Game 1 Unit 10 of 64 1 hr learning time

Lives and Death

Add a lives system with death and respawn.

16% of Neon Nexus

Mark as complete Completed!

What You’re Building

Lives. Death. Stakes.

Lives and Death

Now you can lose.

Lives System

Track lives in zero page:

STARTING_LIVES = 3

lives:        .res 1
invuln_timer: .res 1    ; Invulnerability after respawn
game_over:    .res 1

Death and Respawn

When collision is detected:

player_hit:
    dec lives
    lda lives
    beq @game_over

    ; Respawn at centre
    lda #PLAYER_START_X
    sta player_x
    lda #PLAYER_START_Y
    sta player_y

    ; Grant invulnerability
    lda #INVULN_TIME
    sta invuln_timer
    rts

@game_over:
    lda #1
    sta game_over
    rts

Invulnerability

After respawning, the player is briefly invulnerable. This prevents instant re-death:

INVULN_TIME = 90      ; 1.5 seconds at 60fps

check_collisions:
    ; Skip collision check if invulnerable
    lda invuln_timer
    beq @check
    dec invuln_timer
    rts

@check:
    ; Normal collision detection...

During invulnerability, the player flashes (same flash effect as Unit 9).

Lives Display

Show remaining lives as sprites:

update_lives_display:
    ldy #20             ; OAM offset for lives

    ldx lives
    beq @hide_all

    ; Show life 1
    lda #8              ; Y position
    sta oam_buffer, y
    iny
    lda #SPRITE_LIFE
    sta oam_buffer, y
    ; ...repeat for each life

Game Over

When lives reach zero:

main_loop:
    lda game_over
    bne @game_over_loop

    ; Normal game logic...
    jmp main_loop

@game_over_loop:
    ; Freeze - game is over
    jmp @game_over_loop

The game stops. The player sees their final position.

The Code

; =============================================================================
; NEON NEXUS - Unit 10: Lives and Death
; =============================================================================
; Add lives system with death and respawn.
; =============================================================================

; -----------------------------------------------------------------------------
; NES Hardware Addresses
; -----------------------------------------------------------------------------
PPUCTRL   = $2000
PPUMASK   = $2001
PPUSTATUS = $2002
OAMADDR   = $2003
PPUSCROLL = $2005
PPUADDR   = $2006
PPUDATA   = $2007
OAMDMA    = $4014

JOYPAD1   = $4016
JOYPAD2   = $4017

; Controller buttons
BTN_A      = %10000000
BTN_B      = %01000000
BTN_SELECT = %00100000
BTN_START  = %00010000
BTN_UP     = %00001000
BTN_DOWN   = %00000100
BTN_LEFT   = %00000010
BTN_RIGHT  = %00000001

; -----------------------------------------------------------------------------
; Game Constants
; -----------------------------------------------------------------------------
PLAYER_START_X  = 124
PLAYER_START_Y  = 116
PLAYER_SPEED    = 2
ENEMY_SPEED     = 1

NUM_ENEMIES     = 4
STARTING_LIVES  = 3
COLLISION_DIST  = 6
INVULN_TIME     = 90      ; 1.5 seconds of invulnerability

; Tile indices
TILE_EMPTY     = 0
TILE_BORDER    = 1
TILE_FLOOR     = 2
TILE_CORNER_TL = 3
TILE_CORNER_TR = 4
TILE_CORNER_BL = 5
TILE_CORNER_BR = 6

SPRITE_PLAYER  = 7
SPRITE_ENEMY   = 8
SPRITE_LIFE    = 9        ; Life icon

; Arena boundaries
ARENA_LEFT   = 16
ARENA_RIGHT  = 232
ARENA_TOP    = 24         ; Leave room for HUD
ARENA_BOTTOM = 208

DIR_RIGHT = 1
DIR_LEFT  = $FF
DIR_DOWN  = 1
DIR_UP    = $FF

BG_COLOUR = $0F

; -----------------------------------------------------------------------------
; Memory Layout
; -----------------------------------------------------------------------------
.segment "ZEROPAGE"
player_x:       .res 1
player_y:       .res 1
buttons:        .res 1
temp:           .res 1
row_counter:    .res 1
frame_count:    .res 1
lives:          .res 1
invuln_timer:   .res 1    ; Invulnerability countdown
game_over:      .res 1    ; Non-zero when game is over

enemy_x:        .res NUM_ENEMIES
enemy_y:        .res NUM_ENEMIES
enemy_dir_x:    .res NUM_ENEMIES
enemy_dir_y:    .res NUM_ENEMIES

.segment "OAM"
oam_buffer:     .res 256

.segment "BSS"

; -----------------------------------------------------------------------------
; iNES Header
; -----------------------------------------------------------------------------
.segment "HEADER"
    .byte "NES", $1A
    .byte 2
    .byte 1
    .byte $01
    .byte $00
    .byte 0,0,0,0,0,0,0,0

; -----------------------------------------------------------------------------
; Code
; -----------------------------------------------------------------------------
.segment "CODE"

reset:
    sei
    cld
    ldx #$40
    stx $4017
    ldx #$FF
    txs
    inx
    stx PPUCTRL
    stx PPUMASK
    stx $4010

@vblank1:
    bit PPUSTATUS
    bpl @vblank1

    lda #0
@clear_ram:
    sta $0000, x
    sta $0100, x
    sta $0200, x
    sta $0300, x
    sta $0400, x
    sta $0500, x
    sta $0600, x
    sta $0700, x
    inx
    bne @clear_ram

