How To Make Health Decrease

Questions & Answers
1

I am very new to Unity Script and am in the middle of learning it. One thing I want to do is create a variable(e.g. health) which automatically decreases after a few seconds. I understand Time.deltaTime means every second. This is the script I have made:

//Health Textures
var health9 : Texture2D;
var health8 : Texture2D;
var health7 : Texture2D;
var health6 : Texture2D;
var health5 : Texture2D;
var health4 : Texture2D;
var health3 : Texture2D;
var health2 : Texture2D;
var health1 : Texture2D;

//Intigers
static var Player_Health = 9;

//Textures
var HealthGUI : GUITexture;

	switch (Player_Health)
	{
	     case 9:
			HealthGUI.texture = health9;
		break;
	    case 8:
			HealthGUI.texture = health8;
		break;
	    case 7:
			HealthGUI.texture = health7;
		break;
	    case 6:
			HealthGUI.texture = health6;
		break;
		case 5:
			HealthGUI.texture = health5;
		break;
		case 4:
			HealthGUI.texture = health4;
		break;
		case 3:
			HealthGUI.texture = health3;
		break;
		case 2:
			HealthGUI.texture = health2;
		break;
		case 1:
			HealthGUI.texture = health1;
			//Don't forget to add a death script here!
		break;
	}
	
	function Update()
	{
	   Player_Health -= Time.deltaTime;
	}

I am not sure why the last function doesn’t work. It may be something to do with thee function that I am not aware of(I am a noob) or something wrong with the switch thing. Please tell me how to do this(all I want is Player_Health to decrease every second-I can mess with other things later) Thanks for helping and reading!

5

I would use a coroutine here. Coroutines are sort of like a new thread (more like timesharing) that can stop execution and resume at the same point next frame.

forgive my JS, I usually use C#…

#pragma strict

var Player_Health = 9;

function StartDecreasingHealth(){
	StartCoroutine("SetHealth");
}

function StopDecreasingHealth(){
	StopAllCoroutines();
}

function SetHealth() {
	
	while(true)
	{
		switch (player_Health)
		{
			case 9:
			HealthGUI.texture = health9;
			break;
			case 8:
			HealthGUI.texture = health8;
			break;
			case 7:
			HealthGUI.texture = health7;
			break;
			case 6:
			HealthGUI.texture = health6;
			break;
			case 5:
			HealthGUI.texture = health5;
			break;
			case 4:
			HealthGUI.texture = health4;
			break;
			case 3:
			HealthGUI.texture = health3;
			break;
			case 2:
			HealthGUI.texture = health2;
			break;
			case 1:
			HealthGUI.texture = health1;
			//Don't forget to add a death script here!
			//You can also stop the coroutine here, since we're dead (dying?)
			StopAllCoroutines();
			break;
		}
		
		//decrease health for next tick
		Player_Health -= 1;
		
		/**
		 * set the waiting time in seconds here. The script will continue execution from here in 1 second, 
		 * i.e. go back to the beginning of the while loop
		 **/
		 yield WaitForSeconds(1);
	}
}

Now, whenever you call StartDecreasingHealth() the health drops by oen every second. StopDecreasingHealth() stops the decrese.

I would also use an array or list for the health images. Makes it easier on the eyes.

2

Time.deltaTime is the fraction of a second that has elapsed since the last frame. It is not “every second.” You declare your Player_Health as:

static var Player_Health = 9;

which makes it an integer. So I would expect it to go to 0 almost immediately (9 frames). What you want is to make it a float:

static var Player_Health = 9.0;

Then in your switch statement you would round it to an integer:

switch (Mathf.RoundToInt(Player_Health)) {

Note that you switch statement is not inside Update (or any function), so it will only be executed once. I think you can to call it every frame, or use Invoke() to call it at a regular interval. Putting it all together, you get something like:

#pragma strict

//Health Textures
var health9 : Texture2D;
var health8 : Texture2D;
var health7 : Texture2D;
var health6 : Texture2D;
var health5 : Texture2D;
var health4 : Texture2D;
var health3 : Texture2D;
var health2 : Texture2D;
var health1 : Texture2D;

//Intigers
static var player_Health = 9.0;

var speed = 0.5; 

//Textures
var HealthGUI : GUITexture;

function Update()
{
   player_Health -= Time.deltaTime * speed;
   if (player_Health < 0.0)
     player_Health = 0.0;
   SetHealth();
}

function SetHealth() {
    switch (Mathf.RoundToInt(player_Health))
    {
         case 9:
         HealthGUI.texture = health9;
       break;
        case 8:
         HealthGUI.texture = health8;
       break;
        case 7:
         HealthGUI.texture = health7;
       break;
        case 6:
         HealthGUI.texture = health6;
       break;
       case 5:
         HealthGUI.texture = health5;
       break;
       case 4:
         HealthGUI.texture = health4;
       break;
       case 3:
         HealthGUI.texture = health3;
       break;
       case 2:
         HealthGUI.texture = health2;
       break;
       case 1:
         HealthGUI.texture = health1;
         //Don't forget to add a death script here!
       break;
    }
}
3

Time.deltaTime doesn’t actually mean “every second”, it means time since the last frame.

Your approach is probably not working because health is an int, but you are decreasing it by a tiny float, which is probably just rounding back up to the nearest whole value.

What you’ll actually want to do is create a “tick” that subtracts 1 every second, rather than subtract the Time.deltaTime. Like so:

var tickInterval : float = 1;
var counter : float = 0;

function Update(){
    if(counter < tickInterval){
        counter += Time.deltaTime;
    }else{
        Player_Health -= 1;
        counter = 0;
    }
}
4

You should declare Player_Health as a float - the way you did, Player_Health is assumed to be an integer by the JS compiler:

static var Player_Health: float = 9;

or, alternatively:

static var Player_Health = 9.0; // assigning a float constant defines the variable as float

I prefer the first alternative, since the variable type is explicitly declared and will not be changed if we later modify the initialization constant.