XNA: Sample Program 1

The best way to learn programming concepts is to go through a sample program. In this article, we will cover a sample program for XNA in a Windows game. The game is very simple, but shows the various parts of an XNA program. The game is a one-person version of Pong (racquetball).

Download Source Code - https://dcjtech.info/wp-content/uploads/2014/11/Racquetball.zip

The game works as the user controls a "paddle" which they can move up and down. A ball bounces off the top, bottom and right wall of the window. The ball cannot pass the paddle which is placed to the left of the window. If the ball passes the paddle, the game is over. In the case of this game, the ball reappears on the screen and the game continues. Managing a "game over" screen is a simple thing, but let's start with the basics first and improve the game as we go along.

Let's start with something similar to Pong, but a one player game. We'll look at Racquetball. In Racquetball there are three walls: top, right and bottom. The ball will bounce off of these walls. A paddle is placed on the left side of the screen which is moved up and down by the player. If the ball gets past the paddle, the game resets. The code is as follows:

''' <summary>
''' This is the main type for your game
''' </summary>
Public Class Game1
Inherits Microsoft.Xna.Framework.Game
Private WithEvents graphics As GraphicsDeviceManager
Private WithEvents spriteBatch As SpriteBatch

Dim t_paddle1 As Texture2D
Dim t_ball As Texture2D
Dim paddle1 As Paddle1
Dim ball As Ball
Dim rand As New Random()
Dim currentState As KeyboardState
Dim currentPad As GamePadState
Dim r As Integer

''' <summary>
''' Allows the game to perform any initialization it needs to before starting to run.
''' This is where it can query for any required services and load any non-graphic
''' related content. Calling MyBase.Initialize will enumerate through any components
''' and initialize them as well.
''' </summary>
Protected Overrides Sub Initialize()
' TODO: Add your initialization logic here
MyBase.Initialize()
ResetGame()
End Sub

''' <summary>
''' LoadContent will be called once per game and is the place to load
''' all of your content.
''' </summary>
Protected Overrides Sub LoadContent()
' Create a new SpriteBatch, which can be used to draw textures.
spriteBatch = New SpriteBatch(GraphicsDevice)
t_paddle1 = Content.Load(Of Texture2D)("paddle1")
t_ball = Content.Load(Of Texture2D)("ball")
' TODO: use Me.Content to load your game content here
End Sub

''' <summary>
''' UnloadContent will be called once per game and is the place to unload
''' all content.
''' </summary>
Protected Overrides Sub UnloadContent()
' TODO: Unload any non ContentManager content here
End Sub

''' <summary>
''' Allows the game to run logic such as updating the world,
''' checking for collisions, gathering input, and playing audio.
''' </summary>
'''Provides a snapshot of timing values.
Protected Overrides Sub Update(ByVal gameTime As GameTime)
' Allows the game to exit
If GamePad.GetState(PlayerIndex.One).Buttons.Back = ButtonState.Pressed Then
    Me.Exit()
End If
UpdateBall()
UpdatePaddles()
CheckCollisions()
' MyBase.Update(gameTime)
' TODO: Add your update logic here
MyBase.Update(gameTime)
End Sub

''' <summary>
''' This is called when the game should draw itself.
''' </summary>
'''Provides a snapshot of timing values.
Protected Overrides Sub Draw(ByVal gameTime As GameTime)

' TODO: Add your drawing code here
GraphicsDevice.Clear(Color.LightBlue)
spriteBatch.Begin()
spriteBatch.Draw(t_paddle1, New Rectangle(paddle1.pos.X, paddle1.pos.Y, t_paddle1.Width, t_paddle1.Height), Color.White)
spriteBatch.Draw(t_ball, New Rectangle(ball.pos.X, ball.pos.Y, t_ball.Width, t_ball.Height), Color.White)
spriteBatch.[End]()
MyBase.Draw(gameTime)
End Sub
Sub ResetGame()
paddle1 = New Paddle1(10, 200)
ball = New Ball(385, 285)
End Sub

Public Sub New()
graphics = New GraphicsDeviceManager(Me)
Content.RootDirectory = "Content"
End Sub
Sub UpdateBall()
'update positions
ball.pos.X += ball.h_speed
ball.pos.Y += ball.v_speed
'check for boundaries
'bottom
If ball.pos.Y > (Window.ClientBounds.Height - t_ball.Height) Then
    ball.v_speed *= -1
End If
'top
If ball.pos.Y < 0 Then ball.v_speed *= -1 End If 'right If ball.pos.X > Window.ClientBounds.Width - t_paddle1.Width + 1 Then
    ' Fill in this part
    ball.h_speed *= -1
End If

End Sub

Sub UpdatePaddles()
'get keyboard keys
currentState = Keyboard.GetState()
Dim currentKeys As Keys() = currentState.GetPressedKeys()
'check for up and down arrow keys
For Each key As Keys In currentKeys
If key = Keys.Up Then
    paddle1.pos.Y -= paddle1.speed
End If
If key = Keys.Down Then
    paddle1.pos.Y += paddle1.speed
End If
If key = Keys.Escape Then
    Me.[Exit]()
End If
Next
'check for up and down arrow keys

