Remove the Air Speed Cap
From Sonic Retro
Revision as of 21:46, 20 December 2015 by Scarred Sun (talk | contribs) (Text replacement - "<asm>" to "<syntaxhighlight lang="asm">")
(Guide written by Selbi; code by Puto, taken from the Sonic 1 Speed Cap page)
In Sonic 1 is a function, that limits Sonic's top speed when you are keep pressing in the direction you are looking at (you can feel that best when running down a hill). In Sonic 2 this function doesn't apply; well, at least not completely. Running on the ground works just fine, but in the air you still have it. So let's fix that:
Go to Sonic_ChgJumpDir, which should look like this in Xenowhirl's 2007 Sonic 2 disassembly:
Sonic_ChgJumpDir:
move.w (Sonic_top_speed).w,d6
move.w (Sonic_acceleration).w,d5
asl.w #1,d5
btst #4,status(a0) ; did Sonic jump from rolling?
bne.s Obj01_Jump_ResetScr ; if yes, branch to skip midair control
move.w x_vel(a0),d0
btst #2,(Ctrl_1_Held_Logical).w
beq.s + ; if not holding left, branch
bset #0,status(a0)
sub.w d5,d0 ; add acceleration to the left
move.w d6,d1
neg.w d1
cmp.w d1,d0 ; compare new speed with top speed
bgt.s + ; if new speed is less than the maximum, branch
move.w d1,d0 ; limit speed in air going left, even if Sonic was already going faster (speed limit/cap)
+
btst #3,(Ctrl_1_Held_Logical).w
beq.s + ; if not holding right, branch
bclr #0,status(a0)
add.w d5,d0 ; accelerate right in the air
cmp.w d6,d0 ; compare new speed with top speed
blt.s + ; if new speed is less than the maximum, branch
move.w d6,d0 ; limit speed in air going right, even if Sonic was already going faster (speed limit/cap)
; Obj01_JumpMove:
+ move.w d0,x_vel(a0)
If you look closely, you will notice that this code works excactly like in Sonic 1. This is good, because we can use the excact same methods to fix it. After the line bgt.s + ; if new speed is less than the maximum, branch add these lines:
add.w d5,d0 ; +++ remove this frame's acceleration change
cmp.w d1,d0 ; +++ compare speed with top speed
ble.s + ; +++ if speed was already greater than the maximum, branch
Do the same thing after blt.s + ; if new speed is less than the maximum, branch by using these lines:
sub.w d5,d0 ; +++ remove this frame's acceleration change
cmp.w d6,d0 ; +++ compare speed with top speed
bge.s + ; +++ if speed was already greater than the maximum, branch
The final result should look like this:
Sonic_ChgJumpDir:
move.w (Sonic_top_speed).w,d6
move.w (Sonic_acceleration).w,d5
asl.w #1,d5
btst #4,status(a0) ; did Sonic jump from rolling?
bne.s Obj01_Jump_ResetScr ; if yes, branch to skip midair control
move.w x_vel(a0),d0
btst #2,(Ctrl_1_Held_Logical).w
beq.s + ; if not holding left, branch
bset #0,status(a0)
sub.w d5,d0 ; add acceleration to the left
move.w d6,d1
neg.w d1
cmp.w d1,d0 ; compare new speed with top speed
bgt.s + ; if new speed is less than the maximum, branch
add.w d5,d0 ; +++ remove this frame's acceleration change
cmp.w d1,d0 ; +++ compare speed with top speed
ble.s + ; +++ if speed was already greater than the maximum, branch
move.w d1,d0 ; limit speed in air going left, even if Sonic was already going faster (speed limit/cap)
+
btst #3,(Ctrl_1_Held_Logical).w
beq.s + ; if not holding right, branch
bclr #0,status(a0)
add.w d5,d0 ; accelerate right in the air
cmp.w d6,d0 ; compare new speed with top speed
blt.s + ; if new speed is less than the maximum, branch
sub.w d5,d0 ; +++ remove this frame's acceleration change
cmp.w d6,d0 ; +++ compare speed with top speed
bge.s + ; +++ if speed was already greater than the maximum, branch
move.w d6,d0 ; limit speed in air going right, even if Sonic was already going faster (speed limit/cap)
; Obj01_JumpMove:
+ move.w d0,x_vel(a0)