Porting Sonic 2's HUD code to Sonic 1

The HUD code in Sonic 1 has it where it's part of the normal object system whereas in Sonic 2, 3 and Knuckles, it's manually written into the priority table and gets called from the sprite rendering routine. To port this over to Sonic 1 (Hivebrain), the old HUD code needs to be removed and to do that, go to Obj21 and you should see something like this:

Code:

Obj21:                    ; XREF: Obj_Index
        moveq    #0,d0
        move.b    $24(a0),d0
        move.w    Obj21_Index(pc,d0.w),d1
        jmp    Obj21_Index(pc,d1.w)
; ===========================================================================
Obj21_Index:    dc.w Obj21_Main-Obj21_Index
        dc.w Obj21_Flash-Obj21_Index
; ===========================================================================

Obj21_Main:                ; XREF: Obj21_Main
        addq.b    #2,$24(a0)
        move.w    #$90,8(a0)
        move.w    #$108,$A(a0)
        move.l    #Map_obj21,4(a0)
        move.w    #$6CA,2(a0)
        move.b    #0,1(a0)
        move.b    #0,$18(a0)

Obj21_Flash:                ; XREF: Obj21_Main
        tst.w    ($FFFFFE20).w    ; do you have any rings?
        beq.s    Obj21_Flash2    ; if not, branch
        clr.b    $1A(a0)        ; make all counters yellow
        jmp    DisplaySprite
; ===========================================================================

Obj21_Flash2:
        moveq    #0,d0
        btst    #3,($FFFFFE05).w
        bne.s    Obj21_Display
        addq.w    #1,d0        ; make ring counter flash red
        cmpi.b    #9,($FFFFFE23).w ; have    9 minutes elapsed?
        bne.s    Obj21_Display    ; if not, branch
        addq.w    #2,d0        ; make time counter flash red

Obj21_Display:
        move.b    d0,$1A(a0)
        jmp    DisplaySprite
; ===========================================================================

change it to look like this:

Code:

Obj21:                    ; XREF: Obj_Index
        rts
; ===========================================================================

You won't need the old HUD code anymore because it's handled by this new routine which I will post below.

Now for the new HUD code, add this below the rts in the block of code posted above:

Code:

; ---------------------------------------------------------------------------
; HUD Object code - SCORE, TIME, RINGS
; --------------------------------------------------------------------------- 
loc_40804:
    tst.w    ($FFFFFE20).w
    beq.s    loc_40820
    moveq    #0,d1
    btst    #3,($FFFFFE05).w
    bne.s    BranchTo_loc_40836
    cmpi.b    #9,($FFFFFE23).w
    bne.s    BranchTo_loc_40836
    addq.w    #2,d1

BranchTo_loc_40836
    bra.s    loc_40836
; ===========================================================================

loc_40820:
    moveq    #0,d1
    btst    #3,($FFFFFE05).w
    bne.s    loc_40836
    addq.w    #1,d1
    cmpi.b    #9,($FFFFFE23).w
    bne.s    loc_40836
    addq.w    #2,d1

loc_40836:
    move.w    #$90,d3
    move.w    #$108,d2
    lea    (Map_Obj21).l,a1
    movea.w    #$6CA,a3
    add.w    d1,d1
    adda.w    (a1,d1.w),a1
    moveq    #0,d1
    move.b    (a1)+,d1
    subq.b    #1,d1
    bmi.s    return_40858
    jsr    sub_D762

return_40858:
    rts
; End of function h

This is the HUD code from S2 slightly modified to work with Sonic 1's mapping system. For the rest of the code, go to BuildSprites and change this part:

Code:

BuildSprites:                ; XREF: TitleScreen; et al
        lea    ($FFFFF800).w,a2 ; set address for sprite table
        moveq    #0,d5
        lea    ($FFFFAC00).w,a4
        moveq    #7,d7

to this:

Code:

BuildSprites:                ; XREF: TitleScreen; et al
        lea    ($FFFFF800).w,a2 ; set address for sprite table
        moveq    #0,d5
        moveq    #0,d4
        tst.b    ($FFFFFFD0).w ; this was level_started_flag
        beq.s    BuildSprites_2
        jsr    loc_40804
BuildSprites_2:
        lea    ($FFFFAC00).w,a4
        moveq    #7,d7

For the level_started_flag you can use any unused RAM address for it. I used $FFFFFFD0 for this guide. Go to SegaScreen and then scroll down until you see this line:

Code:

        move.w    #0,($FFFFF660).w

add this below it:

Code:

        move.b    #0,($FFFFFFD0).w

Go to Title_ClrPallet and you should see this line somewhere below it:

Code:

        move.b    #$8A,($FFFFD080).w ; load "SONIC TEAM PRESENTS"    object

add this below it:

Code:

        move.b    #0,($FFFFFFD0).w

Go to Level and you should see this somewhere below it:

Code:

        bset    #7,($FFFFF600).w ; add $80 to screen mode (for pre level sequence)

add this below it:

Code:

        move.b    #0,($FFFFFFD0).w

Further down at loc_3946 you should see this somewhere below the label:

Code:

        move.b    #$21,($FFFFD040).w ; load HUD object

replace that with this:

Code:

        move.b    #1,($FFFFFFD0).w

Go to SS_ClrNemRam and find this line below it:

Code:

        move.b    #9,($FFFFD000).w ; load    special    stage Sonic object

add this below it:

Code:

        move.b    #0,($FFFFFFD0).w

Go to End_LoadSonic and find this line below it:

Code:

        move.b    #$21,($FFFFD040).w ; load HUD object

replace it with this:

Code:

        move.b    #1,($FFFFFFD0).w

Then go to Cred_ClrPallet and find this line below it:

Code:

        move.b    #$8A,($FFFFD080).w ; load credits object

and add this below it:

Code:

        move.b    #0,($FFFFFFD0).w

You're now done and should have a near perfect port of S2's HUD code to Sonic 1. It also fixes the bug where "Time" does not flash if you have 9 minutes on the timer and have rings. The source code with all steps applied is provided below.