Code archives/Algorithms/Scroller

This code has been declared by its author to be Public Domain code.

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Scroller by pc_tek
(Posted 18 years ago)
Here is the link to the files (re-posted)

http://www.denathorn.co.uk/Files/Scrolling.zip
(Thanks goes to Michael Denathorn for hosting)

Please comment on the code because this is my first one. I used it on one game I wrote a few years back. 
;**********************************************************************************
; Scroller by JP Hamilton.
; I use blocks of 64x64 for this example, but could be made for any block size.
; There is no array checking, so make sure you don't scroll of the edge of the map.
; Maze created with the help of 'mazemaker' by Curtastic - Cheers matey!
; Graphics were from a Turrican game somewhere and edited by me for this routine.
;**********************************************************************************
Graphics 640,480,16,1
SetBuffer BackBuffer()
Global framerate=CreateTimer(60)
Global gfxwalls=LoadAnimImage("walls.png",64,64,0,64)

Dim map(476,317) ; the array to hold the map data
filein = ReadFile("level.dat")
For y=0 To 317
	For x=0 To 476
		map(x,y)=ReadInt(filein)
	Next
Next

scrx=-64:scry=-80 	; starting points of both x and y for drawing to the screen
mapx=9:mapy=13 		; Starting position within the map() array
scroll_speed=4		; Scroll speed - adjusted by the +/- keys on the numpad

While Not KeyDown(1)
	WaitTimer(framerate)
	Cls
	If KeyHit(74) Then ; Slow down the scroll speed
		scroll_speed=scroll_speed-1
		If scroll_speed<1 Then scroll_speed=1
	EndIf
	If KeyHit(78) Then ; Speed up the scroll speed
		scroll_speed=scroll_speed+1
		If scroll_speed>64 Then scroll_speed=64
	EndIf

	If KeyDown(203) Then scrx=scrx+(scroll_speed) ;move left
	If KeyDown(205) Then scrx=scrx-(scroll_speed) ;move right
	If KeyDown(208) Then scry=scry-(scroll_speed) ;move up
	If KeyDown(200) Then scry=scry+(scroll_speed) ;move down

	If scrx<=-64 Then scrx=scrx+64:mapx=mapx+1 	; Wrap scrx if <= block width
	If scrx>=0 Then	scrx=scrx-64:mapx=mapx-1	; Wrap scrx if >= block width
	If scry>=-64 Then scry=scry-64:mapy=mapy-1	; Wrap scry if >= -block width
	If scry<=-128 Then scry=scry+64:mapy=mapy+1	; Warp scry if <= -block width times 2

	cntx=0:cnty=0 ; draw the map onto the screen using scrx and scry
	For y=mapy To mapy+9
		For x=mapx To mapx+10
			DrawImage gfxwalls,cntx*64+scrx,cnty*64+scry,map(x,y)
			cntx=cntx+1
		Next
		cntx=0:cnty=cnty+1
	Next

	Text 10,10,"Scroll Speed="+scroll_speed

	Flip
Wend
EndGraphics
End