随着计算机技术的进步，计算机游戏也越来越普及，很多喜爱程序开发的读者朋友都向往游戏编程，但往往又觉得游戏编程序很复杂，高深莫测。诚然，象"帝国时代"、"反恐精英"这样的大型游戏需要写很复杂的程序来实现一些令人"头昏"的算法，需要熟悉DirectX开发知识。但是，对于一般的开发人员，完全可以利用所学的知识开发一些小的游戏，达到自娱自乐的目的。
本文介绍如何在Visual Basic6.0环境下开发射击小游戏，通过实现该小游戏可以帮助一些Visual Basic初学者加深对Visual Basic编程知识的理解，同时它也可以开拓初、中级开发爱好者的编程思路。该射击小游戏程序编译运行后的界面效果如图一所示：
图一、射击游戏界面图
在射击游戏中，安排了两个角色，相互之间可以开枪进行对射，同时为了丰富游戏的功能，游戏的场景中添加定时移动的仙人掌，为射击的双方角色提供保护功能。当其中一个角色中弹后，游戏终止，同时游戏人物角色的图标变更，表示角色死亡。为了实现上述的游戏，最初要作的是设计程序界面，按照游戏的需求，首先生成一个VB应用程序，在Form1上添加一个开始按钮btnStart，一个名为picDesert的Picture控件，该控件用来做为游戏的场景和其它控件的容器，在该控件上添加六个Image控件，分别用来显示游戏的角色、两个移动的仙人掌、分别向右、向左呼啸射击的子弹以及标志角色死亡的图标，它们的图象分别如下：
游戏角色 仙人掌 呼啸的子弹 角色击中标志
为了使程序中的仙人掌、游戏角色和射击时发射的子弹可以移动，需要向项目中添加定时器tmrMouseCnt和Timer1，在这两个定时响应函数中完成不同对象的移动功能。在游戏运行后，为了使用户可以通过键盘和鼠标来操作游戏的角色，实现射击的功能，需要添加鼠标消息和键盘消息处理函数。例如，对于角色1来说，可以通过上下键来移动，空格键来射击，对于角色2来说，鼠标左右键控制移动，双击实现射击。在射击过程中，要处理两个细节，一个细节是子弹与仙人掌及角色的区域重叠问题，当子弹与仙人掌重叠时让子弹隐藏起来，与角色重叠时表示击中目标，游戏结束。这里需要判断何时两个区域有重叠，解决这个问题的方法是使用API函数IntersectRect，用它来判断两个区域是否有重叠。另一个细节是子弹射击过程中需要添加"呼啸"的声音和击中目标时添加人物惨叫的声音，来达到逼真的效果，为了实现这个功能，需要向程序中添加语音文件（程序中的语音文件分别为：BANG.WAV和OH！！.WAV），然后通过API函数sndPlaySound来实现。另外，在对象移动的过程中，需要注意移动到边缘位置的情况处理。
程序的具体实现代码如下：
' SHOOTOUT.BAS
Option Explicit
' Data type required by the IntersectRect function
Type tRect
Left As Long
Top As Long
Right As Long
Bottom As Long
End Type
' Windows API rectangle functions
Declare Function IntersectRect Lib "user32" (lpDestRect As tRect, lpSrc1Rect As tRect, lpSrc2Rect As tRect) As Long
' Functions and constants used to play sounds.
Declare Function sndPlaySound Lib "winmm.dll" Alias "sndPlaySoundA" (ByVal lpszSoundName As String, ByVal uFlags As Long) As Long
' Constant used with sndPlaySound function
Global Const SND_ASYNC = &H1
'----------------------------------------------------------
' SHOOTOUT.FRM
Option Explicit
' KeyCodes for keyboard action.
Const KEY_SPACE = &H20
Const KEY_UP = &H26
Const KEY_DOWN = &H28
' Number of Twips to move player on each key or mouse event.
Const PlayerIncrement = 45
' Constants for mouse action.
Const NO_BUTTON = 0
Const LBUTTON = 1
Const RBUTTON = 2
' Boolean that indicates if mouse button has been pressed down.
Dim MouseButtonDown As Integer
' Number of bullets either player can have in use at one time.
Const NUM_BULLETS = 6
' Booleans indicating if player 0 or player 1 have just fired.
Dim GunFired(0 To 1) As Integer
' Start the game by enabling the main timer and hiding the start button.
Private Sub btnStart_Click()
Timer1.Enabled = True
btnStart.Visible = False
End Sub
' Check if the two Images intersect, using the IntersectRect API call.
Private Function Collided(imgA As Image, imgB As Image) As Integer
Dim A As tRect
Dim B As tRect
Dim ResultRect As tRect
' Copy information into tRect structure
A.Left = imgA.Left
A.Top = imgA.Top
B.Left = imgB.Left
B.Top = imgB.Top
' Calculate the right and bottoms of rectangles needed by the API call.
A.Right = A.Left + imgA.Width - 1
A.Bottom = A.Top + imgA.Height - 1
B.Right = B.Left + imgB.Width - 1
B.Bottom = B.Top + imgB.Height - 1
' IntersectRect will only return 0 (false) if the
' two rectangles do NOT intersect.
Collided = IntersectRect(ResultRect, A, B)
End Function
' Double-clicking the mouse fires Player 1's gun.
Private Sub Form_DblClick()
Dim rc As Integer
If Not Timer1.Enabled Then Exit Sub
GunFired(1) = True
rc = sndPlaySound(App.Path & "\BANG.WAV", SND_ASYNC)
End Sub
' This event handles Player 0's game action via the keyboard.
