基于VB6.0射击游戏的实现

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 1s 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 0s 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 0s 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 1s 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 1s 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。