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