Koffi Redux project, recoding dlists and fixing a bug
[EDITED again - added a Before and After pic below]
Back in 2020, I started to tinker with my old 2002 game, the 32K Atari 5200 homebrew Koffi: Yellow Kopter. I'm calling it Koffi Redux so far. I fixed bugs, tweaked gameplay rules, rewrote various graphics routines to make more efficient, added some colors and graphics, and added 2-player mode. One nasty bug was in the original on stage Windy Vines - it took AA member @RB5200 to find it and report some clues to me. The bug mysteriously kills poor Koffi for no reason down near the vine. I fixed the bug which had a side-effect of simplifying some code there, too.
Even though I reclaimed nearly 1K of ROM by my recoding stuff, I was again running low. I was down to under 400 bytes of ROM left. Originally I figured when I ran out of ROM, I'd call it done and release the current version to play. But there are too many things I want to tweak, and I kept noticing other tables and routines which could take up a much smaller ROM footprint - one of these areas was each screen's Display List. The screens are primarily high-resolution Antic E mode lines, and each display list was 195 bytes.
In Koffi, there are 4 gameplay screens, a title screen, and LoadLevel (between stages) screen. MV Mountain Valley and CF Coniferous Forest screens used the same 195-byte display list, but the other screens all had their own unique 195-byte Display List Tables. This week I implemented the method I used in 5200 Adventure II (which had about 90 different Antic 4 screens), each of the 4 gameplay screens now uses a common display list table, which uses well under 100 bytes to produce the 195 byte Display List. At this point I have 952 free ROM bytes, so I saved over 550 bytes recoding all this.
However, I'll use some of that on the next step - to dynamically set the unique Display List Interrupts into that 195-byte RAM table, a unique footprint for each of the 4 gameplay screens. This method surgically inserts the value $8E overtop an existing $0E byte, one for each place a DLI should exist as you draw down the screen. By using my AdvII table idea called DLIMarkerScr and DLIMarkerRow tables, I won't use too many ROM bytes implementing custom DLI's for the 4 gameplay screens.
Diagram 1: Sample Code which builds the common DLIST from $1000 to $10C2 in RAM. The actual screen RAM is mapped starting at $2000. One thing of note is that this Display List requires an extra LMS jump instruction (3 bytes) before you cross screen RAM of $2xxx to $3xxx - yes, a full Antic E screen needs more than 1 page of RAM memory.
; **************************************************************************************************************
BuildCommonDLIST
dlist1Part1
ldx #$08 ; store 9 bytes from dlist1 table from $1000-$1008:
;*** load initial 9 bytes:
dlloop2A
lda dlist1,x
sta $1000,x
dex ;next byte
cpx #$ff
bne dlloop2A
;*** load 186 bytes, all are "0E" values for Antic E mode lines, from $1009 to $10BF.
dlist1Part2
ldx #$09
lda #$0E ;Antic E mode lines
dloop2B
sta $1000,x
inx
cpx #$C0 ;end of display list at $10BF in RAM.
bne dloop2B
;*** load MID LMS 3 bytes:
dlist1part3
lda #$4E
sta $1064
lda #$00
sta $1065
lda #$30
sta $1066
;*** load end jmp 3 bytes:
lda #$41
sta $10C0
lda #$00
sta $10C1
lda #$10
sta $10C2
;******************************************* end new dlist1 code
rts
;***************************************************************************************************************
Diagram2: shows what the built DLIST looks like with some notes:
Diagram3: shows what stage 1 MV looks like with no display list interrupts turned on yet, and AFTER the DLI's are active. Next I have to add the appropriate DLI rows for CF, WV, and PM stages. At this point I have over 900 bytes left, so it was worth the recoding effort.
Edited by Cafeman
added a before and after pic
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