2D to 3D
How can i translate a 2 dimension screen coordinate in a 3 dimension coordinate because i want to create a 3D object by a mouse clik on the screen.(sorry for my english because i'm french).
Re: 2D to 3D
I don't know if this is any help, but you might use something like MultiGen does:
When you click on the screen, there is a whole line of points in 3d that you could actually mean. MultiGen allows the user to define a grid and position this grid in a plane. When you click, the point snaps to this grid. Using opengl, the user would need to specify the plane, then you could use an orthographic projection such that the x,y in the window match those in the real world. Then you would need to rotate/translate these into the real world.
Hopefully this helps. Your question is a bit broad. It would be easier to answer with more detail.