Fix Vertical Position Issue of Custom iOS Fonts
A similar problem was discussed at Custom installed font not displayed correctly in UILabel. There was no solution given.
Here's the solution that worked for my custom font which had the same issue in UILabel, UIButton and such. The problem with the font turned out to be the fact that its ascender property was too small compared to the value of system fonts. Ascender is a vertical whitespace above font's characters. To fix your font you will have to download Apple Font Tool Suite command line utilities. Then take your font and do the following:
~$ ftxdumperfuser -t hhea -A d Bold.ttf
This will create Bold.hhea.xml. Open it with a text editor and increase the value of ascender attribute. You will have to experiment a little to find out the exact value that works best for you. In my case I changed it from 750 to 1200. Then run the utility again with the following command line to merge your changes back into the ttf file:
~$ ftxdumperfuser -t hhea -A f Bold.ttf
Then just use the resulting ttf font in your app.
OS X El Capitan
The Apple Font Tool Suite Installer doesn't work anymore on OSX El Capitan because of SIP because it tries to install the binary files into a protected directory. You have to manually extract ftxdumperfuser. First copy the pkg from the dmg to a local directory afterwards unpack the OS X Font Tools.pkg with
~$ xar -xf OS\ X\ Font\ Tools.pkg
Now navigate into the folder fontTools.pkg with
~$ cd fontTools.pkg/
Extract payload with
~$ cat Payload | gunzip -dc | cpio -i
Now the ftxdumperfuser binary is in your current folder. You could move it to /usr/local/bin/ so that you can use it in every folder inside of the terminal application with the following.
~$ mv ftxdumperfuser /usr/local/bin/