Each .ttf/.ttc file may have more than one font. Each font has a sequential
index number starting from 0. Call this function to get the font offset for
a given index; it returns -1 if the index is out of range. A regular .ttf
file will only define one font and it always be at offset 0, so it will
return '0' for index 0, and -1 for all other indices. You can just skip
this step if you know it's that kind of font.
Each .ttf/.ttc file may have more than one font. Each font has a sequential index number starting from 0. Call this function to get the font offset for a given index; it returns -1 if the index is out of range. A regular .ttf file will only define one font and it always be at offset 0, so it will return '0' for index 0, and -1 for all other indices. You can just skip this step if you know it's that kind of font.