I know that by default, OpenGL will do backface culling. Is there a way to turn it off?

If there is not (and even if there is), how does one reverse the normals of a polygon? I have tried reversing the order of the verticies, but to no avail.

PS- The polygons in question are quads

-Thanks in advance.

Actually, I don't think that culling is on by default. You enable and disable it using the following (default is disabled):

glEnable(GL_CULL_FACE);
glDisable(GL_CULL_FACE);

You can specify to cull front or back by using the following ( default is GL_BACK):

glCullFace(GL_FRONT /* or GL_BACK or even GL_FRONT_AND_BACK */);

OpenGL doesn't use normals to determine which is the front and which is the back. It actually uses the winding order of the polygon. The default is counter clockwise, but you can change that using:

glFrontFace(GL_CW /* or GL_CCW */);

To reverse the direction of a normal, you simply multiply it by -1. OpenGL doesn't calculate normals for you, you need to actually supply them yourself. Generally to get the normal of a face, you take the cross product of 2 of the edges, which gives you a vector that is perpendicular to them both...

Are you running into some specific problem? Try to describe that in more detail and maybe we can help.

The specific problem was that the object was "inside out".

Enabling culling and telling it to cull the backs of faces fixed it.

Thanks for the help!

Could it be that the real problem is that you did not enable depth testing? In Linux, you not only need to enable depth testing (glEnable(GL_DEPTH_TEST);), you also need to create your context to have a depth buffer (Windows seems to usually have a depth buffer by default, Linux doesn't in my experience).

How you do that depends on exactly how you are creating your window. For instance, with Glut, you include GLUT_DEPTH in the options of the glutInitDisplayMode call. Also, you need to add GL_DEPTH_BUFFER_BIT to your glClear call. (e.g. glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);)

Enabling backface culling is always good anyway to improve performance, but having it off shouldn't have made the object look "inside out" if the depth testing was working correctly.

Yup. That was it. After performing a few more tests, I became less sure that the problem had to do with culling, since the visibility of faces also changed with the camera angle!