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by dahart
2244 days ago
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> Nurbs or any smooth geometry needs to be subdivided too Not true; lots of smooth surfaces, including NURBS, can be and are ray traced without subdividing. > Polygonal geometry, even subdivided, is typically not a big part of memory or time in rendering in all but the most pathological cases. I don’t buy this either, speaking from experience using multiple commercial renderers. It is true that texture is larger, but not true that polygonal geometry is not a big part of memory consumption. RenderMan, for example, does adaptive tessellation of displacement mapped surfaces because they will run out of memory with a uniform displacement. The balance of geometry vs texture usages is also changing right now with GPU ray tracers, and geometry is taking up a larger portion because it has to be resident for intersection, while textures can be paged. |
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It of course depends on exactly what is being rendered, but typically texture maps of assets for high quality cg are done at roughly the expected resolution of the final renders (rounded to a square power of 2). Typical assets will have three or four maps applied to each group of geometry, with higher quality hero assets having more groups.
> RenderMan, for example, does adaptive tessellation of displacement mapped surfaces because they will run out of memory with a uniform displacement.
It is specifically screen space displacement and this has been effective, but was originally crucial in the days where 8MB of memory cost the same as someone's yearly salary. In PRman actually polygons are even less of a burden on memory because of this with micropolygon and texture caches for efficiency, even with raytracing.
The real point here though is that nurbs don't really have much of an advantage, even in memory, because polygons are already lightweight and can be smoothed. Subdividing of polygons is typically not going to be too different from burbs and heavy polygonal meshes are likely to be extremely difficult to replicate with nurbs.
Don't get too caught up in exactly what is technically possible, this is about why nurbs are not an ideal form of geometry that anyone is trying to use again. Their disadvantages outweigh their advantages by a huge margin.