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SCHG How-to

Fix the HUD blinking

From Sonic Retro

(Original guide by Quickman)

There's a bug in the HUD in Sonic 1 - the timer is supposed to blink if there's less than a minute left to go, which it does if you have no rings, but as soon as you collect a ring it stops blinking. That's silly, so let's fix it.

If you're using the SVN disassembly, open _incObj/21 HUD.asm. The older disassembly by Hivebrain has it as Obj21_Flash in the main sonic.asm file, and will have some labels different, but I assume because you're using an older disassembly you know what you're doing. We want the second routine, which looks like this.

HUD_Flash:	; Routine 2
		tst.w	(v_rings).w	; do you have any rings?
		beq.s	@norings	; if not, branch
		clr.b	obFrame(a0)	; make all counters yellow
		jmp	DisplaySprite
; ===========================================================================

@norings:
		moveq	#0,d0
		btst	#3,(v_framebyte).w
		bne.s	@display
		addq.w	#1,d0		; make ring counter flash red
		cmpi.b	#9,(v_timemin).w ; have	9 minutes elapsed?
		bne.s	@display	; if not, branch
		addq.w	#2,d0		; make time counter flash red

	@display:
		move.b	d0,obFrame(a0)
		jmp	DisplaySprite

When execution flows through this routine, the first thing that happens is it checks whether you have any rings. Only if you have none is the remainder of the code (which flashes the RINGS and, if appropriate, TIME counters) executed. To fix the bug, we need to revise the routine so it first checks if you have rings, and skips flashing the RINGS counter if you do to check the game time and, if appropriate, flash the TIME counter. The result should resemble this:

HUD_Flash:	; Routine 2
		moveq	#0,d0
		btst	#3,(v_framebyte).w
		bne.s	@display
		tst.w	(v_rings).w	; do you have any rings?
		bne.s	@rings		; if so, branch
		addq.w	#1,d0		; make ring counter flash red

	@rings:
		cmpi.b	#9,(v_timemin).w ; have	9 minutes elapsed?
		bne.s	@display	; if not, branch
		addq.w	#2,d0		; make time counter flash red

	@display:
		move.b	d0,obFrame(a0)
		jmp	DisplaySprite

Hivebrain Disassembly

(Addition by Vanya)

Here is the code for the 2005 Hivebrain (ASM68K) version. It's simple enough to find, but extra documentation never hurt anybody.

Obj21_Flash:				; XREF: Obj21_Main
		tst.w	($FFFFFE20).w	; do you have any rings?
		beq.s	Obj21_Flash2	; if not, branch
		clr.b	$1A(a0)		; make all counters yellow
		jmp	DisplaySprite
; ===========================================================================

Obj21_Flash2:
		moveq	#0,d0
		btst	#3,($FFFFFE05).w
		bne.s	Obj21_Display
		addq.w	#1,d0		; make ring counter flash red
		cmpi.b	#9,($FFFFFE23).w ; have	9 minutes elapsed?
		bne.s	Obj21_Display	; if not, branch
		addq.w	#2,d0		; make time counter flash red

Obj21_Display:
		move.b	d0,$1A(a0)
		jmp	DisplaySprite

And this is the fixed version:

Obj21_Flash:				; XREF: Obj21_Main
		moveq	#0,d0
		btst	#3,($FFFFFE05).w
		bne.s	Obj21_Display
		tst.w	($FFFFFE20).w	; do you have any rings?
		bne.s	Obj21_Flash2	; if not, branch
		addq.w	#1,d0		; make ring counter flash red

Obj21_Flash2:
		cmpi.b	#9,($FFFFFE23).w ; have	9 minutes elapsed?
		bne.s	Obj21_Display	; if not, branch
		addq.w	#2,d0		; make time counter flash red

Obj21_Display:
		move.b	d0,$1A(a0)
		jmp	DisplaySprite
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)