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Multipass rendering


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#1 the darkening   Members   -  Reputation: 122

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Posted 04 July 2001 - 07:23 AM

Hi, I recognized that FAST multipass rendering seems to be hard to implement. From a friend of mine I saw a demo which uses 12 lights in- and outside from two cubes and it runs with ~44 fps on a GeForce2GTS. That is really slow I think. As I want to implement something to get more than 8 light sources I''d like to ask you to give me some clues how to make it!? Darkening

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#2 mittens   Moderators   -  Reputation: 1315

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Posted 04 July 2001 - 07:37 AM

Well, the hardware lights (the 8 lights that OGL provides) should only be used when you absolutely need dynamic lighting. Do some research on "light maps" which are a way to do static lighting (for walls, and such... things that never move, and its an inexpensive way to do things).

Also, multi-pass rendering IS slow (multi-pass rendering is different from multitexturing). I would suggest looking into OGL''s multitexturing extension, as it is still pretty fast.

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#3 Azrael   Members   -  Reputation: 128

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Posted 11 July 2001 - 11:16 AM

I initially had the same question about multipass as you do, the reason why multipass is so slow is because is because you actually have to render the geometry twice... think about it,specially if you are using something with a lot of vertices like a terrain this can be extremely slow ,on the other hand using ARB real multi texturing means one render one time and mixing the textures on the fly by hardware, now thats hard to beat...
unfortunately not all card provide real multitexturing so you should try in more than 1 card. a a hint voodoo2 cards dont use real multitexturing.. riva tnt cards do.


#4 Obelix   Members   -  Reputation: 122

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Posted 11 July 2001 - 05:23 PM

Right, but you also has to write multiple times to the backbuffer so multitexturing is also limiting the fill rate needs.

#5 RoastBeef   Members   -  Reputation: 122

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Posted 13 July 2001 - 07:43 PM

Ummm, even if you absolutely NEED dynamic lighting, there are ways with something called, oh, lightmaps. It''s called dynamic lightmapping, and Quake uses it.

Hardware lights are really a last resort, as they can be fairly slow, and since there''s only 8 of them, you can''t do much, unless you do alot of state switching. All in all, you''ll see huge performance decreases.

Lightmapping forever

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#6 smitty1276   Members   -  Reputation: 560

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Posted 14 July 2001 - 10:34 PM

Is there a tutorial around here on light mapping?


#7 Obelix   Members   -  Reputation: 122

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Posted 15 July 2001 - 01:32 AM

Here is an example from ATI http://www.ati.com/na/pages/resource_centre/dev_rel/sdk/rage128sdk/OpenGL/Samples/Rage128LightMap.html

ATI:s oglmultex is available here http://www.ati.com/na/pages/resource_centre/dev_rel/sdk/Rage128sdk/Prog3D.html

A presentation from nvidia that is slightly outdated because of how textires are combined http://partners.nvidia.com/Marketing/Developer/DevRel.nsf/bookmark/77E4EBC0834FB2B08825681F00059257




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