Distance?

[pig132]

Okay i'm going to start working on something and it requires a distance formula between a player and another player(or npc). When I mess around with one distances come up as negatives sometimes depending where the player is. I have ran into one a few times a while back but I can't seem to find it.

Any help would be appreciated, thank you


EDIT: I did a quick mockup of what my end goal is to be (with players only. npc was just to test)
Pretty much the further a player is from another player the less alpha the player has. I just have no idea how I could accomplish this. GANIs? Add a weapon to everyone that has it?

PHP Code:

//#CLIENTSIDE
function onCreated() {
  setshape(1, 32, 32);
  setTimer(0.05);
}

function onTimeout() {
  temp.np = findnearestplayer(this.x, this.y);
  temp.dx = this.x - player.x;
  temp.dy = this.y - player.y;
  this.chat = temp.np @ ": " @ temp.dx @ "," @ temp.dy;
  
  if (temp.dx && temp.dy <= 3) {
    this.alpha = 1;
  }
  
  if (temp.dx && temp.dy > 3) {
    if (temp.dx && temp.dy <= 6) {
      this.alpha = 0.75;
    }
  }
  
  if (temp.dx && temp.dy > 6) {
    if (temp.dx && temp.dy <= 9) {
      this.alpha = 0.5;
    }
  }
  
  if (temp.dx && temp.dy > 9) {
    if (temp.dx && temp.dy <= 12) {
      this.alpha = 0.25;
    }
  }
  
  if (temp.dx && temp.dy > 12) {
    if (temp.dx && temp.dy <= 15) {
      this.alpha = 0;
    }
  }
  setTimer(0.05);
}