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109 lines
3.1 KiB
Markdown
109 lines
3.1 KiB
Markdown
[← Home](../README.md) · [Graphics](README.md)
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# Views and ViewPorts — Display Construction
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## Overview
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The AmigaOS display system builds the actual screen image through a hierarchy: `View` → `ViewPort` → `RasInfo` → `BitMap`. The `MakeVPort`/`MrgCop`/`LoadView` pipeline compiles this into a Copper list that programs the custom chips.
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---
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## Key Structures
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```c
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/* graphics/view.h — NDK39 */
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struct View {
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struct ViewPort *ViewPort; /* first viewport in chain */
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struct cprlist *LOFCprList; /* long-frame copper list */
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struct cprlist *SHFCprList; /* short-frame copper list */
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WORD DyOffset; /* vertical scroll offset */
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WORD DxOffset; /* horizontal scroll offset */
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UWORD Modes; /* display mode flags */
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};
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struct ViewPort {
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struct ViewPort *Next; /* next viewport in chain */
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struct ColorMap *ColorMap; /* palette for this viewport */
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struct CopList *DspIns; /* display copper instructions */
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struct CopList *SprIns; /* sprite copper instructions */
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struct CopList *ClrIns; /* color copper instructions */
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struct CopList *UCopIns; /* user copper instructions */
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WORD DWidth; /* display width */
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WORD DHeight; /* display height */
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WORD DxOffset;
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WORD DyOffset;
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UWORD Modes; /* HIRES, LACE, HAM, EHB, etc. */
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UBYTE SpritePriorities;
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UBYTE ExtendedModes;
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struct RasInfo *RasInfo; /* linked bitmap info */
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};
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struct RasInfo {
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struct RasInfo *Next; /* for dual-playfield */
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struct BitMap *BitMap; /* the actual bitmap */
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WORD RxOffset; /* horizontal scroll within bitmap */
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WORD RyOffset; /* vertical scroll within bitmap */
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};
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```
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---
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## Display Mode Flags
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```c
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/* graphics/view.h */
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#define HIRES 0x8000 /* 640 pixel mode */
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#define LACE 0x0004 /* interlaced */
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#define HAM 0x0800 /* Hold-And-Modify (4096 colors) */
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#define EXTRA_HALFBRITE 0x0080 /* Extra Half-Brite (64 colors) */
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#define DUALPF 0x0400 /* dual playfield */
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#define PFBA 0x0040 /* playfield B has priority */
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#define SUPERHIRES 0x0020 /* 1280 pixel mode (ECS+) */
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#define VP_HIDE 0x2000 /* viewport is hidden */
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```
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---
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## Building a Display
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```c
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struct View view;
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struct ViewPort vp;
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struct RasInfo ri;
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struct BitMap *bm = AllocBitMap(320, 256, 5, BMF_DISPLAYABLE|BMF_CLEAR, NULL);
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InitView(&view);
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InitVPort(&vp);
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view.ViewPort = &vp;
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vp.RasInfo = &ri;
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ri.BitMap = bm;
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vp.DWidth = 320;
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vp.DHeight = 256;
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vp.Modes = 0; /* lores */
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/* Build color map: */
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vp.ColorMap = GetColorMap(32);
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/* Compile to copper: */
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MakeVPort(&view, &vp);
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MrgCop(&view);
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/* Activate: */
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LoadView(&view);
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WaitTOF();
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/* Cleanup: */
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LoadView(GfxBase->ActiView); /* restore system view */
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FreeVPortCopLists(&vp);
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FreeCprList(view.LOFCprList);
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FreeColorMap(vp.ColorMap);
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FreeBitMap(bm);
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```
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---
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## References
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- NDK39: `graphics/view.h`
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- ADCD 2.1: `InitView`, `InitVPort`, `MakeVPort`, `MrgCop`, `LoadView`
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- HRM: display construction chapter
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