Precomputed Radiance transfer

[pat777]

http://artificialstudios.com/engine.php

Reality Engine has a very competitive feature set, such as our native pipeline support for Precomputed Radiance Transfer, a technology that will unify the gap between static lightmaps and harsh but dynamic per-pixel lighting, as well as our groundbreaking networked level development technology.

How can something precomputed be dynamic? I'm interested in this because it seems to allow dynamic GI with only precomputing.

 

[tEd]

not fully dynamic per se. It works only with static/rigid objects but supports dynamic lighting at least that's what the dx doc says

 

[pat777]

not fully dynamic per se. It works only with static/rigid objects but supports dynamic lighting at least that's what the dx doc says

http://artificialstudios.com/techdemos.php

Reality's lighting model scales to previous and next-generation hardware, and is also scalable to moving and deformable objects, providing the ultimate solution for next generation games.

They say you can use moving and deformable objects but the backyard video didn't show any moving/deformable objects.

 

[MDolenc]

I have heard that Serious Sam 2 will do something similar.
And though you can do movement and deformation (you can only rotate SH) this still isn't fully dynamic. You can't put an occluder between the light and the object for example (yes if you use something else for shadowing then SH). And a lot still depends on whether you are doing PRT on per vertex or per pixel basis.

 

[tEd]

not fully dynamic per se. It works only with static/rigid objects but supports dynamic lighting at least that's what the dx doc says

http://artificialstudios.com/techdemos.php

Reality's lighting model scales to previous and next-generation hardware, and is also scalable to moving and deformable objects, providing the ultimate solution for next generation games.

They say you can use moving and deformable objects but the backyard video didn't show any moving/deformable objects.

Then it worked once only on static/rigid objects . The technique improves as times go on and it seems to be the case here.
UE3 also supports this

http://research.microsoft.com/~ppsloan/

you'll find a couple of papers about PRT there

 

[GameCat]

Basically pre computed radiance transfer precomputes visibility information in a special way that enables you to relight static geometry quickly with very fairly high quality (soft shadows and indirect diffuse lighting). The approxiamtion used only works for low-frequency lighting, i.e soft shadows and lighting that doesn't change abruptly and requires lightsources to be very far away from the lit object for good results. So it works excellent for skylight for example, like in their garden demo. It doesn't work very well for e.g. dynamically animated characters and complex shadow interactions between independent dynamic objects.

 

[chrisATI]

This technique was used extensively in ATI's Subsurface Scattering demo as well as the Ruby: Dangerous Curves demo. There have been some advances made to basic PRT that allow for some dynamic mesh deformation as well as mid-range lighting (mid-range here means not exactly local but not infinitely distant either).

--Chris

 

[Mintmaster]

Chris, do you (or anyone else for that matter) have any links to those variants of PRT?

 

[chrisATI]

Jason Sandlin talked about Local Deformable PRT at GDC 2004, the title of his talk was "Advanced Lighting Techniques with D3DX" and is available for download from MSDN. LDPRT extends PRT to allow for mesh deformations (with some limitations). There's also a new sample in the latest DX SDK that does this.

For non-distant, mid-range lighting, read Spherical Harmonic Gradients for Mid-Range Illumination.

--Chris

 

[add n to (x)]

Robin Green at SCEA wrote a nice paper on using spherical harmonics for PRT. You can find it at:-

http://www.research.scea.com/gdc2003/spherical-harmonic-lighting.html