Remove the Speed Cap
From Sonic Retro
(Ground speed cap fix originally by Tweaker; air speed cap fix originally by Puto)
Ground Speed Cap
Removing the speed cap requires taking a look at Sonic 2's version of Sonic_MoveLeft, and Sonic_MoveRight. First off, we should take a look at Sonic_MoveLeft (for example), and look at its code.
Sonic_MoveLeft: ; XREF: Sonic_Move
move.w $14(a0),d0
beq.s loc_13086
bpl.s loc_130B2
loc_13086:
bset #0,$22(a0)
bne.s loc_1309A
bclr #5,$22(a0)
move.b #1,$1D(a0)
loc_1309A:
sub.w d5,d0
move.w d6,d1
neg.w d1
cmp.w d1,d0
bgt.s loc_130A6
move.w d1,d0
loc_130A6:
move.w d0,$14(a0)
move.b #0,$1C(a0); use walking animation
rts
This is the section we're looking for. Now, let's look up one of the lines in here until we find a matching pattern in S2.
loc_1C2A4: ; CODE XREF: h+515C p
move.w $14(a0),d0
beq.s loc_1C2AC
bpl.s loc_1C2DE
loc_1C2AC: ; CODE XREF: h+5334 j
bset #0,$22(a0)
bne.s loc_1C2C0
bclr #5,$22(a0)
move.b #1,$1D(a0)
loc_1C2C0: ; CODE XREF: h+533E j
sub.w d5,d0
move.w d6,d1
neg.w d1
cmp.w d1,d0
bgt.s loc_1C2D2
add.w d5,d0
cmp.w d1,d0
ble.s loc_1C2D2
move.w d1,d0
loc_1C2D2: ; CODE XREF: h+5354 j h+535A j
move.w d0,$14(a0)
move.b #0,$1C(a0)
rts
Success! Now, let's compare the differences here. You'll notice S2's routine has 3 extra lines in it:
add.w d5,d0
cmp.w d1,d0
ble.s loc_1C2D2
So, what we want to do is add this code to Sonic 1's routine. Take these 3 lines and modify them to work with S1. You should end up with this:
Sonic_MoveLeft: ; XREF: Sonic_Move
move.w $14(a0),d0
beq.s loc_13086
bpl.s loc_130B2
loc_13086:
bset #0,$22(a0)
bne.s loc_1309A
bclr #5,$22(a0)
move.b #1,$1D(a0)
loc_1309A:
sub.w d5,d0
move.w d6,d1
neg.w d1
cmp.w d1,d0
bgt.s loc_130A6
add.w d5,d0
cmp.w d1,d0
ble.s loc_130A6
move.w d1,d0
loc_130A6:
move.w d0,$14(a0)
move.b #0,$1C(a0); use walking animation
rts
Now, we have to do the same for Sonic_MoveRight. Once again, let's find the S2 equivalent of the routine using Sonic 1's routine.
Sonic 1's:
Sonic_MoveRight: ; XREF: Sonic_Move
move.w $14(a0),d0
bmi.s loc_13118
bclr #0,$22(a0)
beq.s loc_13104
bclr #5,$22(a0)
move.b #1,$1D(a0)
loc_13104:
add.w d5,d0
cmp.w d6,d0
blt.s loc_1310C
move.w d6,d0
loc_1310C:
move.w d0,$14(a0)
move.b #0,$1C(a0); use walking animation
rts
And, with the same amount of backsearching, we can find Sonic 2's, which is the following:
loc_1C32A: ; CODE XREF: h+5168 p
move.w $14(a0),d0
bmi.s loc_1C35E
bclr #0,$22(a0)
beq.s loc_1C344
bclr #5,$22(a0)
move.b #1,$1D(a0)
loc_1C344: ; CODE XREF: h+53C2 j
add.w d5,d0
cmp.w d6,d0
blt.s loc_1C352
sub.w d5,d0
cmp.w d6,d0
bge.s loc_1C352
move.w d6,d0
loc_1C352: ; CODE XREF: h+53D4 j h+53DA j
move.w d0,$14(a0)
move.b #0,$1C(a0)
rts
Now, once again, you'll notice the difference between the two routines is the following lines:
sub.w d5,d0
cmp.w d6,d0
bge.s loc_1C352
So, once again, let's apply these changes to work with S1, providing our final, result routine for S1:
Sonic_MoveRight: ; XREF: Sonic_Move
move.w $14(a0),d0
bmi.s loc_13118
bclr #0,$22(a0)
beq.s loc_13104
bclr #5,$22(a0)
move.b #1,$1D(a0)
loc_13104:
add.w d5,d0
cmp.w d6,d0
blt.s loc_1310C
sub.w d5,d0
cmp.w d6,d0
bge.s loc_1310C
move.w d6,d0
loc_1310C:
move.w d0,$14(a0)
move.b #0,$1C(a0); use walking animation
rts
And that should be it! Build your new ROM, and the infamous (ground) speed cap should be gone!
