 0.0, 4.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);

 glMatrixMode(GL_MODELVIEW);

 glViewport(0, 0, m_width, m_height);

which gives a range of about -4 to 4 in X and Y at the origin. This is a small range, but changing it now would break a lot of patches.

The specific functions to look at are:

GemMan::windowInit()

GemMan::resetValues()

gemhead::renderGL()