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Display the Press Start Button text

From Sonic Retro

(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. While present in earlier versions of the game, in the final version, it's not there. Well, not really: it is there, but it's invisible.

GitHub Disassembly

This version of the guide is for the GitHub disassembly.

To fix this, you simply need to go to Tit_LoadText:. Find this piece of code:

	
		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

And replace it with this:

		lea	(v_objspace+$80).w,a1
		moveq	#0,d0
		move.w	#$F,d1	; ($40 / 4) - 1

Tit_ClrObj2:
		move.l	d0,(a1)+
		dbf	d1,Tit_ClrObj2

		move.b	#id_TitleSonic,(v_objspace+$40).w ; load big Sonic object

Hivebrain's 2005 Disassembly

This version of the guide is for Hivebrain's 2005 disassembly.

To fix this, you simply need to go to Title_LoadText:. Find this piece of code:

		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

And replace it with this:

		lea	($FFFFD080).w,a1
		moveq	#0,d0
		move.w	#$F,d1	; ($40 / 4) - 1

Title_ClrObjRam2:
		move.l	d0,(a1)+
		dbf	d1,Title_ClrObjRam2

		move.b	#$E,($FFFFD040).w ; load big Sonic object

Result

Now you should be able to see this message:

S1-PressStart.png


Original statement by Quickman on the
Sonic Retro
Forums
:
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.

Quickman

SCHG How-To Guide: Sonic the Hedgehog (16-bit)
Fixing Bugs
Fix Demo Playback | Fix a Race Condition with Pattern Load Cues | Fix the SEGA Sound | Display the Press Start Button Text | Fix the Level Select Menu | Fix the Hidden Points Bug | Fix Accidental Deletion of Scattered Rings | Fix Ring Timers | Fix the Walk-Jump Bug | Correct Drowning Bugs | Fix the Death Boundary Bug | Fix the Camera Follow Bug | Fix Song Restoration Bugs | Fix the HUD Blinking | Fix the Level Select Graphics Bug
Changing Design Choices
Change Spike Behavior | Fix Special Stage Jumping Physics | Improve the Fade In\Fade Out Progression Routines | Fix Scattered Rings' Underwater Physics | Remove the Speed Cap | Port the REV01 Background Effects | Port Sonic 2's Level Art Loader | Retain Rings Between Acts | Add Sonic 2 (Simon Wai Prototype) Level Select | Improve ObjectMove Subroutines
Adding Features
Add Spin Dash ( Part 1 / Part 2 / Part 3 / Part 4 ) | Add Eggman Monitor
Sound Features
Expand Music Index From $94 to $9F | Extend Music Slots | Play Different Songs Per Act | Expand Music Index to Start at $00 | Port Sonic 2 Final Sound Driver | Port Sonic 3's Sound Driver
Extending the Game
Load Chunks From ROM | Add Extra Characters | Make an Alternative Title Screen | Use Dynamic Tilesets | Make GHZ Load Alternate Art | Add a New Zone | Set Up the Goggle Monitor | Add New Moves | Add a Dynamic Collision System | Dynamic Special Stage Walls System | Extend Sprite Mappings and Art Limit | Enigma Credits
Miscellaneous
Convert the Hivebrain 2005 Disassembly to ASM68K
Split Disassembly Guides
Set Up a Split Disassembly | Basic Level Editing | Basic Art Editing | Basic ASM Editing (Spin Dash)