#!/bin/sh
awk '
# adopted from http://users.tkk.fi/~jjsalon2/reddit/raytrace.html

function fix(a) {
	if (a < 0)
		a = 0
	if (a > 255)
		a = 255
	return int(a)
}

function doframe() {
	A = sin(t*.8)*8;
	C = sin(t)*8;
	D = sin(t*.7)*8;
	for(y=-w; y<=w; y++)
		for(x=-w; x<=w; x++){
			c = z = -7;
			G = x-A;
			H = y-A;
			J = x-C;
			K = y-D;
			for(i=0; i++<4; z-=p/Z){
				u=G*G+H*H+z*z;
				v=J*J+K*K+z*z;
				U=u*u/2;
				V=v*v/2;
				X=G/U+J/V;
				Y=H/U+K/V;
				Z=z/U+z/V;
				p=.02-1/u-1/v
			}
			if(p < 3e-4){
				h=(X*D+Y*C-Z*13)/sqrt(X*X+Y*Y+Z*Z);
				c=int(w+(h>0 ? h*h : 0))
			}
			printf "color #%02x%02x%02x\n", fix(c-99), fix(c), fix(2*c)
			print "fillrect", x/w, y/w, "-", (x+1)/w, (y+1)/w
		}
}

BEGIN {
	w = 20
	t = 70
	print "bg black"
	for(t=70; ; t+=.2) {
		print "frame"
		doframe()
		print "flush"
		print "sleep 0.04"
	}
}
'