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08_graphics/sprites.md
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@ -4,7 +4,7 @@
## Overview
The Amiga has **8 hardware sprites**, each 16 pixels wide with 3 colours + transparent. Sprites are entirely DMA-driven — the custom chips fetch sprite data from Chip RAM and composite them over the playfield with zero CPU overhead. The Copper reloads sprite pointers every frame.
The Amiga has **8 hardware sprites**, each 16 pixels wide with 3 colors + transparent. Sprites are entirely DMA-driven — the custom chips fetch sprite data from Chip RAM and composite them over the playfield with zero CPU overhead. The Copper reloads sprite pointers every frame.
Sprite 0 is reserved by Intuition for the **mouse pointer**. Sprites 1–7 are available for application use.
@ -19,7 +19,7 @@ flowchart LR
subgraph "Custom Chips (Denise/Lisa)"
DMA["Sprite DMA<br/>(8 channels)"] --> MUX["Priority MUX"]
PF["Playfield<br/>(bitplane data)"] --> MUX
MUX --> DAC["Colour DAC<br/>→ Video Out"]
MUX --> DAC["Color DAC<br/>→ Video Out"]
end
SD0 --> DMA
@ -58,15 +58,15 @@ Each sprite is stored as a contiguous block in Chip RAM:
└──────────────────────────────────────────┘
```
### Pixel Colour Encoding
### Pixel Color Encoding
```
Pixel colour = (DATB_bit << 1) | DATA_bit
Pixel color = (DATB_bit << 1) | DATA_bit
00 = transparent (playfield shows through)
01 = sprite colour 1
10 = sprite colour 2
11 = sprite colour 3
01 = sprite color 1
10 = sprite color 2
11 = sprite color 3
```
### Header Bit Layout
@ -93,11 +93,11 @@ Word 1 (SPRxCTL):
---
## Sprite Colour Palette
## Sprite Color Palette
Each pair of sprites shares 3 colour registers (colour 0 = transparent for all):
Each pair of sprites shares 3 color registers (color 0 = transparent for all):
| Sprite Pair | Colour Registers | Custom Addresses | Notes |
| Sprite Pair | Color Registers | Custom Addresses | Notes |
|---|---|---|---|
| 0–1 | `COLOR17`–`COLOR19` | `$DFF1A2`–`$DFF1A6` | Pair with mouse pointer |
| 2–3 | `COLOR21`–`COLOR23` | `$DFF1AA`–`$DFF1AE` | |
@ -105,7 +105,7 @@ Each pair of sprites shares 3 colour registers (colour 0 = transparent for all):
| 6–7 | `COLOR29`–`COLOR31` | `$DFF1BA`–`$DFF1BE` | |
```c
/* Set sprite 0-1 colours directly: */
/* Set sprite 0-1 colors directly: */
custom->color[17] = 0xF00; /* red */
custom->color[18] = 0x0F0; /* green */
custom->color[19] = 0xFFF; /* white */
@ -113,24 +113,24 @@ custom->color[19] = 0xFFF; /* white */
---
## Attached Sprites — 15 Colours
## Attached Sprites — 15 Colors
Two sprites from the same pair can be **attached** to form a single 15-colour (+ transparent) sprite:
Two sprites from the same pair can be **attached** to form a single 15-color (+ transparent) sprite:
```mermaid
flowchart LR
subgraph "Normal (2 independent sprites)"
S0["Sprite 0<br/>3 colours"] --- S1["Sprite 1<br/>3 colours"]
S0["Sprite 0<br/>3 colors"] --- S1["Sprite 1<br/>3 colors"]
end
subgraph "Attached (1 wide-colour sprite)"
SA["Sprites 0+1 attached<br/>4 bits per pixel<br/>15 colours + transparent"]
subgraph "Attached (1 wide-color sprite)"
SA["Sprites 0+1 attached<br/>4 bits per pixel<br/>15 colors + transparent"]
end
style SA fill:#c8e6c9,stroke:#2e7d32,color:#333
```
When attached, the even sprite provides bits 0–1 and the odd sprite provides bits 2–3 of the colour index. The 4-bit value indexes into colour registers 16–31.
When attached, the even sprite provides bits 0–1 and the odd sprite provides bits 2–3 of the color index. The 4-bit value indexes into color registers 16–31.
```c
/* Enable attachment: set bit 0 of odd sprite's CTL word */
@ -178,8 +178,8 @@ The Copper waits for a line after one sprite ends, then reprograms the sprite po
| Feature | OCS/ECS | AGA |
|---|---|---|
| Width | 16 pixels | 16, 32, or 64 pixels (via FMODE) |
| Colours (single) | 3 + transparent | 3 + transparent |
| Colours (attached) | 15 + transparent | 15 + transparent |
| Colors (single) | 3 + transparent | 3 + transparent |
| Colors (attached) | 15 + transparent | 15 + transparent |
| Horizontal resolution | Low-res ÷ 2 | Same (unchanged) |
```c