Can I query the measurements of a letter?

[lpaulsen93]

I got a question about the skills of this lib.

Could I use the lib to query the exact measurements of a letter?
E.g. what is the width and hight for letter 'A' in size '12pt' using font 'xyz'.

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[gingerbeardman]

in this circumstance the correct term is the A glyph

[bsweeney]

This question is pretty old, so I assume you've moved on. Just wanted to provide some info in case someone else was interested.

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You can retrieve the metrics of the glyph representing a character, but the actual measurements (pixels, millimeters) depend on usage (medium and size). There are various metrics available so the actual metrics you want depend on your use case.

For example, Cpdf calculates the space taken up by a glyph using the glyph's horizontal metric for the width and the font's ascender/descender (or font bounding box) for the height. This data is pulled from a font metrics file (AFM/UFM) generated from the font data, but to retrieve the metrics directly you would do something like the following:

// Load the font:
$font = Font::load("path/to/file.ttf");
$font->parse();

// Retrieve the units per EM
$funits_per_em = $font->getData("head", "unitsPerEm");

// Retrieve the font bounding box and calculate the height
$bbox = [
    $font->getData("head", "xMin"),
    $font->getData("head", "yMin"),
    $font->getData("head", "xMax").
    $font->getData("head", "yMax")
];
$f_height = $bbox[3] - $bbox[1];

// Retrieve the horizontal metrics for the character "A" (U+0061)
$glyphIndexArray = $font->getUnicodeCharMap();
$glyphIndex = $glyphIndexArray[61];
$hmtx  = $font->getData("hmtx");
$f_width = $hmtx[$glyphIndex][0];

The metrics values you retrieve are in font units (FUnits), which is "the smallest measurable unit in the em square, an imaginary square that is used to size and align glyphs." To determine the actual size of the rendered glyph you need to know the resolution of the target medium (e.g. 72ppi) and the desired size of the text (e.g. 12pt). From there you can calculate the measurement on the target medium by multiplying the metric value by a scale determined using the following formula: unit_size * device_resolution / ( unit_resolution * funits_per_em ). Working in points, the unit resolution is 72 pt per inch.

// calculate the measurement of the character
$unit_size = 12; // 12pt
$device_resolution = 72; // 72ppi
$unit_resolution = 72; // 72ppi
$scale = $unit_size * $device_resolution / $unit_resolution * $funits_per_em;
$width = $f_width * $scale;
$height = $f_height * $scale;

Recommended reading: TrueType Fundamentals