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dungdna

How to calculate PVS without using Portals?

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Please help me again, How to calculate PVS without using Portals? According to Dan''s tutorial, PVS information can be extracted using portals in a BSPTree. But, in some complex scence, the spliting of BSP produce a lot of portals. Is there a way to calculate PVS (for BSP Tree) without using Portals? Any idea, any comments? Please help me! DungDNA.

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Guest Anonymous Poster
There is no way. If you have too much portals, just cluster the leafs together,so you can delete a couple of portals. The quality of the PVS will be less then, but it''s worth a trie.

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Let me explain how Renderware''s basic PVS is calculated without using any portals.

The world is split up into axis aligned boxes called world sectors. These sectors have arbitrary dimensions.

The PVS is calculated for each sector by creating a list of other sectors visible from the current sector. For each sector a number of sample points which lie in that sector are needed. For each sample point, 6 renders of the whole world are done into a buffer (1 for each major direction). During a render each sector in the world is drawn using a certain unique colour. After a render the colours in the buffer indicate which sectors are visible from the sample point. After the 6 renders all sectors visible from the sample point are known, and are added to the current sector''s list.

Obviously, during run time the camera can be almost anywhere within a sector, and it would be impossible to create the PVS using an infinite number of sample points, so what''s needed is a good method for choosing a restricted number of sample points to use.

We are currently using Renderware for a racing game, and we are using their PVS system to cull out sections of the track. So far it''s working ok, and giving a slight speedup. Although now our artists are designing newer tracks with this PVS system in mind, which should help them become quite efficient.

Andy.

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Thanks a lot!

I''ve tried to group "small" sector into bigger cluster. It help reduce the number of portals a lot!!

Thanks so much for the idea of using "sample point"! It help me go further.

DungDNA.

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