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Problems with PRT

Started by cyber_wiz_2007 Mar 25, 2006 at 9:35 AM 3 replies 850+ views

Original Post

cyber_wiz_2007

Mar 25, 2006 at 9:35 AM

Hi, I have been using PRT with directX 9.0c and found the following problems. 1) I can't see much inside buildings. 2) if I enable adaptive mesh tesselation the model has cracks and bad vertex coloring. 3) the spherical light source does not seem to illuminate indoor areas. 4) overall the model does not resemble accurate indoor radiosity. has anyone got either a usage guide to PRT simulator settings or some sort of solution for using PRT for indoor environments? I basically need some advice on how to use the subdivision settings and how to use real lights inside a building/structure.

kovacsp

Mar 25, 2006 at 1:38 PM

Hi,

Quote:
Original post by cyber_wiz_2007
1) I can't see much inside buildings.
3) the spherical light source does not seem to illuminate indoor areas.
4) overall the model does not resemble accurate indoor radiosity.

has anyone got either a usage guide to PRT simulator settings or some sort of solution for using PRT for indoor environments?
I basically need some advice on how to use the subdivision settings and how to use real lights inside a building/structure.

The problem with indoor lighting simulation is that you need _many_ bounces to correctly do it. As with PRT the light always comes from the outside, you have to trace many bounces to correctly reach every part of your room/etc..
But that will take overly long.. I never had the patience to do PRT on an indoor scene correctly.
I don't think that you could place indoor lights with the current implementation of PRT in DX. (as lights are placed afterwards, and light contribution is taken into account only for directional light, that are infinitely far away)

kp

cyber_wiz_2007

Mar 25, 2006 at 2:12 PM

Hi,

I noticed that it usually uses directional lights, but I found a function in the december release:-

D3DXSHEvaluateSphericalLight(...)

which takes a pointer to a vector called vPos as a parameter. I thought that vPos would mean that it could be placed inside the room. I'll have another look tonight to check whether this is the case.

thanks

kovacsp

Mar 25, 2006 at 5:25 PM

Quote:
Original post by cyber_wiz_2007
I noticed that it usually uses directional lights, but I found a function in the december release:-

D3DXSHEvaluateSphericalLight(...)

which takes a pointer to a vector called vPos as a parameter. I thought that vPos would mean that it could be placed inside the room. I'll have another look tonight to check whether this is the case.

wow, I didn't know about that! but even if it is what we think about, it's still true that many bounces are needed for the light coming from the outside to make some "realistic" effect inside. maybe you should let your PC on for tonight computing PRT for a small room, and try what you get :)
if you can achieve good results for an interior scene, I'm very interested in your results (please post some screenshots then)!

kp

circlesoft

Mar 25, 2006 at 7:18 PM

Also notice that there are additional SH lighting functions for:

D3DXSHEvalConeLight()
D3DXSHEvalHemisphereLight()

So this bumps the number of light types to 4:

- Directional
- Point
- Cone
- Hemispherical

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