Tuesday, April 16, 2013

The Nibbles Clone using Visual Basic GTK#

Nibbles

In this part of the Visual Basic GTK# programming tutorial, we will create a Nibbles game clone.
Nibbles is an older classic video game. It was first created in late 70s. Later it was brought to PCs. In this game the player controls a snake. The objective is to eat as many apples as possible. Each time the snake eats an apple, its body grows. The snake must avoid the walls and its own body.

Development

The size of each of the joints of a snake is 10px. The snake is controlled with the cursor keys. Initially, the snake has three joints. The game starts immediately. When the game is finished, we display "Game Over" message in the center of the window.
board.vb
Imports Gtk
Imports Cairo

NameSpace BoardSpace

Public Class Board
Inherits DrawingArea

Const WIDTH As Integer = 300
Const HEIGHT As Integer = 300
Const DOT_SIZE As Integer = 10
Const ALL_DOTS As Integer = 900
Const RAND_POS As Integer = 30
Const DELAY As Integer = 140

Dim x(ALL_DOTS) As Integer
Dim y(ALL_DOTS) As Integer

Dim dots As Integer
Dim apple_x As Integer
Dim apple_y As Integer

Dim left As Boolean = False
Dim right As Boolean = True

Dim up As Boolean = False
Dim down As Boolean = False
Dim inGame As Boolean = True

Dim dot As ImageSurface
Dim apple As ImageSurface
Dim head As ImageSurface


Public Sub New

MyBase.New

ModifyBg(StateType.Normal, New Gdk.Color(0, 0, 0))

Me.InitGame

End Sub


Private Sub InitGame

dots = 3

For z As Integer = 0 To dots-1
x(z) = 50 - z*10
y(z) = 50
Next

Try
dot = New ImageSurface("dot.png")
head = New ImageSurface("head.png")
apple = New ImageSurface("apple.png")
Catch
Console.WriteLine("Images not found")
Environment.Exit(1)
End Try

Me.LocateApple

Dim timer As New GLib.TimeoutHandler(AddressOf Me.OnTimer)

GLib.Timeout.Add(100, timer)
AddHandler Me.ExposeEvent, AddressOf Me.OnExpose

End Sub


Protected Sub OnExpose(ByVal sender As Object, ByVal e As ExposeEventArgs)

Dim cc As Cairo.Context = Gdk.CairoHelper.Create(sender.GdkWindow)

If inGame
Me.DrawObjects(cc)
Else
Me.GameOver(cc)
End If

Dim disposeTarget As IDisposable = CType(cc.Target, IDisposable)
disposeTarget.Dispose

Dim disposeContext As IDisposable = CType(cc, IDisposable)
disposeContext.Dispose

End Sub

Private Sub DrawObjects(ByVal cc As Cairo.Context)

cc.SetSourceSurface(apple, apple_x, apple_y)
cc.Paint

For z As Integer = 0 to dots - 1
If z = 0
cc.SetSourceSurface(head, x(z), y(z))
cc.Paint
Else
cc.SetSourceSurface(dot, x(z), y(z))
cc.Paint
End If
Next

End Sub

Private Sub GameOver(ByVal cc As Cairo.Context)

Dim message As String = "Game Over"

Dim x As Integer = Allocation.Width / 2
Dim y As Integer = Allocation.Height / 2

cc.SetSourceRGB(1, 1, 1)
cc.SetFontSize(18)

Dim extents As TextExtents = cc.TextExtents(message)

cc.MoveTo(x - extents.Width/2, y)
cc.ShowText(message)
inGame = False

End Sub


Private Sub CheckApple

If x(0) = apple_x And y(0) = apple_y

dots += 1
Me.LocateApple

End If

End Sub

Private Sub Move

For z As Integer = dots To 1 Step -1
x(z) = x(z - 1)
y(z) = y(z - 1)
Next

If left
x(0) -= DOT_SIZE
End If

If right
x(0) += DOT_SIZE
End If

If up
y(0) -= DOT_SIZE
End If

If down
y(0) += DOT_SIZE
End If

End Sub


Private Sub CheckCollision

For z As Integer = dots To 1 Step -1
If z > 4 And x(0) = x(z) And y(0) = y(z)
inGame = False
End If
Next

If y(0) > HEIGHT
inGame = False
End If

If y(0) < 0
inGame = False
End If

If x(0) > WIDTH
inGame = False
End If

If x(0) < 0
inGame = False
End If

End Sub


Private Sub LocateApple

Dim rand As New Random

Dim r As Integer = rand.Next(RAND_POS)

apple_x = r * DOT_SIZE
r = rand.Next(RAND_POS)
apple_y = r * DOT_SIZE


End Sub

Private Function OnTimer As Boolean

If inGame

Me.CheckApple
Me.CheckCollision
Me.Move
Me.QueueDraw

Return True

Else
Return False
End If

End Function

Public Sub OnKeyDown(ByVal e As Gdk.EventKey)

Dim key As Integer = e.KeyValue

If key = Gdk.Key.Left AndAlso Not right
left = True
up = False
down = False
End If

If key = Gdk.Key.Right AndAlso Not left
right = True
up = False
down = False
End If

If key = Gdk.Key.Up AndAlso Not down
up = True
right = False
left = False
End If

If key = Gdk.Key.Down AndAlso Not up
down = True
right = False
left = False
End If

