Improve the Fade to White Routines in Sonic 1

Ever since I found Markey Jester's tutorial on improving fade in and fade out progression, it always bothered me the that there wasn't a tutorial for improving the fade to and from white used for Sonic 1's special stage so today, I fixed that. Originally, the fade to white would look like this:

To fix it, replace the beginning of Pal_MakeWhite to the end of Pal_AddColor2 with this: (Made to work with Hivebrain's 2005 Sonic 1 disassembly)

; ---------------------------------------------------------------------------
; Subroutine to fill the pallet with white (special stage)
; ---------------------------------------------------------------------------

; ||||||||||||||| S U B R O U T I N E |||||||||||||||||||||||||||||||||||||||


Pal_MakeWhite: ; XREF: SpecialStage
move.w #$3F,($FFFFF626).w
moveq #0,d0
lea ($FFFFFB00).w,a0
move.b ($FFFFF626).w,d0
adda.w d0,a0
move.w #$EEE,d1
move.b ($FFFFF627).w,d0

PalWhite_Loop:
move.w d1,(a0)+
dbf d0,PalWhite_Loop ; fill pallet with $000 (black)
moveq #$0E,d4 ; MJ: prepare maximum colour check
moveq #$00,d6 ; MJ: clear d6

loc_1EF4:
bsr.w RunPLC_RAM
move.b #$12,($FFFFF62A).w
bsr.w DelayProgram
bchg #$00,d6 ; MJ: change delay counter
beq loc_1EF4 ; MJ: if null, delay a frame
bsr.s Pal_WhiteToBlack
subq.b #$02,d4 ; MJ: decrease colour check
bne loc_1EF4 ; MJ: if it has not reached null, branch
move.b #$12,($FFFFF62A).w ; MJ: wait for V-blank again (so colours transfer)
bra DelayProgram ; MJ: ''
; End of function Pal_MakeWhite


; ||||||||||||||| S U B R O U T I N E |||||||||||||||||||||||||||||||||||||||


Pal_WhiteToBlack: ; XREF: Pal_MakeWhite
moveq #0,d0
lea ($FFFFFB00).w,a0
lea ($FFFFFB80).w,a1
move.b ($FFFFF626).w,d0
adda.w d0,a0
adda.w d0,a1
move.b ($FFFFF627).w,d0

loc_1F20:
bsr.s Pal_DecColor2
dbf d0,loc_1F20
cmpi.b #1,($FFFFFE10).w
bne.s locret_1F4A
moveq #0,d0
lea ($FFFFFA80).w,a0
lea ($FFFFFA00).w,a1
move.b ($FFFFF626).w,d0
adda.w d0,a0
adda.w d0,a1
move.b ($FFFFF627).w,d0

loc_1F44:
bsr.s Pal_DecColor2
dbf d0,loc_1F44

locret_1F4A:
rts
; End of function Pal_WhiteToBlack


; ||||||||||||||| S U B R O U T I N E |||||||||||||||||||||||||||||||||||||||


Pal_DecColor2: ; XREF: Pal_WhiteToBlack
move.b (a1),d5 ; MJ: load blue
move.w (a1)+,d1 ; MJ: load green and red
move.b d1,d2 ; MJ: load red
lsr.b #$04,d1 ; MJ: get only green
andi.b #$0E,d2 ; MJ: get only red
move.w (a0),d3 ; MJ: load current colour in buffer
cmp.b d5,d4 ; MJ: is it time for blue to fade?
bcs FCI2_NoBlue ; MJ: if not, branch
subi.w #$0200,d3 ; MJ: dencrease blue

FCI2_NoBlue:
cmp.b d1,d4 ; MJ: is it time for green to fade?
bcs FCI2_NoGreen ; MJ: if not, branch
subi.b #$20,d3 ; MJ: dencrease green

FCI2_NoGreen:
cmp.b d2,d4 ; MJ: is it time for red to fade?
bcs FCI2_NoRed ; MJ: if not, branch
subq.b #$02,d3 ; MJ: dencrease red

FCI2_NoRed:
move.w d3,(a0)+ ; MJ: save colour
rts ; MJ: return
; End of function Pal_DecColor2

; ---------------------------------------------------------------------------
; Subroutine to make a white flash when you enter a special stage
; ---------------------------------------------------------------------------

; ||||||||||||||| S U B R O U T I N E |||||||||||||||||||||||||||||||||||||||


Pal_MakeFlash: ; XREF: SpecialStage
move.w #$3F,($FFFFF626).w
moveq #$07,d4 ; MJ: set repeat times
moveq #$00,d6 ; MJ: clear d6

loc_1F86:
bsr.w RunPLC_RAM
move.b #$12,($FFFFF62A).w
bsr.w DelayProgram
bchg #$00,d6 ; MJ: change delay counter
beq loc_1F86 ; MJ: if null, delay a frame
bsr.s Pal_ToWhite
dbf d4,loc_1F86
rts
; End of function Pal_MakeFlash


; ||||||||||||||| S U B R O U T I N E |||||||||||||||||||||||||||||||||||||||


Pal_ToWhite: ; XREF: Pal_MakeFlash
moveq #0,d0
lea ($FFFFFB00).w,a0
move.b ($FFFFF626).w,d0
adda.w d0,a0
move.b ($FFFFF627).w,d0

loc_1FAC:
bsr.s Pal_AddColor2
dbf d0,loc_1FAC

moveq #0,d0
lea ($FFFFFA80).w,a0
move.b ($FFFFF626).w,d0
adda.w d0,a0
move.b ($FFFFF627).w,d0

loc_1FC2:
bsr.s Pal_AddColor2
dbf d0,loc_1FC2
rts
; End of function Pal_ToWhite


; ||||||||||||||| S U B R O U T I N E |||||||||||||||||||||||||||||||||||||||


Pal_AddColor2: ; XREF: Pal_ToWhite
move.w (a0),d5 ; MJ: load colour
cmpi.w #$EEE,d5
beq.s FCO2_NoRed
move.w d5,d1 ; MJ: copy to d1
move.b d1,d2 ; MJ: load green and red
move.b d1,d3 ; MJ: load red
andi.w #$0E00,d1 ; MJ: get only blue
cmpi.w #$0E00,d1
beq FCO2_NoBlue ; MJ: if blue is finished, branch
addi.w #$0200,d5 ; MJ: increase blue

FCO2_NoBlue:
andi.w #$00E0,d2 ; MJ: get only green (needs to be word)
cmpi.w #$00E0,d2
beq FCO2_NoGreen ; MJ: if green is finished, branch
addi.b #$20,d5 ; MJ: increase green

FCO2_NoGreen:
andi.b #$0E,d3 ; MJ: get only red
cmpi.b #$0E,d3
beq FCO2_NoRed ; MJ: if red is finished, branch
addq.b #$02,d5 ; MJ: increase red

FCO2_NoRed:
move.w d5,(a0)+ ; MJ: save new colour
rts ; MJ: return
; End of function Pal_AddColor2
Now it should look like this:



Credit goes to Markey Jester for the original code this is based off of.

 

Though, for whatever reason, I prefer the yellower flash, this looks very nice as well. Good work!

 

Yeah, same here. The yellow flash kinda adds that particular feel to it when entering a special stage. Still nice work!

 

Not bad tutorial. I already use it!