Collision

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Usage

In this example, we will make a simple sandbox where shapes can move and collide with each other.

We start by defining an IEntity interface that inherits ICollisionActor, so we can insert the entities into our CollisionComponent.

public interface IEntity : ICollisionActor
{
    public void Update(GameTime gameTime);
    public void Draw(SpriteBatch spriteBatch);
}

Next, we define our entity classes

The OnCollision method and the Bounds property come from the ICollisionActor interface. These will be called by the CollisionComponent

public class CubeEntity : IEntity
{
    private readonly Game1 _game;
    public Vector2 Velocity;
    public IShapeF Bounds { get; }

    public CubeEntity(Game1 game, RectangleF rectangleF)
    {
        _game = game;
        Bounds = rectangleF;
        RandomizeVelocity();
    }

    public virtual void Draw(SpriteBatch spriteBatch)
    {
        spriteBatch.DrawRectangle((RectangleF) Bounds, Color.Red, 3);
    }

    public virtual void Update(GameTime gameTime)
    {
        Bounds.Position += Velocity * gameTime.GetElapsedSeconds() * 50;
    }

    public void OnCollision(CollisionEventArgs collisionInfo)
    {
        Velocity.X *= -1;
        Velocity.Y *= -1;
        Bounds.Position -= collisionInfo.PenetrationVector;
    }

    private void RandomizeVelocity()
    {
        Velocity.X = _game.Random.Next(-1, 2);
        Velocity.Y = _game.Random.Next(-1, 2);
    }
}

public class BallEntity : IEntity
{
    private readonly Game1 _game;
    public Vector2 Velocity;
    public IShapeF Bounds { get; }

    public BallEntity(Game1 game, CircleF circleF)
    {
        _game = game;
        Bounds = circleF;
        RandomizeVelocity();
    }

    public void Draw(SpriteBatch spriteBatch)
    {
        spriteBatch.DrawCircle((CircleF) Bounds, 8, Color.Red, 3f);
    }

    public void Update(GameTime gameTime)
    {
        Bounds.Position += Velocity * gameTime.GetElapsedSeconds() * 30;
    }

    public void OnCollision(CollisionEventArgs collisionInfo)
    {
        RandomizeVelocity();
        Bounds.Position -= collisionInfo.PenetrationVector;
    }


    private void RandomizeVelocity()
    {
        Velocity.X = _game.Random.Next(-1, 2);
        Velocity.Y = _game.Random.Next(-1, 2);
    }
}

Setting up the game

First, we define our properties and fields

public readonly Random Random = new Random(Guid.NewGuid().GetHashCode());
private readonly List<IEntity> _entities = new List<IEntity>();
private readonly CollisionComponent _collisionComponent;
const int MapWidth = 500;
const int MapHeight = 500;

Then we Initialize our game by creating entities and adding them to the CollisionComponent.

public Game1()
{
    _graphics = new GraphicsDeviceManager(this);
    _collisionComponent = new CollisionComponent(new RectangleF(0,0, MapWidth, MapHeight));

    Content.RootDirectory = "Content";
    IsMouseVisible = true;
}

protected override void Initialize()
{
    base.Initialize();
    _graphics.PreferredBackBufferHeight = MapHeight;
    _graphics.PreferredBackBufferWidth = MapWidth;
    _graphics.ApplyChanges();

    for (var i = 0; i < 50; i++)
    {
        var size = Random.Next(20, 40);
        var position = new Point2(Random.Next(-MapWidth, MapWidth * 2), Random.Next(0, MapHeight));
        if (i % 2 == 0)
        {
            _entities.Add(new BallEntity(this, new CircleF(position, size)));
        }
        else
        {
            _entities.Add(new CubeEntity(this, new RectangleF(position, new Size2(size, size))));
        }
    }

    foreach (IEntity entity in _entities)
    {
        _collisionComponent.Insert(entity);
    }
}

Updating the game

In the Update method, we update all entities and the CollisionComponent.

protected override void Update(GameTime gameTime)
{
    foreach (IEntity entity in _entities)
    {
        entity.Update(gameTime);
    }

    _collisionComponent.Update(gameTime);

    base.Update(gameTime);
}

Drawing the final result

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

    _spriteBatch.Begin();
    foreach (IEntity entity in _entities)
    {
        entity.Draw(_spriteBatch);
    }

    _spriteBatch.End();

    base.Draw(gameTime);
}

Result