[MX] Problems understanding part of AI script

[pup100]

I have been working through an example of a basic AI script from Jobe Makar's excellent book
“Flash MX games design demystified” there is one section that has really got me stumped.

Basically there are baddies that chase a goodie – code runs to determine where the hero is relative to the bad guys -1 if he is to the left 0 same column 1 to the right + similar sort of thing for “up” & “down” The result is alocated to the variables xsign & ysign now the part I'm having problems with is this section

if (xsign == ysign || xsign == -ysign) {
				var ran = random(2);
				if (ran == 0) {
					var xsign = 0;
				} else {
					var ysign = 0;
				}
			}

this is supposed to tell us if the baddie is in the same row or column – but i can't see how.

I have set out the whole function (part of a larger script) below so you can see it in context, but if anyone can explain how the above achieves what it is supposed to i would be grateful.

function baddyAI() {
	for (var i = 0; i<game.baddies.length; ++i) {
		var ob = game.baddies[i];
		++ob.time;
		var cell_x = Math.ceil(ob.x/game.cellWidth);
		var cell_y = Math.ceil(ob.x/game.cellWidth);
		var cell_over = game.tiles[cell_x][cell_y];
		var cell_x_temp = Math.ceil(ob.tempx/game.cellWidth);
		var cell_y_temp = Math.ceil(ob.tempy/game.cellWidth);
		var cell_over_temp = game.tiles[cell_x_temp][cell_y_temp];
		if (!cell_over_temp.empty || ob.time == ob.maxtime) {
			ob.time = 0;
			ob.maxtime = 30+random(30);
			ob.tempx = ob.x;
			ob.tempy = ob.y;
			var tempDir = ob.dir;
			var xmov = 0;
			var ymov = 0;
			var speed = Math.abs(ob.speed);
			var xsign = (game.char.x-ob.x)/Math.abs((game.char.x-ob.x));
			var ysign = (game.char.y-ob.y)/Math.abs((game.char.y-ob.y));
			if (random(10) == 0) {
				var xsign = -1*xsign;
				var ysign = -1*ysign;
			}
			if (xsign == ysign || xsign == -ysign) {
				var ran = random(2);
				if (ran == 0) {
					var xsign = 0;
				} else {
					var ysign = 0;
				}
			}
			if (xsign != 0) {
				var ymov = 0;
				var xmov = xsign*speed;
				if (xmov>0) {
					var dir = "right";
				} else {
					var dir = "left";
				}
			} else if (ysign != 0) {
				var xmov = 0;
				var ymov = ysign*speed;
				if (ymov>0) {
					var dir = "down";
				} else {
					var dir = "up";
				}
			}
			ob.dir = dir;
			ob.clip.gotoAndStop(dir);
			ob.xmov = xmov;
			ob.ymov = ymov;
		}
	}
}

[tonypa]

The code in the condition
if (xsign == ysign || xsign == -ysign) {
is only being run when enemy is exactly at diagonal from the hero. In such case, the enemy can first move horisontally or vertically. The random function adds basically small bit of randomness into movement, if you remove this part, the enemy will always move horisontally because xsign is checked first.

[pup100]

Hi tonypa thanks for taking the time to reply.

In Jobes's book he gives the line of code :

if (xsign == ysign || xsign == -ysign) {
etc.

as "In line 26 we determine whether the enemy is in the same row or column as the hero. If he is not we randomly choose either the x or y direction to move in....

I can't see how the above will let you know if the bad guy is in the same row or column?

[tonypa]

The row and column are found here:

var xsign = (game.char.x-ob.x)/Math.abs((game.char.x-ob.x));
var ysign = (game.char.y-ob.y)/Math.abs((game.char.y-ob.y));

Maybe the line number (26) is wrong.

[pup100]

Thanks tonypa