Posted 30 November 2012 - 07:26 PM
If we're talking about GPU hardware rasterization, then the only supported primitives are points, lines, and triangles. To approximate curved surfaces with actual geometry you would need to tessellate to triangles. If you don't want to do that, you can shade surfaces as if the surface geo was actually curved. This can be accomplished with normal maps, or even with really simple techniques like interpolating smooth vertex normals across a triangle. It's also possible to discard pixels and manually output depth values, which can give you the outline, shading, and resulting depth buffer of a curved surface. However doing this isn't really practical, since it doesn't play nice with GPU hardware optimizations.