Samiam’s Scribble Pad

November 12, 2011

trying to calculate localVisibility with Spherical Harmonics

Filed under: Uncategorized — Tags: , , — admin @ 5:59 pm
Spherical Harmonics Coefficients of Local Visibility

Spherical Harmonics Coefficients of Local Visibility

In hidsight, baking a lookup table of vectors and the spherical harmonics, might lead to artifacts, but with 1024 samples it doesnt look too bad

Feel free to download the source to sing along, its all based on the Sony Paper from 2003 see the PDF from SCEA

Python executable that write Spherical Harmonics Renderman header: sh1.py

Please find the resulting header file attached: SH.h

And a simple shader to calculate transmission based on the table of stratified samples above: localVisibility.sl

Its a bit clunky because I couldn’t work out how to do two dimensional arrays in RSL, im glad to fix it up if it is possible.

The preprocessor thing isnt that sweet either :/

As below:

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#include "SH.h"
 
surface localVisibility(
        uniform float maxDistance = 10; 
        uniform string outputFolder = "";
)
{
        SHVECTOR
        SHSPH0
        SHSPH1
        SHCOEFF0
        SHCOEFF1
        SHCOEFF2
        SHCOEFF3
        SHCOEFF4
        SHCOEFF5
        SHCOEFF6
        SHCOEFF7
        SHCOEFF8
        vector Nworld = vector(transform("world",N));
        point Pworld = transform("world",P);
        uniform float numSamples = 1024;
        uniform float numCoeffs = 9;
        varying float results[9]={0,0,0,0,0,0,0,0,0};
        uniform float i,j;
        varying float faceforward = 0;
        varying float occl = 0;
        for(i=0;i<numSamples;i=i+1){
                float Hs = samplesVector[i].Nworld;
                point destinationWorld = Pworld + samplesVector[i]*maxDistance;
                point destinationCurrent = transform("world","current",destinationWorld);
                if (Hs > 0){
                        faceforward += 1;
                        float isHit = comp(transmission(P,destinationCurrent),0);
                        if (isHit > 0)
                        {
                                occl += 1;
                                for(j=0;j<numCoeffs;j=j+1){
                                        varying float value = isHit;
                                        if (j == 0)
                                        {
                                                value *= samplesCoeffs0[i];
                                        }
                                        if (j == 1)
                                        {
                                                value *= samplesCoeffs1[i];
                                        }
                                        if (j == 2)
                                        {
                                                value  *= samplesCoeffs2[i];
                                        }
                                        if (j == 3)
                                        {
                                                value *= samplesCoeffs3[i];
                                        }
                                        if (j == 4)
                                        {
                                                value *= samplesCoeffs4[i];
                                        }
                                        if (j == 5)
                                        {
                                                value *= samplesCoeffs5[i];
                                        }
                                        if (j == 6)
                                        {
                                                value *= samplesCoeffs6[i];
                                        }
                                        if (j == 7)
                                        {
                                                value *= samplesCoeffs7[i];
                                        }
                                        if (j == 8)
                                        {
                                                value *= samplesCoeffs8[i];
                                        }
                                        results[j] += value;
 
                                        }       
                                }
                        } 
                }
        for (j=0;j<numCoeffs;j=j+1){    
                results[j] /= faceforward;
                }
        occl /= faceforward;
        faceforward /= numSamples;
        Ci = color(results[0],results[1],results[2]);
        Oi = 1;
        Ci *= Oi;
 
}

I dont think it is working yet, but it compiles and renders

Sam

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