If currentPad.Triggers.Left > 0.0 Then
    paddle1.pos.Y -= paddle1.speed
End If
If currentPad.Triggers.Right > 0.0 Then
    paddle1.pos.Y += paddle1.speed
End If
'check boundaries
If paddle1.pos.Y <= 1 Then paddle1.pos.Y = 1 End If If paddle1.pos.Y + t_paddle1.Height + 1 >= Window.ClientBounds.Height Then
    paddle1.pos.Y = Window.ClientBounds.Height - t_paddle1.Height + 1
End If
End Sub

Sub CheckCollisions()
'check paddle1 if ball moving left
If ball.h_speed < 0 Then
'check if ball has surpassed paddle
If ball.pos.X < paddle1.pos.X + 43 Then
'check if ball has hit paddle or went through
If (ball.pos.Y + t_ball.Height < paddle1.pos.Y) OrElse (ball.pos.Y > paddle1.pos.Y + t_paddle1.Height) Then
    'LOST!
    ResetGame()
Else
'ball hit - calculate new speeds
'speed of ball changes randomly - 3 to 6
If ball.h_speed < 0 Then
    ball.h_speed = rand.[Next](3, 7)
Else
    ball.h_speed = rand.[Next](-6, -2)
End If
If ball.v_speed < 0 Then
    ball.v_speed = rand.[Next](3, 7)
Else
    ball.v_speed = rand.[Next](-6, -2)
End If
End If
End If
End If
End Sub
End Class

Public Class Paddle1
'position of paddle
Public pos As Point
Public speed As Integer
'constructor - position
Public Sub New(x As Integer, y As Integer)
pos = New Point(x, y)
speed = 6
End Sub
End Class

Public Class Ball
'position of ball
Public pos As Point
Public h_speed As Integer, v_speed As Integer
'constructor - position
Public Sub New(x As Integer, y As Integer)
pos = New Point(x, y)
Dim rand As New Random()
h_speed = rand.[Next](3, 7)
If rand.[Next](0, 2) = 0 Then
    h_speed *= -1
End If
rand = New Random()
v_speed = rand.[Next](3, 7)
If rand.[Next](0, 2) = 0 Then
    v_speed *= -1
End If
End Sub
End Class

The game can be copied and pasted into a Visual Studio window to be played or is attached to the article with the images. If you read the previous article: XNA Parts of the Program, then some of this may look familiar. I will go into each section in more detail.

The Initialize subroutine is as follows:

Protected Overrides Sub Initialize()
' TODO: Add your initialization logic here
    MyBase.Initialize()
    ResetGame()
End Sub

The subroutine is the basic auto-generated sub for every XNA program. In this instance, nothing is done here except the call to ResetGame().

The ResetGame() sub is the following:

Sub ResetGame()
    paddle1 = New Paddle1(10, 200)
    ball = New Ball(385, 285)
End Sub

Here, a paddle and ball instance are created or overwritten.

The next main subroutine is LoadContent() as follows:

Protected Overrides Sub LoadContent()
    ' Create a new SpriteBatch, which can be used to draw textures.
    spriteBatch = New SpriteBatch(GraphicsDevice)
    t_paddle1 = Content.Load(Of Texture2D)("paddle1")
    t_ball = Content.Load(Of Texture2D)("ball")
End Sub

This is where the Sprites are created and the textures are loaded for the paddle and ball.

The next sub is the UnloadContent(), which if you look back, it does not have any content in this program.

The next two subroutines are the Game Loop, which are Update and Draw.

The Update() sub is:

Protected Overrides Sub Update(ByVal gameTime As GameTime)
' Allows the game to exit
If GamePad.GetState(PlayerIndex.One).Buttons.Back = ButtonState.Pressed Then
    Me.Exit()
End If
UpdateBall()
UpdatePaddles()
CheckCollisions()
' MyBase.Update(gameTime)
' TODO: Add your update logic here
MyBase.Update(gameTime)
End Sub

Here you can see that if the back button is pressed on the GamePad, the program exits. The next thing is to update the Ball (UpdateBall), Paddles (UpdatePaddles) and Check for Collisions (CheckCollisions). If you understand Visual Basic, the subroutines should make sense to you.

The last subroutine is Draw as shown:

Protected Overrides Sub Draw(ByVal gameTime As GameTime)
    GraphicsDevice.Clear(Color.LightBlue)
    spriteBatch.Begin()
    spriteBatch.Draw(t_paddle1, New Rectangle(paddle1.pos.X, paddle1.pos.Y, t_paddle1.Width, t_paddle1.Height), Color.White)
    spriteBatch.Draw(t_ball, New Rectangle(ball.pos.X, ball.pos.Y, t_ball.Width, t_ball.Height), Color.White)
    spriteBatch.[End]()
    MyBase.Draw(gameTime)
End Sub

The Draw() sub first sets up the screen color as LightBlue. Next, the Sprite Batch is started to update the textures all at once. First, the paddle is set. Second, the Ball is set. Finally, the Sprite Batch is ended which causes the two textures to be refreshed at once. The final command, MyBase(gameTime), is run to finalize the refresh.

Try the code and play the game a few times. Look over the code to understand it better. In my next article, we'll make modifications.

Further Reading

• XNA Reading Guide - https://dcjtech.info/topic/gaming/#xna