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{ RCSid $Id$ } |
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{ |
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Compute fractal clouds over image |
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Greg Ward 11/1/95 |
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Needs also noise2.cal |
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Usage: |
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pcomb -f noise2.cal -f clouds.cal planet.pic > cloudy.pic |
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Typically, this will be used to add clouds to Earth.pic or |
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bigEarth.pic in the standard library distribution. |
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} |
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{ Modify the following two constants to your liking: } |
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cover_frac : 0.65; { average cloud cover (non-clear fraction) } |
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cloud_refl : 0.7; { average cloud reflectance (always white) } |
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{ Leave the rest alone. } |
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PI : 3.14159265358979323846; |
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clouds(u,v,s) = if(s-.5, noise2(sin(2*PI/xmax*x)+13.5,sin(2*PI/ymax*y)-10.3), |
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noise2(u/s,v/s)*s + clouds(u,v,2*s)); |
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minres : if(xmax-ymax, ymax, xmax); |
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clamp(x) : if(x, if(x-1, 1, x), 0); |
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coef = clamp( 1 + |
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(.5/sqrt(cover_frac)) * (clouds(x/minres, y/minres, 10/minres) - 1) |
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) ; |
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cv = coef * cloud_refl; |
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pv = 1 - coef; |
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ro = cv + pv*ri(1); |
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go = cv + pv*gi(1); |
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bo = cv + pv*bi(1); |
