Smooth Rotation in Special Stages

You may have seen a game genie code online to make the special stage's rotation much smoother. But how do you do that in ASM for your ROM hack? I'll show you. It's really simple.

The fix

This targets the hivebrain disassembly. The Github disassembly has the exact same steps so it can apply there too. Open up sonic1.asm (sonic.asm for Git) and find SS_ShowLayout. Replace everything from their to move.w #$F,d7 with this:

SS_ShowLayout:				; XREF: SpecialStage
		bsr.w	SS_AniWallsRings
		bsr.w	SS_AniItems
		move.w	d5,-(sp)
		lea	($FFFF8000).w,a1
		move.b	($FFFFF780).w,d0
		jsr	(CalcSine).l
		move.w	d0,d4
		move.w	d1,d5
		muls.w	#$18,d4
		muls.w	#$18,d5
		moveq	#0,d2
		move.w	($FFFFF700).w,d2
		divu.w	#$18,d2
		swap	d2
		neg.w	d2
		addi.w	#-$B4,d2
		moveq	#0,d3
		move.w	($FFFFF704).w,d3
		divu.w	#$18,d3
		swap	d3
		neg.w	d3
		addi.w	#-$B4,d3
		move.w	#$F,d7

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 \| Fix a remember sprite related bug
Changing Design Choices
Change Spike Behavior \| Collide with Water After Being Hurt \| 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 \| Port Sonic 2 Level Select
Adding Features
Add Spin Dash ( Part 1 / Part 2 / Part 3 / Part 4 ) \| Add Eggman Monitor \| Add Super Sonic \| Add the Air Roll
Sound Features
Expand the Sound Index \| Play Different Songs Per Act \| Port Sonic 2 Final Sound Driver \| Port Sonic 3's Sound Driver \| Port Flamewing's Sonic 3 & Knuckles Sound Driver \| Change The SEGA Sound
Extending the Game
Load Chunks From ROM \| Add Extra Characters \| Make an Alternative Title Screen \| Use Dynamic Tilesets \| Make GHZ Load Alternate Art \| Make Ending 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 \| Use Dynamic Palettes
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)

Written by XPointZPoint

SCHG How-to

Smooth Rotation in Special Stages

From Sonic Retro

The fix