Font and glyph metrics

Most applications only need TextMeasurer. When you write your own layout code, or need the raw numbers from the font, read the metrics directly.

Font metrics

Font.FontMetrics gives the metrics of the font's face. All values are in font units. To convert a value to pixels, use this rule:

pixels = value × pointSize × DPI / (72 × UnitsPerEm)

using PinataLabs.Typography;

FontMetrics metrics = font.FontMetrics;
HorizontalMetrics h = metrics.HorizontalMetrics;

Console.WriteLine($"Units per em: {metrics.UnitsPerEm}"); // 2048 for Open Sans
Console.WriteLine($"Ascender:     {h.Ascender}");          // Above the baseline: positive.
Console.WriteLine($"Descender:    {h.Descender}");         // Below the baseline: negative.
Console.WriteLine($"Line gap:     {h.LineGap}");
Console.WriteLine($"Line height:  {h.LineHeight}");

float ascenderPx = h.Ascender * font.Size * 72F / (72F * metrics.UnitsPerEm); // At 72 DPI.

Property	Meaning
UnitsPerEm	The size of the design grid.
ScaleFactor	UnitsPerEm × 72. Divide a value in font units by this, then multiply by point size × DPI, to get pixels.
HorizontalMetrics	Ascender, descender, line gap, line height and maximum advances for horizontal text.
VerticalMetrics	The same values for vertical text.
UnderlinePosition, UnderlineThickness	Where and how thick to draw an underline.
StrikeoutPosition, StrikeoutSize	Where and how thick to draw a strike-out line.
SubscriptXOffset, SubscriptYOffset, SubscriptXSize, SubscriptYSize	How to place and scale subscript text.
SuperscriptXOffset, SuperscriptYOffset, SuperscriptXSize, SuperscriptYSize	How to place and scale superscript text.
ItalicAngle	The slant of the italic style, in degrees. Zero for upright fonts.
Description	The font description.

You can also read the metrics of a style without making a Font:

if (family.TryGetMetrics(FontStyle.Bold, out FontMetrics? bold))
{
    Console.WriteLine(bold.Description.FontNameInvariantCulture);
}

Glyph metrics

Font.TryGetGlyphs gives the glyphs for one code point. Most code points have one glyph. A color emoji can have more than one, one for each color layer.

using PinataLabs.Typography.Unicode;

if (font.TryGetGlyphs(new CodePoint('A'), out IReadOnlyList<Glyph>? glyphs))
{
    GlyphMetrics g = glyphs[0].GlyphMetrics;
    Console.WriteLine($"Glyph id:          {g.GlyphId}");
    Console.WriteLine($"Advance width:     {g.AdvanceWidth}");   // Font units.
    Console.WriteLine($"Left side bearing: {g.LeftSideBearing}");
    Console.WriteLine($"Width x height:    {g.Width} x {g.Height}");
}

TryGetGlyphs returns false only when it cannot make a glyph. When the font has no glyph for the code point, you get the font's fallback glyph (glyph 0, often an empty box) with GlyphType.Fallback. Check GlyphType to find characters that the font cannot show.

Glyph.BoundingBox(mode, location, dpi) gives the ink box of the glyph in pixels, placed at location.

Kerning

Font.TryGetKerningOffset gives the kerning adjustment between two glyphs from the font's kern table:

font.TryGetGlyphs(new CodePoint('A'), out IReadOnlyList<Glyph>? a);
font.TryGetGlyphs(new CodePoint('V'), out IReadOnlyList<Glyph>? v);

if (font.TryGetKerningOffset(a![0], v![0], 72, out System.Numerics.Vector2 offset))
{
    Console.WriteLine($"Kerning between A and V: {offset.X}px");
}

You do not need this when you use TextMeasurer or TextRenderer: they apply kerning for you, from the kern table and from the GPOS table. See OpenType features.