XNA Health Bar continually decreasing

Question

As per the Health bar tutorial on ... http://www.xnadevelopment.com/tutorials/notsohealthy/NotSoHealthy.shtml

I have set up the above, how do I make it decrease by 1 health per second?

I want to create a mini survival game, and this is an important factor.

Where am i going wrong? I want it to visibly decrease every second.

    using System;
    using System.Collections.Generic;
    using System.Linq;
    using Microsoft.Xna.Framework;
    using Microsoft.Xna.Framework.Audio;
    using Microsoft.Xna.Framework.Content;
    using Microsoft.Xna.Framework.GamerServices;
    using Microsoft.Xna.Framework.Graphics;
    using Microsoft.Xna.Framework.Input;
    using Microsoft.Xna.Framework.Media;

    namespace Health
    {
/// <summary>
/// This is the main type for your game
/// </summary>
public class Game1 : Microsoft.Xna.Framework.Game
{
    GraphicsDeviceManager graphics;
    SpriteBatch spriteBatch;

    Texture2D healthBar;
    int currentHealth = 100;
    float seconds;
    public Game1()
    {
        graphics = new GraphicsDeviceManager(this);
        Content.RootDirectory = "Content";
    }

    /// <summary>
    /// Allows the game to perform any initialization it needs to before starting to run.
    /// This is where it can query for any required services and load any non-graphic
    /// related content.  Calling base.Initialize will enumerate through any components
    /// and initialize them as well.
    /// </summary>
    protected override void Initialize()
    {
        // TODO: Add your initialization logic here

        base.Initialize();
    }

    /// <summary>
    /// LoadContent will be called once per game and is the place to load
    /// all of your content.
    /// </summary>
    protected override void LoadContent()
    {
        // Create a new SpriteBatch, which can be used to draw textures.
        spriteBatch = new SpriteBatch(GraphicsDevice);

        healthBar = Content.Load<Texture2D>("HealthBar");

        // TODO: use this.Content to load your game content here
    }

    /// <summary>
    /// UnloadContent will be called once per game and is the place to unload
    /// all content.
    /// </summary>
    protected override void UnloadContent()
    {
        // TODO: Unload any non ContentManager content here
    }

    /// <summary>
    /// Allows the game to run logic such as updating the world,
    /// checking for collisions, gathering input, and playing audio.
    /// </summary>
    /// <param name="gameTime">Provides a snapshot of timing values.</param>
    protected override void Update(GameTime gameTime)
    {
        // Allows the game to exit
        if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed)
            this.Exit();

        // TODO: Add your update logic here

        currentHealth = (int)MathHelper.Clamp(currentHealth, 0, 100);

        seconds += (float)gameTime.ElapsedGameTime.TotalSeconds;
        if (seconds >= 1)
        {
            currentHealth -= 1;
        }
        seconds = 0;

        base.Update(gameTime);
    }

    /// <summary>
    /// This is called when the game should draw itself.
    /// </summary>
    /// <param name="gameTime">Provides a snapshot of timing values.</param>
    protected override void Draw(GameTime gameTime)
    {
        GraphicsDevice.Clear(Color.CornflowerBlue);
        spriteBatch.Begin();
        spriteBatch.Draw(healthBar, new Rectangle(this.Window.ClientBounds.Width / 2 - healthBar.Width / 2, 30, healthBar.Width, 44), new Rectangle(0, 45, healthBar.Width, 44), Color.Gray);
        spriteBatch.Draw(healthBar, new Rectangle(this.Window.ClientBounds.Width / 2 - healthBar.Width / 2, 30, (int)(healthBar.Width * ((double)currentHealth / 100)), 44), new Rectangle(0, 45, healthBar.Width, 44), Color.Red);
        spriteBatch.Draw(healthBar, new Rectangle(this.Window.ClientBounds.Width / 2 - healthBar.Width / 2, 30, healthBar.Width, 44), new Rectangle(0, 0, healthBar.Width, 44), Color.White);
        spriteBatch.End();

        base.Draw(gameTime);
    }
}
    }

Cheers!

Answer 1

You could do this using a float.

At the top of your Game1.cs, add:

float timer = 0f;

Then in Update:

timer += gameTime.ElapsedGameTime.Milliseconds;
if (timer >= 1000) // Your time, in milliseconds
{
    mCurrentHealth -= 1;
    timer -= 1000;
}

Answer 2

The reason YOUR code doesn't work is this:

seconds += (float)gameTime.ElapsedGameTime.TotalSeconds;
if (seconds >= 1)
{
    currentHealth -= 1;
}
seconds = 0;

You reset seconds every frame, so it can NEVER be >= 1. seconds = 0; should be inside your if. THat would fix it. Like this:

seconds += (float)gameTime.ElapsedGameTime.TotalSeconds;
if (seconds >= 1)
{
    currentHealth --;
    seconds = 0;
}

However, I have a more elegant solution to your problem, if you want your HP-bar to decrease smoothly;

replace:

int currentHealth = 100;

with:

float currentHealth = 100;

Replace

seconds += (float)gameTime.ElapsedGameTime.TotalSeconds;
if (seconds >= 1)
{
    currentHealth -= 1;
}
seconds = 0;

with

//DeltaTime = Change in time. (delta means "change in" in physics/maths)
//This is always usefull in physics calc etc, so keep it and pass to other objects update instead of gametime:
float deltaTime = (float)gameTime.ElapsedGameTime.TotalSeconds;

if (currentHealth > 0)
    currentHealth = Math.Max(0f, currentHeath - deltaTime);
else
    Die();