@vblank2:
    bit PPUSTATUS
    bpl @vblank2

    jsr load_palette
    jsr draw_arena
    jsr set_attributes
    jsr init_game

    ; Hide all sprites initially
    lda #$FF
    ldx #0
@hide_all:
    sta oam_buffer, x
    inx
    bne @hide_all

    jsr update_all_sprites

    lda #0
    sta PPUSCROLL
    sta PPUSCROLL
    sta frame_count

    lda #%10000000
    sta PPUCTRL
    lda #%00011110
    sta PPUMASK

main_loop:
    lda game_over
    bne @game_over_loop

    jsr read_controller
    jsr move_player
    jsr move_enemies
    jsr check_collisions
    jsr update_all_sprites
    jmp main_loop

@game_over_loop:
    ; Game over - just loop (player can see final state)
    jmp @game_over_loop

; -----------------------------------------------------------------------------
; Initialise Game
; -----------------------------------------------------------------------------
init_game:
    lda #STARTING_LIVES
    sta lives
    lda #0
    sta game_over
    sta invuln_timer

    lda #PLAYER_START_X
    sta player_x
    lda #PLAYER_START_Y
    sta player_y

    jsr init_enemies
    rts

; -----------------------------------------------------------------------------
; Initialise Enemies
; -----------------------------------------------------------------------------
init_enemies:
    lda #48
    sta enemy_x+0
    lda #48
    sta enemy_y+0
    lda #DIR_RIGHT
    sta enemy_dir_x+0
    lda #DIR_DOWN
    sta enemy_dir_y+0

    lda #200
    sta enemy_x+1
    lda #48
    sta enemy_y+1
    lda #DIR_LEFT
    sta enemy_dir_x+1
    lda #DIR_DOWN
    sta enemy_dir_y+1

    lda #48
    sta enemy_x+2
    lda #176
    sta enemy_y+2
    lda #DIR_RIGHT
    sta enemy_dir_x+2
    lda #DIR_UP
    sta enemy_dir_y+2

    lda #200
    sta enemy_x+3
    lda #176
    sta enemy_y+3
    lda #DIR_LEFT
    sta enemy_dir_x+3
    lda #DIR_UP
    sta enemy_dir_y+3
    rts

; -----------------------------------------------------------------------------
; Check Collisions
; -----------------------------------------------------------------------------
check_collisions:
    ; Skip if invulnerable
    lda invuln_timer
    beq @check
    dec invuln_timer
    rts

@check:
    ldx #0
@check_enemy:
    lda player_x
    sec
    sbc enemy_x, x
    bpl @check_x_pos
    eor #$FF
    clc
    adc #1
@check_x_pos:
    cmp #COLLISION_DIST
    bcs @next_enemy

    lda player_y
    sec
    sbc enemy_y, x
    bpl @check_y_pos
    eor #$FF
    clc
    adc #1
@check_y_pos:
    cmp #COLLISION_DIST
    bcs @next_enemy

    ; Collision! Lose a life
    jsr player_hit
    rts

@next_enemy:
    inx
    cpx #NUM_ENEMIES
    bne @check_enemy
    rts

; -----------------------------------------------------------------------------
; Player Hit - Lose life and respawn
; -----------------------------------------------------------------------------
player_hit:
    dec lives
    lda lives
    beq @game_over

    ; Respawn at start position
    lda #PLAYER_START_X
    sta player_x
    lda #PLAYER_START_Y
    sta player_y

    ; Start invulnerability
    lda #INVULN_TIME
    sta invuln_timer
    rts

@game_over:
    lda #1
    sta game_over
    rts

; -----------------------------------------------------------------------------
; Update All Sprites
; -----------------------------------------------------------------------------
update_all_sprites:
    jsr update_player_sprite
    jsr update_enemy_sprites
    jsr update_lives_display
    rts

; -----------------------------------------------------------------------------
; Update Player Sprite
; -----------------------------------------------------------------------------
update_player_sprite:
    ; Check if game over
    lda game_over
    beq @alive
    ; Hide player
    lda #$FF
    sta oam_buffer+0
    rts

@alive:
    ; Check invulnerability flash
    lda invuln_timer
    beq @no_flash
    and #%00000100
    beq @show
    ; Hide during flash
    lda #$FF
    sta oam_buffer+0
    rts

@show:
@no_flash:
    lda player_y
    sta oam_buffer+0
    lda #SPRITE_PLAYER
    sta oam_buffer+1
    lda #0
    sta oam_buffer+2
    lda player_x
    sta oam_buffer+3
    rts

; -----------------------------------------------------------------------------
; Update Enemy Sprites
; -----------------------------------------------------------------------------
update_enemy_sprites:
    ldx #0
    ldy #4              ; Start after player sprite

@loop:
    lda enemy_y, x
    sta oam_buffer, y
    iny
    lda #SPRITE_ENEMY
    sta oam_buffer, y
    iny
    lda #%00000001
    sta oam_buffer, y
    iny
    lda enemy_x, x
    sta oam_buffer, y
    iny
    inx
    cpx #NUM_ENEMIES
    bne @loop
    rts

