Building Games for Windows Phone 7

Building Games for Windows Phone 7

009

Rob MilesUniversity of Hull

[email protected]

twitter.com/RobMiles

robmiles.com

mailto:[email protected]

• Introducing the Windows Phone• The platform and the development tools

• Writing games for Windows Phone• Game Development Options• Useful code samples

• What to do now• How to Get Started

Agenda

• Windows Phone 7 series is a significant advance on previous generations

• It provides a whole new way of interacting with mobile devices

• You will find out more about this tomorrow at the keynote• For us it provides a compelling new

platform to make great new applications and games

Windows Phone 7 series

• You write in C# using managed code

• You create your programs using Visual Studio 2010• You can write Silverlight

and XNA Apps

• There is also an emulator you can use for testing

Development Options

• The phone is a very capable application platform

• It is very easy to create quick line of business applications

• Silverlight provides some very useful features for game Developers

Windows Phone for Applications

DemoDamage Calc Application

• We can use Silverlight data binding to connect the Price and Damage elements to the underlying code

• You can also use this to manage the position and content of game objects

Databinding inDamageCalc

set{ if (priceChangeActive) return; priceChangeActive = true; latestPrice = value; Damage = twoDecimalPlaces((value / exchangeRate) * taxRate); if (PropertyChanged != null) { PropertyChanged(this, new PropertyChangedEventArgs("Damage")); } priceChangeActive = false;}

Databound Price Property

• This event is fired when the user changes the price



• It calculates the new value of the Damage property



• It fires a property changed event to update the Damage display



• I use an interlock to stop updates from repeating

Damage Calc Extensions

• It would be easy to make the program automatically update the exchange rates

• It could also use location based services to determine the local tax rate

• XNA is a great place to write games

• But some kinds of games are a bit hard to write in XNA• Sometimes you end up writing

your own user interface

• Silverlight makes “form based” games really easy to create

Writing Games in Silverlight

DemoPattern Match Silverlight Game

• An XNA game has Draw and Update methods which are called regularly by the game framework

• Silverlight does not provide game events• You need to create your own game clock• The CompositionTarget.Rendering event can

be used for this

Getting Game Events

• The Rendering event fires each time the form is rendered

• This can be used as our game “tick”

Catching the Rendering Event

CompositionTarget.Rendering += new EventHandler(CompositionTarget_Rendering);

void CompositionTarget_Rendering(object sender, EventArgs e){ gameTick();}

private DateTime lastTick;

private void gameTick(){ DateTime now = DateTime.Now; TimeSpan interVal = now - lastTick; lastTick = now;

Update(interVal);}

Creating an Update behaviour

• The Draw method implements my game state machine

• It has a case for each game state

The Draw method

• Unlike an XNA game, the Update method will not be called at fixed intervals

• Instead the game will need to use the TimeSpan value provided to the Update call to perform game timing

Updating Gameplay in Silverlight

private int currentWait = 0;

private bool testUpdateTime(TimeSpan timeStamp, int updateDelay){ currentWait += timeStamp.Milliseconds;

if (currentWait < updateDelay) { return false; } currentWait -= updateDelay; return true;}

Using the timestamps

• The method returns true if the delay time has passed

private int flashInterval = 800;

...

if (testUpdateTime(interval, flashInterval)){ // Update randomly flashing buttons int oldLitButton = litButtonNo; while (oldLitButton == litButtonNo) { litButtonNo = attractRand.Next(gameButtons.Length); }}

Flashing the Buttons

• This update code changes the lit button every 800 ms

• Your games must automatically persist state information so that they resume where they left off

• Windows Phone provides local storage to make this possible

• Each application has its own area of isolated storage

Persisting State

private void saveHighScore(){ IsolatedStorageFile myStorage =

IsolatedStorageFile.GetUserStoreForApplication(); IsolatedStorageFileStream outputStream =

myStorage.OpenFile("HiScore",FileMode.CreateNew); StreamWriter output = new StreamWriter(outputStream); output.WriteLine(highScore.ToString()); output.Close(); myStorage.Dispose();}

Storing a High Score

• Each application has its own storage area

private void saveHighScore(){ IsolatedStorageFile myStorage =

IsolatedStorageFile.GetUserStoreForApplication(); IsolatedStorageFileStream outputStream =

myStorage.OpenFile("HiScore",FileMode.CreateNew); StreamWriter output = new StreamWriter(outputStream); output.WriteLine(highScore.ToString()); output.Close(); myStorage.Dispose();}

Storing a High Score

• The game can create files and store values in them

IsolatedStorageFile myStorage = IsolatedStorageFile.GetUserStoreForApplication();IsolatedStorageFileStream inputStream =

myStorage.OpenFile("HiScore", FileMode.Open);StreamReader input = new StreamReader(inputStream);

string highScoreText = input.ReadLine();highScore = int.Parse(highScoreText);highscorTextBlock.Text = "Score: " + highScore.ToString();

input.Close();myStorage.Dispose();

Loading a High Score

• The storage can be read when the game starts

• The user never stops a program:• The back button takes you “up” a

level in an application or back to the previous application

• The Start button takes you to the Start Screen

• As far as our game is concerned, in either of these situations the program ends

Windows Phone Navigation

• Your program can bind to the BackKeyPress event and respond appropriately

• It can absorb the back key event if it is sensible to do this

Handling the Back Button

Handling the Exit Event

• You can also bind an event handler to the Exit event to detect when your program is being stopped• this doesn’t seem to work quite right

in the present emulator though..

