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Terrain for RTS

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Hello! I am working on a 3d rts and I am now looking for a good LOD algo. The terrain is fixed sized(no paging, but small <-> large), without overhangs(only a simple heightmap), but it is dynamic(explosions can form it). After looking at vterrain.org I decided for Geometry clipmaps: - fast - It doesn't require recalculation after changing the data. - Implementations for older and newer gpus. - I already implemented it in the past. Questions: Are there any better algos for my needs? Things to watch out for? Tips?

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Don't worry about it until its a problem. I, personally don't do it and hardly notice any slow down. We wasted more CPU cycles trying to lighten the GPU load we bogged down the CPU leaving the GPU to stall :)

Until you can prove its hurting the GPU to render a few thousand polygons, don't worry about it.

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It all depends on workload. On the newer GPUs with unified architectures it is almost always beneficial to remove polygons, because cycles saved in the vertex shader can be applied to the pixel shader. On the other hand, these new GPUs can easily handle 1 or 2 million polys per frame, because the reverse is also true.

On older chips, 1 or 2 million polygons will easily saturate the vertex pipes, so an LOD and culling scheme will help your graphics performance if you have the CPU cycles for it.

I'm partial to block-based approaches myself, especially if your terrain is a fixed size. I recently implemented a system where I use a mip-map of the terrain heightfield and geomorph between mip levels within each block at the outer edge of each LOD ring. If you set this up right you can do it in a crack-free manner, and I personally like this approach better than the extra degenerates that are required for clipmaps.

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If your rts is a top down view, like Command & Conquer Generals, but without rot rotation, then you could easily do without any LOD scheme. Simply clip the triangles being rendered to what's inside the viewport. It would basically be the same as if it was a regular 2D grid.

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How large is your terrain? If it is < 2Million Polygons just render it with frustum-clipping. The main problem for some algorithms will be that you have to change your terrain at runtime.

If it is larger you can use geoclipmaps.

By the way, whats going on at the geometry clipmap patenting front? Sometime ago I read about a patent by microsoft at freshpatents. But now, I tried to search the patent with the official U.S. patent website and I didnt find it... In addition H. Hoppe's website doesnt say something about patenting anymore.

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Thanks for the replies!

rotalever:
I don't know about the size, because I am still in the planning stage. But I want big maps like in Total Annihilation.

I don't know about the patent.

soconne:
You will be able to rotate the camera.

jbarcz1:
Any papers or tutorials about your aproach?

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Quote:
Original post by Orchaldir
jbarcz1:
Any papers or tutorials about your aproach?


Not really, I kindof made it up as I went along. There might be papers out there that do similar things to what I did, but I haven't tried to hunt for them.

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A very good site on terrains would be vterrain.org.

Simple Frustum culling should be enough for a Top Down RTS. Even if you
can turn the camera so it is horizontal. Lowering the Far Z Plane Distance
would be a good idea too, no need to see much of the map.

Anyway, if you feel as though you must do a LOD algorithm. I can only
recommend the one I use, which is 'Chunked LOD'. It takes up some memory,
and its best for static terrains, but it has very little CPU impact and it
seems to be easier to impliment than most other LOD algorithms, in theory
anyway.

-Twixn-

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