docs(amiga): complete AmigaOS 3.1/3.2 developer reference — 172 files across 17 sections

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.

08_graphics/rastport.md

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+[← Home](../README.md) · [Graphics](README.md)
+
+# RastPort — Drawing Primitives and Layers
+
+## Overview
+
+`RastPort` is the primary drawing context in AmigaOS. All graphics primitives (pixel, line, rectangle, polygon, text) operate through a `RastPort`, which links a `BitMap`, drawing pen colours, pattern, font, and optional `Layer` for clipping.
+
+---
+
+## struct RastPort
+
+```c
+/* graphics/rastport.h — NDK39 */
+struct RastPort {
+    struct Layer   *Layer;       /* associated layer (NULL = no clipping) */
+    struct BitMap  *BitMap;      /* target bitmap */
+    UWORD          *AreaPtrn;   /* area fill pattern */
+    struct TmpRas  *TmpRas;     /* temp raster for area fills/floods */
+    struct AreaInfo *AreaInfo;   /* area fill vertex buffer */
+    struct GelsInfo *GelsInfo;   /* GEL (BOB/VSprite) list */
+    UBYTE           Mask;        /* plane mask (which planes to draw to) */
+    BYTE            FgPen;       /* foreground pen colour index */
+    BYTE            BgPen;       /* background pen colour index */
+    BYTE            AOlPen;      /* area outline pen */
+    BYTE            DrawMode;    /* JAM1, JAM2, COMPLEMENT, INVERSVID */
+    BYTE            AreaPtSz;    /* area pattern size (log2) */
+    BYTE            linpatcnt;   /* line pattern counter */
+    BYTE            dummy;
+    UWORD           Flags;       /* FRST_DOT etc. */
+    UWORD           LinePtrn;    /* 16-bit line dash pattern */
+    WORD            cp_x, cp_y;  /* current pen position */
+    UWORD           minterms[8];
+    WORD            PenWidth;
+    WORD            PenHeight;
+    struct TextFont *Font;       /* current text font */
+    UBYTE           AlgoStyle;   /* algorithmic style flags */
+    UBYTE           TxFlags;
+    UWORD           TxHeight;
+    UWORD           TxWidth;
+    UWORD           TxBaseline;
+    WORD            TxSpacing;
+    APTR           *RP_User;
+    /* ... */
+};
+```
+
+---
+
+## Draw Modes
+
+```c
+#define JAM1        0   /* draw FgPen only; background transparent */
+#define JAM2        1   /* draw FgPen and BgPen (opaque) */
+#define COMPLEMENT  2   /* XOR with existing pixels */
+#define INVERSVID   4   /* invert video (swap fg/bg for text) */
+```
+
+---
+
+## Drawing Primitives
+
+```c
+/* Set pen colour: */
+SetAPen(rp, 1);       /* foreground = colour 1 */
+SetBPen(rp, 0);       /* background = colour 0 */
+SetDrMd(rp, JAM1);    /* transparent background */
+
+/* Move to position: */
+Move(rp, 100, 50);
+
+/* Draw line from current position to (x,y): */
+Draw(rp, 200, 100);
+
+/* Write pixel: */
+WritePixel(rp, 160, 120);
+
+/* Read pixel: */
+LONG colour = ReadPixel(rp, 160, 120);
+
+/* Filled rectangle: */
+RectFill(rp, 10, 10, 100, 50);
+
+/* Draw text at current position: */
+Move(rp, 20, 30);
+Text(rp, "Hello", 5);
+
+/* Blitter copy between RastPorts: */
+ClipBlit(srcRP, sx, sy, dstRP, dx, dy, w, h, minterm);
+```
+
+---
+
+## Layers
+
+When `rp->Layer != NULL`, all drawing is clipped to the layer's bounds and damage regions. Layers are managed by `layers.library`:
+
+```c
+struct Layer_Info *li = NewLayerInfo();
+struct Layer *layer = CreateUpfrontLayer(li, bm, x1, y1, x2, y2, flags, NULL);
+rp = layer->rp;   /* use this RastPort for drawing */
+/* ... draw ... */
+DeleteLayer(0, layer);
+DisposeLayerInfo(li);
+```
+
+---
+
+## References
+
+- NDK39: `graphics/rastport.h`, `graphics/gfxmacros.h`
+- ADCD 2.1: `SetAPen`, `Move`, `Draw`, `Text`, `RectFill`, `ClipBlit`