source: 2010/27/sijoseha/BuildingBuilder/Peli.cs @ 1118

using System;
using Jypeli;
using Jypeli.Widgets;
using Jypeli.Assets;

public class Peli : PhysicsGame
{
    //PhysicsObject block;
    PhysicsObject ground;
    PhysicsObject newestBlock;

    PhysicsObject dropArrow;
    Image dropArrowImage;
    Boolean drop;
    WandererBrain dropArrowBrain;

    protected override void Begin()
    {
        LoadContent();
        CreateLevel();
        Keyboard.Listen(Key.Space, ButtonState.Released, CreateBlock, "");
        //CreateBlock(new Vector(0, 200));
        //CreateBlock(new Vector(10, 350));
        //CreateBlock(new Vector(-10, 500));
    }
    void LoadContent()
    {
        dropArrowImage = LoadImage("dropArrow");
    }
    void CreateLevel()
    {
        ground = Level.CreateGround(Level.Bottom, 20, 10, Color.Green, 10);
        Camera.ZoomToLevel();
        Gravity = new Vector(0, -400);
        drop = true;

        CreateDropArrow();
    }

    void CreateDropArrow()
    {
        dropArrow = new PhysicsObject(48, 48);
        dropArrow.Image = dropArrowImage;
        dropArrow.Position = new Vector(Camera.X, Camera.Y + 350);
        Add(dropArrow);

        UpdateDropArrowBrain();
    }

    void UpdateDropArrowBrain()
    {
        dropArrow.Y = Camera.Y + 350;
        dropArrowBrain = new WandererBrain();
        Vector point1 = new Vector(Camera.X - 150, Camera.Y + 350);
        Vector point2 = new Vector(Camera.X + 150, Camera.Y + 350);
        dropArrowBrain.Add(point1, point2);
        dropArrowBrain.Active = true;
        dropArrowBrain.MovingSpeed = 100;
        dropArrow.Brain = dropArrowBrain;
    }

    void CreateBlock()
    {
        if (drop)
        {
            drop = false;
            PhysicsObject block = new PhysicsObject(100, 100, Shapes.Rectangle);
            block.Position = new Vector(dropArrow.X, Camera.Y + 200);
            block.KineticFriction = 1.0;
            block.AngularVelocity = 0;
            //block.CanRotate = false;
            block.LinearDamping = 1.0;
            block.Restitution = 0.2;
            block.Tag = "block";
            Add(block);
            newestBlock = block;
            AddCollisionHandler(block, BlockCollision);
        }
    }

    void BlockCollision(PhysicsObject collider, PhysicsObject target)
    {
        if (collider == newestBlock)
        {
            drop = true;
        }
        if (collider.Y > Camera.Y)
        {
            Camera.Y += 100;
            UpdateDropArrowBrain();
        }
    }
}