; -----------------------------------------------------------------------------
; Update Lives Display - Show life icons at top of screen
; -----------------------------------------------------------------------------
update_lives_display:
    ; OAM slots 20-31 for lives display (up to 3 lives)
    ldy #20             ; OAM offset

    ldx lives
    beq @hide_all_lives

    ; Show life 1
    lda #8              ; Y position (top of screen)
    sta oam_buffer, y
    iny
    lda #SPRITE_LIFE
    sta oam_buffer, y
    iny
    lda #0
    sta oam_buffer, y
    iny
    lda #16             ; X position
    sta oam_buffer, y
    iny

    cpx #1
    beq @hide_rest

    ; Show life 2
    lda #8
    sta oam_buffer, y
    iny
    lda #SPRITE_LIFE
    sta oam_buffer, y
    iny
    lda #0
    sta oam_buffer, y
    iny
    lda #26
    sta oam_buffer, y
    iny

    cpx #2
    beq @hide_rest

    ; Show life 3
    lda #8
    sta oam_buffer, y
    iny
    lda #SPRITE_LIFE
    sta oam_buffer, y
    iny
    lda #0
    sta oam_buffer, y
    iny
    lda #36
    sta oam_buffer, y
    iny
    rts

@hide_rest:
    ; Hide remaining life slots
@hide_loop:
    cpy #32
    bcs @done
    lda #$FF
    sta oam_buffer, y
    iny
    iny
    iny
    iny
    jmp @hide_loop

@hide_all_lives:
    ldy #20
    jmp @hide_loop

@done:
    rts

; -----------------------------------------------------------------------------
; Move Enemies
; -----------------------------------------------------------------------------
move_enemies:
    ldx #0

@enemy_loop:
    lda enemy_x, x
    clc
    adc enemy_dir_x, x
    sta enemy_x, x

    cmp #ARENA_LEFT
    bcs @check_right
    lda #DIR_RIGHT
    sta enemy_dir_x, x
    lda #ARENA_LEFT
    sta enemy_x, x
    jmp @move_y

@check_right:
    cmp #ARENA_RIGHT
    bcc @move_y
    lda #DIR_LEFT
    sta enemy_dir_x, x
    lda #ARENA_RIGHT
    sec
    sbc #1
    sta enemy_x, x

@move_y:
    lda enemy_y, x
    clc
    adc enemy_dir_y, x
    sta enemy_y, x

    cmp #ARENA_TOP
    bcs @check_bottom
    lda #DIR_DOWN
    sta enemy_dir_y, x
    lda #ARENA_TOP
    sta enemy_y, x
    jmp @next_enemy

@check_bottom:
    cmp #ARENA_BOTTOM
    bcc @next_enemy
    lda #DIR_UP
    sta enemy_dir_y, x
    lda #ARENA_BOTTOM
    sec
    sbc #1
    sta enemy_y, x

@next_enemy:
    inx
    cpx #NUM_ENEMIES
    bne @enemy_loop
    rts

; -----------------------------------------------------------------------------
; Load Palette
; -----------------------------------------------------------------------------
load_palette:
    bit PPUSTATUS
    lda #$3F
    sta PPUADDR
    lda #$00
    sta PPUADDR
    ldx #0
@loop:
    lda palette_data, x
    sta PPUDATA
    inx
    cpx #32
    bne @loop
    rts

; -----------------------------------------------------------------------------
; Draw Arena
; -----------------------------------------------------------------------------
draw_arena:
    bit PPUSTATUS
    lda #$20
    sta PPUADDR
    lda #$00
    sta PPUADDR

    lda #0
    sta row_counter

@draw_row:
    lda row_counter
    cmp #0
    beq @top_row
    cmp #1
    beq @top_row
    cmp #28
    beq @bottom_row
    cmp #29
    beq @bottom_row
    jmp @middle_row

@top_row:
    lda row_counter
    cmp #0
    bne @top_row_inner
    lda #TILE_CORNER_TL
    sta PPUDATA
    lda #TILE_BORDER
    ldx #30
@top_fill:
    sta PPUDATA
    dex
    bne @top_fill
    lda #TILE_CORNER_TR
    sta PPUDATA
    jmp @next_row

@top_row_inner:
    lda #TILE_BORDER
    ldx #32
@top_inner_fill:
    sta PPUDATA
    dex
    bne @top_inner_fill
    jmp @next_row

@bottom_row:
    lda row_counter
    cmp #29
    bne @bottom_row_inner
    lda #TILE_CORNER_BL
    sta PPUDATA
    lda #TILE_BORDER
    ldx #30
@bottom_fill:
    sta PPUDATA
    dex
    bne @bottom_fill
    lda #TILE_CORNER_BR
    sta PPUDATA
    jmp @next_row

@bottom_row_inner:
    lda #TILE_BORDER
    ldx #32
@bottom_inner_fill:
    sta PPUDATA
    dex
    bne @bottom_inner_fill
    jmp @next_row

@middle_row:
    lda #TILE_BORDER
    sta PPUDATA
    sta PPUDATA
    lda #TILE_FLOOR
    ldx #28
@floor_fill:
    sta PPUDATA
    dex
    bne @floor_fill
    lda #TILE_BORDER
    sta PPUDATA
    sta PPUDATA

@next_row:
    inc row_counter
    lda row_counter
    cmp #30
    beq @done_drawing
    jmp @draw_row

@done_drawing:
    rts

; -----------------------------------------------------------------------------
; Set Attribute Table
; -----------------------------------------------------------------------------
set_attributes:
    bit PPUSTATUS
    lda #$23
    sta PPUADDR
    lda #$C0
    sta PPUADDR

    ldx #8
    lda #$00
@attr_top:
    sta PPUDATA
    dex
    bne @attr_top

    ldx #6
@attr_floor:
    lda #$00
    sta PPUDATA
    lda #%01010101
    sta PPUDATA
    sta PPUDATA
    sta PPUDATA
    sta PPUDATA
    sta PPUDATA
    sta PPUDATA
    lda #$00
    sta PPUDATA
    dex
    bne @attr_floor

    ldx #8
    lda #$00
@attr_bottom:
    sta PPUDATA
    dex
    bne @attr_bottom
    rts

