Meziantou.Framework

Installed fonts

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Find an installed font

SystemFontCollection.Default is an index of the fonts installed on the machine. Match finds the face of a family that is the closest to a weight and an italic, and the descriptor gives the file to load:

// The fonts of the machine are scanned once per process; only the tables that describe a face are read.
var fonts = SystemFontCollection.Default;
if (fonts.Match("Arial", weight: 700, isItalic: false) is { } face)
{
    using var stream = File.OpenRead(face.FilePath);
    var font = FontLoader.Load(stream, new PooledFontEnvironment(FontResourceLimits.Default, 64 * 1024 * 1024))[face.FaceIndex];
    Console.WriteLine($"{font.FamilyName} {font.SubfamilyName}: {font.UnitsPerEm} units per em");
}
  • The fonts are scanned the first time Default is read, once per process. Only the tables that describe a face are read, not the glyphs. A font installed later is not seen.
  • Match uses the font matching of CSS: the normal width first, then the style, then the weight. The weight is from 1 to 1000 (400 is normal, 700 bold); an italic face is preferred when isItalic is set, then an oblique face, then an upright one. It returns null when no font has the family: another family is never used instead.
  • A variable font matches the weights and the widths of its axes; choosing the instance is up to you (see Variable fonts).
  • GetFamily gives every face of a family, and FindByName finds a face by its full name or its PostScript name, as the local() function of CSS does. Names are compared without case, in every language of the fonts.
  • The file of a descriptor may have changed or been removed since the scan: loading it can fail.

The installed fonts are found in the fonts directory of Windows, in the fonts installed for the user and in the files the registry lists; in the Library/Fonts directories of macOS and in the fonts it downloads on demand; and on Linux in the directories of the fontconfig configuration and in the XDG font directories.

Find a font that has a character

SystemFontDescriptor.Covers tells whether a face has a glyph for a character, to choose a fallback font:

// The characters of a face are read from its file the first time they are asked for, then kept with the collection.
var grinningFace = new Rune(0x1F600);
var emojiFont = SystemFontCollection.Default.Fonts.FirstOrDefault(face => face.Covers(grinningFace));
Console.WriteLine($"U+1F600: {emojiFont?.FamilyName ?? "no installed font"}");

The characters of a face are read from its file the first time Covers asks for one, and kept with the collection within a bounded amount of memory: scanning the fonts reads none of them.

Use the fonts of a directory

SystemFontCollection.Create indexes the fonts of directories (and their subdirectories) and of font files, such as the fonts your application ships:

static string? FindFont(string directory, string familyName)
{
    // The fonts of a directory and of its subdirectories: only the tables that describe a face are read
    var fonts = SystemFontCollection.Create([directory]);
    var face = fonts.Match(familyName, weight: 700); // the closest face of the family, as CSS chooses it
    return face is null ? null : string.Create(CultureInfo.InvariantCulture, $"{face.FamilyName} {face.SubfamilyName}, weight {face.Weight}, face {face.FaceIndex} of {Path.GetFileName(face.FilePath)}");
}

With a directory that holds the regular face of Noto Sans, FindFont(directory, "noto sans") gives Noto Sans Regular, weight 400, face 0 of NotoSans-Regular.subset.ttf: the family has no bold face, so the closest one is used.

  • The .ttf, .otf, .ttc, .otc, .woff and .woff2 files are indexed; the other files are ignored, and so is a path that does not exist.
  • A file is left out when one of its faces cannot be loaded: a face that is malformed, or that has neither outlines (glyf, CFF or CFF2) nor color bitmaps (CBDT or sbix). A face whose only glyphs are in an SVG table is left out, since SVG glyphs are not supported (see Limitations). So is a collection of more fonts than the default MaxCollectionFaces (1,024).
  • A collection is immutable and can be used by several threads at the same time.

The fonts of a machine are not those of another one: a text drawn with an installed font can look different elsewhere. To get the same result everywhere, ship the font files with your application.