| 1 |
greg |
1.2 |
{ RCSid $Id: WalterBTDF.cal,v 1.1 2014/03/18 16:16:37 greg Exp $ } |
| 2 |
greg |
1.1 |
{ |
| 3 |
greg |
1.2 |
Isotropic BTDF model by Walter et al. |
| 4 |
greg |
1.1 |
} |
| 5 |
|
|
{ Model parameters (change these) } |
| 6 |
|
|
ksint : 0.126221381019119; |
| 7 |
|
|
sigma_i : 1.434228082595141; |
| 8 |
|
|
sigma_o : 1.656368055960319; |
| 9 |
|
|
f0 : 0.2; |
| 10 |
|
|
alpha : 0.149990535073450; |
| 11 |
|
|
|
| 12 |
|
|
{ Useful functions } |
| 13 |
|
|
s(x) : x*x; |
| 14 |
|
|
abs(x) : if(x, x, -x); |
| 15 |
greg |
1.2 |
noneg(x) : if(x, x, 0); |
| 16 |
|
|
|
| 17 |
|
|
{ Lobe calculation } |
| 18 |
greg |
1.1 |
G(x) : 2/(1 + sqrt(1 + s(alpha)*(1-s(x))/s(x))); |
| 19 |
|
|
F(w) : f0 + (1-f0)*(1-w)^5; |
| 20 |
|
|
D(htn) : s(alpha)/PI/s( s(htn)*(s(alpha)-1) + 1 ); |
| 21 |
|
|
|
| 22 |
greg |
1.2 |
lobe3(wiht,woht,win,won,htn) : abs(wiht*woht/(win*won)) * |
| 23 |
greg |
1.1 |
s(sigma_o)*(1-F(wiht))*D(htn)*G(win)*G(won) / |
| 24 |
|
|
s(sigma_i*wiht + sigma_o*woht); |
| 25 |
|
|
|
| 26 |
|
|
lobe2(ix,iy,iz,ox,oy,oz,htx,hty,htz,nf) : lobe3((ix*htx+iy*hty+iz*htz)*nf, |
| 27 |
|
|
(ox*htx+oy*hty+oz*htz)*nf, iz, oz, htz*nf); |
| 28 |
|
|
|
| 29 |
|
|
lobe1(ix,iy,iz,ox,oy,oz,htx,hty,htz) : lobe2(ix,iy,iz,ox,oy,oz,htx,hty,htz, |
| 30 |
|
|
1/sqrt(s(htx)+s(hty)+s(htz))); |
| 31 |
|
|
|
| 32 |
|
|
{ Final function call - transmission only! } |
| 33 |
|
|
{ vectors normalized, pointing away from surface } |
| 34 |
|
|
walter(ix,iy,iz,ox,oy,oz) : if(iz*oz, 0, |
| 35 |
greg |
1.2 |
ksint*noneg(lobe1(ix,iy,iz,ox,oy,oz, |
| 36 |
greg |
1.1 |
-sigma_i*ix-sigma_o*ox, |
| 37 |
|
|
-sigma_i*iy-sigma_o*oy, |
| 38 |
greg |
1.2 |
-sigma_i*iz-sigma_o*oz)) ); |
