Re[4]: [Algorithms] create lightmap for arbitrary scene

[Oles V. S. <ol...@gs...>]

Hello jason,

Wednesday, July 03, 2002, 21:37:23, you wrote:

jz> Thank you for the hints about what speed could be reasonable.
jz> Now I'll look into the codes to find the bottle neck.
jz> By the way, what spatial partition algorithm do you use for ray-trace?

We use rather simple structure:
1. 3D grid
2. In each cell: no-leaf-AABB-tree

Another suggestion(s).
1. Try to localize/cull your lights before ray-tracing using all
vis-info u have.
(we have sector-portal info + dedicated (simple) geometry for
occlusion culling)
2. Try to cache occluder polygons per light - usually lumels from
which rays r casted are spatially near.

>> jz>       It is better than brutal-force method.  But It is still slow. Much slower than
>> jz> that of bsp-scene and too slow that radiosity computation seems impossible.  
>> jz> There is a program called lightscape with 3dsmax(Do you heard of it?).  It can 
>> jz> compute the game scene within a few hours incluing radiosity, and my program  needs
>> jz> a few days approximately . I wonder whether there is a magic method I had never 
>> jz> thought of.
>> 
>> Well, I don't know why u r getting such poor performance...
>> 
>> Our brute-force solution uses ~6 hours for the following conditions
>> (last level compiled):
>> 
>> * 1.8 M tris on level
>> * 412 light sources
>> * 11 lightmaps created (packed)
>> * 1024x1024 lmap size
>> * 9 ray-casts per lumel per light (jittering)
>> * around 30% partially-transparent triangles (which we ray-casted using
>> alpha calculated from shader definition and texture(s) combination)
>> 
>> But this time also includes sub-lightmaps color/gradients analysis
>> and around 40% recalculations under condition that lightmap can be
>> shrinked down.
>> Plus, all sub-lightmaps was specifically packed to allow DXT1
>> compression (this takes some time too).
>> 
>> So, all I can suggest - use good spatial partition for ray-testing.


-- 
Best regards,
 Oles V. Shishkovtsov
 GSC-Game World
 ol...@gs...