Game 1 Unit 10 of 128 1 hr learning time

Multiple Creatures

Three creatures walk independently using a data table. Each entry holds position, direction, and state. A loop processes every creature each frame using the same subroutine.

8% of Exodus

Mark as complete Completed!

One creature is a tech demo. A terrain puzzle needs a crowd. In this unit, three creatures walk the terrain independently — each with its own position, direction, and state. A data table holds their variables, and a loop processes them all every frame.

Exodus Unit 10

Three creatures on screen: one on the platform, one on the high ground, one on the low ground. They walk, turn, and fall independently. The same update_creature subroutine handles all of them.

The Creature Data Table

Until now, creature variables were standalone labels — creature_x, creature_y, creature_dx. That works for one creature. For multiple creatures, we need a data table — a block of memory where each creature’s data occupies a fixed-size entry:

; Creature data table offsets (bytes per field)
CR_X                equ 0           ; .w x position
CR_Y                equ 2           ; .w y position
CR_DX               equ 4           ; .w direction
CR_STATE            equ 6           ; .w state (0=walk, 1=fall)
CR_STEP             equ 8           ; .w step timer
CR_SIZE             equ 10          ; Total bytes per creature

NUM_CREATURES       equ 3

            ; ...

creatures:
            dcb.b   CR_SIZE*NUM_CREATURES,0

Each creature occupies CR_SIZE (10) bytes. The EQU constants define byte offsets within each entry. To read creature 0’s x position: move.w CR_X(a2),d0 where A2 points to the creature’s entry. To read creature 1’s x position: add CR_SIZE to A2 first.

This is a structure — a block of fields accessed by offset. The 68000’s displacement addressing mode (CR_X(a2)) makes this natural. The register points to the start of the entry, and the offset selects the field.

The Processing Loop

Each frame, a loop walks through the table and calls update_creature for each entry:

            ; --- Process all creatures ---
            lea     creatures,a2
            moveq   #NUM_CREATURES-1,d7

.creature_loop:
            bsr     update_creature
            add.w   #CR_SIZE,a2
            dbra    d7,.creature_loop

A2 starts at the beginning of the table. D7 counts down from NUM_CREATURES-1 (because DBRA counts to -1, not 0). After processing one creature, A2 advances by CR_SIZE bytes to point at the next entry. The same subroutine handles every creature — it doesn’t know or care which one it’s updating.

The Update Subroutine

update_creature is the single-creature logic from previous units, rewritten to read and write through A2 instead of named variables:

;──────────────────────────────────────────────────────────────
; update_creature — Update one creature (A2 = creature data)
;──────────────────────────────────────────────────────────────
update_creature:
            move.w  CR_STATE(a2),d0
            cmp.w   #STATE_FALLING,d0
            beq     .do_fall

            ; --- Walking ---
            move.w  CR_X(a2),d0
            add.w   CR_DX(a2),d0
            add.w   #FOOT_OFFSET_X,d0
            move.w  CR_Y(a2),d1
            add.w   #FOOT_OFFSET_Y,d1
            bsr     check_pixel

            tst.b   d0
            beq.s   .walk_no_floor

            ; Floor ahead — move forward
            move.w  CR_X(a2),d0
            add.w   CR_DX(a2),d0
            move.w  d0,CR_X(a2)

            ; ...floor check and falling logic...

Where Unit 8 had move.w creature_x,d0, we now have move.w CR_X(a2),d0. Where it had move.w d0,creature_x, we now have move.w d0,CR_X(a2). The logic is identical — only the addressing changed.

This is the power of subroutines and data tables together. Write the logic once, call it for each entry. Adding a fourth creature means adding one more entry to the table and incrementing NUM_CREATURES — no code changes needed.

Three Sprites

Each creature needs its own hardware sprite. Sprites 0, 1, and 2 each have their own data block and pointer in the Copper list. After the creature loop updates all positions, a second pass writes each creature’s position into its sprite data:

            lea     creatures,a2
            lea     sprite0_data,a0
            bsr     write_sprite_pos

            lea     creatures+CR_SIZE,a2
            lea     sprite1_data,a0
            bsr     write_sprite_pos

            lea     creatures+CR_SIZE*2,a2
            lea     sprite2_data,a0
            bsr     write_sprite_pos

write_sprite_pos is the same position-packing code from Unit 4, but now it reads from the creature table (A2) and writes to the specified sprite data (A0).

