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{ RCSid $Id$ } |
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{ |
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Ashikhmin-Shirley BRDF model |
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|
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Includes Schlick estimate of Fresnel fraction, |
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but unlike Radiance material, does not remove |
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this from diffuse component. |
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} |
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{ Parameters (change these) } |
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MF : 30; |
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lcorr(r,g,b) : MF*(.265*r + .670*g + .065*b); |
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rho_d : lcorr(0.0039510616569, 0.0036905000484, 0.0027494885161); |
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rho_s : lcorr(0.0090625419097, 0.0083144131101, 0.0060292909118); |
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f0 : 0.9999999990000; |
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nu : 962.839595; |
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nv : 72.3236783; |
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{ Lobe calculation } |
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abs(x) : if(x, x, -x); |
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max(a,b) : if(a-b, a, b); |
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Schlick(odoth) : f0 + (1-f0)*(1-odoth)^5; |
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lobe2(iz,oz,hx,hy,hz,odoth) : Schlick(odoth)*sqrt((nu+1)*(nv+1)) / |
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(8*PI*max(abs(iz),abs(oz))*odoth) * |
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abs(hz)^((hx*hx*nu + hy*hy*nv)/(1-hz*hz)); |
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lobe1(iz,ox,oy,oz,hx,hy,hz,nf) : |
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lobe2(iz,oz,hx*nf,hy*nf,hz*nf,(ox*hx+oy*hy+oz*hz)*nf); |
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lobe(iz,ox,oy,oz,hx,hy,hz) : lobe1(iz,ox,oy,oz,hx,hy,hz, |
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1/sqrt(hx*hx+hy*hy+hz*hz)); |
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|
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ashikhmin(ix,iy,iz,ox,oy,oz) : if( -iz*oz, 0, |
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rho_d/PI + rho_s*lobe(iz,ox,oy,oz,ix+ox,iy+oy,iz+oz) ); |
