UIFont and Diacriticals

Question

I'm writing a iPhone app that needs to render i18n text that includes diacriticals (tildes, accents, etc.). Apple provides the UIFont class which can be used to get a given typeface/font-size combination's leading, ascent, descent, etc.

The problem is that this information does not accurately reflect diacriticals. Specifically, diacriticals on capital letters often exceed the lineHeight (the UIFont property formerly known as leading).

The same problem exists throughout the frameworks, ie. NSString:sizeWithFont has the same issue.

I need to know the true bounding box for text as I am using OpenGL which does not have text drawing support and therefore requires rendering text to a texture.

Currently, I'm using a hack to get around this issue. Is there a better way?

Answer 1

It's not possible with NSString, since it just returns a size. You can try CoreText which seems to support returning bounding boxes, but that's a bit overkill.

It's a difficult problem when Unicode supports things like è̀̀̀ (see also: zalgo); things can render above the top of a line so you can't just draw the characters. Some text-drawing APIs make you specify the baseline and give you the bounding box so you can get both ascenders and descenders, but UIKit doesn't do this.

Then, you have crazy cursive fonts with the occasional huge ascender. It's unclear how to handle these either.

The lazy way is to render to a texture with margins at the top and bottom (0.5 lines? 1 line?) and not care too much about the extra overhead of some transparent pixels.

I haven't looked at CoreText much, but it doesn't look particularly promising.