View source for Add Spin Dash to Sonic 1/Part 4

{{GuideBy|Mercury}}<br>
''(Guide updated by [[User:JGMR|JGMR]])''

This final part of the guide will fix a few final bugs to our ported Spin Dash code from Sonic 2 in Sonic 1 after following the [[SCHG How-to:Add Spin Dash to Sonic 1/Part 1|previous]] [[SCHG How-to:Add Spin Dash to Sonic 1/Part 2|three]] [[SCHG How-to:Add Spin Dash to Sonic 1/Part 3|guides]].

==Hivebrain's 2005 disassembly==
This section is designed for users of the legacy Hivebrain 2005 disassembly of Sonic 1. For users of the GitHub disassembly of Sonic 1, head over to the GitHub section below.

===Fixing camera bugs===
This will fix the issue which causes weird camera movements if the player performs a Spin Dash at the very beginning of a level since the camera will try to follow bad data from the array of Sonic's previous positions. The following code therefore clears the aforementioned array and should be added right after the loc_60D0 label:
<syntaxhighlight lang="asm">		clr.w	($FFFFF7A8).w	; reset Sonic's position tracking index
		lea	($FFFFCB00).w,a2	; load the tracking array into a2
		moveq	#63,d2	; begin a 64-step loop

@looppoint:
		move.w	d1,(a2)+	; fill in X
		move.w	d0,(a2)+	; fill in Y
		dbf	d2,@looppoint	; loop</syntaxhighlight>

===Fixing the Spring object bug===
Another issue is that when using objects like a spring after Spin Dashing, the game does not know how to accommodate this after you suddenly change direction. Fourtunately, this is a fairly easy fix, so go to '''Obj41_AniLR''' and right below the label, add this line:
<syntaxhighlight lang="asm">		clr.w	($FFFFC904).w	; clear screen delay counter</syntaxhighlight>

===Fixing the Caterkiller bug===
And finally, there's an annoying bug that occurs when rolling into a [[Caterkiller]] too fast, which will result Sonic in taking damage despite the head being destroyed already. This happens because the spiked body segments are actually not getting deleted immediately after destroying the head, but rather one frame later. To fix this, go to loc_16C7C: and right below the label add:
<syntaxhighlight lang="asm">		clr.b	$20(a1)		; immediately remove all touch response values when destroying the head to avoid taking damage</syntaxhighlight>

==GitHub disassembly==
This section is designed for those using the GitHub disassembly of Sonic 1. It will assume that you have followed [[SCHG How-to:Add Spin Dash to Sonic 1 (GitHub)|DikinBaus' revamped guide]] and the GitHub versions of [[SCHG How-to:Add Spin Dash to Sonic 1/Part 2#GitHub disassembly|Part 2]] and [[SCHG How-to:Add Spin Dash to Sonic 1/Part 3#GitHub disassembly|Part 3]] in that order. The following codes are designed for the AS version of the Sonic 1 GitHub disassembly.

===Fixing camera bugs===
This will fix the issue which causes weird camera movements if the player performs a Spin Dash at the very beginning of a level since the camera will try to follow bad data from the array of Sonic's previous positions. The following code therefore clears the aforementioned array. Open '''_inc\LevelSizeLoad & BgScrollSpeed (JP1).asm''' (or its non-JP1 counterpart if you have the REV00 revision enabled), and add these lines at the beginning of the '''LevSz_SkipStartPos''' label: 

<syntaxhighlight lang="asm">
		clr.w	(v_trackpos).w	; reset Sonic's position tracking index 
		lea	(v_tracksonic).w,a2	; load the tracking array into a2 
		moveq	#63,d2	; begin a 64-step loop

	.looppoint: 
		move.w	d1,(a2)+	; fill in X 
		move.w	d0,(a2)+	; fill in Y 
		dbf d2,.looppoint	; loop</syntaxhighlight>

===Fixing the Spring object bug===
Another issue is that when using objects like a spring after Spin Dashing, the game does not know how to accommodate this after you suddenly change direction. Fourtunately, this is a fairly easy fix, so open up '''_incObj\41 Springs.asm''' and find '''Spring_AniLR''', and right below the label, add this line:
<syntaxhighlight lang="asm">		clr.w	(v_sgfx_buffer+$104).w	; clear screen delay counter</syntaxhighlight>

===Fixing the Caterkiller bug===
And finally, there's an annoying bug that occurs when rolling into a [[Caterkiller]] too fast, which will result Sonic in taking damage despite the head being destroyed already. This happens because the spiked body segments are actually not getting deleted immediately after destroying the head, but rather one frame later. To fix this, open up '''_incObj\78 Caterkiller.asm''' and go to '''.delete''' under '''loc_16C64:''' and right below the label add:
<syntaxhighlight lang="asm">		clr.b	obColType(a1)	; immediately remove all touch response values when destroying the head to avoid taking damage</syntaxhighlight>

==Conclusion==
That's it! You now have a fully working Spin Dash from Sonic 2, complete with the proper animations, sounds, physics, and the like! Enjoy your newly-ported Spin Dash!

{{S1Howtos}}
|Add Spin Dash to Sonic 1/Part 4]]