Structures in Blitz

Organization, a programmer’s nightmare,However, using good structure means that a code can be both easily reparable and easily reusable . Why reinvent the wheel?

In this article I am going to walk you through and article on how to structure blitz code. The game is called retro space shooter, and it won’t work unless you create two of your own images. You need a white on black title that says “Retro Space Shooter”, and you need a start background that is 800×600. Let’s begin.

First we start with the header, here I usually include five things.

Graphics 800,600,32,1
AutoMidHandle True
SetBuffer BackBuffer()
SeedRnd MilliSecs()
AppTitle "Retro Space Shooter"

First I declare the Graphics Mode, then I set all image handles to the center, I set the drawing buffer to the BackBuffer(), I seed the random generator and I set the application title, this way, you never forget these very important things.

Next, I set up all the types, in this game, I did this.

Type ship
	Field x,y
End Type

Type ufo
	Field x,y
End Type

Type bullet
	Field x,y
	Field who ;1 = shot by player, 2 = shot by ufo
End Type

This makes sure that I create all of the characters and objects that I need in the game, it also means that I can’t create any of the variables before the type is created, very smart.

Then I do constants, this is good because it allows me to get everything that just needs to be declared written down, so I don’t forget anything.

Const shipspeed = 10
Const shippic$ = "|/^|"
Const killscore = 1000
Const levelscore = 5000
Const shootdeduct = 25
Const ufopic$ = "-0-"
Const bulletspeed = 20
Const bulletpic$ = "*"

Now that those are set, I can declare all my Globals.

Global ufospeed = 7
Global count = 0
Global level = 1
Global numofufos = Rand(3,5) + level
Global timer = 0
Global timerspeed = 2
Global score = ReturnScore()
Global totalkills = 0
Global totalshots = 0
Global cont = 1
Global title = LoadImage("GraphicsRetrotitle.bmp")
Global font = LoadFont("blitz",18)

Global starfield = LoadImage("Graphicsstarfield.bmp")

Global scrollx = 0

Global s.ship = New ship
sx = 400
sy = 500

It is a good idea to declare your type variables immediately after the fact, so you don’t forget them.

Next up the interface

SetFont font
DrawImage(title,400,300)
Text 400,500,"Press Any Key to continue",True
Flip
Delay 3000
WaitKey
Cls
Text 400,100,"Welcome to Retro Space Shooter",True
Text 400,200,"This is a simple space shooter game",True
Text 400,300,"You will need to use the arrow keys to move left and right",True
Text 400,400,"Spacebar fires your weapon",True
Text 400,500,"Score is based on levels and kills, but too many shots will deduct",True
Flip
Delay 3000
Cls
Text 400,300,"Get Ready to Play",True
Flip
Delay 3000

Declare your interface either into the loop or immediately before.

The loop should be clear and concise, use functions whenever possible, but don’t over do it. If your loop is 50 lines, so be it. Try to clump related code into functions.

Cls
LevelMake()
While cont = 1
Cls
TileImage(starfield,scrollx,300)
scrollx = scrollx + 5

UpdatePlayer()
AI()
If count = numofufos Then
count = 0
timerspeed = timerspeed + 1
numofufos = numofufos + 1
level = level + 1
LevelMake()
EndIf
score = ReturnScore()
Text 650,50,"Score: " + score

Flip
If KeyHit(1) Then
	cont = 0
EndIf
Wend

Place your credits right after.

Cls
DrawImage(title,400,150)
Text 400,300,"Final Score: " + score,True
Text 400,400,"Credits",True
Text 400,500,"Tyler Chaney and Michael Cogswell",True
Flip
Delay 5000

Then write out your functions, try to do this in order of usage, it helps immensely.

Function LevelMake()
Cls 

For b.bullet = Each bullet
Delete b
Next
For u.ufo = Each ufo
Delete u
Next
For e = 1 To numofufos
u.ufo = New ufo
ux = Rand(51,749)
uy = Rand(50,300)
Next
sx = 400
sy = 500
Text 400,300,"Level " + level,True,False
Flip
Delay 3000
End Function

Function UpdatePlayer()

If KeyDown(205) Then
	sx = sx + shipspeed
Else If KeyDown(203) Then
	sx = sx - shipspeed
EndIf 

If KeyHit(57) Then
	b.bullet = New bullet
	bx = sx
	by = sy
	bwho = 1
	totalshots = totalshots + 1
EndIf 

For b.bullet = Each bullet
	by = by - bulletspeed
	Color 0,0,0
	Rect bx,by,StringWidth(bulletpic$),StringHeight(bulletpic$),0
	Color 255,255,255
	Text bx,by,bulletpic$

	For u.ufo = Each ufo
	If RectsOverlap(ux,uy,StringWidth(ufopic$),StringHeight(ufopic$),bx,by,StringWidth(bulletpic$),StringHeight(bulletpic$)) 

	count = count + 1
	totalkills = totalkills + 1

	Delete u
	EndIf
	Next 

	If by = 750 Then
		ufospeed = -7
	EndIf
	If ux = 800 Or ux = 600 Then
		uy = uy + 10
		timer = 0
	EndIf
   Color 0,0,0
	Rect ux,uy,StringWidth(ufopic$),StringHeight(ufopic$),False
	Color 255,255,255
	Text ux,uy,ufopic$

	Next
End Function 

Function Test()
Text 100,500,"shots" + totalshots
End Function 

Function ReturnScore()
Return  (((level * levelscore) + (totalkills * killscore)) - (totalshots * shootdeduct)) - 5000
End Function

Thanks for reading, hope it helps and happy coding.