mirror of
https://github.com/alfishe/amiga-bootcamp.git
synced 2026-06-13 00:26:28 +00:00
21751c0025
Comprehensive technical documentation covering: - Hardware: OCS/ECS/AGA custom chip registers, Copper & Blitter deep dives - Boot sequence: cold boot through startup-sequence - Binary format: HUNK executable spec, relocation, debug info - Linking & ABI: .fd files, LVO tables, register calling conventions - Exec kernel: tasks, interrupts, memory, signals, semaphores - AmigaDOS: file I/O, FFS/OFS layout, CLI/Shell scripting - Graphics: planar bitmaps, Copper programming, HAM/EHB modes - Intuition: screens, windows, IDCMP, BOOPSI - Devices: trackdisk, SCSI, serial, timer, audio, keyboard - Libraries: utility, expansion, IFFParse, locale, ARexx - Networking: bsdsocket API, SANA-II, TCP/IP stack comparison - Toolchain: GCC, vasm/vlink, SAS/C, NDK, debugging - Reverse engineering: IDA/Ghidra setup, compiler fingerprints, case studies - CPU & MMU: 68040/060 emulation libs, PMMU, cache management - Driver development: SANA-II, Picasso96/RTG, AHI audio All files include breadcrumb navigation. No local paths or proprietary content.
117 lines
3 KiB
Markdown
117 lines
3 KiB
Markdown
[← Home](../README.md) · [Graphics](README.md)
|
||
|
||
# BitMap — Planar Bitmap Structure and Layout
|
||
|
||
## Overview
|
||
|
||
Amiga display memory uses **planar** layout: each bitplane is a separate contiguous memory region. A pixel's colour index is formed by reading one bit from each plane at the same x,y position. This is fundamentally different from chunky (packed-pixel) or interleaved formats.
|
||
|
||
---
|
||
|
||
## struct BitMap
|
||
|
||
```c
|
||
/* graphics/gfx.h — NDK39 */
|
||
struct BitMap {
|
||
UWORD BytesPerRow; /* bytes per row per plane (must be even) */
|
||
UWORD Rows; /* height in pixels */
|
||
UBYTE Flags; /* BMF_* flags */
|
||
UBYTE Depth; /* number of bitplanes (1–8) */
|
||
UWORD pad;
|
||
PLANEPTR Planes[8]; /* pointers to each bitplane buffer */
|
||
};
|
||
```
|
||
|
||
---
|
||
|
||
## BMF_ Flags
|
||
|
||
```c
|
||
#define BMF_CLEAR (1<<0) /* clear planes on allocation */
|
||
#define BMF_DISPLAYABLE (1<<1) /* allocated in displayable (Chip) RAM */
|
||
#define BMF_INTERLEAVED (1<<2) /* planes are interleaved in memory */
|
||
#define BMF_STANDARD (1<<3) /* use standard allocation */
|
||
#define BMF_MINPLANES (1<<4) /* minimum number of planes */
|
||
```
|
||
|
||
---
|
||
|
||
## Planar Memory Layout
|
||
|
||
For a 320×256×4 display (16 colours):
|
||
|
||
```
|
||
BytesPerRow = 320/8 = 40 bytes
|
||
Rows = 256
|
||
Depth = 4
|
||
|
||
Plane 0: 40 × 256 = 10,240 bytes (bit 0 of colour index)
|
||
Plane 1: 40 × 256 = 10,240 bytes (bit 1)
|
||
Plane 2: 40 × 256 = 10,240 bytes (bit 2)
|
||
Plane 3: 40 × 256 = 10,240 bytes (bit 3)
|
||
|
||
Total = 4 × 10,240 = 40,960 bytes
|
||
```
|
||
|
||
Pixel colour at (x, y):
|
||
```
|
||
bit0 = (Planes[0][y * BytesPerRow + x/8] >> (7 - x%8)) & 1
|
||
bit1 = (Planes[1][y * BytesPerRow + x/8] >> (7 - x%8)) & 1
|
||
bit2 = (Planes[2][y * BytesPerRow + x/8] >> (7 - x%8)) & 1
|
||
bit3 = (Planes[3][y * BytesPerRow + x/8] >> (7 - x%8)) & 1
|
||
colour_index = (bit3 << 3) | (bit2 << 2) | (bit1 << 1) | bit0
|
||
```
|
||
|
||
---
|
||
|
||
## Allocation
|
||
|
||
```c
|
||
/* OS 3.0+ — AllocBitMap: */
|
||
struct BitMap *bm = AllocBitMap(320, 256, 4,
|
||
BMF_CLEAR | BMF_DISPLAYABLE, NULL);
|
||
/* Always in Chip RAM when BMF_DISPLAYABLE */
|
||
|
||
/* Manual allocation (OS 1.x compatible): */
|
||
struct BitMap bm;
|
||
InitBitMap(&bm, 4, 320, 256);
|
||
for (int i = 0; i < 4; i++)
|
||
bm.Planes[i] = AllocRaster(320, 256); /* MEMF_CHIP */
|
||
|
||
/* Free: */
|
||
FreeBitMap(bm); /* or FreeRaster per plane */
|
||
```
|
||
|
||
---
|
||
|
||
## Interleaved BitMaps
|
||
|
||
With `BMF_INTERLEAVED`, all planes are stored sequentially row by row:
|
||
```
|
||
Row 0, Plane 0: 40 bytes
|
||
Row 0, Plane 1: 40 bytes
|
||
Row 0, Plane 2: 40 bytes
|
||
Row 0, Plane 3: 40 bytes
|
||
Row 1, Plane 0: 40 bytes
|
||
...
|
||
```
|
||
|
||
BytesPerRow becomes `40 × Depth = 160`, and each `Planes[i]` pointer is offset by `i * 40` from the base. This layout is more cache-friendly and allows single-pass blits.
|
||
|
||
---
|
||
|
||
## AGA 8-Bit Bitmaps
|
||
|
||
AGA (A1200/A4000) supports up to 8 bitplanes = 256 colours:
|
||
```c
|
||
struct BitMap *bm = AllocBitMap(320, 256, 8, BMF_CLEAR | BMF_DISPLAYABLE, NULL);
|
||
/* 8 planes × 10,240 = 81,920 bytes of Chip RAM */
|
||
```
|
||
|
||
---
|
||
|
||
## References
|
||
|
||
- NDK39: `graphics/gfx.h`
|
||
- ADCD 2.1: `AllocBitMap`, `FreeBitMap`, `InitBitMap`
|
||
- HRM: *Amiga Hardware Reference Manual* — bitplane DMA chapter
|