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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 BSDF model by Walter et al. |
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} |
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{ BRDF parameters (change these) } |
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kdinr : 0.; |
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ksinr : 1.; |
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f0r : 0.277605834967475; |
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alpha_r : 0.077419771872748; |
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{ BTDF 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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f0t : 0.2; |
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alpha_t : 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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{ Reflection functions } |
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Gr(x) : 2/(1 + sqrt(1 + s(alpha_r)*(1-s(x))/s(x))); |
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Fr(w) : f0r + (1-f0r)*(1-w)^5; |
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Dr(htn) : s(alpha_r)/PI/s( s(htn)*(s(alpha_r)-1) + 1 ); |
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|
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lobe3r(wihr,win,won,htn) : Fr(wihr)*Dr(htn)*Gr(win)*Gr(won) / (4*win*won); |
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lobe2r(ix,iy,iz,ox,oy,oz,htx,hty,htz,nf) : lobe3r((ix*htx+iy*hty+iz*htz)*nf, |
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iz, oz, htz*nf); |
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lobe1r(ix,iy,iz,ox,oy,oz,htx,hty,htz) : lobe2r(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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{ Transmission functions } |
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Gt(x) : 2/(1 + sqrt(1 + s(alpha_t)*(1-s(x))/s(x))); |
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Ft(w) : f0t + (1-f0t)*(1-w)^5; |
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Dt(htn) : s(alpha_t)/PI/s( s(htn)*(s(alpha_t)-1) + 1 ); |
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|
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lobe3t(wiht,woht,win,won,htn) : abs(wiht*woht/(win*won)) * |
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s(sigma_o)*(1-Ft(wiht))*Dt(htn)*Gt(win)*Gt(won) / |
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s(sigma_i*wiht + sigma_o*woht); |
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|
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lobe2t(ix,iy,iz,ox,oy,oz,htx,hty,htz,nf) : lobe3t((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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lobe1t(ix,iy,iz,ox,oy,oz,htx,hty,htz) : lobe2t(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 - reflection & transmission } |
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{ vectors normalized, pointing away from surface } |
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walter(ix,iy,iz,ox,oy,oz) : if(iz*oz, kdinr/PI + |
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ksinr*lobe1r(ix,iy,iz,ox,oy,oz, |
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ix+ox, iy+oy, iz+oz), |
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ksint*noneg(lobe1t(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)) ); |