Sprites 0, 1, and 2 all belong to the same sprite group (pairs 0-1), so they share colours 17-19. All three creatures look identical — which is exactly right for a terrain puzzle where they’re all the same type of creature.

Starting Positions

The three creatures start in different places to show the terrain interaction:

            ; Creature 0: on platform
            move.w  #80,CR_X(a0)
            move.w  #92,CR_Y(a0)

            ; Creature 1: on low ground, walking right
            move.w  #16,CR_X+CR_SIZE(a0)
            move.w  #140,CR_Y+CR_SIZE(a0)

            ; Creature 2: on high ground, walking left
            move.w  #280,CR_X+CR_SIZE*2(a0)
            move.w  #108,CR_Y+CR_SIZE*2(a0)

Creature 0 starts on the floating platform (it will fall off the edge). Creature 1 walks along the low ground. Creature 2 starts on the high ground walking left — it will reach the cliff edge and turn around. Different step timer offsets (0, 4, 2) stagger the footstep sounds so they don’t all click at once.

Experiment: Add a Fourth Creature

NUM_CREATURES       equ 4

Change the count and initialise one more entry. You’ll also need a fourth sprite (SPR3PTH/SPR3PTL at $DFF12C/$DFF12E) and sprite3_data. The Amiga has 8 hardware sprites — that’s the hard limit for this approach.

The Complete Code

;──────────────────────────────────────────────────────────────
; EXODUS - A terrain puzzle for the Commodore Amiga
; Unit 10: Multiple Creatures
;
; Three creatures walk independently using a data table.
; Each has its own position, direction, and state.
; A loop processes all creatures every frame.
;──────────────────────────────────────────────────────────────

;══════════════════════════════════════════════════════════════
; TWEAKABLE VALUES
;══════════════════════════════════════════════════════════════

COLOUR_SKY_DEEP     equ $0016
COLOUR_SKY_UPPER    equ $0038
COLOUR_SKY_MID      equ $005B
COLOUR_SKY_LOWER    equ $007D
COLOUR_SKY_HORIZON  equ $009E

COLOUR_TERRAIN      equ $0741

COLOUR_SPR0_1       equ $0FFF
COLOUR_SPR0_2       equ $0F80
COLOUR_SPR0_3       equ $0000

CREATURE_SPEED      equ 1
FALL_SPEED          equ 2

FOOT_OFFSET_X       equ 8
FOOT_OFFSET_Y       equ 12

STEP_PERIOD         equ 400
STEP_VOLUME         equ 48

NUM_CREATURES       equ 3

; Creature data table offsets (bytes per field)
CR_X                equ 0           ; .w x position
CR_Y                equ 2           ; .w y position
CR_DX               equ 4           ; .w direction
CR_STATE            equ 6           ; .w state (0=walk, 1=fall)
CR_STEP             equ 8           ; .w step timer
CR_SIZE             equ 10          ; Total bytes per creature

; Terrain
GROUND_L_X          equ 0
GROUND_L_Y          equ 152
GROUND_L_W          equ 128
GROUND_L_H          equ 104

GROUND_R_X          equ 128
GROUND_R_Y          equ 120
GROUND_R_W          equ 192
GROUND_R_H          equ 136

PLATFORM_X          equ 24
PLATFORM_Y          equ 104
PLATFORM_W          equ 72
PLATFORM_H          equ 8

;══════════════════════════════════════════════════════════════
; DISPLAY CONSTANTS
;══════════════════════════════════════════════════════════════

SCREEN_WIDTH    equ 320
SCREEN_HEIGHT   equ 256
BYTES_PER_ROW   equ SCREEN_WIDTH/8
BITPLANE_SIZE   equ BYTES_PER_ROW*SCREEN_HEIGHT

SPRITE_HEIGHT   equ 12

STATE_WALKING   equ 0
STATE_FALLING   equ 1

STEP_INTERVAL   equ 8

;══════════════════════════════════════════════════════════════
; HARDWARE REGISTERS
;══════════════════════════════════════════════════════════════

