Replacement for gluPerspective (with glFrustrum)

Question

How would you convert a gluPerspective function to glFrustum? I have tried to use this equation, but have not had any luck as it did not generate the same image as it did with gluPerspective.

top = tan(fov*3.14159/360.0) * near bottom = -top

left = aspect * bottom right = aspect * top

I can't seem to convert my field of view correctly. Say, for example, if my FOV was 45, what would be the 'top' param in the Frustum call?

Answer 1

Here we go - you can use the following method as a replacement of the gluPerspective:

void perspectiveGL( GLdouble fovY, GLdouble aspect, GLdouble zNear, GLdouble zFar )
{
    const GLdouble pi = 3.1415926535897932384626433832795;
    GLdouble fW, fH;

    //fH = tan( (fovY / 2) / 180 * pi ) * zNear;
    fH = tan( fovY / 360 * pi ) * zNear;
    fW = fH * aspect;

    glFrustum( -fW, fW, -fH, fH, zNear, zFar );
}

You can find some more explanation of the code on the nehe page.