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greg |
1.1 |
{ RCSid $Id$ } |
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{ |
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Shirley-Chiu coordinate calculation for BRDF data types (plasdata, metdata) |
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Assumes material in X-Y plane with Y axis "up" and surface normal is Z-axis |
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} |
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Up(i) = arg(AC-3+i); { up vector does not need to be normalized } |
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Vux = cross(1,Up,N); |
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Vuy = cross(2,Up,N); |
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Vuz = cross(3,Up,N); |
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vnorm = 1/sqrt(Vux*Vux + Vuy*Vuy + Vuz*Vuz); |
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Vnx = Vux*vnorm; |
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Vny = Vuy*vnorm; |
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Vnz = Vuz*vnorm; |
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Vn(i) = select(i, Vnx, Vny, Vnz); |
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Unx = cross(1,N,Vn); |
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Uny = cross(2,N,Vn); |
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Unz = cross(3,N,Vn); |
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{ Transform vectors, normalized (dx,dy,dz) away from surf } |
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surf_dx(dx,dy,dz) = dx*Unx + dy*Uny + dz*Unz; |
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surf_dy(dx,dy,dz) = dx*Vnx + dy*Vny + dz*Vnz; |
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surf_dz(dx,dy,dz) = dx*Nx + dy*Ny + dz*Nz; |
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inc_dx = surf_dx(-Dx,-Dy,-Dz); |
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inc_dy = surf_dy(-Dx,-Dy,-Dz); |
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inc_dz = Rdot; |
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{ Compute square position from disk coordinates } |
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norm_radians(p) : if(-p - PI/4, p + 2*PI, p); |
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idr(idx,idy) = sqrt(idx*idx + idy*idy); |
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idp(idx,idy) = norm_radians(atan2(idy, idx)); |
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idrgn(idp) = floor((idp + PI/4)/(PI/2)) + 1; |
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square_a(idr,idp) = select(idrgn(idp), |
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idr, |
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(PI/2 - idp)*idr/(PI/4), |
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-idr, |
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(idp - 3*PI/2)*idr/(PI/4)); |
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square_b(idr,idp) = select(idrgn(idp), |
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idp*idr/(PI/4), |
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idr, |
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(PI - idp)*idr/(PI/4), |
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-idr); |
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square_x(idx,idy) = (square_a(idr(idx,idy),idp(idx,idy)) + 1)/2; |
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square_y(idx,idy) = (square_b(idr(idx,idy),idp(idx,idy)) + 1)/2; |
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inc_sqx = square_x(-inc_dx,-inc_dy); { Negative because of Klems reversal } |
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inc_sqy = square_y(-inc_dx,-inc_dy); |
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sqx_in(sx,sy,sz) = inc_sqx; { Only a function of incident ray direction } |
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sqy_in(sx,sy,sz) = inc_sqy; |
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sqx_out(sx,sy,sz) = square_x(surf_dx(sx,sy,sz),surf_dy(sx,sy,sz)); |
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sqy_out(sx,sy,sz) = square_y(surf_dx(sx,sy,sz),surf_dy(sx,sy,sz)); |
