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Plasma effect: Difference between revisions
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(demo/plasma)</lang>
=={{header|Forth}}==
{{works with|gforth|0.7.3}}
Ouputs a PPM file.
<lang forth>: sqrt ( u -- sqrt ) ( Babylonian method )
dup 2/ ( first square root guess is half )
dup 0= if drop exit then ( sqrt[0]=0, sqrt[1]=1 )
begin dup >r 2dup / r> + 2/ ( stack: square old-guess new-guess )
2dup > while ( as long as guess is decreasing )
nip repeat ( forget old-guess and repeat )
drop nip ;
: sgn 0< if -1 else 1 then ;
: isin
256 mod 128 - \ full circle is 255 "degrees"
dup dup sgn * 128 swap - * \ second order approximation
negate 32 / ; \ amplitude is +/-128
: color-shape 256 mod 6 * 765 - abs 256 - 0 max 255 min ; \ trapezes
: hue
dup color-shape . \ red
dup 170 + color-shape . \ green
85 + color-shape . ; \ blue
: plasma
outfile-id >r
s" plasma.ppm" w/o create-file throw to outfile-id
s\" P3\n500 500\n255\n" type
500 0 do
500 0 do
i 2 * isin 128 +
j 4 * isin 128 + +
i j + isin 2 * 128 + +
i i * j j * + sqrt 4 * isin 128 + +
4 /
hue
s\" \n" type
loop
s\" \n" type
loop
outfile-id close-file throw
r> to outfile-id ;
plasma</lang>
=={{header|FreeBASIC}}==
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