Use OpenType Features for Numbers and Fractions

This recipe shows the most common way people first encounter discretionary OpenType features: asking fonts through TextOptions.FeatureTags to align figures more neatly or substitute fraction glyphs for number-heavy text.

Align numeric columns with tabular figures

using SixLabors.Fonts;
using SixLabors.Fonts.Tables.AdvancedTypographic;

Font font = SystemFonts.CreateFont("Segoe UI", 18);
TextOptions options = new(font)
{
    FeatureTags = [KnownFeatureTags.TabularFigures]
};

This is useful for scoreboards, tables, counters, and any UI where digits should line up cleanly.

Request diagonal fractions

using SixLabors.Fonts;
using SixLabors.Fonts.Tables.AdvancedTypographic;

Font font = SystemFonts.CreateFont("Segoe UI", 18);
TextOptions options = new(font)
{
    FeatureTags = [KnownFeatureTags.Fractions]
};

This only has an effect if the font actually provides the requested feature.

Feature requests are not guaranteed substitutions. Fonts decide which features they expose and which scripts, languages, and glyph sequences those features apply to. If output must be exact, test with the production font files rather than assuming a tag will be honored everywhere.

Combine multiple features

using SixLabors.Fonts;
using SixLabors.Fonts.Tables.AdvancedTypographic;

Font font = SystemFonts.CreateFont("Segoe UI", 18);
TextOptions options = new(font)
{
    FeatureTags =
    [
        KnownFeatureTags.TabularFigures,
        KnownFeatureTags.OldstyleFigures,

        // 'ss01' is the first of OpenType's stylistic sets (ss01..ss20),
        // which a font can use to expose an alternate glyph design.
        Tag.Parse("ss01")
    ]
};

Use the same TextOptions for both TextMeasurer and TextRenderer so the measured result matches the rendered result.

OpenType features can change glyph choice, advance widths, ligature formation, and mark placement. That means they are layout inputs, not just visual decoration applied after measuring.

For the fuller feature model, see OpenType Features.

Practical guidance

• Verify that the production font actually exposes the requested feature tags.
• Use the same feature tags for measurement and rendering.
• Be careful combining mutually exclusive numeric features such as figure styles.
• Prefer KnownFeatureTags for standard features and Tag.Parse(...) for font-specific stylistic sets.