CUSTOM      equ $dff000
DMACON      equ $096
INTENA      equ $09a
INTREQ      equ $09c
COP1LC      equ $080
COPJMP1     equ $088
BPLCON0     equ $100
BPLCON1     equ $102
BPLCON2     equ $104
BPL1MOD     equ $108
DIWSTRT     equ $08e
DIWSTOP     equ $090
DDFSTRT     equ $092
DDFSTOP     equ $094
BPL1PTH     equ $0e0
BPL1PTL     equ $0e2
SPR0PTH     equ $120
SPR0PTL     equ $122
SPR1PTH     equ $124
SPR1PTL     equ $126
SPR2PTH     equ $128
SPR2PTL     equ $12a
COLOR00     equ $180
COLOR01     equ $182
COLOR17     equ $1a2
COLOR18     equ $1a4
COLOR19     equ $1a6
VPOSR       equ $004

AUD0LC      equ $0a0
AUD0LEN     equ $0a4
AUD0PER     equ $0a6
AUD0VOL     equ $0a8

;══════════════════════════════════════════════════════════════
; CODE (Chip RAM)
;══════════════════════════════════════════════════════════════

            section code,code_c

start:
            lea     CUSTOM,a5

            move.w  #$7fff,INTENA(a5)
            move.w  #$7fff,INTREQ(a5)
            move.w  #$7fff,DMACON(a5)

            ; --- Initialise creatures ---
            lea     creatures,a0

            ; Creature 0: on platform
            move.w  #80,CR_X(a0)
            move.w  #92,CR_Y(a0)
            move.w  #CREATURE_SPEED,CR_DX(a0)
            move.w  #STATE_WALKING,CR_STATE(a0)
            move.w  #0,CR_STEP(a0)

            ; Creature 1: on low ground, walking right
            move.w  #16,CR_X+CR_SIZE(a0)
            move.w  #140,CR_Y+CR_SIZE(a0)
            move.w  #CREATURE_SPEED,CR_DX+CR_SIZE(a0)
            move.w  #STATE_WALKING,CR_STATE+CR_SIZE(a0)
            move.w  #4,CR_STEP+CR_SIZE(a0)

            ; Creature 2: on high ground, walking left
            move.w  #280,CR_X+CR_SIZE*2(a0)
            move.w  #108,CR_Y+CR_SIZE*2(a0)
            move.w  #-CREATURE_SPEED,CR_DX+CR_SIZE*2(a0)
            move.w  #STATE_WALKING,CR_STATE+CR_SIZE*2(a0)
            move.w  #2,CR_STEP+CR_SIZE*2(a0)

            ; --- Draw terrain ---
            move.w  #GROUND_L_X,d0
            move.w  #GROUND_L_Y,d1
            move.w  #GROUND_L_W,d2
            move.w  #GROUND_L_H,d3
            bsr     draw_rect

            move.w  #GROUND_R_X,d0
            move.w  #GROUND_R_Y,d1
            move.w  #GROUND_R_W,d2
            move.w  #GROUND_R_H,d3
            bsr     draw_rect

            move.w  #PLATFORM_X,d0
            move.w  #PLATFORM_Y,d1
            move.w  #PLATFORM_W,d2
            move.w  #PLATFORM_H,d3
            bsr     draw_rect

            ; --- Patch bitplane pointer ---
            lea     bitplane,a0
            move.l  a0,d0
            swap    d0
            lea     bpl1pth_val,a1
            move.w  d0,(a1)
            swap    d0
            lea     bpl1ptl_val,a1
            move.w  d0,(a1)

            ; --- Patch sprite pointers ---
            ; Sprite 0
            lea     sprite0_data,a0
            move.l  a0,d0
            swap    d0
            lea     spr0pth_val,a1
            move.w  d0,(a1)
            swap    d0
            lea     spr0ptl_val,a1
            move.w  d0,(a1)

            ; Sprite 1
            lea     sprite1_data,a0
            move.l  a0,d0
            swap    d0
            lea     spr1pth_val,a1
            move.w  d0,(a1)
            swap    d0
            lea     spr1ptl_val,a1
            move.w  d0,(a1)

            ; Sprite 2
            lea     sprite2_data,a0
            move.l  a0,d0
            swap    d0
            lea     spr2pth_val,a1
            move.w  d0,(a1)
            swap    d0
            lea     spr2ptl_val,a1
            move.w  d0,(a1)

            ; --- Install Copper list ---
            lea     copperlist,a0
            move.l  a0,COP1LC(a5)
            move.w  d0,COPJMP1(a5)

            ; --- Enable DMA ---
            move.w  #$83a1,DMACON(a5)

