Display the Press Start Button text
From Sonic Retro
Revision as of 13:13, 9 December 2014 by UltraEpicLeader100 (talk | contribs)
(Original guide by Quickman. Updated for GitHub Disassembly by Egor305)
In Sonic 1 There is an object for a PRESS START BUTTON message on the title screen. However, in the final version it's not there. Well, not really. It is there, but it's invisible.
GitHub Disassembly
This version of guide is for GitHub Disassembly. (Known before as, and based on SVN Disassembly)
To fix that you simply need to go to Tit_LoadText:. Find this piece of code:
<asm> lea (v_objspace+$80).w,a1
moveq #0,d0
move.w #7,d1
Tit_ClrObj2: move.l d0,(a1)+ dbf d1,Tit_ClrObj2
move.b #id_TitleSonic,(v_objspace+$40).w ; load big Sonic object</asm> And replace it with this: <asm> lea (v_objspace+$80).w,a1
- moveq #0,d0
- move.w #7,d1
- Tit_ClrObj2
- move.l d0,(a1)+
- dbf d1,Tit_ClrObj2
jsr DeleteChild ; clear object RAM to make room for the "Press Start Button" object move.b #id_TitleSonic,(v_objspace+$40).w ; load big Sonic object</asm>
Hivebrian 2005 Disassembly
This is old version of guide, made for Hivebrain's Sonic 1 Disassembly 2005 (updated to ASM68K).
To fix that you simply need to go to Title_LoadText:. Find this piece of code: <asm> lea ($FFFFD080).w,a1 moveq #0,d0 move.w #7,d1
Title_ClrObjRam2: move.l d0,(a1)+ dbf d1,Title_ClrObjRam2
move.b #$E,($FFFFD040).w ; load big Sonic object</asm> And replace it with this: <asm> lea ($FFFFD080).w,a1
- moveq #0,d0
- move.w #7,d1
- Title_ClrObjRam2
- move.l d0,(a1)+
- dbf d1,Title_ClrObjRam2
jsr DeleteObject2 ; clear object RAM to make room for the "Press Start Button" object move.b #$E,($FFFFD040).w ; load big Sonic object</asm>
Result
Now you should be able to see this message:
“ | I've finally isolated precisely why the PRESS START BUTTON (PSB) text doesn't appear on the Sonic 1 title screen, and given the nature I suspect it to be a bug in Sonic Team's original code. (You may now be shocked.)
Now, the PSB object is initialised in object RAM slot $D080 on line 3237 of the disassembly I'm currently using (modified by Pu7o to work on Linux; it's just under the label Title_ClrObjRam2, in case it's not the same line in an unmodified Sonic 1 disassembly). That same chunk of RAM is previously used for the SONIC TEAM PRESENTS (STP) object earlier in the TitleScreen routine (line 3162, adjust as necessary). The reason the PSB text doesn't appear is because the STP object scribbles in object RAM, but the TitleScreen routine only clears the top $1C bytes. Any data between $D09C and $D0A0 previously touched by the STB object is unmodified. The correction is simple enough; delete the object RAM for the object at $D080 more thoroughly. |
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— Quickman |