Unique Collision Per Act in Sonic 1 (now with Project Sonic: Two-Eight support)

You might remember this guide, it was poorly optimised and takes a lot of cycles; well, after some experimenting I've managed to create a heavily optimised method that doesn't require checking multiple times and shoves everything into a single table.

At ColIndexLoad:, you'll see this code:

Code (Text):

1. ColIndexLoad:                ; XREF: Level
2.         moveq    #0,d0
3.         move.b    ($FFFFFE10).w,d0
4.         lsl.w    #2,d0
5.         move.l    ColPointers(pc,d0.w),($FFFFF796).w
6.         rts
7. ; End of function ColIndexLoad

What this does grabs the current zone and loads its collision based on what it gets; for example, $00 would be GHZ and $01 LZ. Since we want it per act, replace the code with this:

Code (Text):

1. ColIndexLoad:                ; XREF: Level
2.         move.w    ($FFFFFE10).w,d0
3.         lsl.b    #6,d0
4.         lsr.w    #4,d0
5.         move.l    ColPointers(pc,d0.w),($FFFFF796).w
6.         rts
7. ; End of function ColIndexLoad

This code instead grabs the current act and shifts the entry closer before dividing by 4, resulting in per act collision; then replace the table in Collision index pointers.asm with this:

Code (Text):

1.     dc.l Col_GHZ1
2.     dc.l Col_GHZ2
3.     dc.l Col_GHZ3
4.     dc.l Col_GHZ4
5.     dc.l Col_LZ1
6.     dc.l Col_LZ2
7.     dc.l Col_LZ3
8.     dc.l Col_LZ4
9.     dc.l Col_MZ1
10.     dc.l Col_MZ2
11.     dc.l Col_MZ3
12.     dc.l Col_MZ4
13.     dc.l Col_SLZ1
14.     dc.l Col_SLZ2
15.     dc.l Col_SLZ3
16.     dc.l Col_SLZ4
17.     dc.l Col_SYZ1
18.     dc.l Col_SYZ2
19.     dc.l Col_SYZ3
20.     dc.l Col_SYZ4
21.     dc.l Col_SBZ1
22.     dc.l Col_SBZ2
23.     dc.l Col_SBZ3
24.     dc.l Col_SBZ4

The ending zone ($06) is loaded separately, so at End_LoadData: replace Col_GHZ with Col_GHZ1 or Col_Ending. Obviously new entries will have to be create, so copy-paste all the collision data and add a number at the end; SonLVL INIs will also have to be edited to reflect the new data.

Now, I know some of you will probably be using MarkeyJester's Two-Eight, so replace ColIndexLoad: with this:

Code (Text):

1. ; ---------------------------------------------------------------------------
2. ; Collision index loading subroutine
3. ; ---------------------------------------------------------------------------
4.  
5. ; ||||||||||||||| S U B    R O U T    I N E |||||||||||||||||||||||||||||||||||||||
6.  
7.  
8. ColIndexLoad:                ; XREF: Level
9.         move.w    ($FFFFFE10).w,d0
10.         lsl.b    #6,d0
11.         lsr.w    #3,d0                    ; MJ: multiply by 8 not 4
12.         move.l    ColPointers(pc,d0.w),($FFFFFFD0).w    ; MJ: get first collision set
13.         add.w    #4,d0                    ; MJ: increase to next location
14.         move.l    ColPointers(pc,d0.w),($FFFFFFD4).w    ; MJ: get second collision set
15.         rts
16. ; End of function ColIndexLoad

And Collision index pointers.asm with this:

Code (Text):

1. ; ---------------------------------------------------------------------------
2. ; Collision index pointers
3. ; ---------------------------------------------------------------------------
4.     dc.l Col_GHZ1_1
5.     dc.l Col_GHZ1_2
6.     dc.l Col_GHZ2_1
7.     dc.l Col_GHZ2_2
8.     dc.l Col_GHZ3_1
9.     dc.l Col_GHZ3_2
10.     dc.l Col_GHZ4_1
11.     dc.l Col_GHZ4_2
12.     dc.l Col_LZ1_1
13.     dc.l Col_LZ1_2
14.     dc.l Col_LZ2_1
15.     dc.l Col_LZ2_2
16.     dc.l Col_LZ3_1
17.     dc.l Col_LZ3_2
18.     dc.l Col_LZ4_1
19.     dc.l Col_LZ4_2
20.     dc.l Col_MZ1_1
21.     dc.l Col_MZ1_2
22.     dc.l Col_MZ2_1
23.     dc.l Col_MZ2_2
24.     dc.l Col_MZ3_1
25.     dc.l Col_MZ3_2
26.     dc.l Col_MZ4_1
27.     dc.l Col_MZ4_2
28.     dc.l Col_SLZ1_1
29.     dc.l Col_SLZ1_2
30.     dc.l Col_SLZ2_1
31.     dc.l Col_SLZ2_2
32.     dc.l Col_SLZ3_1
33.     dc.l Col_SLZ3_2
34.     dc.l Col_SLZ4_1
35.     dc.l Col_SLZ4_2
36.     dc.l Col_SYZ1_1
37.     dc.l Col_SYZ1_2
38.     dc.l Col_SYZ2_1
39.     dc.l Col_SYZ2_2
40.     dc.l Col_SYZ3_1
41.     dc.l Col_SYZ3_2
42.     dc.l Col_SYZ4_1
43.     dc.l Col_SYZ4_2
44.     dc.l Col_SBZ1_1
45.     dc.l Col_SBZ1_2
46.     dc.l Col_SBZ2_1
47.     dc.l Col_SBZ2_2
48.     dc.l Col_SBZ3_1
49.     dc.l Col_SBZ3_2
50.     dc.l Col_SBZ4_1
51.     dc.l Col_SBZ4_2

Two-Eight combines both collision sets into the same table to save space, so our calculations had to be slightly altered.

And there you go!

EDIT: Added support for MarkeyJester's Project Sonic 1: Two-Eight.

 

In Sonic 1 reading FFFFFE10 as a byte means per zone, as a word it means per act; changing the move.b ($FFFFFE10).w,d0 to a word isn't enough and thusly some changes had to be done.

 

Now I just need to create a version compatible with MarkeyJester's Project: Sonic 128.