Selection

Hi,

you have different options to implement picking in your modeler. Basically you'll want to select objects, faces, points and lines.

To select objects a common and easy to way to do it is to use glReadPixels: for each object you assign a different single color and then you read the pixel's color you have under the mouse click:
Good link

To select faces, you could use the OpenGL selection, (which on some implementations runs in software mode and it's not very fast):
Good link
A better approach is to do 3D picking: basically you shoot a ray in your world to select the faces that return a hit (ray/polygon intersection test). 3D picking can be a little longer to implement but, if it's associated with some kind of culling technique (to reduce intersection test), can be a lot faster than OpenGL selection.

Once you get used to pick faces, it's simple to pick points: if you use 3D picking, once you get the face that hit, you could project the hit point on the near plane among with the other face's point and select the one with min distance. Same for edge.

Here's a pretty good overview of the techniques above:
3dkingdoms
TomC

Have fun!

Libe