Mike wrote:
>OK I looked at the source again and I found where the change is made. It
>scales the up and right vectors, but I don't understand exactly by what
>values.
>What is k1/k2 equal to?

I would guess, the idea is to make the comparision between perspective
and orthographic camera in the image plane. If a perspective camera
has a greater focal length (direction vector), it coveres the area given
by "up" and "right" *in its image plane* (which is located at a distance
given by the distance vector).
At unit distance (where the area covered by the orthographic camera
is defined), the given perspective camera with greater focal length
will cover a smaller area, as given by up*k1/k2 and right*k1/k2
where
   up = length("up")
   right= length("right")
   k1 = length("look_at")
   k2 = length("direction")

IIRC, the "look_at" vector is normalized somewhere beforhand.

Did I express myself clear???

Hermann

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