; -----------------------------------------------------------------------------
; Read Controller
; -----------------------------------------------------------------------------
read_controller:
    lda #1
    sta JOYPAD1
    lda #0
    sta JOYPAD1
    ldx #8
@read_loop:
    lda JOYPAD1
    lsr a
    rol buttons
    dex
    bne @read_loop
    rts

; -----------------------------------------------------------------------------
; Move Player
; -----------------------------------------------------------------------------
move_player:
    lda buttons
    and #BTN_UP
    beq @check_down
    lda player_y
    sec
    sbc #PLAYER_SPEED
    cmp #ARENA_TOP
    bcc @check_down
    sta player_y

@check_down:
    lda buttons
    and #BTN_DOWN
    beq @check_left
    lda player_y
    clc
    adc #PLAYER_SPEED
    cmp #ARENA_BOTTOM
    bcs @check_left
    sta player_y

@check_left:
    lda buttons
    and #BTN_LEFT
    beq @check_right
    lda player_x
    sec
    sbc #PLAYER_SPEED
    cmp #ARENA_LEFT
    bcc @check_right
    sta player_x

@check_right:
    lda buttons
    and #BTN_RIGHT
    beq @done
    lda player_x
    clc
    adc #PLAYER_SPEED
    cmp #ARENA_RIGHT
    bcs @done
    sta player_x

@done:
    rts

; === NMI ===
nmi:
    pha
    txa
    pha
    tya
    pha

    lda #0
    sta OAMADDR
    lda #>oam_buffer
    sta OAMDMA

    inc frame_count

    lda #0
    sta PPUSCROLL
    sta PPUSCROLL

    pla
    tay
    pla
    tax
    pla
    rti

irq:
    rti

; -----------------------------------------------------------------------------
; Data
; -----------------------------------------------------------------------------
palette_data:
    .byte BG_COLOUR, $11, $21, $31
    .byte BG_COLOUR, $13, $23, $33
    .byte BG_COLOUR, $19, $29, $39
    .byte BG_COLOUR, $16, $26, $36
    .byte BG_COLOUR, $30, $27, $17    ; Player + lives
    .byte BG_COLOUR, $16, $26, $36    ; Enemies
    .byte BG_COLOUR, $30, $27, $17
    .byte BG_COLOUR, $30, $27, $17

; -----------------------------------------------------------------------------
; Vectors
; -----------------------------------------------------------------------------
.segment "VECTORS"
    .word nmi
    .word reset
    .word irq

; -----------------------------------------------------------------------------
; CHR-ROM
; -----------------------------------------------------------------------------
.segment "CHARS"

; Tile 0: Empty
.byte $00,$00,$00,$00,$00,$00,$00,$00
.byte $00,$00,$00,$00,$00,$00,$00,$00

; Tile 1: Border
.byte %11111111,%10000001,%10000001,%11111111
.byte %11111111,%00010001,%00010001,%11111111
.byte %00000000,%01111110,%01111110,%00000000
.byte %00000000,%11101110,%11101110,%00000000

; Tile 2: Floor
.byte %00000000,%00000000,%00000000,%00000000
.byte %00000000,%00000000,%00000000,%10000001
.byte %00000000,%00000000,%00000000,%00000000
.byte %00000000,%00000000,%00000000,%00000000

; Tile 3: Corner TL
.byte %11111111,%11000000,%10100000,%10010000
.byte %10001000,%10000100,%10000010,%10000001
.byte %00000000,%00111111,%01011111,%01101111
.byte %01110111,%01111011,%01111101,%01111110

; Tile 4: Corner TR
.byte %11111111,%00000011,%00000101,%00001001
.byte %00010001,%00100001,%01000001,%10000001
.byte %00000000,%11111100,%11111010,%11110110
.byte %11101110,%11011110,%10111110,%01111110

; Tile 5: Corner BL
.byte %10000001,%10000010,%10000100,%10001000
.byte %10010000,%10100000,%11000000,%11111111
.byte %01111110,%01111101,%01111011,%01110111
.byte %01101111,%01011111,%00111111,%00000000

; Tile 6: Corner BR
.byte %10000001,%01000001,%00100001,%00010001
.byte %00001001,%00000101,%00000011,%11111111
.byte %01111110,%10111110,%11011110,%11101110
.byte %11110110,%11111010,%11111100,%00000000

; Tile 7: Player
.byte %00011000,%00011000,%00111100,%01111110
.byte %11111111,%10111101,%00100100,%00100100
.byte %00000000,%00011000,%00011000,%00111100
.byte %01000010,%01000010,%00011000,%00000000

; Tile 8: Enemy
.byte %00011000,%00111100,%01111110,%11111111
.byte %11111111,%01111110,%00111100,%00011000
.byte %00000000,%00011000,%00100100,%01000010
.byte %01000010,%00100100,%00011000,%00000000

; Tile 9: Life icon (small heart/ship)
.byte %00000000,%00100100,%01111110,%01111110
.byte %00111100,%00011000,%00000000,%00000000
.byte %00000000,%00000000,%00000000,%00100100
.byte %00011000,%00000000,%00000000,%00000000

; Fill rest
.res 8192 - 160, $00

Build It

ca65 nexus.asm -o nexus.o
ld65 -C nes.cfg nexus.o -o nexus.nes

Die three times and it’s over. The game now has stakes.

