Defcom1 - XNA Level 1 Lesson 7 Loops and Arrays

What if we want to add more than one asteroid? We can simply add a new asteroid position

Well don't know about you, but I'm not going to do that because it's going to take ages!! But there is an easier way. We are going to use an array

Arrays allow us group data together in a table so we can easily work through them

Lets say asteroid was an actual datatype to create an array of asteroids we would simply say something like

...but we don't need to do that, we only need the position of 25 asteroids because we are going to use the same image for each one (saves memory and time)

In the initialise function after the UFO position we are going to set the starting positions of all asteroids

To do this we use a for loop. A for loop reapeats the same set of instruction for a given amount of time.

We will do the same For Loop again in the update function to update the position of all of the asteroids and we now have to check if the ufo has hit any of the asteroids so yes you guessed it.. another For Loop

            //update all asteroid positions
            for (int i = 0; i < numberOfAsteroids; i++)
            {
                asteroid[i].Y += 5;
                if (asteroid[i].Y > screenHeight)
                {
                    Random rand = new Random();
                    asteroid[i].X = rand.Next(screenWidth - asteroidTex.Width);
                    asteroid[i].Y = 0 - (numberOfAsteroids * (250-score/10))-128;  //put to top
                    score += 10;
                }
            }


            //Get Midpoint of ufo
            int x = (int)ufoPos.X + (ufoTex.Width / 2);
            int y = (int)ufoPos.Y + (ufoTex.Height / 2);

            //check if midpoint is inside each asteroid 
            for (int i = 0; i < numberOfAsteroids; i++)
            {
                if (x > asteroid[i].X && x < asteroid[i].X + asteroidTex.Width)
                {
                    if (y > asteroid[i].Y && y < asteroid[i].Y + asteroidTex.Height)
                    {
                        score = 0; //reset score
                    }
                }
            }

And finally in the draw function we need another For Loop to draw all of our asteroids

public class Game1 : Microsoft.Xna.Framework.Game
{
    GraphicsDeviceManager graphics;
    SpriteBatch spriteBatch;

    //screen size
    public int screenHeight;
    public int screenWidth;

    // This is a texture we can render.
    Texture2D ufoTex;
    Texture2D asteroidTex;

    SpriteFont font;

    // Set the coordinates to draw the sprite at.
    Vector2 ufoPos = Vector2.Zero;

    //create an array of 10 asteroid coordinates (we will use the same image for each one)
    static int numberOfAsteroids = 25;
    Vector2[] asteroid = new Vector2[numberOfAsteroids];

    Random rand = new Random();

    int score = 0;
        

    public Game1()
    {
        graphics = new GraphicsDeviceManager(this);
        Content.RootDirectory = "Content";
    }


    protected override void Initialize()
    {
        //set Screen size
        screenWidth = 800;
        screenHeight = 600;

        graphics.PreferredBackBufferWidth = screenWidth;
        graphics.PreferredBackBufferHeight = screenHeight;

        graphics.IsFullScreen = false;
        graphics.ApplyChanges();

        //ufo starting position
        ufoPos.Y = screenHeight-128;    //height of screen - hieght of ufo


        //Starting Position of all asteroids
        for (int i = 0; i < numberOfAsteroids; i++)
        {
            //position within screen width - ufo width
            asteroid[i].X = rand.Next(screenWidth-128); 
            asteroid[i].Y = 0 - ((i * 250) + 128);
            //float y = asteroid[i].Y;
        }

        base.Initialize();
    }

    protected override void LoadContent()
    {
        // Create a new SpriteBatch, which can be used to draw textures.
        spriteBatch = new SpriteBatch(GraphicsDevice);

        //load our graphic
        ufoTex = Content.Load<Texture2D>("ufo");
        asteroidTex = Content.Load<Texture2D>("asteroid");

        font = Content.Load<SpriteFont>("mainFont");

    }


    protected override void UnloadContent()
    {
        // TODO: Unload any non ContentManager content here
    }

    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

            
        //update all asteroid positions
        for (int i = 0; i < numberOfAsteroids; i++)
        {
            asteroid[i].Y += 5;
            if (asteroid[i].Y > screenHeight)
            {
                Random rand = new Random();
                asteroid[i].X = rand.Next(screenWidth - asteroidTex.Width);
                asteroid[i].Y = 0 - (numberOfAsteroids * (250-score/10))-128;  //put to top
                score += 10;
            }
        }


        //Get Midpoint of ufo
        int x = (int)ufoPos.X + (ufoTex.Width / 2);
        int y = (int)ufoPos.Y + (ufoTex.Height / 2);

        //check if midpoint is inside each asteroid 
        for (int i = 0; i < numberOfAsteroids; i++)
        {
            if (x > asteroid[i].X && x < asteroid[i].X + asteroidTex.Width)
            {
                if (y > asteroid[i].Y && y < asteroid[i].Y + asteroidTex.Height)
                {
                    score = 0; //reset score
                }
            }
        }




        //update ufo
        KeyboardState key = Keyboard.GetState();

        if (key.IsKeyDown(Keys.Left) && ufoPos.X > 0)
        {
            ufoPos.X -= 5;
        }
        if (key.IsKeyDown(Keys.Right) && ufoPos.X < 800 - ufoTex.Width)
        {
            ufoPos.X += 5;
        }
        if (key.IsKeyDown(Keys.Up) && ufoPos.Y > 0)
        {
            ufoPos.Y -= 5;
        }
        if (key.IsKeyDown(Keys.Down) && ufoPos.Y < 600 - ufoTex.Height)
        {
            ufoPos.Y += 5;
        }



        base.Update(gameTime);
    }

    protected override void Draw(GameTime gameTime)
    {
        GraphicsDevice.Clear(Color.Black);

        // TODO: Add your drawing code here

        spriteBatch.Begin();
        spriteBatch.Draw(ufoTex, ufoPos, Color.White);
            
                        
            
        //draw all asteroids
        for (int i = 0; i < numberOfAsteroids; i++)
        {
            spriteBatch.Draw(asteroidTex, asteroid[i], Color.White);
        }

        spriteBatch.DrawString(font, "Score: " + score, new Vector2(20, 10), Color.White);

        spriteBatch.End();

        base.Draw(gameTime);
    }
}