🚀 go-pugleaf

How is the perspective matrix computed in GL?  I'm familar with the
Foley / Van Dam stuff where the diagonal is 1's and then using 1/d
(d = distance to viewing plane) etc. etc.  I just assumed that this
would be the case after calling "perspective" and "d" would be found
from the view angle.  However this was not the case as the values
in the diagonal where not all 1.  (Doing a getmatrix after a perspective
call).

Anyhow, why I ask and have the attention of all you graphics people, is
because I've been trying to match up the images from my raytracer to the
images produced using the GL.  For small view angles the images match up
fairly well.  For large viewangles my images are slightly larger.  Sort
of like the eye point is a bit too close or the view angle a bit too small.
(Yeah I've checked out both of those)  So now I figure I'm missing a key
concept on perspective.  But it all seems so easy.........

Thanks.



-- 
-Tim Hall
I felt the water coming up to my chin, up to my nose.  When I woke up
my body was all greasy from the holy oil.  I remember being disappointed
I was still alive.  -Harry Call