Extend the level index past $10 in Sonic 2

Authoring Notes

(Original guide by kram, current revision that fixes major bugs and extends properly by GARY 'M 9)

(Updated again by kram, adding back custom titlecard mappings howto, due to guide being unfinished, thus finally fixing the "ZONE ZONE" bug. Replace all the empty levels with your new ones.)

(Some implementations by silent.creature. More fixes about level crashes)

Introduction

WARNING: Unless you are working with Xenowhirl's 2007 Sonic 2 disassembly, I [b]strongly[/b] recommend you port the Sonic 1 sound driver first before proceeding. There will be a lot of shifting data and data addition here, and this may even break any array built under Sonic 2 or Sonic 2 Beta sound driver. In Xenowhirl's disassembly, the Sound Driver is assembled within the ROM, so it can handle a massive data shift. This time, I will leave for the reader the option to add data as long as necessary, instead of labeling and inserting all data (maybe not everyone has all the data done, right?)

You probably noticed that all the indexes in the game stop at $10 and when you try to extend it, by extending the MLLB (Main Level Load Blocks), you get weird glitches or even crashes, that is because you haven't extended all the indexes that need to be extended.

Extending the Titlecard index

First we find:

<asm> Obj34_TitleCardData:

   dc.b    8,    0, $80, $1B
   dc.w $240, $120, $B8

   dc.b   $A,  $11, $40, $1C
   dc.w  $28, $148, $D0

   dc.b   $C,  $12, $18, $1C
   dc.w  $68, $188, $D0

   dc.b    2,    0,   0,   0
   dc.w    0,    0,   0

   dc.b    4,  $15, $48,   8
   dc.w $2A8, $168,$120

   dc.b    6,  $16,   8, $15
   dc.w  $80,  $F0, $F0

</asm>

and change it to: <asm> Obj34_TitleCardData:

   dc.b    8,    0, $80, $1B ; this is the zone string start index and  placement
   dc.w $240, $120, $B8

   dc.b   $A,  $21, $40, $1C ; "ZONE" string index number and placement
   dc.w  $28, $148, $D0

   dc.b   $C,  $22, $18, $1C ; act number start index and placement
   dc.w  $68, $188, $D0

   dc.b    2,    0,   0,   0 ; this part of the titlecard is totally unknown, colored backdrop possibly
   dc.w    0,    0,   0

   dc.b    4,  $25, $48,   8 ; red strip edge index and placement
   dc.w $2A8, $168,$120

   dc.b    6,  $26,   8, $15 ; red "Sonic The Hedgehog" string and placement
   dc.w  $80,  $F0, $F0

</asm>

next, find: <asm> loc_13DEE:

   jsr       sub_13D10(pc)
   move.b    (Current_Zone).w,d0
   cmpi.b    #$10,d0
   beq.s     BranchTo9_DeleteObject
   cmpi.b    #6,d0
   beq.s     BranchTo9_DeleteObject
   cmpi.b    #$E,d0
   beq.s     BranchTo9_DeleteObject
   move.b    (Current_Act).w,d1
   addi.b    #$12,d1
   cmpi.b    #5,d0
   bne.s     loc_13E18
   moveq     #$14,d1

loc_13E18:

   (...)

</asm>

and change it to: <asm> loc_13DEE:

   jsr       sub_13D10(pc)
   move.b    (Current_Zone).w,d0
   cmpi.b    #$10,d0
   beq.s     BranchTo9_DeleteObject
   cmpi.b    #6,d0
   beq.s     BranchTo9_DeleteObject
   cmpi.b    #$E,d0
   beq.s     BranchTo9_DeleteObject
   cmpi.b    #5,d0
   beq.s     loc_13E17
   move.b    (Current_Act).w,d1
   addi.b    #$22,d1                  ; Act number mappings (Act 1)
   bra.w    loc_13E18

loc_13E17:

   moveq     #$24,d1                  ; Act number mappings (Act 3).  Used for drawing MTZ (0x05) titlecard only

loc_13E18:

   (...)

</asm>

In order to easily fix title cards of added 3-acted zones, we inverted the data using the label loc_13E17.

