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75 lines
2 KiB
Markdown
75 lines
2 KiB
Markdown
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[← Home](../README.md) · [Graphics](README.md)
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# Display Modes — Display Database, ModeID, Monitor Specs
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## Overview
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OS 3.0+ provides a **display database** that abstracts monitor/chipset capabilities. Applications query available modes by `ModeID` rather than hardcoding `HIRES`/`LACE` flags.
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---
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## ModeID Format
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A ModeID is a ULONG:
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```
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bits 31–16: Monitor ID
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bits 15–0: Mode within that monitor
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```
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| ModeID | Name | Resolution |
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|---|---|---|
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| `$00000000` | LORES | 320×256 (PAL) / 320×200 (NTSC) |
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| `$00008000` | HIRES | 640×256/200 |
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| `$00000004` | LORES-LACE | 320×512/400 |
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| `$00008004` | HIRES-LACE | 640×512/400 |
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| `$00080000` | SUPERHIRES | 1280×256 (ECS+) |
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| `$00080004` | SUPERHIRES-LACE | 1280×512 |
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| `$00039000` | DBLPAL-LORES | 320×256 (AGA scan-doubled) |
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| `$00039004` | DBLPAL-HIRES | 640×256 (AGA) |
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| `$00011000` | DBLNTSC-LORES | 320×200 (AGA) |
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---
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## Querying the Display Database
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```c
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/* graphics.library 39+ */
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ULONG modeID = INVALID_ID;
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struct DisplayInfo di;
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struct DimensionInfo dims;
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while ((modeID = NextDisplayInfo(modeID)) != INVALID_ID) {
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if (GetDisplayInfoData(NULL, (UBYTE *)&di, sizeof(di),
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DTAG_DISP, modeID)) {
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if (GetDisplayInfoData(NULL, (UBYTE *)&dims, sizeof(dims),
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DTAG_DIMS, modeID)) {
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Printf("ModeID $%08lx: %ldx%ld, %ld colours\n",
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modeID,
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dims.Nominal.MaxX - dims.Nominal.MinX + 1,
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dims.Nominal.MaxY - dims.Nominal.MinY + 1,
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1 << di.NotAvailable ? 0 : dims.MaxDepth);
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}
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}
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}
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```
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---
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## Best Mode Selection
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```c
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ULONG bestMode = BestModeIDA((struct TagItem[]){
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{ BIDTAG_NominalWidth, 640 },
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{ BIDTAG_NominalHeight, 480 },
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{ BIDTAG_Depth, 8 },
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{ TAG_DONE, 0 }
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});
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```
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---
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## References
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- NDK39: `graphics/displayinfo.h`, `graphics/modeid.h`
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- ADCD 2.1: `NextDisplayInfo`, `GetDisplayInfoData`, `BestModeIDA`
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