XPLMMeasureString
XPLM_API float XPLMMeasureString(
XPLMFontID inFontID,
const char * inChar,
int inNumChars);
This routine returns the width in pixels of a string using a given font. The string is passed as a pointer plus length (and does not need to be null terminated); this is used to allow for measuring substrings. The return value is floating point; it is possible that future font drawing may allow for fractional pixels.