glScissor - rectangles

hi there,
using glScissor will cut out a rectangle from the scene.
Now i thought about cutting out circles and stuff…for example,i thought about creating a scene with a view through binoculars…

o.k.,i could put some large disks and stuff in front of the scene making it look like binoculars ,but i don’t want to.
So ,is there a function to do this?

look for the stencil buffer, it is what you need.