Now we have the offset data of where to load the mappings for the titlecards shifted so that we can now start working on updating the mappings and not have that strange "ZONE ZONE" bug that GARY 'M 9 left behind and I intended to correct.

Next off, in this part of the hack the first thing before converting to a better manageable datatype, we want to replace the byte_15820 handler with a better one. The original pointer format posted here doesn't fit correctly. We need to adjust the pointers to fit data as it was before. The routine itself works, but its data references, not. Let's work on this.

look for: <asm>

loc_157D2

LoadTitleCard:

   bsr.s    LoadTitleCard0
   moveq    #0,d0
   move.b    (Current_Zone).w,d0
   move.b    byte_15820(pc,d0.w),d0
   lea    word_15832(pc),a0
   lea    (a0,d0.w),a0
   move.l    #$7BC00002,d0

</asm>

and we want to replace it with: <asm>

loc_157D2

LoadTitleCard:

   bsr.s    LoadTitleCard0
   moveq    #0,d0
   move.b    (Current_Zone).w,d0
   add.w    d0,d0
   move.w    Off_Titlecardtext(pc,d0.w),d0
   lea    Off_Titlecardtext(pc,d0.w),a0
   move.l    #$7BC00002,d0

</asm>

That takes care of the loader, now time to update the string data.

find: <asm>

unknown

byte_15820:

   dc.b   0,  0,  0,  0,$10,$10,$98,$20,$2C,  0,$3C,$46,$58,$68,$A8,$7A
   dc.b $8A,  0    ; 16

unknown

word_15832:

   dc.w $2A06,$3804,    4,$2604, $C04,$1804,$1C02,$FFFF
   dc.w $2A06,$4004,$3804,$3004,$2604,$1C02,$3C04,$FFFF; 8
   dc.w $1804,$1C02,$2604,$4004,$3004,$FFFF,$1804,$1C02; 16
   dc.w  $C04,$3004,    4,$2604, $804,$FFFF,$1C02,$2604; 24
   dc.w  $804,    4,$FFFF,$2A06,$5604,$3C04,$4004,$1C02; 32
   dc.w  $804,    4,$4804,$FFFF, $804,    4,$3C04,$1C02; 40
   dc.w $1404,$1804,$4004,$FFFF, $804,$1804,$2A06,$1C02; 48
   dc.w     4,$2604,$3004,$4004,$FFFF,    4,$3404,$4404; 56
   dc.w $4004,$1C02, $804,$3804,$FFFF,$3C04,$2204,$5604; 64
   dc.w  $804,$1804,    4,$FFFF,$4C06,$1C02,$1404,$1004; 72
   dc.w $3804,$4004,$3C04,$FFFF, $C04,    4,$4004,$1804; 80
   dc.w $1404,$FFFF    ; 88

</asm>

and replace it with: <asm>

byte_15820

Off_Titlecardtext:

