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Ilia Sharin 2026-04-26 14:46:18 -04:00
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08_graphics/rastport.md
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@ -4,7 +4,7 @@
## Overview
`RastPort` is the primary drawing context in AmigaOS — the equivalent of a "device context" (Windows) or "graphics context" (X11). All graphics primitives (pixel, line, rectangle, polygon, text) operate through a RastPort, which bundles together a target `BitMap`, drawing pen colours, patterns, font, draw mode, and an optional `Layer` for clipping.
`RastPort` is the primary drawing context in AmigaOS — the equivalent of a "device context" (Windows) or "graphics context" (X11). All graphics primitives (pixel, line, rectangle, polygon, text) operate through a RastPort, which bundles together a target `BitMap`, drawing pen colors, patterns, font, draw mode, and an optional `Layer` for clipping.
Every Intuition window and screen has its own RastPort. When you draw into a window, you're drawing through its RastPort.
@ -44,8 +44,8 @@ struct RastPort {
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 FgPen; /* foreground pen color index */
BYTE BgPen; /* background pen color index */
BYTE AOlPen; /* area outline pen */
BYTE DrawMode; /* JAM1, JAM2, COMPLEMENT, INVERSVID */
BYTE AreaPtSz; /* area pattern size (log2) */
@ -111,12 +111,12 @@ flowchart LR
### Pen and Position Setup
```c
/* Set pen colours: */
SetAPen(rp, 1); /* foreground = colour register 1 */
SetBPen(rp, 0); /* background = colour register 0 */
/* Set pen colors: */
SetAPen(rp, 1); /* foreground = color register 1 */
SetBPen(rp, 0); /* background = color register 0 */
SetDrMd(rp, JAM1); /* transparent background mode */
/* OS 3.0+ — use named pen for correct Workbench colours: */
/* OS 3.0+ — use named pen for correct Workbench colors: */
SetAPen(rp, screen->RastPort.BitMap->Depth > 1 ?
ObtainBestPen(screen->ViewPort.ColorMap,
0xFF000000, 0x00000000, 0x00000000, /* red */
@ -153,7 +153,7 @@ Draw(rp, 10, 10); /* close: left edge */
/* Single pixel: */
WritePixel(rp, 160, 120);
LONG colour = ReadPixel(rp, 160, 120);
LONG color = ReadPixel(rp, 160, 120);
/* Dashed lines: */
SetDrPt(rp, 0xF0F0); /* 16-bit pattern: 1111000011110000 */
@ -240,8 +240,8 @@ FreeRaster(tmpRasData, 320, 256);
/* Flood fill from a seed point: */
/* Requires TmpRas (same setup as area fills) */
Flood(rp, 1, 50, 50);
/* mode 1 = fill until FgPen colour boundary */
/* mode 0 = fill all connected pixels of same colour as seed */
/* mode 1 = fill until FgPen color boundary */
/* mode 0 = fill all connected pixels of same color as seed */
```
### Blitting (Block Transfer)
@ -384,9 +384,9 @@ rp->Mask = 0xFF; /* all planes — default */
rp->Mask = 0x01; /* only plane 0 — fast for single-plane effects */
rp->Mask = 0x03; /* planes 0 and 1 only */
/* Use case: draw a 2-colour overlay without disturbing other planes: */
/* Use case: draw a 2-color overlay without disturbing other planes: */
rp->Mask = 0x04; /* only plane 2 */
SetAPen(rp, 4); /* colour index with bit 2 set */
SetAPen(rp, 4); /* color index with bit 2 set */
RectFill(rp, 0, 0, 319, 255);
rp->Mask = 0xFF; /* restore */
```