End Sub

End Class

End Namespace
First we will define some globals used in our game.
The WIDTH and HEIGHT constants determine the size of the Board. The DOT_SIZE is the size of the apple and the dot of the snake. The ALL_DOTS constant defines the maximum number of possible dots on the Board. The RAND_POS constant is used to calculate a random position of an apple. The DELAY constant determines the speed of the game.
Dim x(ALL_DOTS) As Integer 
Dim y(ALL_DOTS) As Integer
These two arrays store x, y coordinates of all possible joints of a snake.
The InitGame method initializes variables, loads images and starts a timeout function.
 If inGame
Me.DrawObjects(cc)
Else
Me.GameOver(cc)
End If
Inside the OnExpose method, we check the inGamevariable. If it is true, we draw our objects. The apple and the snake joints. Otherwise we display "Game over" text.
 Private Sub DrawObjects(ByVal cc As Cairo.Context) 

cc.SetSourceSurface(apple, apple_x, apple_y)
cc.Paint

For z As Integer = 0 to dots - 1
If z = 0
cc.SetSourceSurface(head, x(z), y(z))
cc.Paint
Else
cc.SetSourceSurface(dot, x(z), y(z))
cc.Paint
End If
Next

End Sub
The DrawObjects method draws the apple and the joints of the snake. The first joint of a snake is its head, which is represented by a red circle.
 Private Sub CheckApple

If x(0) = apple_x And y(0) = apple_y

dots += 1
Me.LocateApple

End If

End Sub
The CheckApple method checks, if the snake has hit the apple object. If so, we add another snake joint and call the LocateApple method, which randomly places a new apple object.
In the Move method we have the key algorithm of the game. To understand it, look at how the snake is moving. You control the head of the snake. You can change its direction with the cursor keys. The rest of the joints move one position up the chain. The second joint moves where the first was, the third joint where the second was etc.
For z As Integer = dots To 1 Step -1
x(z) = x(z - 1)
y(z) = y(z - 1)
Next
This code moves the joints up the chain.
If left
x(0) -= DOT_SIZE
End If
Move the head to the left.
In the CheckCollision method, we determine if the snake has hit itself or one of the walls.
For z As Integer = dots To 1 Step -1
If z > 4 And x(0) = x(z) And y(0) = y(z)
inGame = False
End If
Next
Finish the game, if the snake hits one of its joints with the head.
If y(0) > HEIGHT 
inGame = False
End If
Finish the game, if the snake hits the bottom of the Board.
The LocateApple method locates an apple randomly on the board.
Dim rand As New Random

Dim r As Integer = rand.Next(RAND_POS)
We get a random number from 0 to RAND_POS - 1.
apple_x = r * DOT_SIZE
...
apple_y = r * DOT_SIZE
These line set the x, y coordinates of the apple object.
 If inGame

Me.CheckApple
Me.CheckCollision
Me.Move
Me.QueueDraw

Return True

Else
Return False
End If
Every 140 ms, the OnTimer method is called. If we are in the game, we call three methods, that build the logic of the game. Otherwise we return False, which stops the timer event.
In the OnKeyDown method of the Board class, we determine the keys that were pressed.
 If key = Gdk.Key.Left AndAlso Not right
left = True
up = False
down = False
End If
If we hit the left cursor key, we set left variable to true. This variable is used in the Movemethod to change coordinates of the snake object. Notice also, that when the snake is heading to the right, we cannot turn immediately to the left.
nibbles.vb
' ZetCode Mono Visual Basic GTK# tutorial
'
' In this program, we create
' a Nibbles game clone
'
' author jan bodnar
' last modified May 2009
' website www.zetcode.com

Imports Gtk

Public Class GtkVBApp
Inherits Window

Dim WIDTH As Integer = 250
Dim HEIGHT As Integer = 150
Dim board As BoardSpace.Board

Public Sub New

MyBase.New("Nibbles")

board = New BoardSpace.Board
Me.Add(board)

AddHandler Me.DeleteEvent, AddressOf Me.OnDelete

Me.Resize(310, 310)
Me.Move(300, 300)
Me.ShowAll

End Sub

Private Sub OnDelete(ByVal sender As Object, _
ByVal args As DeleteEventArgs)
Application.Quit
End Sub


Protected Overrides Function OnKeyPressEvent(ByVal e As Gdk.EventKey) As Boolean
board.OnKeyDown(e)
Return True
End Function

Public Shared Sub Main

Application.Init
Dim app As New GtkVBApp
Application.Run

End Sub

End Class
In this class, we set up the Nibbles game.
 Protected Overrides Function OnKeyPressEvent(ByVal e As Gdk.EventKey) As Boolean
board.OnKeyDown(e)
Return True
End Function
In this class, we catch the key press events. And delegate the processing to the OnKeyDown method of the board class.

Nibbles
Figure: Nibbles
The following command compiles the game.
vbnc -r:/usr/lib/mono/gtk-sharp-2.0/gtk-sharp.dll 
-r:/usr/lib/mono/gtk-sharp-2.0/gdk-sharp.dll -r:/usr/lib/mono/2.0/Mono.Cairo.dll
-r:/usr/lib/mono/gtk-sharp-2.0/glib-sharp.dll nibbles.vb board.vb

This was the Nibbles computer game programmed with the GTK# library and the Visual Basic programming language.

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