Espozo wrote:
Normal mapping doesn't quite replace more polygons, as the edges of an object are still as jagged, and subdivision is part of the problem, as it just adds more vertices.
I am not quite clear about what you want, then, but here's another try...
You can use a texture with an alpha mask to cut curves off of polygons. You can render a sphere as a single quad with a normal map and a circular alpha cutout, for example.
(This is sort of a combination of the 4th thing in my previous post, i.e. using textures to draw curves across polygons, and the 2nd thing, using textures to provide surface shape for lighting.)
There's lots of tricks for producing busy-volume objects with few polygons, typically used for things like trees, hair, etc.
For example, maybe for a tree you just have two quads (like an X from above) but use
alpha to coverate to blend away the face that's currently more edge-on from your viewpoint.
Your question about what you have CPU/GPU resources to do is not easily answerable. Depends on the situation. Sometimes it's better to throw more polygons at the model. Sometimes subdivision surfaces perform very well. Sometimes too much stuff in your pixel shader is worse than too many polygons. It's not really something that's easy to speculate on, but lowering polygons is far from the only way to try and improve GPU performance (and how much it can affect it really depends on the nature of the system we're talking about).