Function to Auto-Build Display List List

[PacManPlus]

Hello All:

 

I started looking around at sample code...

I think I have created a function that can automatically build a DLL, depending on these settings:

;
;		PROGRAM EQUATES
;
NTSC		equ	243;number of active scanlines for NTSC
PAL		equ	293;number of active scanlines for PAL
;
REGION		equ	NTSC;change this to 'PAL' for PAL regions
;
YRES		equ	208;screen resolution (must be a factor of DLHIGH)
DLHIGH		equ	16;display list height (only 8 or 16 allowed)
NUMBLANK		equ	REGION-YRES;number of blank lines needed in total
NUMBTOP		equ	NUMBLANK/2;number of blank lines at top of screen
NUMBBOT		equ	(NUMBLANK/2)+1;number of blank lines at bottom of screen
NUMDL		equ	YRES/DLHIGH;number of display lists
DLLEN		equ	5;display list entry length
NUMSPR		equ	2;number of sprites
;
;		DISPLAY LIST
;
DLLRAM		equ	$1800;DLL runs from $1800-$19FF (512 bytes max)
DLRAM		equ	$1A00;DL runs from $1A00-$1EFF
NULLDL		equ	$1EFD;Blank Display List (3 bytes)
DLEND		equ	$1EFF;End of Display List

 

Just by changing some of the above settings, the display list list can be built for you by calling this routine:

 

BuildDisplayListList
;
;	Top blank lines
;
ldx	#$00
ldy	#NUMBTOP
BuildDLL_TopLoop
cpy	#$10
bmi	BuildDLL_TopLT16
BuildDLL_TopGT16
tya
sec
sbc	#$10;subtract 16 lines
tay
lda	#$10
jmp	BuildDLL_PutTopEntry
BuildDLL_TopLT16
tya
ldy	#$00;last entry - remainder lines
BuildDLL_PutTopEntry
sec
sbc	#$01;entry is always "Number of Lines - 1"
sta	DLLRAM,x			
inx
lda	>NULLDL;NULLDL = blank DL
sta	DLLRAM,x
inx
lda	<NULLDL
sta	DLLRAM,x
inx
cpy	#$00
bne	BuildDLL_TopLoop				   
;
;	#YRES MODE LINES DIVIDED INTO #NUMDL REGIONS
;
ldy	#$00
BuildDLL_MainLoop
lda	#DLHIGH-1;DLHIGH lines
ora	(#DLHIGH<<2);take DLHIGH value, shift it left 2 bits to be in line with 'Holey DMA' value
sta	DLLRAM,x		
inx
lda	DLPOINTH,y
sta	DLLRAM,x
inx
lda	DLPOINTL,y
sta	DLLRAM,x
inx
iny
cpy	#NUMDL;#NUMDL DLL entries
bne	BuildDLL_MainLoop
;
;	Bottom blank lines
;
ldy	#NUMBBOT
BuildDLL_BotLoop
cpy	#$10
bmi	BuildDLL_BotLT16
BuildDLL_BotGT16
tya
sec
sbc	#$10;subtract 16 lines
tay
lda	#$10
jmp	BuildDLL_PutBotEntry
BuildDLL_BotLT16
tya
ldy	#$00;last entry - remainder lines
BuildDLL_PutBotEntry
sec
sbc	#$01;entry is always "Number of Lines - 1"
sta	DLLRAM,x			
inx
lda	>NULLDL;NULLDL = blank DL
sta	DLLRAM,x
inx
lda	<NULLDL
sta	DLLRAM,x
inx
cpy	#$00
bne	BuildDLL_BotLoop
BuildDLL_FinalEntry
lda	#$00
sta	DLLRAM,x
inx
sta	DLLRAM,x
inx
sta	DLLRAM,x
inx
BuildDLL_Rts
rts

 

What do you guys think of this? My goal here is to also create a subroutine to automatically build a DL as well, with another setting that will allow for a Character Mode entry. It may need some tweaking, but Hopefully I can create something that can help people (including myself) not worry about display lists so much.

 

Bob

Edited July 7, 2008 by PacManPlus