I am not familiar with RSMs but, judging from the code you posted, I believe SH suit your needs.

Remember that SH represent a signal defined over a spherical domain. In this case the signal is the total incoming light from all the secondary sources. A SH probe has an associated position in world space. For a <light, probe> pair, the signal is (cosThetaI * lR * Flux) in the direction defined by R (normalized). The cosThetaJ term depends on the receiver's normal and will be taken into account later at runtime when shading a surface.

Some pseudo-code:

for each probe

SH = 0

for each light

signal = R / | R | * (cosThetaI * lR * Flux)

SH += signalToSH(signal)

signalToSH is a function that encodes a directional light in the SH basis. See D3DXSHEvalDirectionalLight for an implementation.

At runtime, when shading a pixel, pick the probe spatially closest to it. The pixel has a normal associated. Assuming that the BRDF is purely diffuse, you have to convolve the cosine lobe around the pixel's normal with the signal encoded in the probe, achieved with a SH rotation and dot product. See the paper http://www.cs.berkeley.edu/~ravir/papers/envmap/envmap.pdf

I suggest you read more material on SH in order to have a better understanding of their properties and use cases. As for myself, I will read the RSM paper asap and edit my reply if I've made wrong assumptions.

Please let me know if you have more questions.

Stefano

Ok first thanks for response and yes I need to dig into SH realms better.... but let's make it simple Stefano (well not so simple ): given a normal vector n (x,y,z) I can get second order SH coefficents c = (c0,c1,c2,c3)

where:

c0 = sqrt(pi) / 2

c1 = -sqrt(pi/3) * y

c2 = sqrt(pi/3) * z

c3 = - sqrt(pi/3) * x

so for every VPL ( virtual point light ) I'll have a n vector and an associated SH coefficents c.

The question is how I can go back and compute reflected radiance from those second order SH coefficents?

Thanks

Mauro

Mauro, can you explain the meaning of that normal vector n ? Is it the normal of the receiving or emitting surface ? Or is it the vector connecting the emitter and receiver ? And how did you derive the four SH coefficients ?

Mauro, that sounds like the correct approach. About storing the irradiance with SH, what is unclear about the description I wrote in my previous post ? To recap, given a probe and a light, the radiance from the light to the probe has an analytical formula and you can calculate directly the corresponding SH coefficients.

well almoust clear...working on this...hope to post reusults soon...also exploring "shooting" rays from the probe to get incoming radiance....

back on work now....

EDIT: the bad news is that I'll probably not go throught Light Propagation Volume but stick with Irradiance Volume...mostly becouse LPV requires DX11 hardware to be efficently implemented (even if volume textures can be handled in DX9 using some tricky code)