Death is the stick. Unit 11 adds the carrot: collectibles.

What Changed

Unit 9 → Unit 10

+274-151

1	1		`; =============================================================================`
2		-	`; NEON NEXUS - Unit 9: Collision Detection`
	2	+	`; NEON NEXUS - Unit 10: Lives and Death`
3	3		`; =============================================================================`
4		-	`; Detect when player touches enemies. Visual feedback on collision.`
	4	+	`; Add lives system with death and respawn.`
5	5		`; =============================================================================`
6	6
7	7		`; -----------------------------------------------------------------------------`
			...
32	32		`; -----------------------------------------------------------------------------`
33	33		`; Game Constants`
34	34		`; -----------------------------------------------------------------------------`
35		-	`PLAYER_START_X = 124`
36		-	`PLAYER_START_Y = 116`
37		-	`PLAYER_SPEED = 2`
38		-	`ENEMY_SPEED = 1`
	35	+	`PLAYER_START_X = 124`
	36	+	`PLAYER_START_Y = 116`
	37	+	`PLAYER_SPEED = 2`
	38	+	`ENEMY_SPEED = 1`
39	39
40		-	`NUM_ENEMIES = 4`
41		-	`SPRITE_SIZE = 8 ; 8x8 pixel sprites`
42		-	`COLLISION_DIST = 6 ; Overlap distance for collision`
	40	+	`NUM_ENEMIES = 4`
	41	+	`STARTING_LIVES = 3`
	42	+	`COLLISION_DIST = 6`
	43	+	`INVULN_TIME = 90 ; 1.5 seconds of invulnerability`
43	44
44	45		`; Tile indices`
45	46		`TILE_EMPTY = 0`
			...
52	53
53	54		`SPRITE_PLAYER = 7`
54	55		`SPRITE_ENEMY = 8`
	56	+	`SPRITE_LIFE = 9 ; Life icon`
55	57
56	58		`; Arena boundaries`
57	59		`ARENA_LEFT = 16`
58	60		`ARENA_RIGHT = 232`
59		-	`ARENA_TOP = 16`
	61	+	`ARENA_TOP = 24 ; Leave room for HUD`
60	62		`ARENA_BOTTOM = 208`
61	63
62	64		`DIR_RIGHT = 1`
			...
70	72		`; Memory Layout`
71	73		`; -----------------------------------------------------------------------------`
72	74		`.segment "ZEROPAGE"`
73		-	`player_x: .res 1`
74		-	`player_y: .res 1`
75		-	`buttons: .res 1`
76		-	`temp: .res 1`
77		-	`temp2: .res 1`
78		-	`row_counter: .res 1`
79		-	`frame_count: .res 1`
80		-	`collision_flag: .res 1 ; Non-zero if collision detected`
81		-	`flash_timer: .res 1 ; Timer for visual feedback`
	75	+	`player_x: .res 1`
	76	+	`player_y: .res 1`
	77	+	`buttons: .res 1`
	78	+	`temp: .res 1`
	79	+	`row_counter: .res 1`
	80	+	`frame_count: .res 1`
	81	+	`lives: .res 1`
	82	+	`invuln_timer: .res 1 ; Invulnerability countdown`
	83	+	`game_over: .res 1 ; Non-zero when game is over`
82	84
83		-	`enemy_x: .res NUM_ENEMIES`
84		-	`enemy_y: .res NUM_ENEMIES`
85		-	`enemy_dir_x: .res NUM_ENEMIES`
86		-	`enemy_dir_y: .res NUM_ENEMIES`
	85	+	`enemy_x: .res NUM_ENEMIES`
	86	+	`enemy_y: .res NUM_ENEMIES`
	87	+	`enemy_dir_x: .res NUM_ENEMIES`
	88	+	`enemy_dir_y: .res NUM_ENEMIES`
87	89
88	90		`.segment "OAM"`
89		-	`oam_buffer: .res 256`
	91	+	`oam_buffer: .res 256`
90	92
91	93		`.segment "BSS"`
92	94
			...
142	144		`jsr load_palette`
143	145		`jsr draw_arena`
144	146		`jsr set_attributes`
145		-	`jsr init_enemies`
146		-
147		-	`lda #PLAYER_START_X`
148		-	`sta player_x`
149		-	`lda #PLAYER_START_Y`
150		-	`sta player_y`
151		-
152		-	`lda #0`
153		-	`sta collision_flag`
154		-	`sta flash_timer`
155		-
156		-	`; Player sprite`
157		-	`lda player_y`
158		-	`sta oam_buffer+0`
159		-	`lda #SPRITE_PLAYER`
160		-	`sta oam_buffer+1`
161		-	`lda #0`
162		-	`sta oam_buffer+2`
163		-	`lda player_x`
164		-	`sta oam_buffer+3`
165		-
166		-	`jsr update_enemy_sprites`
	147	+	`jsr init_game`
167	148
168		-	`; Hide remaining sprites`
	149	+	`; Hide all sprites initially`
169	150		`lda #$FF`
170		-	`ldx #20`
171		-	`@hide_sprites:`
	151	+	`ldx #0`
	152	+	`@hide_all:`
172	153		`sta oam_buffer, x`
173	154		`inx`
174		-	`bne @hide_sprites`
	155	+	`bne @hide_all`
	156	+
	157	+	`jsr update_all_sprites`
175	158
176	159		`lda #0`
