Question

How can I scale a random 3d model to fit in an opengl viewport? I am able to center the model in the middle of the view port. How do I scale it to fit it in the viewport. The model could be an airplane, a cone, an 3d object or any other random model.

Appreciate any help.

Answer 1

You’ll need the following information:

• r: the radius of the object’s bounding sphere
• z: the distance from the object to the camera
• fovy: the vertical field of view (let’s say in degrees) of the camera, as you might have passed it to gluPerspective

Make a little sketch of the situation, find the right triangle in there, and deduce the maximum radius of a sphere that would fit exactly. Given the above parameters, you should find r_max = z * sin(fovy*M_PI/180 / 2).

From that, the scale factor is r_max / r.

All this assumes that the viewport is wider than it is high; if it’s not, you should derive fovx first, and use that instead of fovy.