   dc.w   Text_EHZ-Off_Titlecardtext ; EHZ Titlecard 00
   dc.w   Text_LZ-Off_Titlecardtext  ;  LZ Titlecard 01
   dc.w   Text_WZ-Off_Titlecardtext  ;  WZ Titlecard 02
   dc.w   Text_DHZ-Off_Titlecardtext ; DHZ Titlecard 03
   dc.w   Text_MTZ-Off_Titlecardtext ; MTZ Titlecard 04
   dc.w   Text_MTZ-Off_Titlecardtext ; MTZ Titlecard 05
   dc.w   Text_WFZ-Off_Titlecardtext ; WFZ Titlecard 06
   dc.w   Text_HTZ-Off_Titlecardtext ; HTZ Titlecard 07
   dc.w   Text_HPZ-Off_Titlecardtext ; HPZ Titlecard 08
   dc.w   Text_GCZ-Off_Titlecardtext ; GCZ Titlecard 09
   dc.w   Text_OOZ-Off_Titlecardtext ; OOZ Titlecard 0A
   dc.w   Text_MCZ-Off_Titlecardtext ; MCZ Titlecard 0B
   dc.w   Text_CNZ-Off_Titlecardtext ; CNZ Titlecard 0C
   dc.w   Text_CPZ-Off_Titlecardtext ; CPZ Titlecard 0D
   dc.w   Text_DEZ-Off_Titlecardtext ; DEZ Titlecard 0E
   dc.w   Text_ARZ-Off_Titlecardtext ; ARZ Titlecard 0F
   dc.w   Text_SCZ-Off_Titlecardtext ; SCZ Titlecard 10
   dc.w   Text_NZ-Off_Titlecardtext  ;  NZ Titlecard 11
   dc.w   Text_NZ-Off_Titlecardtext  ;  NZ Titlecard 12
   dc.w   Text_NZ-Off_Titlecardtext  ;  NZ Titlecard 13
   dc.w   Text_NZ-Off_Titlecardtext  ;  NZ Titlecard 14
   dc.w   Text_NZ-Off_Titlecardtext  ;  NZ Titlecard 15
   dc.w   Text_NZ-Off_Titlecardtext  ;  NZ Titlecard 16
   dc.w   Text_NZ-Off_Titlecardtext  ;  NZ Titlecard 17
   dc.w   Text_NZ-Off_Titlecardtext  ;  NZ Titlecard 18
   dc.w   Text_NZ-Off_Titlecardtext  ;  NZ Titlecard 19
   dc.w   Text_NZ-Off_Titlecardtext  ;  NZ Titlecard 1A
   dc.w   Text_NZ-Off_Titlecardtext  ;  NZ Titlecard 1B
   dc.w   Text_NZ-Off_Titlecardtext  ;  NZ Titlecard 1C
   dc.w   Text_NZ-Off_Titlecardtext  ;  NZ Titlecard 1D
   dc.w   Text_NZ-Off_Titlecardtext  ;  NZ Titlecard 1E
   dc.w   Text_NZ-Off_Titlecardtext  ;  NZ Titlecard 1F
   dc.w   Text_NZ-Off_Titlecardtext  ;  NZ Titlecard 20

word_15832

Text_EHZ:

   dc.w    $2A06,$3804,    4,$2604, $C04,$1804,$1C02    ;'MRALDHI'
   dc.w    $FFFF

Text_MTZ:

   dc.w    $2A06,$4004,$3804,$3004,$2604,$1C02,$3C04    ;'MTRPLIS'
   dc.w    $FFFF

Text_HTZ:

   dc.w    $1804,$1C02,$2604,$4004,$3004    ;'HILTP'
   dc.w    $FFFF
   

Text_HPZ:

   dc.w    $1804,$1C02, $C04,$3004,    4,$2604, $804    ;'HIDPALC'
   dc.w    $FFFF

Text_OOZ:

   dc.w    $1C02,$2604, $804,    4    ;'ILCA'
   dc.w    $FFFF
   

Text_MCZ:

   dc.w    $2A06,$5604,$3C04,$4004,$1C02, $804,    4,$4804    ;'MYSTICAV'
   dc.w    $FFFF

Text_CNZ:

   dc.w     $804,    4,$3C04,$1C02,$1404,$1804,$4004    ;'CASIGHT'
   dc.w    $FFFF
   

Text_CPZ:

   dc.w     $804,$1804,$2A06,$1C02,    4,$2604,$3004,$4004    ;'CHMIALPT'
   dc.w    $FFFF

Text_ARZ:

   dc.w        4,$3404,$4404,$4004,$1C02, $804,$3804    ;'AQUTICR'
   dc.w    $FFFF

Text_SCZ:

   dc.w    $3C04,$2204,$5604, $804,$1804,    4    ;'SKYCHA'
   dc.w    $FFFF

Text_WFZ:

   dc.w    $4C06,$1C02,$1404,$1004,$3804,$4004,$3C04    ;'WIGFRTS'
   dc.w    $FFFF

Text_DEZ:

   dc.w     $C04,    4,$4004,$1804,$1404    ;'DATHG'
   dc.w    $FFFF

Text_NZ: dc.b $4C06 ; 'W'

     dc.w $FFFF ; '<EOF>'

</asm>

This extends the title card index to $20, adds titlecards for Wood Zone, Labyrinth Zone, Dust Hill Zone, Genocide City Zone, and an empty New Zone titlecard for every single level above SCZ, compacts the titlecard text data for all titlecards, and makes it more easier to manage. you will be wondering probably what to do with the mappings. Well that is what is next.