177	160		`sta PPUSCROLL`
			...
184	167		`sta PPUMASK`
185	168
186	169		`main_loop:`
	170	+	`lda game_over`
	171	+	`bne @game_over_loop`
	172	+
187	173		`jsr read_controller`
188	174		`jsr move_player`
189	175		`jsr move_enemies`
190	176		`jsr check_collisions`
191		-	`jsr update_player_sprite`
192		-	`jsr update_enemy_sprites`
	177	+	`jsr update_all_sprites`
193	178		`jmp main_loop`
	179	+
	180	+	`@game_over_loop:`
	181	+	`; Game over - just loop (player can see final state)`
	182	+	`jmp @game_over_loop`
194	183
195	184		`; -----------------------------------------------------------------------------`
196		-	`; Check Collisions - Player vs all enemies`
	185	+	`; Initialise Game`
197	186		`; -----------------------------------------------------------------------------`
198		-	`check_collisions:`
	187	+	`init_game:`
	188	+	`lda #STARTING_LIVES`
	189	+	`sta lives`
199	190		`lda #0`
200		-	`sta collision_flag`
	191	+	`sta game_over`
	192	+	`sta invuln_timer`
	193	+
	194	+	`lda #PLAYER_START_X`
	195	+	`sta player_x`
	196	+	`lda #PLAYER_START_Y`
	197	+	`sta player_y`
	198	+
	199	+	`jsr init_enemies`
	200	+	`rts`
	201	+
	202	+	`; -----------------------------------------------------------------------------`
	203	+	`; Initialise Enemies`
	204	+	`; -----------------------------------------------------------------------------`
	205	+	`init_enemies:`
	206	+	`lda #48`
	207	+	`sta enemy_x+0`
	208	+	`lda #48`
	209	+	`sta enemy_y+0`
	210	+	`lda #DIR_RIGHT`
	211	+	`sta enemy_dir_x+0`
	212	+	`lda #DIR_DOWN`
	213	+	`sta enemy_dir_y+0`
	214	+
	215	+	`lda #200`
	216	+	`sta enemy_x+1`
	217	+	`lda #48`
	218	+	`sta enemy_y+1`
	219	+	`lda #DIR_LEFT`
	220	+	`sta enemy_dir_x+1`
	221	+	`lda #DIR_DOWN`
	222	+	`sta enemy_dir_y+1`
	223	+
	224	+	`lda #48`
	225	+	`sta enemy_x+2`
	226	+	`lda #176`
	227	+	`sta enemy_y+2`
	228	+	`lda #DIR_RIGHT`
	229	+	`sta enemy_dir_x+2`
	230	+	`lda #DIR_UP`
	231	+	`sta enemy_dir_y+2`
	232	+
	233	+	`lda #200`
	234	+	`sta enemy_x+3`
	235	+	`lda #176`
	236	+	`sta enemy_y+3`
	237	+	`lda #DIR_LEFT`
	238	+	`sta enemy_dir_x+3`
	239	+	`lda #DIR_UP`
	240	+	`sta enemy_dir_y+3`
	241	+	`rts`
	242	+
	243	+	`; -----------------------------------------------------------------------------`
	244	+	`; Check Collisions`
	245	+	`; -----------------------------------------------------------------------------`
	246	+	`check_collisions:`
	247	+	`; Skip if invulnerable`
	248	+	`lda invuln_timer`
	249	+	`beq @check`
	250	+	`dec invuln_timer`
	251	+	`rts`
201	252
	253	+	`@check:`
202	254		`ldx #0`
203	255		`@check_enemy:`
204		-	`; Check X overlap`
205		-	`; \|player_x - enemy_x\| < COLLISION_DIST`
206	256		`lda player_x`
207	257		`sec`
208	258		`sbc enemy_x, x`
209		-	`bpl @check_x_positive`
210		-	`; Negative - negate it`
	259	+	`bpl @check_x_pos`
211	260		`eor #$FF`
212	261		`clc`
213	262		`adc #1`
214		-	`@check_x_positive:`
	263	+	`@check_x_pos:`
215	264		`cmp #COLLISION_DIST`
216		-	`bcs @next_enemy ; No X overlap`
	265	+	`bcs @next_enemy`
217	266
218		-	`; Check Y overlap`
219	267		`lda player_y`
220	268		`sec`
221	269		`sbc enemy_y, x`
222		-	`bpl @check_y_positive`
	270	+	`bpl @check_y_pos`
223	271		`eor #$FF`
224	272		`clc`
225	273		`adc #1`
226		-	`@check_y_positive:`
	274	+	`@check_y_pos:`
227	275		`cmp #COLLISION_DIST`
228		-	`bcs @next_enemy ; No Y overlap`
	276	+	`bcs @next_enemy`
229	277
230		-	`; Collision detected!`
231		-	`lda #1`
232		-	`sta collision_flag`
233		-	`lda #30 ; Flash for 30 frames`
234		-	`sta flash_timer`
235		-	`rts ; Exit early on first collision`
	278	+	`; Collision! Lose a life`
	279	+	`jsr player_hit`
	280	+	`rts`
236	281
237	282		`@next_enemy:`
238	283		`inx`
			...
241	286		`rts`
242	287
243	288		`; -----------------------------------------------------------------------------`
244		-	`; Update Player Sprite - Flash when hit`
