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{ RCSid $Id: diskcoords.cal,v 1.1 2018/11/30 17:49:59 greg Exp $ } |
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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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{ 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)); |
