贪食蛇 - 《ZetCode 中文系列教程》

开发

原文： http://zetcode.com/gui/vbgtk/nibbles/

在 Visual Basic GTK# 编程教程的这一部分中，我们将创建贪食蛇游戏克隆。

贪食蛇是较旧的经典视频游戏。它最初是在 70 年代后期创建的。后来它被带到 PC 上。在这个游戏中，玩家控制蛇。目的是尽可能多地吃苹果。蛇每次吃一个苹果，它的身体就会长大。蛇必须避开墙壁和自己的身体。

开发

蛇的每个关节的大小为 10px。蛇由光标键控制。最初，蛇具有三个关节。游戏立即开始。游戏结束后，我们在窗口中心显示"Game Over"消息。

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

首先，我们将定义一些在游戏中使用的全局变量。

WIDTH和HEIGHT常数确定电路板的大小。 DOT_SIZE是苹果的大小和蛇的点。 ALL_DOTS常数定义了板上可能的最大点数。 RAND_POS常数用于计算苹果的随机位置。 DELAY常数确定游戏的速度。

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

这两个数组存储蛇的所有可能关节的 x，y 坐标。

InitGame方法初始化变量，加载图像并启动超时功能。

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

在OnExpose方法内部，我们检查inGame变量。如果为真，则绘制对象。苹果和蛇的关节。否则，我们显示"Game Over"文本。

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

DrawObjects方法绘制苹果和蛇的关节。蛇的第一个关节是其头部，用红色圆圈表示。

Private Sub CheckApple
    If x(0) = apple_x And y(0) = apple_y
        dots += 1
        Me.LocateApple
    End If 
End Sub

CheckApple方法检查蛇是否击中了苹果对象。如果是这样，我们添加另一个蛇形关节并调用LocateApple方法，该方法将随机放置一个新的 Apple 对象。

在Move方法中，我们有游戏的关键算法。要了解它，请看一下蛇是如何运动的。您控制蛇的头。您可以使用光标键更改其方向。其余关节在链上向上移动一个位置。第二关节移动到第一个关节的位置，第三关节移动到第二个关节的位置，依此类推。

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

该代码将关节向上移动。

If left
    x(0) -= DOT_SIZE
End If

将头向左移动。

在CheckCollision方法中，我们确定蛇是否击中了自己或撞墙之一。

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

如果蛇用头撞到关节之一，我们就结束游戏。

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

如果蛇击中了棋盘的底部，我们就结束了游戏。

LocateApple方法在板上随机放置一个苹果。

Dim rand As New Random
Dim r As Integer = rand.Next(RAND_POS)

我们得到一个从 0 到RAND_POS-1的随机数。

apple_x = r * DOT_SIZE
...
apple_y = r * DOT_SIZE

这些行设置了apple对象的 x，y 坐标。

If inGame
    Me.CheckApple
    Me.CheckCollision
    Me.Move
    Me.QueueDraw
    Return True
Else 
    Return False
End If

每 140 毫秒，将调用OnTimer方法。如果我们参与了游戏，我们将调用三种构建游戏逻辑的方法。否则，我们返回False，它将停止计时器事件。

在Board类的OnKeyDown方法中，我们确定按下的键。

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

如果单击左光标键，则将left变量设置为true。在Move方法中使用此变量来更改蛇对象的坐标。还要注意，当蛇向右行驶时，我们不能立即向左转。

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

在这个类中，我们设置了贪食蛇游戏。

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

在这个类中，我们捕获按键事件。并将处理委托给板类的OnKeyDown方法。

贪食蛇 - 图1

图：贪食蛇

以下命令编译游戏。

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

这是使用 GTK# 库和 Visual Basic 编程语言编写的贪食蛇电脑游戏。