// raytracying MEL
// Atsushi Morimoto(for Mayonnaize Production)
// $Id: ray.mel,v 0.1 2001/10/30 01:35:35 jagajin Exp jagajin $

global proc vector make_eye(int $x, int $y)
{
	vector $v;
	$v = << -2.0 + $x/50.0, 2.0 - $y/50.0, 3.0>>;
	return $v;
}

global proc shading(int $fp, float $t, vector $from, vector $to, vector $point)
{
	vector	$l, $v;
	float	$d;
	int		$col;

	$l = <<0.5773, 0.5773, -0.5773>>;
	$v = $from + $to * $t -$point;
	// normalize
	$d = sqrt($v.x * $v.x + $v.y * $v.y + $v.z * $v.z);
	$v = << $v.x / $d, $v.y / $d, $v.z / $d >>;

	$d = $l * $v;
	$col = (int)(255.0 * $d) + 50;
	if ( $col > 255 ) 
		$col = 255;
	if ( $col < 0)
		$col = 0;
	fprint $fp (""+$col+" 0 0 ");
}

global proc float intersect(vector $from, vector $to, vector $point, float $rad)
{
	vector	$v;
	float	$b, $c, $d, $det, $t;
	$v = $from - $point;
	$b = $to * $v;
	$c = ($v * $v) - ($rad * $rad);
	$d = $b * $b -$c;
	if ( $d < 0 )
		return -1.0;
	$det = sqrt($d);
	$t = -$b + $det;
	return $t;
}

global proc ray()
{
	int		$fp;
	int		$x, $y;
	vector	$from, $to, $point;
	float	$t, $rad;

	$fp = `fopen "ray.ppm" "w"`;

	fprint $fp "P3\r\n200 200\r\n255\r\n";

	$rad = 1.0;
	$to = << 0, 0, -1>>;
	$point = << 0, 0, 0 >>;

	for ( $y = 0; $y < 200; $y++) {
		for ( $x = 0; $x < 200; $x++) {
			$from = make_eye($x, $y);
			$t = intersect($from, $to, $point, $rad);
			if ( $t >= 0 )
				shading($fp, $t, $from, $to, $point);
			else
				fprint $fp "100 100 100 ";
		}
		fprint $fp "\r\n";
	}	

	fclose $fp;
}