Zune HD: XNA Accelerometer

October 24th, 2009 Categories: WP7, XNA, Zune HD

As far as I am aware, the accelerometer code here is the same as would be used for the new Windows Phone 7 devices.

My Zune HD arrived last week and after getting over the initial disappointment of a disgracefully empty marketplace for it, I was really itching to try out some XNA and play around with the accelerometer. First things first, I needed to download the XNA extensions that would provide the necessary framework to use the accelerometer in the Zune HD; these can be found right here. As far as I’m aware, XNA for the older Zune won’t let you use the 3D API (I could be wrong??) and I don’t think this has been rectified by the XNA 3.1 Zune Extensions however hopefully an XNA 3.2 or 4.0 will come along in the near future and open that up.

UPDATE:

I verified that the 3D API isn’t available. The likes of the Effect class aren’t available on the Zune.

In order to play with the accelerometer, I made a quick test project that allows the user to roll a ball about in a lovely blank black background. See this video:

Ok, so it’s not quite a ball….its a big white dot! Who cares?

This was actually incredibly simple to achieve and was much easier than I had originally anticipated. The XNA extensions provide a new class under Microsoft.Xna.Framework.Input called Accelerometer. As with the other input devices, this class provides a GetState() method so it very much keeps in line with what XNA developers are already used to. This method returns an object of type AccelerometerState which has a Vector3 property called Acceleration. This property holds all the information you need for detecting tilt on the device.

Since the code is so simple, I don’t think I will walk through it step by step but rather I will just post my very quick code below. Please ignore the rubbish boundary collisions – I didn’t feel like it was very important to make them perfect. Rough and ready…just the way I like it!

Code Snippet

using System;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Input;
namespace AccelerometerTest
{
 public class Game1 : Microsoft.Xna.Framework.Game
 {
 private const float rollSpeed = 50f;
 private GraphicsDeviceManager graphics;
 private SpriteBatch spriteBatch;
 private Rectangle boundary;
 private Texture2D ballTexture;
 private Vector2 ballPosition;
 public Game1()
 {
 graphics = new GraphicsDeviceManager(this);
 Content.RootDirectory = “Content”;
 // Frame rate is 30 fps by default for Zune.
 TargetElapsedTime = TimeSpan.FromSeconds(1 / 30.0);
 }
 protected override void Initialize()
 {
 boundary = GraphicsDevice.Viewport.TitleSafeArea;
 base.Initialize();
 }
 protected override void LoadContent()
 {
 spriteBatch = new SpriteBatch(GraphicsDevice);
 ballTexture = Content.Load<Texture2D>(“ball”);
 ballPosition = new Vector2(boundary.Width / 2, boundary.Height / 2);
 }
 protected override void UnloadContent()
 {
 // TODO: Unload any non ContentManager content here
 }
 protected override void Update(GameTime gameTime)
 {
 if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed)
 this.Exit();
 Vector3 acceleration = Accelerometer.GetState().Acceleration;
 Vector2 velocity = new Vector2(acceleration.X, -acceleration.Y) * rollSpeed;
 Vector2 projectedPosition = ballPosition + velocity;
 Rectangle projectedRectangle = new Rectangle((int)projectedPosition.X, (int)projectedPosition.Y, ballTexture.Width, ballTexture.Height);
 if (projectedRectangle.Left < boundary.Left || projectedRectangle.Right > boundary.Right)
 velocity.X = 0;
 if (projectedRectangle.Top < boundary.Top || projectedRectangle.Bottom > boundary.Bottom)
 velocity.Y = 0;
 ballPosition += velocity;
 base.Update(gameTime);
 }
 protected override void Draw(GameTime gameTime)
 {
 GraphicsDevice.Clear(Color.Black);
 spriteBatch.Begin(SpriteBlendMode.AlphaBlend);
 spriteBatch.Draw(ballTexture, ballPosition, Color.White);
 spriteBatch.End();
 base.Draw(gameTime);
 }
 }
}