Question

In this part of the Mono Winforms programming tutorial, we will create a Nibbles game clone.

Nibbles game

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 worm. The objective is to eat as many apples as possible. Each time the worm eats an apple, its body grows. It must avoid the walls and its own body.

Development

The size of each of the joints of a worm is 10px. The worm is controlled with the cursor keys. Initially the worm has three joints. The game is started by pressing one of the cursor keys. If the game is finished, we display Game Over message in the middle of the Board.

board.vb

Imports System
Imports System.Collections
Imports System.ComponentModel
Imports System.Drawing
Imports System.Data
Imports System.Windows.Forms

NameSpace BoardSpace

public class Board 
  Inherits UserControl 


  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 = 27
  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

  Private Dim timer As Timer

  Private Dim dot As Bitmap
  Private Dim apple As Bitmap
  Private Dim head As Bitmap

  Private Dim components As IContainer
  
  Public Dim BORDER_WIDTH As Integer
  Public Dim TITLEBAR_HEIGHT As Integer


  Public Sub New
    
    components = New Container
    Me.BackColor = Color.Black
    Me.DoubleBuffered = True
    Me.ClientSize = New Size(WIDTH, HEIGHT)

    Try 
      dot = New Bitmap("dot.png")
      apple = New Bitmap("apple.png")
      head = New Bitmap("head.png")

    Catch e As Exception
      Console.WriteLine(e.Message)
      Environment.Exit(1)
    End Try
     
    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

    Me.LocateApple

    AddHandler Me.KeyUp, AddressOf Me.OnKeyUp

    timer = New Timer(Me.components)
    timer.Enabled = True
    timer.Interval = DELAY

    AddHandler timer.Tick, AddressOf Me.OnTick
    AddHandler Me.Paint, AddressOf Me.OnPaint
    
  End Sub


  Private Sub OnPaint(ByVal sender As Object, _
         ByVal e As PaintEventArgs) 

    Dim g As Graphics = e.Graphics

    If inGame
      Me.DrawObjects(g)
    Else 
      Me.GameOver(g)
    End If
    
  End Sub

  Private Sub DrawObjects(ByVal g As Graphics) 
    g.DrawImage(apple, apple_x, apple_y)

    For z As Integer = 0 To dots-1
      If z = 0 
        g.DrawImage(head, x(z), y(z))
      Else 
        g.DrawImage(dot, x(z), y(z))
      End If
    Next
  End Sub

  Private Sub GameOver(ByVal g As Graphics) 
  
    Dim msg As String = "Game Over"
    Dim rectF As RectangleF = RectangleF.op_Implicit(Me.ClientRectangle)
    
    Dim format As New StringFormat
    format.Alignment = StringAlignment.Center
    format.LineAlignment = StringAlignment.Center
    
    g.DrawString(msg, Font, Brushes.White, rectF , format)
    timer.Stop
    
  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 - DOT_SIZE - TITLEBAR_HEIGHT
      inGame = False
    End If
  
    If y(0) < 0 
      inGame = False
    End If
  
    If x(0) >=  WIDTH - DOT_SIZE - BORDER_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 Sub OnTick(ByVal sender As Object, ByVal e As EventArgs)

    If inGame
      Me.CheckApple
      Me.CheckCollision
      Me.Move
    End If
    
    Me.Refresh
  
  End Sub

  
  Private Sub OnKeyUp(ByVal sender As Object, ByVal e As KeyEventArgs)

    Dim key As Integer = e.KeyCode
    
    If key = Keys.Left And Not right
      left = True
      up = False
      down = False
    End If

    If key = Keys.Right And Not left
      right = True
      up = False
      down = False
    End If

    If key = Keys.Up And Not down
      up = True
      right = False
      left = False
    End if

    If key = Keys.Down And Not up 
      down = True
      right = False
      left = False
    End If
    
  End Sub
  
End Class

End Namespace

First we will define the constants 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 worm. The ALL_DOTS constant defines the maximum number of possible dots on the Board. (900 = 300*300/10*10) 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 joints of a worm.

In the Move method we have the key algorithm of the game. To understand it, look at how the worm is moving. You control the head of the worm. 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 worm 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

We finish the game if the worm hits one of its joints with the head.

If y(0) >= HEIGHT - DOT_SIZE - TITLEBAR_HEIGHT
  inGame = False
End If

We finish the game if the worm hits the bottom of the Board.

The following image helps understand the collision of the worm object with the bottom of the board.

Figure: Collision

The locateApple method locates an apple randomly on the form.

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.

In the OnKeyUp method, we deternime which keys the player hit.

If key = Keys.Left And 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 Move method to change coordinates of the worm object. Notice also that when the worm is heading to the right, we cannot turn immediately to the left.

nibbles.vb

' ZetCode Mono Visual Basic Winforms tutorial
'
' In this program, we create
' a Nibbles game clone
'
' author jan bodnar
' last modified May 2009
' website www.zetcode.com

Imports System
Imports System.Drawing
Imports System.Windows.Forms

Public Class WinVBApp 
  Inherits Form

  Public Sub New
  
    Me.Text = "Nibbles"     

    Me.FormBorderStyle = FormBorderStyle.FixedSingle
    
    Dim borderWidth As Integer = (Me.Width - Me.ClientSize.Width) / 2
    Dim titleBarHeight As Integer = Me.Height - Me.ClientSize.Height - borderWidth
    
    Dim board As New BoardSpace.Board
    board.BORDER_WIDTH = borderWidth
    board.TITLEBAR_HEIGHT = titleBarHeight

    Me.Controls.Add(board)
    Me.CenterToScreen
    
  End Sub
  
  Public Shared Sub Main
    Application.Run(New WinVBApp)
  End Sub

End Class

This is the main class.

Figure: Nibbles

This was the Nibbles game programmed using the Mono Winforms library and the Visual Basic language.