amiga-bootcamp/08_graphics/sprites.md

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Hardware Sprites — SimpleSprite, MoveSprite

Overview

The Amiga has 8 hardware sprites, each 16 pixels wide with 3 colours + transparent. Sprites are DMA-driven — the Copper sets their pointers each frame and the display hardware renders them with zero CPU overhead.

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Sprite DMA Data Format

Each sprite scanline is two words (4 bytes):

Word 0 (DATA): bits 15–0 = pixel colour bit 0 for this line
Word 1 (DATB): bits 15–0 = pixel colour bit 1 for this line

Pixel colour = (DATB_bit << 1) | DATA_bit
  00 = transparent
  01 = colour 1 (from sprite palette)
  10 = colour 2
  11 = colour 3

Sprite Header

WORD 0: VSTART (vertical start position) + HSTART high bits
WORD 1: VSTOP  (vertical stop position) + control bits

End marker

WORD 0: 0x0000
WORD 1: 0x0000

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Sprite Colour Palette

Sprite pair	Colour registers	Custom addresses
0–1	COLOR17–COLOR19	$DFF1A2–$DFF1A6
2–3	COLOR21–COLOR23	$DFF1AA–$DFF1AE
4–5	COLOR25–COLOR27	$DFF1B2–$DFF1B6
6–7	COLOR29–COLOR31	$DFF1BA–$DFF1BE

Sprite pairs can be attached to form a single 15-colour sprite (using both sets of 2 bits = 4 bits per pixel).

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OS-Level Sprite API

/* graphics.library */
struct SimpleSprite ss;
WORD sprnum;

/* Obtain a free sprite: */
sprnum = GetSprite(&ss, -1);   /* -1 = any available */
if (sprnum >= 0) {
    ss.x = 100;
    ss.y = 50;
    ss.height = 16;

    /* Move sprite to position: */
    MoveSprite(NULL, &ss, 100, 50);

    /* Set sprite image data: */
    ChangeSprite(NULL, &ss, spriteData);

    /* Release: */
    FreeSprite(sprnum);
}

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Sprite Pointer Registers

Register	Address	Sprite
SPR0PTH/L	$DFF120–$DFF122	Sprite 0
SPR1PTH/L	$DFF124–$DFF126	Sprite 1
SPR2PTH/L	$DFF128–$DFF12A	Sprite 2
SPR3PTH/L	$DFF12C–$DFF12E	Sprite 3
SPR4PTH/L	$DFF130–$DFF132	Sprite 4
SPR5PTH/L	$DFF134–$DFF136	Sprite 5
SPR6PTH/L	$DFF138–$DFF13A	Sprite 6
SPR7PTH/L	$DFF13C–$DFF13E	Sprite 7

These must be set every frame — typically via the Copper list.

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References

• HRM: Amiga Hardware Reference Manual — Sprites chapter
• NDK39: graphics/sprite.h
• ADCD 2.1: GetSprite, MoveSprite, ChangeSprite, FreeSprite