	289	+	`; Player Hit - Lose life and respawn`
	290	+	`; -----------------------------------------------------------------------------`
	291	+	`player_hit:`
	292	+	`dec lives`
	293	+	`lda lives`
	294	+	`beq @game_over`
	295	+
	296	+	`; Respawn at start position`
	297	+	`lda #PLAYER_START_X`
	298	+	`sta player_x`
	299	+	`lda #PLAYER_START_Y`
	300	+	`sta player_y`
	301	+
	302	+	`; Start invulnerability`
	303	+	`lda #INVULN_TIME`
	304	+	`sta invuln_timer`
	305	+	`rts`
	306	+
	307	+	`@game_over:`
	308	+	`lda #1`
	309	+	`sta game_over`
	310	+	`rts`
	311	+
	312	+	`; -----------------------------------------------------------------------------`
	313	+	`; Update All Sprites`
	314	+	`; -----------------------------------------------------------------------------`
	315	+	`update_all_sprites:`
	316	+	`jsr update_player_sprite`
	317	+	`jsr update_enemy_sprites`
	318	+	`jsr update_lives_display`
	319	+	`rts`
	320	+
	321	+	`; -----------------------------------------------------------------------------`
	322	+	`; Update Player Sprite`
245	323		`; -----------------------------------------------------------------------------`
246	324		`update_player_sprite:`
247		-	`; Update position`
248		-	`lda player_y`
	325	+	`; Check if game over`
	326	+	`lda game_over`
	327	+	`beq @alive`
	328	+	`; Hide player`
	329	+	`lda #$FF`
249	330		`sta oam_buffer+0`
250		-	`lda player_x`
251		-	`sta oam_buffer+3`
	331	+	`rts`
252	332
253		-	`; Check if flashing`
254		-	`lda flash_timer`
	333	+	`@alive:`
	334	+	`; Check invulnerability flash`
	335	+	`lda invuln_timer`
255	336		`beq @no_flash`
256		-
257		-	`; Decrement timer`
258		-	`dec flash_timer`
259		-
260		-	`; Flash by toggling visibility every 4 frames`
261	337		`and #%00000100`
262		-	`beq @show_player`
263		-	`; Hide player (move off screen)`
	338	+	`beq @show`
	339	+	`; Hide during flash`
264	340		`lda #$FF`
265	341		`sta oam_buffer+0`
266	342		`rts`
267	343
268		-	`@show_player:`
	344	+	`@show:`
	345	+	`@no_flash:`
269	346		`lda player_y`
270	347		`sta oam_buffer+0`
	348	+	`lda #SPRITE_PLAYER`
	349	+	`sta oam_buffer+1`
	350	+	`lda #0`
	351	+	`sta oam_buffer+2`
	352	+	`lda player_x`
	353	+	`sta oam_buffer+3`
271	354		`rts`
272	355
273		-	`@no_flash:`
	356	+	`; -----------------------------------------------------------------------------`
	357	+	`; Update Enemy Sprites`
	358	+	`; -----------------------------------------------------------------------------`
	359	+	`update_enemy_sprites:`
	360	+	`ldx #0`
	361	+	`ldy #4 ; Start after player sprite`
	362	+
	363	+	`@loop:`
	364	+	`lda enemy_y, x`
	365	+	`sta oam_buffer, y`
	366	+	`iny`
	367	+	`lda #SPRITE_ENEMY`
	368	+	`sta oam_buffer, y`
	369	+	`iny`
	370	+	`lda #%00000001`
	371	+	`sta oam_buffer, y`
	372	+	`iny`
	373	+	`lda enemy_x, x`
	374	+	`sta oam_buffer, y`
	375	+	`iny`
	376	+	`inx`
	377	+	`cpx #NUM_ENEMIES`
	378	+	`bne @loop`
274	379		`rts`
275	380
276	381		`; -----------------------------------------------------------------------------`
277		-	`; Initialise Enemies`
	382	+	`; Update Lives Display - Show life icons at top of screen`
278	383		`; -----------------------------------------------------------------------------`
279		-	`init_enemies:`
280		-	`lda #48`
281		-	`sta enemy_x+0`
282		-	`lda #48`
283		-	`sta enemy_y+0`
284		-	`lda #DIR_RIGHT`
285		-	`sta enemy_dir_x+0`
286		-	`lda #DIR_DOWN`
287		-	`sta enemy_dir_y+0`
	384	+	`update_lives_display:`
	385	+	`; OAM slots 20-31 for lives display (up to 3 lives)`
	386	+	`ldy #20 ; OAM offset`
288	387
289		-	`lda #200`
290		-	`sta enemy_x+1`
291		-	`lda #48`
292		-	`sta enemy_y+1`
293		-	`lda #DIR_LEFT`
294		-	`sta enemy_dir_x+1`
295		-	`lda #DIR_DOWN`
296		-	`sta enemy_dir_y+1`
	388	+	`ldx lives`
	389	+	`beq @hide_all_lives`
297	390
298		-	`lda #48`
299		-	`sta enemy_x+2`
300		-	`lda #176`
301		-	`sta enemy_y+2`
302		-	`lda #DIR_RIGHT`
