Game Programming in Visual Basic
By Greg
English
Introduction
Welcome
to the second of a series of tutorials about “Game Programming in Visual
Basic”. This lesson will get you down into the nitty gritty of the Win32 API.
So go ahead and read on and get coding J.
Getting Started
In this lesson,
you will learn the techniques of the Win32 API to make a catchy little game for
you and your friends to play. All game programming is are techniques that you
learn and put them together to make the next Quake 3 Engine! We will start off
with good old bitblt. The lesson itself won’t be big, but you can reference my
Sample Project of Asteroids in which I made in 3 hours J.
BitBlt
What is BitBlt?
BitBlt is the main graphics drawing function for the Win32
GDI, there are others like StretchBlt, but they aren’t really needed here. So
lets take a look at the function
Public Declare Function BitBlt Lib "gdi32" (ByVal
hDestDC As Long, ByVal X As Long, ByVal Y As Long, ByVal nWidth
As Long, ByVal nHeight As Long, ByVal hSrcDC As Long, ByVal xSrc
As Long, ByVal ySrc As Long, ByVal dwRop As Long) As Long
hDestDC – The destination DC(Device
Context) example: frmMain.hdc/picGame.hdc
X,Y – The coordinates of where you want the Top/Left
part of the graphics being drawn
nWidth, nHeight – The dimensions of the graphic
to be drawn.
hSrcDC – The source DC from which the graphic comes from.
xSrc, ySrc – The source coordinates from the
hSrcDC you get the image from(nWidth and nHeight determine xSrc2 and ySrc2)
dwRop – The rasterization option. Example: SRCCOPY =
Copy as is, SRCINVERT = Inverts the colors, SRCAND = Copies all but the white,
SRCPAINT = Copies all but the black.
Tip For Debugging BitBlt
If you haven’t noticed, BitBlt is a function, so it will
return a value. If the value returned is less than or equal to zero, then the
execution of BitBlt has failed. Below is sample code for debugging BitBlt
[Code Start]
Dim RetVal as long
RetVal =
BitBlt(frmMain.hdc,0,0,640,480,picLogo.hdc,0,0,SRCCOPY)
If RetVal = 0 Then
MsgBox
“BitBlt has failed!”
Exit
Sub/Function
End If
[Code Stop]
Extra BitBlt Stuff
Getting Transparent Blts
Sometimes you
will need to get an image by itself(say a character sprite with a green
background, you would need a Mask for the graphic. A Mask is just a Black and
White picture of the graphic.
You would draw
the Mask first using SRCAND, then draw the real graphic EXACTLY AFTER IT, using
SRCINVERT. You can get mask creators off PSC, because I don’t have the time to
make one.
[Code Start]
BitBlt frmMain.hdc,0,0,640,480,picLogo.hdc,0,0,SRCAND
BitBlt
frmMain.hdc,0,0,640,480,picLogoMask.hdc,0,0,SRCINVERT
[Code Stop]
GetAsyncKeyState
What is GetAsyncKeyState?
This function allows the programmer to access character
input throughout the program without the use of the default
Form_KeyPress/KeyDown/KeyUp events allowing more versatility I would say.Lets take a look at the function, its VERY
VERY VERY simple.
Public Declare Function GetAsyncKeyState Lib
"user32" (ByVal vKey As Long) As Integer
vKey – You insert the key constant here to check its
current state, you can use the basic vbKey constants with this.
This API is very simple to use.
[Code Start]
Dim btnDown as Boolean
btnDown = GetAsyncKeyState(vbKeyDown)
If btnDown = True Then ‘//the key is being pressed
‘//code
here
Else
‘//code
here
End If
[Code Stop]
A cool way to use this API can be looked at modEngine.bas
in the Asteroids directory.
SndPlaySound
What is SndPlaySound?
This function is pretty easy to use as well, but at the
same time, it can cause some big problems if the flags given are kinda awkward.
So let’s take a look at this function.
Public Declare
Function sndPlaySound Lib "winmm.dll" Alias "sndPlaySoundA"
(ByVal lpszSoundName As String, ByVal uFlags As Long) As Long
LpszSoundName
= The filename for the
WAVE sound(must be .WAV sound file)
UFlags - Flags for the sound when it’s played.
SND_ASYNC - &H1 lets you
play a new wav sound, interrupting another
SND_LOOP - &H8 loops the
wav sound
SND_NODEFAULT - &H2 if
wav file not there, then make sure NOTHING plays
SND_SYNC - &H0 no
control to program til wav is done playing
SND_NOSTOP - &H10 if a
wav file is already playing then it wont interrupt
[Code Start]
sndPlaySound App.Path & “\Audio\Sound.wav”, SND_ASYNC
or SND_NODEFAULT
[Code Stop]
For some basic subs and functions on using sndPlaySound,
refer to the Asteroids example.
IntersectRect
What is IntersectRect?
This function takes to RECT types and determines whether
they overlap each other. Let’s take a look at this function.
Public Declare Function IntersectRect Lib
"user32" (lpDestRect As RECT, lpSrc1Rect As RECT, lpSrc2Rect As RECT)
As Long
lpDestRect – This RECT will receive the area that
the 2 RECTs crossed over. You would be able to use this RECT for pixel perfect
detection. More on that in a later lesson (maybe…)
lpSrc1Rect – The first source RECT
lpSrc2Rect – The second source RECT
[Code Start]
Dim tmpRECT as RECT
Dim PlayerX as Integer, PlayerY As Integer
Dim CompX As Integer, CompY as Integer
Dim PlayerRect as RECT, CompRect As RECT
‘//We are assuming the dimenions of the player are 50x50
and the comp 50x50
‘//createrect is a helper function I wrote for creating
rects.
PlayerRect = CreateRect(PlayerX, PlayerY, PlayerX +50, PlayerY
+ 50)
CompRect = CreateRect(CompX,CompY,CompX + 50, CompY + 50)
If IntersectRect(tmpRECT,PlayerRect,CompRect) = True Then ‘//there
was an overlap between the 2 rects
‘//code
here
End If
[Code Stop]
Using IntersectRect
can provide a mere decent collision detection like I used in the Asteroids
game. Refer to modEngine.bas for my short Collide function for collision
detection.
Other APIs Used
I’m well aware of the other 6 or 7 APIs I used in the
lesson, but if you go to voodoovb.thenexus.bc.ca, there are some good tutorials
on all the DC stuff, they are very good and that’s where I learned from. Or you
can check out a kick-azz VB community at rookscape.com/vbgaming, with lots of
other cool tutorials on such stuff, including some APIs I used.
Conclusion
With these simple techniques, you can effectively create
a nice 2d game, better than my Asteroids game I made because I made it in 1 – 2
Hours. You must remember, these are just the techniques NEEDED to create the
game, you gotta learn to put them together by yourself, and when you can
program a cool game(even a simple one), you can probably say to yourself, you
can program anything because games require all the basics of the language like
strings(chars in C++ unless in an array), simple math operations, arrays etc… Until
next time, see ya later J
If you have any questions, comments, or ideas about this
lesson please email me at EnglishM1@aol.com
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