Nibbles
In this part of the Visual Basic Qyoto 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.
Imports Qyoto
NameSpace BoardSpace
public class Board
Inherits QFrame
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 timer As QBasicTimer
Dim ball As QImage
Dim apple As QImage
Dim head As QImage
Public Sub New()
Me.SetStyleSheet("QWidget { background-color: black }")
Me.FocusPolicy = Qt.FocusPolicy.StrongFocus
Try
ball = New QImage("dot.png")
apple = New QImage("apple.png")
head = New QImage("head.png")
Catch e As Exception
Console.WriteLine("Cannot read images")
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()
timer = New QBasicTimer()
timer.Start(DELAY, Me)
End Sub
Protected Overrides Sub PaintEvent(ByVal e As QPaintEvent)
Dim painter As New QPainter()
painter.Begin(Me)
If inGame
Me.DrawObjects(painter)
Else
Me.GameOver(painter)
End If
painter.End()
End Sub
Private Sub DrawObjects(ByVal painter As QPainter)
painter.DrawImage(apple_x, apple_y, apple)
For z As Integer = 0 to dots - 1
If z = 0
painter.DrawImage(x(z), y(z), head)
Else
painter.DrawImage(x(z), y(z), ball)
End If
Next
End Sub
Private Sub GameOver(ByVal painter As QPainter)
Dim msg As String = "Game Over"
Dim small As New QFont("Helvetica", 12)
small.SetBold(True)
Dim metr As New QFontMetrics(small)
Dim textWidth As Integer = metr.Width(msg)
Dim h As Integer = Me.Height
Dim w As Integer = Me.Width
painter.SetPen(New QPen(New QBrush(Qt.GlobalColor.white), 1))
painter.SetFont(small)
painter.Translate(New QPoint(w/2, h/2))
Dim text_x As Integer = -textWidth / 2
Dim text_y As Integer = 0
painter.DrawText(text_x, text_y, msg)
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
Protected Overrides Sub TimerEvent(ByVal e As QTimerEvent)
If inGame
Me.CheckApple()
Me.CheckCollision()
Me.Move()
Else
timer.Stop()
End If
Me.Repaint()
End Sub
Protected Overrides Sub KeyPressEvent(ByVal e As QKeyEvent)
Dim key As Integer = e.Key()
If key = Qt.Key.Key_Left And Not right
left = True
up = False
down = False
End If
If key = Qt.Key.Key_Right And Not left
right = True
up = False
down = False
End If
If key = Qt.Key.Key_Up And Not down
up = True
right = False
left = False
End If
If key = Qt.Key.Key_Down And 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(painter)
Else
Me.GameOver(painter)
End If
Inside the PaintEvent() method, we check the inGame variable. If it is true, we draw our objects. The apple and the snake joints. Otherwise we display "Game over" text.
Private Sub DrawObjects(ByVal painter As QPainter)
painter.DrawImage(apple_x, apple_y, apple)
For z As Integer = 0 to dots - 1
If z = 0
painter.DrawImage(x(z), y(z), head)
Else
painter.DrawImage(x(z), y(z), ball)
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()
Else
timer.Stop()
End If
Every 140 ms, the TimerEvent() method is called. If we are in the game, we call three methods, that build the logic of the game. Otherwise we stop the timer.
In the KeyPressEvent() method of the Board class, we determine the keys that were pressed.
If key = Qt.Key.Key_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 snake object. Notice also, that when the snake is heading to the right, we cannot turn immediately to the left.
' ZetCode Mono Visual Basic Qt tutorial
'
' In this program, we create
' a Nibbles game clone
'
' author jan bodnar
' last modified May 2009
' website www.zetcode.com
Imports Qyoto
Imports BoardSpace
Public Class VBQApp
Inherits QMainWindow
Dim WIDTH As Integer = 250
Dim HEIGHT As Integer = 150
Public Sub New()
Me.SetWindowTitle("Nibbles")
Dim board As New BoardSpace.Board()
Me.SetCentralWidget(board)
Me.Resize(310, 310)
Me.Move(300, 300)
Me.Show()
End Sub
Public Shared Sub Main(ByVal args() As String)
Dim qapp As New QApplication(args)
Dim app As New VBQApp
QApplication.Exec()
End Sub
End Class
In this class, we set up the Nibbles game.
This was the Nibbles computer game programmed with the Qyoto library and the Visual Basic programming language.