            ; === Main Loop ===
mainloop:
            move.l  #$1ff00,d1
.vbwait:
            move.l  VPOSR(a5),d0
            and.l   d1,d0
            bne.s   .vbwait

            ; --- Process all creatures ---
            lea     creatures,a2
            moveq   #NUM_CREATURES-1,d7

.creature_loop:
            bsr     update_creature
            add.w   #CR_SIZE,a2
            dbra    d7,.creature_loop

            ; --- Update all sprites ---
            lea     creatures,a2
            lea     sprite0_data,a0
            bsr     write_sprite_pos

            lea     creatures+CR_SIZE,a2
            lea     sprite1_data,a0
            bsr     write_sprite_pos

            lea     creatures+CR_SIZE*2,a2
            lea     sprite2_data,a0
            bsr     write_sprite_pos

            btst    #6,$bfe001
            bne     mainloop

.halt:
            bra.s   .halt

;──────────────────────────────────────────────────────────────
; update_creature — Update one creature (A2 = creature data)
;──────────────────────────────────────────────────────────────
update_creature:
            move.w  CR_STATE(a2),d0
            cmp.w   #STATE_FALLING,d0
            beq     .do_fall

            ; --- Walking ---
            move.w  CR_X(a2),d0
            add.w   CR_DX(a2),d0
            add.w   #FOOT_OFFSET_X,d0
            move.w  CR_Y(a2),d1
            add.w   #FOOT_OFFSET_Y,d1
            bsr     check_pixel

            tst.b   d0
            beq.s   .walk_no_floor

            ; Floor ahead — move forward
            move.w  CR_X(a2),d0
            add.w   CR_DX(a2),d0
            move.w  d0,CR_X(a2)

            ; Footstep sound
            move.w  CR_STEP(a2),d0
            subq.w  #1,d0
            bgt.s   .no_step
            bsr     play_step
            move.w  #STEP_INTERVAL,d0
.no_step:
            move.w  d0,CR_STEP(a2)

            ; Check floor under current position
            move.w  CR_X(a2),d0
            add.w   #FOOT_OFFSET_X,d0
            move.w  CR_Y(a2),d1
            add.w   #FOOT_OFFSET_Y,d1
            bsr     check_pixel

            tst.b   d0
            bne.s   .done
            move.w  #STATE_FALLING,CR_STATE(a2)
            bra.s   .done

.walk_no_floor:
            neg.w   CR_DX(a2)
            bra.s   .done

            ; --- Falling ---
.do_fall:
            move.w  CR_Y(a2),d0
            add.w   #FALL_SPEED,d0

            cmp.w   #SCREEN_HEIGHT-SPRITE_HEIGHT,d0
            blt.s   .fall_ok
            move.w  #SCREEN_HEIGHT-SPRITE_HEIGHT,d0
            move.w  d0,CR_Y(a2)
            move.w  #STATE_WALKING,CR_STATE(a2)
            bra.s   .done

.fall_ok:
            move.w  d0,CR_Y(a2)

            move.w  CR_X(a2),d0
            add.w   #FOOT_OFFSET_X,d0
            move.w  CR_Y(a2),d1
            add.w   #FOOT_OFFSET_Y,d1
            bsr     check_pixel

            tst.b   d0
            beq.s   .done

            move.w  #STATE_WALKING,CR_STATE(a2)

.done:
            rts

;──────────────────────────────────────────────────────────────
; write_sprite_pos — Write position from creature data to sprite
;   A2 = creature data, A0 = sprite data
;──────────────────────────────────────────────────────────────
write_sprite_pos:
            move.w  CR_Y(a2),d0
            add.w   #$2c,d0
            move.w  d0,d1
            add.w   #SPRITE_HEIGHT,d1

            move.w  CR_X(a2),d2
            add.w   #$80,d2

            move.b  d0,d3
            lsl.w   #8,d3
            move.w  d2,d4
            lsr.w   #1,d4
            or.b    d4,d3
            move.w  d3,(a0)+

            move.b  d1,d3
            lsl.w   #8,d3
            moveq   #0,d4
            btst    #8,d0
            beq.s   .no_vs8
            bset    #2,d4
.no_vs8:
            btst    #8,d1
            beq.s   .no_ve8
            bset    #1,d4
.no_ve8:
            btst    #0,d2
            beq.s   .no_h0
            bset    #0,d4
.no_h0:
            or.b    d4,d3
            move.w  d3,(a0)

