I'm a little beginner.. I need some help, please !

Hi! Sorry for my poor english, I'll try to be as clear as possible.
How can I determine the size on the screen of a segment given by its two vertices in the scene?

[Le Bayonnais]

Tu ne serais pas francais des fois???
For init the OpenGL Panel, you have specified the size of the window and the type: projection or persceptive..
you have to make projection with cos and sin with these window parameters
Le Bayonnais

a^2+b^2=c^2
c=sqrt(a^2+b^2)???