Problems of CTLineGetTypographicBounds

Question

The code is extracted from SimpleTextInput sampe code, with a bit modification.

Create the frame:

self.font = [UIFont systemFontOfSize:18.f];
CTFontR         


        

Answer 1

http://developer.apple.com/library/mac/#documentation/TextFonts/Conceptual/CocoaTextArchitecture/TypoFeatures/TextSystemFeatures.html read this doc and you will know how line-height is calculated, but I still don't get why CTLineGetTypographicBounds got a zero leading