Application.Current.Exit += new EventHandler(Current_Exit);

• XNA games will run very well on Windows Phone

• Support is provided for 2D and 3D games

• Games can use multi-touch and the accelerometer

Moving into XNA

• Unlike the Zune HD, the accelerometer input for XNA games is presently via the Sensor library

• However, it is easy to create an emulation of the AccellerometerState class for XNA games

Accelerometer Input

DemoAccelerometer Simulation

• Windows Phone programs can consume web services and read web pages

• This is a very powerful feature• I connect the Windows Phone

program to an XNA program that serves out X, Y and Z values read from the Gamepad

An Accelerometer Server

• The Update method requests a page from the Accelerometer server

Reading a Web Pagepublic void Update(){ Uri uri = new Uri("http://127.0.0.1:8080/Accelerometer"); WebClient client = new WebClient(); client.DownloadStringCompleted +=

new DownloadStringCompletedEventHandler(client_DownloadCompleted); client.DownloadStringAsync(uri);}

• Get the response and build the acceleration data

Reading a Web Pagestatic void client_DownloadCompleted (object sender,

DownloadStringCompletedEventArgs e){ if (e.Error == null) { string[] numbers = e.Result.Split(new char[] { ',' }); state.Acceleration.X = float.Parse(numbers[0]); state.Acceleration.Y = float.Parse(numbers[1]); state.Acceleration.Z = float.Parse(numbers[2]); }}

• There is no emulation support• Although you can fake it as

shown above• There are also emulations that

use the Nintendo Wii remote

Working with the Accelerometer

• XNA provides support for multi-touch input• Up to four touch events

can be tracked at once• Each event is uniquely

identified• You get touch down, up

and moved events

Multi-Touch

DemoWindows Phone Piano

• This gets a the current touch events

Processing Touch EventsTouchCollection touchState = TouchPanel.GetState();

foreach (TouchLocation touch in touchState) { Point touchPoint = new Point((int)touch.Position.X, (int)touch.Position.Y); foreach (keyDetails key in noteKeys) { if (key.keyRectangle.Contains(touchPoint) && touch.State == TouchLocationState.Pressed) { key.keySound.Play(); break; } }}

• We then work through each event in turn



• I use a keyDetails class which holds the key position as a Rectangle and the soundeffect to play when the key is pressed



• If you want to emulate multi-touch you can get a multi-touch monitor • Windows 7 multi-touch is used

directly the emulator

• There are some multi-touch emulators that use multiple mice

Working with Multi-Touch

• XNA supports 3D• Windows phones

contain hardware acceleration

• There is shader support, but you can’t write your own shader code

XNA in 3D

DemoDrawing Triangles in 3D

• The way that you specify Vertices has changed in XNA 4.0

• Do not be surprised if sample code for earlier versions of XNA fail to work

• The new design is much easier to understand though

• Samples are now available on the web

XNA 4.0 Changes

• The Windows Phone update rate is set to 30Hz

• This is sensible given the type of display in use

• You can use a frame counter to measure the actual update rate

Measuring Performance

DemoMeasuring Performance

public override void Update(GameTime gameTime){ elapsedTime += gameTime.ElapsedGameTime;

if (elapsedTime > TimeSpan.FromSeconds(1)) { elapsedTime -= TimeSpan.FromSeconds(1); frameRate = frameCounter; frameCounter = 0; }}

XNA Performance Counter

• This Update method clears the frame counter every second• The counter is increased each time Draw is called

• It is easy to get a frame rate counter in Silverlight

• Setting the above property in your program will display one

Sliverlight Performance

Application.Current.Host.Settings.EnableFrameRateCounter = true;

• One way to get experience of Windows Phone XNA development is to get hold of a Zune HD

• You can write XNA 3.1 games in 2D for this platform

• It provides multi-touch and accelerometer support

Using the Zune HD

DemoZune HD Album Shaker

• Download the development environment and other cool stuff:

developer.windowsphone.com/ • Read the sample chapters from the free ebook

by Charles Petzold• Get writing code!• All samples, resources and links are on my

blog:www.robmiles.com

What To Do Now

http://developer.windowsphone.com/

http://www.robmiles.com/

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Documents

Building Games for Windows Phone 7