303		-	`sta enemy_dir_x+2`
304		-	`lda #DIR_UP`
305		-	`sta enemy_dir_y+2`
	391	+	`; Show life 1`
	392	+	`lda #8 ; Y position (top of screen)`
	393	+	`sta oam_buffer, y`
	394	+	`iny`
	395	+	`lda #SPRITE_LIFE`
	396	+	`sta oam_buffer, y`
	397	+	`iny`
	398	+	`lda #0`
	399	+	`sta oam_buffer, y`
	400	+	`iny`
	401	+	`lda #16 ; X position`
	402	+	`sta oam_buffer, y`
	403	+	`iny`
306	404
307		-	`lda #200`
308		-	`sta enemy_x+3`
309		-	`lda #176`
310		-	`sta enemy_y+3`
311		-	`lda #DIR_LEFT`
312		-	`sta enemy_dir_x+3`
313		-	`lda #DIR_UP`
314		-	`sta enemy_dir_y+3`
	405	+	`cpx #1`
	406	+	`beq @hide_rest`
	407	+
	408	+	`; Show life 2`
	409	+	`lda #8`
	410	+	`sta oam_buffer, y`
	411	+	`iny`
	412	+	`lda #SPRITE_LIFE`
	413	+	`sta oam_buffer, y`
	414	+	`iny`
	415	+	`lda #0`
	416	+	`sta oam_buffer, y`
	417	+	`iny`
	418	+	`lda #26`
	419	+	`sta oam_buffer, y`
	420	+	`iny`
	421	+
	422	+	`cpx #2`
	423	+	`beq @hide_rest`
	424	+
	425	+	`; Show life 3`
	426	+	`lda #8`
	427	+	`sta oam_buffer, y`
	428	+	`iny`
	429	+	`lda #SPRITE_LIFE`
	430	+	`sta oam_buffer, y`
	431	+	`iny`
	432	+	`lda #0`
	433	+	`sta oam_buffer, y`
	434	+	`iny`
	435	+	`lda #36`
	436	+	`sta oam_buffer, y`
	437	+	`iny`
	438	+	`rts`
	439	+
	440	+	`@hide_rest:`
	441	+	`; Hide remaining life slots`
	442	+	`@hide_loop:`
	443	+	`cpy #32`
	444	+	`bcs @done`
	445	+	`lda #$FF`
	446	+	`sta oam_buffer, y`
	447	+	`iny`
	448	+	`iny`
	449	+	`iny`
	450	+	`iny`
	451	+	`jmp @hide_loop`
	452	+
	453	+	`@hide_all_lives:`
	454	+	`ldy #20`
	455	+	`jmp @hide_loop`
315	456
	457	+	`@done:`
316	458		`rts`
317	459
318	460		`; -----------------------------------------------------------------------------`
			...
373	515		`inx`
374	516		`cpx #NUM_ENEMIES`
375	517		`bne @enemy_loop`
376		-	`rts`
377		-
378		-	`; -----------------------------------------------------------------------------`
379		-	`; Update Enemy Sprites`
380		-	`; -----------------------------------------------------------------------------`
381		-	`update_enemy_sprites:`
382		-	`ldx #0`
383		-	`ldy #4`
384		-
385		-	`@loop:`
386		-	`lda enemy_y, x`
387		-	`sta oam_buffer, y`
388		-	`iny`
389		-	`lda #SPRITE_ENEMY`
390		-	`sta oam_buffer, y`
391		-	`iny`
392		-	`lda #%00000001`
393		-	`sta oam_buffer, y`
394		-	`iny`
395		-	`lda enemy_x, x`
396		-	`sta oam_buffer, y`
397		-	`iny`
398		-	`inx`
399		-	`cpx #NUM_ENEMIES`
400		-	`bne @loop`
401	518		`rts`
402	519
403	520		`; -----------------------------------------------------------------------------`
			...
535	652		`bne @attr_top`
536	653
537	654		`ldx #6`
538		-	`@attr_floor_rows:`
	655	+	`@attr_floor:`
539	656		`lda #$00`
540	657		`sta PPUDATA`
541	658		`lda #%01010101`
			...
548	665		`lda #$00`
549	666		`sta PPUDATA`
550	667		`dex`
551		-	`bne @attr_floor_rows`
	668	+	`bne @attr_floor`
552	669
553	670		`ldx #8`
554	671		`lda #$00`
			...
661	778		`.byte BG_COLOUR, $11, $21, $31`
662	779		`.byte BG_COLOUR, $13, $23, $33`
663	780		`.byte BG_COLOUR, $19, $29, $39`
664		-	`.byte BG_COLOUR, $16, $26, $36`
665		-	`.byte BG_COLOUR, $30, $27, $17`
666	781		`.byte BG_COLOUR, $16, $26, $36`
	782	+	`.byte BG_COLOUR, $30, $27, $17 ; Player + lives`
	783	+	`.byte BG_COLOUR, $16, $26, $36 ; Enemies`
667	784		`.byte BG_COLOUR, $30, $27, $17`
668	785		`.byte BG_COLOUR, $30, $27, $17`
669	786
			...
731	848		`.byte %11111111,%01111110,%00111100,%00011000`
732	849		`.byte %00000000,%00011000,%00100100,%01000010`
733	850		`.byte %01000010,%00100100,%00011000,%00000000`
	851	+
	852	+	`; Tile 9: Life icon (small heart/ship)`
	853	+	`.byte %00000000,%00100100,%01111110,%01111110`
	854	+	`.byte %00111100,%00011000,%00000000,%00000000`
	855	+	`.byte %00000000,%00000000,%00000000,%00100100`
	856	+	`.byte %00011000,%00000000,%00000000,%00000000`
734	857
735	858		`; Fill rest`
736		-	`.res 8192 - 144, $00`
	859	+	`.res 8192 - 160, $00`
737	860