View Full Version : Confused about fovy

10-25-2015, 01:33 PM
I was just looking at Angel's book about derivation from Frustum to Perspective

it is written
Perspective(fovy, aspect, near, -far) // I don't understand why -far
Frustum( left, right, top, bottom, near, far)

Now ,top derived as follows:

top = near*tan(fovy)

Should not be top defined as follows:
top = near*tan(fovy/2)

What is fovy in perspective? Isn't the angle between top and bottom with near plane?

So what should we use in glPerspective: fovy/2 or fovy?