After Image in Sonic 1

After Image in Sonic 1



Here a compiled ROM with this tutorial applied.
http://goo.gl/nKwIW

Tutorial made to Hivebrain's 2005 disassembly.

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The After Image is a "copy", "shadow" of the character (Sonic), using the same character's sprite, but without collisions and other things, is a object that is only the character's sprite.

As the sprite need to be the same of the character, all the information about the animation, map, art, horizontal / vertical mirror ...... will be the same of the character.

I will create the object 8D to do the After Image, if you have used the Object 8D, use another object that has not been used, or create other like 8E, 8F...

This After Image that i will show is based on inertia like Sonic Advance 2, and if you want, you can program it to be based on X-Velocity, Y-Velocity, or what you think better.

----------------------------

Above the Obj0A, add this code:

Code:

; ---------------------------------------------------------------------------
; Object 8D - After Image
; ---------------------------------------------------------------------------

Obj8D:               ; XREF: Obj_Index
      cmpi.b   #$18,($FFFFD01C).w   ; is "death" animation?
      beq.w   Obj8D_Delete      ; if yes, delete the After Image

      moveq   #0,d0
      move.b   $24(a0),d0
      move.w   Obj8D_Index(pc,d0.w),d1
      jmp   Obj8D_Index(pc,d1.w)

; ===========================================================================
Obj8D_Index:
      dc.w Obj8D_NoShow-Obj8D_Index
      dc.w Obj8D_NoShow-Obj8D_Index
      dc.w Obj8D_NoShow-Obj8D_Index
      dc.w Obj8D_Sprite_priority_start-Obj8D_Index
      dc.w Obj8D_NoShow-Obj8D_Index
      dc.w Obj8D_NoShow-Obj8D_Index
      dc.w Obj8D_Sprite_priority_next-Obj8D_Index
      dc.w Obj8D_Delete-Obj8D_Index
; ===========================================================================
Obj8D_NoShow:
      addq.b   #2,$24(a0)         ; go to next item of index, at the next frame
      rts
; ===========================================================================
Obj8D_Sprite_priority_start:
      move.b   #2,$18(a0)         ; set sprite priority to 2
      bra.s   Obj8D_Show
; ===========================================================================
Obj8D_Sprite_priority_next:
      addq.b   #1,$18(a0)         ; set a lower sprite priority
; ===========================================================================
Obj8D_Show:
      addq.b   #2,$24(a0)            ; go to next item of index
      jsr   (RandomNumber).l         ; get a random number
      andi.b   #2,d0               ; get a number equal or lower than 2 (0 until 2)
      bne.s   Obj8D_Show_exception   ; if is not 0, branch
      rts                        ; if is 0, don't show the after-image

Obj8D_Show_exception:
      move.w   ($FFFFD002).w,2(a0)      ; copy Sonic map to after-image map
       move.b   ($FFFFD001).w,1(a0)      ; copy Sonic frame infos (horizontal/vertical mirror, coordinate system......)
       move.l   ($FFFFD01A).w,$1A(a0)   ; copy the Sonic animation frame
      jmp   DisplaySprite
; ===========================================================================
Obj8D_Delete:
      jmp   DeleteObject

; ===========================================================================

In Sonic_Display, change this:

Code:

Sonic_Display:            ; XREF: loc_12C7E
      move.w   $30(a0),d0
      beq.s   Obj01_Display
      subq.w   #1,$30(a0)
      lsr.w   #3,d0
      bcc.s   Obj01_ChkInvin

Obj01_Display:
      jsr   DisplaySprite

To this:

Code:

Sonic_Display:            ; XREF: loc_12C7E
      move.w   $30(a0),d0
      beq.s   Obj01_Display_AfterImage
      subq.w   #1,$30(a0)
      lsr.w   #3,d0
      bcc.s   Obj01_ChkInvin

Obj01_Display_AfterImage:
      move.w   $14(a0),d0         ; get inertia
      tst.w   d0               ; is inertia greater than 0?
      bge.s   Obj01_AfterImage_Start   ; if yes, don't negate it
      neg      d0               ; if not, negate it

Obj01_AfterImage_Start:
      cmpi.w   #$600,d0      ; is the sonic inertia greater than 600?
      blt.s   Obj01_Display   ; if not, don't show the After Image

      bsr.w   SingleObjLoad   ; search a free space in object RAM
      bne.s   Obj01_Display   ; if not have, don't load the After Image
      move.b  #$8D,0(a1)      ; load after-image object
      move.l   4(a0),4(a1)      ; copy Sonic mappings to after-image mappings
      move.w   8(a0),8(a1)      ; copy Sonic x-pos to after-image x-pos
      move.w   $C(a0),$C(a1)   ; copy Sonic y-pos to after-image y-pos

Obj01_Display:
      jsr   DisplaySprite

As we created the object 8D, we need add it in object pointers.

