amiga-bootcamp/11_libraries/diskfont.md

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diskfont.library — Disk-Based Font Loading

Overview

diskfont.library loads bitmap fonts from disk (the FONTS: assign). Only two fonts are built into ROM — topaz 8 and topaz 9. All other fonts (helvetica, times, courier, etc.) must be loaded from disk via this library.

flowchart LR
    APP["Application"] -->|"OpenDiskFont(&ta)"| DFL["diskfont.library"]
    DFL -->|"Scans FONTS: directory"| FONTS["FONTS:<br/>helvetica.font<br/>helvetica/24"]
    DFL -->|"Returns loaded font"| TF["struct TextFont"]
    TF -->|"SetFont(rp, font)"| RP["RastPort"]

    ROM["ROM"] -->|"OpenFont(&ta)"| TOPAZ["topaz 8/9<br/>(always available)"]

    style DFL fill:#e8f4fd,stroke:#2196f3,color:#333
    style FONTS fill:#c8e6c9,stroke:#2e7d32,color:#333

---

Font Directory Structure

Amiga bitmap fonts are stored as a descriptor file plus per-size data files:

FONTS:
  helvetica.font          ← font descriptor (FontContents header)
  helvetica/
    9                      ← bitmap data for 9-pixel height
    11                     ← bitmap data for 11-pixel height
    13                     ← bitmap data for 13-pixel height
    18                     ← bitmap data for 18-pixel height
    24                     ← bitmap data for 24-pixel height
  times.font
  times/
    11
    13
    18
    24

The .font descriptor file contains a FontContentsHeader listing all available sizes, styles, and flags.

---

Loading a Disk Font

struct Library *DiskfontBase = OpenLibrary("diskfont.library", 0);

/* Request a specific font and size: */
struct TextAttr ta = {"helvetica.font", 24, 0, 0};
struct TextFont *font = OpenDiskFont(&ta);

if (font)
{
    SetFont(rp, font);
    Move(rp, 10, 30);
    Text(rp, "Disk Font Text", 14);

    /* When done with the font: */
    CloseFont(font);
}
else
{
    /* Font not found — fall back to ROM font: */
    struct TextAttr fallback = {"topaz.font", 8, 0, FPF_ROMFONT};
    struct TextFont *topaz = OpenFont(&fallback);
    SetFont(rp, topaz);
}

CloseLibrary(DiskfontBase);

Size Matching

If the exact requested size is not available, OpenDiskFont returns NULL. To find the nearest available size, use AvailFonts to enumerate, then request the closest match.

---

Enumerating Available Fonts

/* AvailFonts returns all fonts in ROM and on disk: */
LONG bufSize = 4096;
APTR buf = AllocMem(bufSize, MEMF_ANY | MEMF_CLEAR);

LONG shortfall = AvailFonts(buf, bufSize, AFF_DISK | AFF_MEMORY);
if (shortfall > 0)
{
    /* Buffer too small — reallocate and retry: */
    FreeMem(buf, bufSize);
    bufSize += shortfall;
    buf = AllocMem(bufSize, MEMF_ANY | MEMF_CLEAR);
    AvailFonts(buf, bufSize, AFF_DISK | AFF_MEMORY);
}

struct AvailFontsHeader *afh = (struct AvailFontsHeader *)buf;
struct AvailFonts *af = (struct AvailFonts *)&afh[1];

for (int i = 0; i < afh->afh_NumEntries; i++)
{
    Printf("%s  size %-3ld  %s\n",
           af[i].af_Attr.ta_Name,
           af[i].af_Attr.ta_YSize,
           (af[i].af_Type & AFF_DISK) ? "disk" :
           (af[i].af_Type & AFF_MEMORY) ? "ROM" : "scaled");
}

FreeMem(buf, bufSize);

---

Font Types

Flag	Source	Notes
AFF_MEMORY	ROM or already loaded in memory	topaz, or previously opened disk fonts
AFF_DISK	Available on FONTS:	Requires disk access to load
AFF_SCALED	Algorithmically scaled from another size	Lower quality; avoid when native size exists
AFF_BITMAP	Bitmap (pixel) font	Standard Amiga font format
AFF_TAGGED	Tagged (OS 3.0+ extended) font	Supports colour fonts, outlined fonts

---

Colour Fonts (OS 3.0+)

OS 3.0 introduced colour bitmap fonts — each glyph can have multiple bitplanes:

/* Colour fonts use ColorTextFont — an extension of TextFont: */
struct ColorTextFont {
    struct TextFont ctf_TF;          /* standard TextFont */
    UWORD  ctf_Flags;               /* CT_COLORFONT etc. */
    UBYTE  ctf_Depth;               /* number of bitplanes */
    UBYTE  ctf_FgColor;             /* default foreground pen */
    UBYTE  ctf_Low;                 /* lowest colour used */
    UBYTE  ctf_High;                /* highest colour used */
    APTR   ctf_PlanePick;           /* plane selection */
    APTR   ctf_PlaneOnOff;          /* plane on/off defaults */
    struct ColorFontColors *ctf_ColorTable;
    APTR   ctf_CharData[8];         /* per-plane glyph data */
};

---

References

• NDK39: diskfont/diskfont.h, graphics/text.h
• ADCD 2.1: diskfont.library autodocs
• See also: text_fonts.md — TextFont structure and rendering