Add Spin Dash to Sonic 1/Part 4
From Sonic Retro
Revision as of 21:44, 20 December 2015 by Scarred Sun (talk | contribs) (Text replacement - "<asm>" to "<syntaxhighlight lang="asm">")
(Original guide by Mercury)
2005 HiveBrain's disassembly
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:
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
There is one stupid bug we haven't looked at: Going through objects. This is rather annoying bug, and can be used to glitch the game. So why not fix this. Obviously it wont fix all the problems, but using springs to make screen delay like crazy is easiest way to do this glitch. So, add following just before Obj41_AniLR: label:
move.w #0,($FFFFC904).w ; clear screen delay counter
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:
clr.b $20(a1) ; immediately remove all touch response values when destroying the head to avoid taking damage
GitHub disassembly
This will fix the issue which causes weird camera movements if the player performs a Spin Dash at the very beginning of a level since the camera will try to follow bad data from the array of Sonic's previous positions. The following code therefore clears the aforementioned array. Open _inc\LevelSizeLoad & BgScrollSpeed.asm (or its JP1 counterpart if you have the JP1 revision enabled), and add theese lines at the beggining or the LevSz_SkipStartPos label:
clr.w (v_trackpos).w ; reset Sonic's position tracking index
lea (v_tracksonic).w,a2 ; load the tracking array into a2
moveq #63,d2 ; begin a 64-step loop
@looppoint:
move.w d1,(a2)+ ; fill in X
move.w d0,(a2)+ ; fill in Y
dbf d2,@looppoint ; loop
There is one little bug we haven't looked at: Going through objects. This is rather annoying bug, and can be used to glitch the game, so why not fix this. Obviously it wont fix all the problems, but using springs to make screen delay like crazy is easiest way to do this glitch. So, add following just before Spring_AniLR label:
move.w #0,($FFFFC904).w ; clear screen delay counter
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:
clr.b obColType(a1) ; immediately remove all touch response values when destroying the head to avoid taking damage
That's it!