I am currently working on a game in flash (with AS3), and I ran into a weird issue with the line of sight of the enemies. It's easier to explain with a picture. Blue = walls. Green = enemy. Red = area the enemy can't see the player.

This is the codes:

var playerVisible:Boolean = true;
var angleRadian = Math.atan2(_player.y - _enemy[i].y, _player.x - _enemy[i].x);
var angleDegree = angleRadian * 180 / Math.PI;

var enemyDistancex:Number = _player.x - _enemy[i].x;
var enemyDistancey:Number = _player.y - _enemy[i].y;
if(enemyDistancex < 0)
	enemyDistancex *= -1;
if(enemyDistancey < 0)
	enemyDistancey *= -1;
var enemyDistance:Number = Math.sqrt((enemyDistancex * enemyDistancex) + (enemyDistancey * enemyDistancey));

while(enemyDistance > 0 && playerVisible)
{
	if(_walls.hitTestPoint(_enemy[i].x - (Math.sin(angleDegree * (Math.PI / 180)) * enemyDistance), _enemy[i].y - (Math.cos(angleDegree * (Math.PI / 180) * -1) * enemyDistance), true))
	{
		playerVisible = false;
	}
	
	enemyDistance--;
}

I tried a lot, but I can't seem to figure it out. Could someone help me out?

I'm not quite understanding the picture. Is that the current behavior or the behavior you want to implement?

That's the current behavior the code below the picture creates.

By the way, I use the same codes to calculate the enemy rotation for targeting the player and it works fine, but somehow it is buggy when I use it for the line of sight.

Why aren't you using vectors? Calling atan2 and then calling sin, cos with the result is usually a sure sign you should be using 2d vectors instead of trigonometry for the problem.

Using vectors how? Sorry I'm kind of a newbie when it comes to maths.

Well you calculate the vector

player - enemy

and do a load of unnecessary trig stuff with it when that gives you the 2d direction vector from the enemy to the player directly...

I'd definitely recommend reading up on vectors, you rarely need to use trig and the stuff you do need/are using involving vectors is just the very basic stuff.

I managed to fix it, thanks for the help :)