Font Hacking

gistfile1.txt

import CoreText

func rollFontString(string: String) -> NSAttributedString {
    let primaryFont = TextStyle.sfCompact.uiFont
    let fallbackFont = UIFont.systemFont(ofSize: 14, weight: .medium)

    let attributedString = NSMutableAttributedString(string: string, attributes: [
        .kern: 1,
        .font: primaryFont,
    ])

    let ctFont = CTFontCreateWithName(primaryFont.fontName as CFString, primaryFont.pointSize, nil)

    string.enumerateSubstrings(in: string.startIndex ..< string.endIndex, options: .byComposedCharacterSequences) { substring, substringRange, _, _ in

        let uniChar = UniChar(substring.unicodeScalars.first.value)
        var glyph: CGGlyph = 0
        let hasGlyph = CTFontGetGlyphsForCharacters(ctFont, [uniChar], &glyph, 1)

        if !hasGlyph {
            attributedString.addAttribute(
                .font, 
                value: fallbackFont, 
                range: NSRange(substringRange, in: string)
            )
        }
    }
    return attributedString
}