Marcin Krzyzanowski1d ago

The text "Line Height" calculation on iOS/Mac is THE rocket science 🔬

There is literally one public method that can calculate it right: `NSLayoutManager.defaultLineHeight(for:)`. The logic behind it does not consistently match CoreText
CTLine, CTFramesetter, or a plain (ascent + descent + leading) calculation 🍿

Literal rocket science build on top of years of assumptions, mistakes, historic use. why? becasue reasons. magic delta values depends on the font name/style/size.

Show threadMarcin Krzyzanowski1d ago

one may naively think: font provide all the metrics needed to correctly calculate the size. WRONG. It provides some of information, the other part is either deducted, hardcoded or yoyo. Example, Helvetica at one point ha

lineHeight = ascent + ((ascent + descent) * 0.15) + descent, then there's language aware adjustment on top of that.

I can't make this shit up.

Show threadJurgis Kirsakmens
@krzyzanowskim Eventually everything keeps together only by hope and cheese. A lots of cheese.
Apr 4 at 6:49pmIvory for iOS