Private Sub Form_KeyDown(KeyCode As Integer, Shift As Integer)
Dim rc As Integer
Static InKeyDown As Integer
If Not Timer1.Enabled Then Exit Sub
If InKeyDown Then Exit Sub
InKeyDown = True
DoEvents
Select Case KeyCode
Case KEY_UP
imgPlayer(0).Top = imgPlayer(0).Top - PlayerIncrement
If imgPlayer(0).Top < 0 Then imgPlayer(0).Top = 0
Case KEY_SPACE
GunFired(0) = True
rc = sndPlaySound(App.Path & "\BANG.WAV", SND_ASYNC)
Case KEY_DOWN
imgPlayer(0).Top = imgPlayer(0).Top + PlayerIncrement
If imgPlayer(0).Top > (picDesert.ScaleHeight -
imgPlayer(0).Height) Then
imgPlayer(0).Top = picDesert.ScaleHeight -
imgPlayer(0).Height
End If
End Select
InKeyDown = False
End Sub
Private Sub Form_Load()
Dim i As Integer
Timer1.Interval = 22
Timer1.Enabled = False
MouseButtonDown = NO_BUTTON
For i = 1 To NUM_BULLETS - 1
Load imgLBullet(i)
Load imgRBullet(i)
Next
End Sub
Private Sub Form_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single)
MouseButtonDown = Button
End Sub
Private Sub Form_MouseUp(Button As Integer, Shift As Integer, X As Single, Y As Single)
MouseButtonDown = NO_BUTTON
End Sub
' The main game timer.
Private Sub Timer1_Timer()
Const CactusIncrement = 30
Const BulletIncrement = 300
Const NumCacti = 2
Dim i As Integer
Dim rc As Integer
' Move the roving cacti.
For i = 0 To NumCacti - 1
imgCactus(i).Top = imgCactus(i).Top - CactusIncrement
If imgCactus(i).Top < -imgCactus(i).Height Then
imgCactus(i).Top = picDesert.Height
End If
Next
' Did player 0 fire a bullet?
If GunFired(0) Then
GunFired(0) = False
' Find a spare (invisible) bullet.
For i = 0 To NUM_BULLETS - 1
If Not imgLBullet(i).Visible Then
imgLBullet(i).Top = imgPlayer(0).Top
imgLBullet(i).Left = imgPlayer(0).Left +
(imgPlayer(0).Width / 2)
imgLBullet(i).Visible = True
Exit For
End If
Next
End If
' Did player 1 fire a bullet?
If GunFired(1) Then
GunFired(1) = False
' Find a spare (invisible) bullet.
For i = 0 To NUM_BULLETS - 1
If Not imgRBullet(i).Visible Then
imgRBullet(i).Top = imgPlayer(1).Top
imgRBullet(i).Left = imgPlayer(1).Left -
(imgPlayer(1).Width / 2)
imgRBullet(i).Visible = True
Exit For
End If
Next
End If
' Move Visible Bullets
For i = 0 To NUM_BULLETS - 1
' Move player 0's bullets.
If imgLBullet(i).Visible Then
imgLBullet(i).Left = imgLBullet(i).Left + BulletIncrement
If Collided(imgLBullet(i), imgCactus(0)) Then
imgLBullet(i).Visible = False
ElseIf Collided(imgLBullet(i), imgCactus(1)) Then
imgLBullet(i).Visible = False
ElseIf imgLBullet(i).Left > picDesert.ScaleWidth Then
imgLBullet(i).Visible = False
ElseIf Collided(imgLBullet(i), imgPlayer(1)) Then
imgLBullet(i).Visible = False
imgPlayer(1).Picture = imgRIP.Picture
Timer1.Enabled = False
rc = sndPlaySound(App.Path & "\OH!!.WAV", SND_ASYNC)
End If
End If
' Move player 1's bullets.
If imgRBullet(i).Visible Then
imgRBullet(i).Left = imgRBullet(i).Left - BulletIncrement
If Collided(imgRBullet(i), imgCactus(0)) Then
imgRBullet(i).Visible = False
ElseIf Collided(imgRBullet(i), imgCactus(1)) Then
imgRBullet(i).Visible = False
ElseIf imgRBullet(i).Left < -imgRBullet(i).Width Then
imgRBullet(i).Visible = False
ElseIf Collided(imgRBullet(i), imgPlayer(0)) Then
imgRBullet(i).Visible = False
imgPlayer(0).Picture = imgRIP.Picture
Timer1.Enabled = False
rc = sndPlaySound(App.Path & "\OH!!.WAV", SND_ASYNC)
End If
End If
Next
End Sub
' Handle Player 1's movement (up and down).
Private Sub tmrMouseCntl_Timer()
If Not Timer1.Enabled Then Exit Sub
Select Case MouseButtonDown
Case RBUTTON
imgPlayer(1).Top = imgPlayer(1).Top - PlayerIncrement
If imgPlayer(1).Top < 0 Then imgPlayer(1).Top = 0
Case LBUTTON
imgPlayer(1).Top = imgPlayer(1).Top + PlayerIncrement
If imgPlayer(1).Top > (picDesert.ScaleHeight -
imgPlayer(1).Height) Then
imgPlayer(1).Top = picDesert.ScaleHeight -
imgPlayer(1).Height
End If
End Select
End Sub
文章的上述内容对射击游戏中的各个实现功能进行了详细的介绍，读者朋友可以根据文章中的程序代码自己动手实验一下。本程序在Windows2000、Visual Basic6.0环境下编译通过，运行正常。