Homing Attack in Sonic 1 - Step 5 - Robotnik Very Easy

For the bosses are not very easy as stands now, We have two ways to fix it, removing the Robotnik of enemy list or cancel the Homing Attack in each hit.

A way: Modify the enemy list

The easiest way is remove the Robotnik of enemy list, as we saw in step 2.

Modify this:

Code:

      cmpi.b   #$F,$20(a1)      ; is some enemy of the list above?
      bls.s   HA_calcdistance ; if yes, branch

To this:

Code:

      cmpi.b   #$E,$20(a1)      ; is some enemy of the list above?
      bls.s   HA_calcdistance ; if yes, branch

Why modify $F to $E?
As you can see in the list, $F is the Eggman.

BLS = branch low or same (Unsigned)
As is "low or same", if it is low than or same to $F, Homing Attack works against Eggman. But we do not want to work against Eggman, then, modify it to $E, because if low than or same to $E, Homing Attack does not work against Eggman, because $F is not equal or low than $E. ($E < $F)


Other way: Cancel the Homing Attack in each hit

For the Homing Attack works against Eggman, and Sonic not attacking Eggman until the Homing Attack's time is over, we need reset the time's value when Sonic hits Eggman, and this goes for every boss.


GHZ BOSS

Search for loc_177E6, and at the end of it, you will see:

Code:

      bne.s   Obj3D_ShipFlash
      move.b   #$20,$3E(a0)   ; set number of   times for ship to flash
      move.w   #$AC,d0
      jsr   (PlaySound_Special).l ;   play boss damage sound

Between this two lines:

Code:

      bne.s   Obj3D_ShipFlash
      move.b   #$20,$3E(a0)   ; set number of   times for ship to flash

Add this:

Code:

      clr.b   ($FFFFFFD1).w    ; cancel the Homing Attack, clearing the number of frames Sonic can chasing the object

LZ BOSS

Search for loc_17F48, and at the end of it, you will see:

Code:

      bne.s   loc_17F70
      move.b   #$20,$3E(a0)
      move.w   #$AC,d0
      jsr   (PlaySound_Special).l

Between this two lines:

Code:

      bne.s   loc_17F70
      move.b   #$20,$3E(a0)

Add this:

Code:

      clr.b   ($FFFFFFD1).w    ; cancel the Homing Attack, clearing the number of frames Sonic can chasing the object

MZ BOSS

Again, search for loc_1833E, and at the end of it, you will see:

Code:

      bne.s   loc_18374
      move.b   #$28,$3E(a0)
      move.w   #$AC,d0
      jsr   (PlaySound_Special).l ;   play boss damage sound

Between this two lines:

Code:

      bne.s   loc_18374
      move.b   #$28,$3E(a0)

Add this:

Code:

      clr.b   ($FFFFFFD1).w    ; cancel the Homing Attack, clearing the number of frames Sonic can chasing the object

SLZ BOSS

Again, search for loc_189FE, and at the end of it, you will see:

Code:

      bne.s   loc_18A28
      move.b   #$20,$3E(a0)
      move.w   #$AC,d0
      jsr   (PlaySound_Special).l ;   play boss damage sound

Between this two lines:

Code:

      bne.s   loc_18A28
      move.b   #$20,$3E(a0)

Add this:

Code:

      clr.b   ($FFFFFFD1).w    ; cancel the Homing Attack, clearing the number of frames Sonic can chasing the object

SYZ BOSS

Once again, search for loc_19202, and at the end of it, you will see:

Code:

      bne.s   loc_1923A
      move.b   #$20,$3E(a0)
      move.w   #$AC,d0
      jsr   (PlaySound_Special).l ;   play boss damage sound

Between this two lines:

Code:

      bne.s   loc_1923A
      move.b   #$20,$3E(a0)

Add this:

Code:

      clr.b   ($FFFFFFD1).w    ; cancel the Homing Attack, clearing the number of frames Sonic can chasing the object

FZ BOSS

The Eggman's ship only appears when he tries to escape, and as we did in all other bosses, search for loc_1A1D4, and at the end of it, you will see:

Code:

      bne.s   loc_1A216
      move.w   #$1E,$30(a0)
      move.w   #$AC,d0
      jsr   (PlaySound_Special).l ;   play boss damage sound

Between this two lines:

Code:

      bne.s   loc_1A216
      move.w   #$1E,$30(a0)

Add this:

Code:

      clr.b   ($FFFFFFD1).w    ; cancel the Homing Attack, clearing the number of frames Sonic can chasing the object

Cancel the Homing Attack in final hit

An bug still continues, the last hit on the boss leaves the Sonic stopped for a time in air, this is done because in the last hit, the "normal code" is not read, but the code of the boss defeated "BossDefeated" is read.

So, to fix this, search for BossDefeated and you will see this:

Code:

BossDefeated:
      move.b   ($FFFFFE0F).w,d0
      andi.b   #7,d0
      bne.s   locret_178A2
      jsr   SingleObjLoad
      bne.s   locret_178A2
      move.b   #$3F,0(a1)   ; load explosion object
      move.w   8(a0),8(a1)
      move.w   $C(a0),$C(a1)
      jsr   (RandomNumber).l
      move.w   d0,d1
      moveq   #0,d1
      move.b   d0,d1
      lsr.b   #2,d1
      subi.w   #$20,d1
      add.w   d1,8(a1)
      lsr.w   #8,d0
      lsr.b   #3,d0
      add.w   d0,$C(a1)

locret_178A2:
      rts   
; End of function BossDefeated

Below the text "BossDefeated:" add this line:

Code:

      clr.b   ($FFFFFFD1).w    ; cancel the Homing Attack, clearing the number of frames Sonic can chasing the object

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