Air Speed Cap
However, that still keeps the cap in mid-air. So let's adapt that to fix the speed cap in mid-air too.
Here's the original code:
Sonic_ChgJumpDir: ; XREF: Obj01_MdJump; Obj01_MdJump2
move.w ($FFFFF760).w,d6
move.w ($FFFFF762).w,d5
asl.w #1,d5
btst #4,$22(a0)
bne.s Obj01_ResetScr2
move.w $10(a0),d0
btst #2,($FFFFF602).w; is left being pressed?
beq.s loc_13278; if not, branch
bset #0,$22(a0)
sub.w d5,d0
move.w d6,d1
neg.w d1
cmp.w d1,d0
bgt.s loc_13278
move.w d1,d0
loc_13278:
btst #3,($FFFFF602).w; is right being pressed?
beq.s Obj01_JumpMove; if not, branch
bclr #0,$22(a0)
add.w d5,d0
cmp.w d6,d0
blt.s Obj01_JumpMove
move.w d6,d0
As you can see, it works exactly the same way as the MoveLeft/Right routines. So let's apply the same fix. After bgt.s loc_13278, add the following lines:
add.w d5,d0 ; +++ remove this frame's acceleration change
cmp.w d1,d0 ; +++ compare speed with top speed
ble.s loc_13278 ; +++ if speed was already greater than the maximum, branch
And do a similar thing after blt.s Obj01_JumpMove:
sub.w d5,d0 ; +++ remove this frame's acceleration change
cmp.w d6,d0 ; +++ compare speed with top speed
bge.s Obj01_JumpMove ; +++ if speed was already greater than the maximum, branch
Final result:
Sonic_ChgJumpDir: ; XREF: Obj01_MdJump; Obj01_MdJump2
move.w ($FFFFF760).w,d6
move.w ($FFFFF762).w,d5
asl.w #1,d5
btst #4,$22(a0)
bne.s Obj01_ResetScr2
move.w $10(a0),d0
btst #2,($FFFFF602).w; is left being pressed?
beq.s loc_13278; if not, branch
bset #0,$22(a0)
sub.w d5,d0
move.w d6,d1
neg.w d1
cmp.w d1,d0
bgt.s loc_13278
add.w d5,d0 ; +++ remove this frame's acceleration change
cmp.w d1,d0 ; +++ compare speed with top speed
ble.s loc_13278 ; +++ if speed was already greater than the maximum, branch
move.w d1,d0
loc_13278:
btst #3,($FFFFF602).w; is right being pressed?
beq.s Obj01_JumpMove; if not, branch
bclr #0,$22(a0)
add.w d5,d0
cmp.w d6,d0
blt.s Obj01_JumpMove
sub.w d5,d0 ; +++ remove this frame's acceleration change
cmp.w d6,d0 ; +++ compare speed with top speed
bge.s Obj01_JumpMove ; +++ if speed was already greater than the maximum, branch
move.w d6,d0
|Remove the Speed Cap]]