Hardware Sprites

Overview

A sprite (the VIC-II calls them movable object blocks) is a small bitmap — 24×21 pixels — that the chip draws over the background entirely in hardware. The C64 has eight of them. Each has its own position, colour, and shape, moves with a single register write, and costs the CPU nothing to display. Sprites are how almost every C64 game draws its player, enemies, and bullets.

Setting one up is four steps: point it at its shape, position it, colour it, switch it on.

Code

; =============================================================================
; HARDWARE SPRITES - C64
; Show sprite 0: point it at data, position it, colour it, enable it
; CPU: None (the VIC-II draws it) | Memory: 63 bytes of shape data
; =============================================================================

SPR_ENABLE  = $D015         ; Sprite enable — one bit per sprite
SPR0_X      = $D000         ; Sprite 0 X position (sprite n X = $D000 + 2*n)
SPR0_Y      = $D001         ; Sprite 0 Y position (sprite n Y = $D001 + 2*n)
SPR_X_MSB   = $D010         ; X position bit 8 — one bit per sprite (X >= 256)
SPR0_COLOR  = $D027         ; Sprite 0 colour ($D027..$D02E for sprites 0..7)

SCREEN      = $0400         ; Default screen RAM
SPR0_PTR    = SCREEN + $3F8 ; Sprite pointers live at the end of screen RAM ($07F8)

SHAPE       = $0340         ; Put the shape in the spare cassette buffer
SHAPE_BLOCK = SHAPE / 64    ; Pointer value = address / 64  (= 13)

init_sprite:
    ; --- 1. Point sprite 0 at its shape ---
    lda #SHAPE_BLOCK        ; The pointer is a 64-byte block number, not an address
    sta SPR0_PTR

    ; --- 2. Position it (X=160, Y=120 — middle of the screen) ---
    lda #160
    sta SPR0_X
    lda #120
    sta SPR0_Y
    lda #0
    sta SPR_X_MSB           ; X < 256, so its high bit is clear

    ; --- 3. Colour it ---
    lda #1                  ; 1 = white
    sta SPR0_COLOR

    ; --- 4. Switch it on ---
    lda #%00000001          ; Bit 0 = sprite 0
    sta SPR_ENABLE
    rts

; --- The shape: 24 wide x 21 tall = 63 bytes (3 bytes per row) ---
    * = SHAPE
    !byte %00000000,%01111110,%00000000
    !byte %00000001,%11111111,%10000000
    !byte %00000111,%11111111,%11100000
    !byte %00001111,%11111111,%11110000
    ; ... 16 more rows make up the 21-row, 63-byte shape ...
    !byte %00000000,%01111110,%00000000

Trade-offs

Aspect	Cost
CPU	None — the VIC-II composites the sprite during display
Memory	63 bytes of shape data per frame, plus a 1-byte pointer
Limitation	Eight sprites only; 24×21 each. More needs multiplexing

When to use: Players, enemies, bullets, the cursor — anything that moves over the background independently.

When to avoid: Large or numerous moving areas — past eight objects you must reuse sprites down the screen (see Sprite Multiplexing), or draw into the bitmap instead.

Sprite registers

All live in the VIC-II at $D000. For sprite n, replace the index:

Register	Purpose
$D000 + 2n / $D001 + 2n	X / Y position
$D010	X bit 8 (one bit per sprite — X positions 256–511)
$D015	Enable (one bit per sprite)
$D027 + n	Colour
$D01D / $D017	Expand X / Expand Y (double width / height)
$D01B	Priority — set bit n to draw the sprite behind the background
$D01C	Multicolour select (one bit per sprite)
$D025 / $D026	The two shared multicolour sprite colours

The pointer is a block number

A sprite pointer isn’t an address — it’s the address divided by 64. So shape data at $0340 gives a pointer of $0340 / 64 = 13. The eight pointers sit at the very end of screen RAM ($07F8–$07FF for a screen at $0400), so moving the screen moves the pointers with it.

Multicolour sprites

Setting a sprite’s bit in $D01C switches it to multicolour mode: pixels are read in pairs, giving four colours (transparent, the two shared colours in $D025/$D026, and the sprite’s own colour) at half the horizontal resolution — 12 fat pixels instead of 24. The trade is colour for detail, and it’s how most C64 game characters were drawn.

Related

Patterns: Sprite Movement & Bounds, Game Loop (Basic)

Vault: VIC-II | Commodore 64