            rts

;──────────────────────────────────────────────────────────────
; play_step — Trigger the footstep sample on Paula channel 0
;──────────────────────────────────────────────────────────────
play_step:
            lea     CUSTOM,a6
            lea     step_sample,a0
            move.l  a0,AUD0LC(a6)
            move.w  #STEP_SAMPLE_LEN/2,AUD0LEN(a6)
            move.w  #STEP_PERIOD,AUD0PER(a6)
            move.w  #STEP_VOLUME,AUD0VOL(a6)
            move.w  #$8201,DMACON(a6)
            rts

;──────────────────────────────────────────────────────────────
; check_pixel — Test a single pixel in the bitplane
;──────────────────────────────────────────────────────────────
check_pixel:
            lea     bitplane,a0
            mulu    #BYTES_PER_ROW,d1
            add.l   d1,a0
            move.w  d0,d2
            lsr.w   #3,d2
            add.w   d2,a0
            not.w   d0
            and.w   #7,d0
            btst    d0,(a0)
            sne     d0
            and.b   #1,d0
            rts

;──────────────────────────────────────────────────────────────
; draw_rect — Fill a byte-aligned rectangle in the bitplane
;──────────────────────────────────────────────────────────────
draw_rect:
            lea     bitplane,a0
            mulu    #BYTES_PER_ROW,d1
            add.l   d1,a0
            lsr.w   #3,d0
            add.w   d0,a0
            lsr.w   #3,d2

            subq.w  #1,d3
.row:
            move.w  d2,d5
            subq.w  #1,d5
            move.l  a0,a1
.col:
            move.b  #$ff,(a1)+
            dbra    d5,.col

            add.w   #BYTES_PER_ROW,a0
            dbra    d3,.row
            rts

;══════════════════════════════════════════════════════════════
; COPPER LIST
;══════════════════════════════════════════════════════════════

copperlist:
            dc.w    DIWSTRT,$2c81
            dc.w    DIWSTOP,$2cc1
            dc.w    DDFSTRT,$0038
            dc.w    DDFSTOP,$00d0

            dc.w    BPLCON0,$1200
            dc.w    BPLCON1,$0000
            dc.w    BPLCON2,$0000
            dc.w    BPL1MOD,$0000

            dc.w    BPL1PTH
bpl1pth_val:
            dc.w    $0000
            dc.w    BPL1PTL
bpl1ptl_val:
            dc.w    $0000

            dc.w    SPR0PTH
spr0pth_val:
            dc.w    $0000
            dc.w    SPR0PTL
spr0ptl_val:
            dc.w    $0000

            dc.w    SPR1PTH
spr1pth_val:
            dc.w    $0000
            dc.w    SPR1PTL
spr1ptl_val:
            dc.w    $0000

            dc.w    SPR2PTH
spr2pth_val:
            dc.w    $0000
            dc.w    SPR2PTL
spr2ptl_val:
            dc.w    $0000

            dc.w    COLOR00,COLOUR_SKY_DEEP
            dc.w    COLOR01,COLOUR_TERRAIN
            dc.w    COLOR17,COLOUR_SPR0_1
            dc.w    COLOR18,COLOUR_SPR0_2
            dc.w    COLOR19,COLOUR_SPR0_3

            dc.w    $3401,$fffe
            dc.w    COLOR00,COLOUR_SKY_UPPER
            dc.w    $4401,$fffe
            dc.w    COLOR00,COLOUR_SKY_MID
            dc.w    $5401,$fffe
            dc.w    COLOR00,COLOUR_SKY_LOWER
            dc.w    $6001,$fffe
            dc.w    COLOR00,COLOUR_SKY_HORIZON
            dc.w    $6801,$fffe
            dc.w    COLOR00,$0000

            dc.w    $ffff,$fffe

;══════════════════════════════════════════════════════════════
; SPRITE DATA — One block per creature
;══════════════════════════════════════════════════════════════

