Wall Recoil Porting Tutorial

Here is a tutorial that I made on how to port the wall recoil from Sonic the Hedgehog 2 early prototype to Sonic the Hedgehog:


How to port the Wall Recoil to Sonic 1

Basic Tutorial by Twilight

Version 1.0


This is my first contribution to Sonic Retro. Before following this tutorial, refer to Qjimbo's guide on how to set up a Sonic the Hedgehog disassembly. Also, check out his basic ASM tutorial on how to port the spindash from the early prototype of Sonic the Hedgehog 2 to Sonic the Hedgehog. Both of those contain download links to recommended tools that I'll be using in this tutorial. Once you've set up the disassembly and the tools, read on.

Alright, let's get started. Open up sonic1.asm and Sonic 2 (Early prototype).asm in ConText. In sonic1.asm, search for "Obj01_MdNormal:". You should get this:

http://www.hostdump.com/host/out.php/i3326...j01MdNormal.gif


From there, scroll down until you get to loc_13024:

http://www.hostdump.com/host/out.php/i33274_loc13024.gif


In Sonic 2 (Early prototype).asm, find "loc_FE8E:":

http://www.hostdump.com/host/out.php/i33280_locFE8E.gif


Compare loc_13024 with loc_FE8E. Loc_FE8E has two extra lines, which are:

cmpi.w #$600,$10(a0)
bge.s Sonic_WallRecoil

Paste these lines in loc_13024 in sonic1.asm, after beq.s loc_13060.


You should end up with this:

http://www.hostdump.com/host/out.php/i33288_cmpi.w.gif


Now, there's another area of code that you need to paste: the actual code for the Wall Recoil. In Sonic 2 (Early prototype).asm, search for "Sonic_WallRecoil:":

http://www.hostdump.com/host/out.php/i3329...cWallRecoil.gif


Copy this:

http://www.hostdump.com/host/out.php/i3329...lightedcode.gif


Paste it in sonic1.asm, overwriting this:

http://www.hostdump.com/host/out.php/i33295_SonicMove.gif


Now, you should see this:

http://www.hostdump.com/host/out.php/i33298_finalcode.gif


Save it, build it, and test it. Let's see....

http://www.hostdump.com/host/out.php/i3330...ecoilingame.gif


It's using the incorrect animation!


Change it to this:

http://www.hostdump.com/host/out.php/i3330...edanimation.gif


Now, it should work properly. You have just ported the wall recoil to Sonic the Hedgehog. This concludes my tutorial.


What do you think of it?

 

I know. I just thought I should post it, because I haven't seen a tutorial on it yet and I figured out how to do it myself. The reason why the images are in .gif format is because the image host I used doesn't support that many image formats. Yes, I can post the code in ASM tags:

Code (Text):

1. loc_13024:
2.         move.b  $26(a0),d0
3.         add.b   d1,d0
4.         move.w  d0,-(sp)
5.         bsr.w   Sonic_WalkSpeed
6.         move.w  (sp)+,d0
7.         tst.w   d1
8.         bpl.s   locret_1307C
9.         asl.w   #8,d1
10.         addi.b  #$20,d0
11.         andi.b  #$C0,d0
12.         beq.s   loc_13078
13.         cmpi.b  #$40,d0
14.         beq.s   loc_13066
15.         cmpi.b  #$80,d0
16.         beq.s   loc_13060
17.         cmpi.w  #$600,$10(a0)
18.         bge.s   Sonic_WallRecoil
19.         add.w   d1,$10(a0)
20.         bset    #5,$22(a0)
21.         move.w  #0,$14(a0)
22.         rts
23. ; ===========================================================================
24.  
25. loc_13060:
26.         sub.w   d1,$12(a0)
27.         rts
28. ; ===========================================================================
29.  
30. loc_13066:
31.         sub.w   d1,$10(a0)
32.         bset    #5,$22(a0)
33.         move.w  #0,$14(a0)
34.         rts
35. ; ===========================================================================
36.  
37. loc_13078:
38.         add.w   d1,$12(a0)
39.  
40. locret_1307C:
41.         rts
42. ; ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
43. ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
44.  
45. Sonic_WallRecoil:       ; CODE XREF: Sonic_Move+180j
46.                 ; Sonic_Move+1A0j
47.         move.b  #4,$24(a0)
48.         bsr.w   Sonic_ResetOnFloor
49.         bset    #1,$22(a0)
50.         move.w  #$FE00,d0
51.         tst.w   $10(a0)
52.         bpl.s   Sonic_WallRecoil_Right
53.         neg.w   d0
54.  
55. Sonic_WallRecoil_Right:     ; CODE XREF: Sonic_Move+1D2j
56.         move.w  d0,$10(a0)
57.         move.w  #$FC00,$12(a0)
58.         move.w  #0,$14(a0)
59.         move.b  #$1A,$1C(a0)
60.         move.b  #1,$25(a0)
61.         move.w  #$A3,d0; '£'
62.         jsr (PlaySound_Special).l
63.         rts
64. ; End of function Sonic_Move