What does font size mean in ios?

Question

It seems that the font size does not define anything.

Here are two lines, one using the font zapfino, the other - system font. They both have a size of 30, but the line height or other font metrics are really different.

This drawing looks like YYLabel , which uses a layout coretextand draws text using this structure, we can easily see the border of a single glyph.

Below is another drawing that uses two UILabelwith a different font and views it in StroyBoard.

So, what does font size mean in coretextsingle-line layout?

Answer 1

Wiki ():

, , em- . em square, , - [.]

, , , . M, . Zapfino, , . Helvetica, :

, X, Zapfino, , , CoreText, , Helvetica. , . , , , .

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