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laeuchli

Rain City and Visibitly Algorithm

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Dear All, I was planning on writing a 3D engine, the sole purpose of which would be to render 3D cities. In addition, because I like dark moody cities, most of the time it will be raining in the city :-). Given that their wouldn''t be to many occluded triangles in a situation like this, would it be worth it to implement a Visibitly Alogorthim? More generally, how much occluded stuff do you need, before it becomes worth it to impelment a Visibility Algorithim. While I see it would be quite worthwhile in things like quake3(on a related note, what sytem do they use in quake3?Was it Octrees?), I can think of several gray areas where I''m not sure if it would be worth it. What do you all usally do? Thanks, Jesse www.laeuchli.com/jesse/

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Occlusion culling is a advanced topic, you might want to write some code and have something running before addressing it. There are some more or less complex solution to this topic, I like keeping things simple and implemented a "brute force" solution that just splits the world in unifrom cells where each cell knows what is in its view given a viewing direction. The visibility info is precomputed. See my (much too short) docu at
http://www.dawntec.com/docu/conVisDet.htm

I would say the solution to your problem depends on your time and experience in managing complex code, so keep it simple and improve in the long run.

- thomas

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You can save your city''s in bsp formats... They have bould in visibility data if you are in a given location... All this is precomputed when compiling the map. It tames time but the result is good... (Think of CS, Half-life and Quake 3)

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For outdoor sceneries like the mentioned city bsp might not be the ideal solution. Simple quadtrees, much easier to implement, will do as well as the third vertical dimension has not much to cull. Even if the buildings are high, they basically consist of simple boxes that are not worth to cut. I suggest quadtrees for the given scenery.

- thomas

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I would also suggest a quadtree like structure for the high level culling. And occlusion culling will probably give a huge speedup in city scenes. This type of environment typically exhibits very good occlusion behaviour (large uniform surfaces, low visible depth range, dense geometry, etc).

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