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{ RCSid $Id: WalterBTDF.cal,v 1.1 2014/03/18 16:16:37 greg Exp $ } |
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{ |
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Isotropic BTDF model by Walter et al. |
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} |
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{ Model parameters (change these) } |
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ksint : 0.126221381019119; |
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sigma_i : 1.434228082595141; |
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sigma_o : 1.656368055960319; |
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f0 : 0.2; |
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alpha : 0.149990535073450; |
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|
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{ Useful functions } |
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s(x) : x*x; |
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abs(x) : if(x, x, -x); |
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noneg(x) : if(x, x, 0); |
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|
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{ Lobe calculation } |
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G(x) : 2/(1 + sqrt(1 + s(alpha)*(1-s(x))/s(x))); |
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F(w) : f0 + (1-f0)*(1-w)^5; |
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D(htn) : s(alpha)/PI/s( s(htn)*(s(alpha)-1) + 1 ); |
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|
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lobe3(wiht,woht,win,won,htn) : abs(wiht*woht/(win*won)) * |
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s(sigma_o)*(1-F(wiht))*D(htn)*G(win)*G(won) / |
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s(sigma_i*wiht + sigma_o*woht); |
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|
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lobe2(ix,iy,iz,ox,oy,oz,htx,hty,htz,nf) : lobe3((ix*htx+iy*hty+iz*htz)*nf, |
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(ox*htx+oy*hty+oz*htz)*nf, iz, oz, htz*nf); |
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|
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lobe1(ix,iy,iz,ox,oy,oz,htx,hty,htz) : lobe2(ix,iy,iz,ox,oy,oz,htx,hty,htz, |
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1/sqrt(s(htx)+s(hty)+s(htz))); |
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|
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{ Final function call - transmission only! } |
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{ vectors normalized, pointing away from surface } |
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walter(ix,iy,iz,ox,oy,oz) : if(iz*oz, 0, |
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ksint*noneg(lobe1(ix,iy,iz,ox,oy,oz, |
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-sigma_i*ix-sigma_o*ox, |
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-sigma_i*iy-sigma_o*oy, |
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-sigma_i*iz-sigma_o*oz)) ); |
