Glyph metrics

Measure a glyph when you place text yourself, size a label, or compare faces: glyphMetrics() reports the advance width and the left side bearing in the font's design units, before shaping, kerning, or rasterization. Divide a value by face()->unitsPerEm and multiply by the target size to scale it.

Read metrics for a character

Place a font at fonts/Inter-Regular.ttf and run this script beside vendor. Passing one character resolves it and reports a clear failure if it is absent:

<?php

require __DIR__.'/vendor/autoload.php';

use Alto\Font\Font;

$font = Font::fromFile(__DIR__.'/fonts/Inter-Regular.ttf');
$metrics = $font->glyphMetrics('A');

printf("Glyph: %d\n", $metrics->glyphId->value);
printf("Advance: %d\n", $metrics->advanceWidth);
printf("Side bearing: %d\n", $metrics->leftSideBearing);

Passing invalid UTF-8, an empty string, or more than one Unicode codepoint raises InvalidTextException. A valid character absent from the font raises GlyphNotFoundException. Use glyphIdForCodepoint() first when absence is expected.

Read metrics by identifier

An identifier obtained from a previous call or from glyphIdForCodepoint() reads the same measurements without resolving a character again:

<?php

$glyphId = $metrics->glyphId;
$metrics = $font->glyphMetrics($glyphId);

The advance width and side bearing use the font's design units, not pixels.

In this Inter fixture, A advances by 1,413 units and has a 52-unit left side bearing. Advance width is the distance to the next origin before shaping; it is not the width of the visible ink. The measurements use the bundled Inter fixture.

Measure at another weight

For a variable font, select coordinates first; the view reports the metrics at that position in the design space:

<?php

$bold = $font->withVariations(['wght' => 700]);

printf("Default A advance: %g\n", $font->glyphMetrics('A')->advanceWidth);
printf("Selected A advance: %g\n", $bold->glyphMetrics('A')->advanceWidth);

Both values may be equal when that glyph's advance does not vary. See Variable fonts for axes, instances, and limits.

Contract

GlyphMetrics exposes glyphId: GlyphId, advanceWidth: int, and leftSideBearing: int. The values describe an individual glyph; the distance to the next glyph in real text also depends on kerning and shaping, which the package does not perform.