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 color fonts, outlined fonts

Color Fonts (OS 3.0+)

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

/* Color 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 color used */
    UBYTE  ctf_High;                /* highest color 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

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