贪食蛇 - 《ZetCode 中文系列教程》

贪食蛇游戏
开发

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

在 Mono Winforms 编程教程的这一部分中，我们将创建贪食蛇游戏克隆。

贪食蛇游戏

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，玩家控制蠕虫。目的是尽可能多地吃苹果。蠕虫每次吃一个苹果，它的身体就会长大。它必须避开墙壁和自己的身体。

开发

蠕虫每个关节的大小为 10 像素。蠕虫由光标键控制。最初，蠕虫具有三个关节。通过按下光标键之一开始游戏。如果游戏结束，我们将在棋盘中间显示Game Over消息。

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

首先，我们将定义游戏中使用的常量。

WIDTH和HEIGHT常数确定电路板的大小。 DOT_SIZE是苹果的大小和蠕虫的点。 ALL_DOTS常数定义了板上可能的最大点数。（900 = 300 * 300 / 10 * 10）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

这两个数组存储蠕虫的所有关节的 x，y 坐标。

在Move方法中，我们有游戏的关键算法。要了解它，请查看蠕虫如何移动。您控制蠕虫的头部。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，我们确定蠕虫是否已经击中自己或撞墙之一。

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

如果蠕虫用头撞到关节之一，就结束游戏。

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

如果蠕虫到达了棋盘的底部，我们就结束了游戏。

下图有助于了解蠕虫对象与板子底部的碰撞。

贪食蛇 - 图1

图：碰撞

locateApple方法在表格上随机定位一个苹果。

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。

在OnKeyUp方法中，我们确定了键击玩家击键的时间。

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

如果我们按左光标键，则将left变量设置为True。在Move方法中使用此变量来更改蠕虫对象的坐标。还要注意，当蠕虫向右移动时，我们不能立即向左转。

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

这是主要的类。

贪食蛇 - 图2

图：贪食蛇

这是使用 Mono Winforms 库和 Visual Basic 语言编写的贪食蛇游戏。