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{ RCSid $Id: diskcoords.cal,v 1.2 2018/12/01 02:06:05 greg Exp $ }
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{
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Shirley-Chiu coordinate calculation for BRDF data types (plasdata, metdata)
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}
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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(-Idx,-Idy); { Negative because of Klems reversal }
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inc_sqy = square_y(-Idx,-Idy);
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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(Ldx(sx,sy,sz),Ldy(sx,sy,sz));
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sqy_out(sx,sy,sz) = square_y(Ldx(sx,sy,sz),Ldy(sx,sy,sz));
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