In _inc\Object pointers.asm Add this line in end of the file:

Code:

   dc.l Obj8D

If you want that "each after image" use a different pallet line, change this:

Code:

Obj8D_Show:
      addq.b   #2,$24(a0)            ; go to next item of index
      jsr   (RandomNumber).l         ; get a random number
      andi.b   #2,d0               ; get a number equal or lower than 2 (0 until 2)
      bne.s   Obj8D_Show_exception   ; if is not 0, branch
      rts                        ; if is 0, don't show the after-image

Obj8D_Show_exception:
      move.w   ($FFFFD002).w,2(a0)      ; copy Sonic map to after-image map
       move.b   ($FFFFD001).w,1(a0)      ; copy Sonic frame infos (horizontal/vertical mirror, coordinate system......)
       move.l   ($FFFFD01A).w,$1A(a0)   ; copy the Sonic animation frame
      jmp   DisplaySprite

To this:

Code:

Obj8D_Show:
      addq.b   #2,$24(a0)            ; go to next item of index
      jsr   (RandomNumber).l         ; get a random number
      andi.b   #3,d0               ; get a number equal or lower than 3 (0 until 3)
      bne.s   Obj8D_Show_exception   ; if is not 0, branch
      rts                        ; if is 0, don't show the after-image

Obj8D_Show_exception:
      lsl.w   #8,d0            ; multiply by 2000
      lsl.w   #5,d0
      move.w   ($FFFFD002).w,2(a0)      ; copy Sonic map to after-image map
      add.w   d0,2(a0)            ; set any pallet line
       move.b   ($FFFFD001).w,1(a0)      ; copy Sonic frame infos (horizontal/vertical mirror, coordinate system......)
       move.l   ($FFFFD01A).w,$1A(a0)   ; copy the Sonic animation frame
      jmp   DisplaySprite

----------------------------

How this work?

This After Image Method is like 8 Objects, all with After Image, but each is in a different frame, like below:

Code:

   is being created on Sonic_Display                  ; 1st frame
      dc.w Obj8D_NoShow-Obj8D_Index                  ; 2nd frame
      dc.w Obj8D_NoShow-Obj8D_Index                  ; 3rd frame
      dc.w Obj8D_NoShow-Obj8D_Index                  ; 4th frame
      dc.w Obj8D_Sprite_priority_start-Obj8D_Index   ; 5th frame
      dc.w Obj8D_NoShow-Obj8D_Index                  ; 6th frame
      dc.w Obj8D_NoShow-Obj8D_Index                  ; 7th frame
      dc.w Obj8D_Sprite_priority_next-Obj8D_Index   ; 8th frame
      dc.w Obj8D_Delete-Obj8D_Index                  ; 9th frame

In each frame, the Sonic_Display create 1 After Image, and after 8 frames (in the 9th frame), this After Image is deleted.
After 9 frames activated, it get a cycle, 1 deleted and 1 created in same frame.


This After Image Method uses a Sonic' frozen image, that still stalled until be deleted.
In a time line we can see this:

1st frame - created
2nd frame - not showed
3rd frame - not showed
4th frame - not showed
5th frame - showed
6th frame - not showed
7th frame - not showed
8th frame - showed
9th frame - deleted

Note: the sequence (time line), only will be like this if the Obj8D_Index be same than my tutorial.
You can change the Obj8D_Index like you want, to get the better effect and without create a lot of After Images, because this can cause many lost frames (lag).


Why change the sprite priority?

For older After Images be behind than new After Images.


Why using a random number?

For the condition that say if the After Image need or not be showed, not be always the same.

I'm Sorta new at this, So im not sure, What is Each After Image? I didnt want to apply it with out knowing.
I know what a After image is, i applies that part, but whats the Each after image?

They are the effects when you run like in the Sonic Advance series, calebjhuhlu.

calebjhuhlu wrote:I'm Sorta new at this, So im not sure, What is Each After Image? I didnt want to apply it with out knowing.
I know what a After image is, i applies that part, but whats the Each after image?

When I said "each after image", I am referring to each object that contain an after image that is being showed in the frame. To understand what I said, see the first image of the topic, in one after image the Sonic is green and in the other is brown with white, each after image are with a different color, using a different pallet line.

I tried this in Sonic 2 and it worked with no problems. In Sonic 2 you have to modify this a bit for it to work properly.

:v

U feif

Jdpense wrote:U feif

what

Translation: You theif!

This town needs to be destroyed or at least painted a different color...

These flash thingys GS started to post are annoying >.<

SonicVaan wrote:These flash thingys GS started to post are annoying >.<

I agree. I dont get y he does it but lol

Just an annual year bump!