3 replies to this topic

[ynm]

Hi everyone,

I remember some demos, not exactly Nvidia or a game engine where they showed their model is smoothed, i.e from line to curve. I wonder is there anyway to create a curved model without increasing triangles number? E.g a gun barrel section is a circle not an octagon.

Regards

Edited by ynm, 30 November 2012 - 01:44 PM.

[swiftcoder]

I wonder is there anyway to create a curved model without increasing triangles number?

Nope. You can however fake it in numerous ways.

Normal mapping is a cheap way to give the appearance of smoothly-curved surfaces, although the silhouette will still give it away. GPU tessellation + displacement mapping will solve even the problem of the silhouette, albeit at the cost of adding many more triangles at runtime (though these are purely on the GPU, and thus relatively cheap).

[MJP]

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.

[ynm]

Many thanks