Is it ok to have a mesh rendered like in the top pic, or is it nessesary to tesselelate the plane and render it as in the bottom(to reduce visual artifacts)? The hemisphere lies directly on the plane. On my graphics card(Geforce 2 pro) the top method looks almost ok, but not as good as the bottom.

The bottom method will always look at, since all triangles are connected. But it takes more faces. The top method relies onthe zbuffer to create the intersection. It''s quality highly depends on your near and far clipping ranges.

I''m not using a whole sphere! The sphere is already perfectly clipped to the plane. The problem isn''t zbuffer zigzaging(what you sometimes see in terrain with water demos), it''s zfighting, only on the pixel row of the circle.

> I''m not using a whole sphere! The sphere is already perfectly clipped to the plane

Right. It *is* a zbuffer problem You can''t position it ''perfectly'' on the plane, due to accuracy problems with floating point math. Try to make it float over the plane, just a tiny little bit. The effect should go away.