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OpenGL OpenGL: Basic Coding
12

‘sin’ does not just give better results, it is the right trigonometric function to use.

For the code you need to know:

  • width:height aspect ratio (width / height as floating point number as used by gluPerspective)
  • center and radius of the bounding sphere for the scene
  • direction of the camera (unit length)
  • fov in y (as used by gluPerspective)

The code would be as follows:


half_min_fov_in_radians = 0.5 * (fov * PI / 180);

if (aspect < 1.0)
{
    // fov in x is smaller
    half_min_fov_in_radians = atan(aspect * tan(half_min_fov_in_radians));
}

distance_to_center = radius / sin(half_min_fov_in_radians);
eye = center - dir * distance_to_center;

You may also take advantage of that information to fit your zfar clipping plane (if you do not want to keep it too far).


zfar = distance_to_center + radius;

if (zfar < 1.5 * znear)
{
    // Keep zfar always bigger than znear
    zfar = 1.5 * znear;
}