intersect.c

int
blocked_shot(int e)
{
	int t, a, x, y;
	double adx, ady, edx, edy, div;
	/* AIship_track(e) returns direction of enemy movement */
	t = AIship_track(e);
	/* AIship_aimdir(e) is an autoaim function that returns the
           angle required to hit the enemy ship */
	a = AIship_aimdir(e);
	adx = cos(rad(a));
	ady = sin(rad(a));

	edx = cos(rad(t));
	edy = sin(rad(t));
	
	/* find the intersection of two lines with Cramer's rule */
	div = det(adx, ady, edx, edy);
	if (div == 0) {
		/* enemy ship is flying straight away or at self */
		x = AIradar_x(e);
		y = AIradar_y(e);
	} else {
		x = det(AIradar_x(e) - AIself_x(), AIradar_y(e) - AIself_y(), edx, edy) / div;
		y = det(adx, ady, AIradar_x(e) - AIself_x(), AIradar_y(e) - AIself_y()) / div;
	} 
	
	return AI_wallbetween(AIself_x(), AIself_y(), x, y) != -1;
}

/* determinant of a 2x2 matrix */
double
det(double x1, double y1, double x2, double y2)
{
	return (x1 * y2) - (x2 * y1);
}