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103 lines
2.4 KiB
Markdown
103 lines
2.4 KiB
Markdown
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[← Home](../README.md) · [Graphics](README.md)
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# Hardware Sprites — SimpleSprite, MoveSprite
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## Overview
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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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---
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## Sprite DMA Data Format
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Each sprite scanline is two words (4 bytes):
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```
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Word 0 (DATA): bits 15–0 = pixel colour bit 0 for this line
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Word 1 (DATB): bits 15–0 = pixel colour bit 1 for this line
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Pixel colour = (DATB_bit << 1) | DATA_bit
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00 = transparent
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01 = colour 1 (from sprite palette)
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10 = colour 2
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11 = colour 3
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```
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### Sprite Header
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```
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WORD 0: VSTART (vertical start position) + HSTART high bits
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WORD 1: VSTOP (vertical stop position) + control bits
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```
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### End marker
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```
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WORD 0: 0x0000
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WORD 1: 0x0000
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```
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---
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## Sprite Colour Palette
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| Sprite pair | Colour registers | Custom addresses |
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|---|---|---|
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| 0–1 | `COLOR17`–`COLOR19` | `$DFF1A2`–`$DFF1A6` |
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| 2–3 | `COLOR21`–`COLOR23` | `$DFF1AA`–`$DFF1AE` |
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| 4–5 | `COLOR25`–`COLOR27` | `$DFF1B2`–`$DFF1B6` |
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| 6–7 | `COLOR29`–`COLOR31` | `$DFF1BA`–`$DFF1BE` |
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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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---
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## OS-Level Sprite API
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```c
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/* graphics.library */
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struct SimpleSprite ss;
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WORD sprnum;
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/* Obtain a free sprite: */
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sprnum = GetSprite(&ss, -1); /* -1 = any available */
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if (sprnum >= 0) {
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ss.x = 100;
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ss.y = 50;
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ss.height = 16;
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/* Move sprite to position: */
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MoveSprite(NULL, &ss, 100, 50);
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/* Set sprite image data: */
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ChangeSprite(NULL, &ss, spriteData);
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/* Release: */
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FreeSprite(sprnum);
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}
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```
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---
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## Sprite Pointer Registers
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| Register | Address | Sprite |
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|---|---|---|
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| `SPR0PTH/L` | `$DFF120–$DFF122` | Sprite 0 |
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| `SPR1PTH/L` | `$DFF124–$DFF126` | Sprite 1 |
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| `SPR2PTH/L` | `$DFF128–$DFF12A` | Sprite 2 |
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| `SPR3PTH/L` | `$DFF12C–$DFF12E` | Sprite 3 |
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| `SPR4PTH/L` | `$DFF130–$DFF132` | Sprite 4 |
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| `SPR5PTH/L` | `$DFF134–$DFF136` | Sprite 5 |
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| `SPR6PTH/L` | `$DFF138–$DFF13A` | Sprite 6 |
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| `SPR7PTH/L` | `$DFF13C–$DFF13E` | Sprite 7 |
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These must be set every frame — typically via the Copper list.
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---
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## References
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- HRM: *Amiga Hardware Reference Manual* — Sprites chapter
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- NDK39: `graphics/sprite.h`
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- ADCD 2.1: `GetSprite`, `MoveSprite`, `ChangeSprite`, `FreeSprite`
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