            even
sprite0_data:
            dc.w    $0000,$0000
            dc.w    %0000011111100000,%0000000000000000
            dc.w    %0000111111110000,%0000011111100000
            dc.w    %0001111111111000,%0000111111110000
            dc.w    %0001101110111000,%0001111111111000
            dc.w    %0001111111111000,%0000111111110000
            dc.w    %0000111001110000,%0000011111100000
            dc.w    %0000011111100000,%0000000000000000
            dc.w    %0001111111111000,%0000011111100000
            dc.w    %0001111111111000,%0000111111110000
            dc.w    %0001111111111000,%0000111111110000
            dc.w    %0000110000110000,%0000000000000000
            dc.w    %0000110000110000,%0000000000000000
            dc.w    $0000,$0000

            even
sprite1_data:
            dc.w    $0000,$0000
            dc.w    %0000011111100000,%0000000000000000
            dc.w    %0000111111110000,%0000011111100000
            dc.w    %0001111111111000,%0000111111110000
            dc.w    %0001101110111000,%0001111111111000
            dc.w    %0001111111111000,%0000111111110000
            dc.w    %0000111001110000,%0000011111100000
            dc.w    %0000011111100000,%0000000000000000
            dc.w    %0001111111111000,%0000011111100000
            dc.w    %0001111111111000,%0000111111110000
            dc.w    %0001111111111000,%0000111111110000
            dc.w    %0000110000110000,%0000000000000000
            dc.w    %0000110000110000,%0000000000000000
            dc.w    $0000,$0000

            even
sprite2_data:
            dc.w    $0000,$0000
            dc.w    %0000011111100000,%0000000000000000
            dc.w    %0000111111110000,%0000011111100000
            dc.w    %0001111111111000,%0000111111110000
            dc.w    %0001101110111000,%0001111111111000
            dc.w    %0001111111111000,%0000111111110000
            dc.w    %0000111001110000,%0000011111100000
            dc.w    %0000011111100000,%0000000000000000
            dc.w    %0001111111111000,%0000011111100000
            dc.w    %0001111111111000,%0000111111110000
            dc.w    %0001111111111000,%0000111111110000
            dc.w    %0000110000110000,%0000000000000000
            dc.w    %0000110000110000,%0000000000000000
            dc.w    $0000,$0000

;══════════════════════════════════════════════════════════════
; STEP SAMPLE
;══════════════════════════════════════════════════════════════

            even
step_sample:
            dc.b    $60,$40,$20,$10,$08,$04,$02,$01
            dc.b    $fe,$fc,$f8,$f0,$e0,$d0,$c0,$b0
            dc.b    $50,$30,$18,$0c,$06,$03,$01,$00
            dc.b    $ff,$fd,$fa,$f4,$e8,$d8,$c8,$b8
STEP_SAMPLE_LEN equ *-step_sample

;══════════════════════════════════════════════════════════════
; CREATURE DATA TABLE
;══════════════════════════════════════════════════════════════

            even
creatures:
            dcb.b   CR_SIZE*NUM_CREATURES,0

;══════════════════════════════════════════════════════════════
; BITPLANE DATA
;══════════════════════════════════════════════════════════════

            even
bitplane:
            dcb.b   BITPLANE_SIZE,0

If It Doesn’t Work

Only one creature visible? Check that all three sprite pointers are patched in the Copper list. Each sprite needs its own SPRxPTH/SPRxPTL pair.
Creatures overlap strangely? Make sure each creature writes to its own sprite data block, not the same one. The write_sprite_pos call needs both the creature data (A2) and the correct sprite data (A0).
Creature 2 doesn’t move? Check the initialisation — the offset is CR_SIZE*2 from the base, and the direction should be -CREATURE_SPEED (negative for left).
All creatures move identically? The loop must advance A2 by CR_SIZE each iteration. If A2 isn’t incremented, all three calls update creature 0.

What You’ve Learnt

Data tables — a contiguous block of memory where each entry has the same size and layout. Accessed by base address plus field offset.
Structure offsets — EQU constants define byte offsets within a structure. The 68000’s displacement addressing (field(An)) reads fields naturally.
Processing loops — DBRA counts down from NUM_CREATURES-1. A2 advances by CR_SIZE each iteration to point at the next entry.
Subroutine reuse — the same update_creature code processes every creature. The logic doesn’t change; only the data pointer changes.
Multiple sprites — each hardware sprite has its own data block and Copper pointer. Up to 8 sprites can be active simultaneously.

What’s Next

The creatures walk and fall, but there’s nowhere to go. In Unit 11, we’ll add an exit zone — a target area that creatures walk towards. When a creature reaches the exit, it’s counted as saved.