How do I measure pixel width of a string of text?

[azambuilds]

I want to implement text wrapping for my ui library and it requires measuring the dimensions of a string of text so I can compare it to the line width. Is there an example with this library to do so?

It would need to take into consideration emojis and kerning.

[wezm]

Unfortunately there is no high-level API that will take an arbitrary Unicode string and return dimensions. You will need to divide up the text by script and perform font matching to determine which font will be used for each run of characters. For a given run of characters in a font and script you would do the following:

1. Load the font
2. Shape the text
3. Perform glyph layout
4. Obtain the glyph positions
5. sum up the horizontal advance to calculate the width

https://github.com/yeslogic/allsorts-tools/blob/6ed62c379913fa2c819d52a90c2f4b5efda103ca/src/shape.rs covers steps 1 to 4. Step 5 is something like positions.iter().map(|pos| pos.hori_advance).sum().

glyph_positions returns dimensions in font units. You will need to scale this to your desired font size using the units per em in the head table:

    let font_size = 24.0;
    let head = font.head_table()?.ok_or(ParseError::MissingValue)?;
    let scale = font_size / f32::from(head.units_per_em);

[azambuilds]

Ah I see, thanks for the suggested steps! It's much appreciated!