January 19th 2020
Compute a character index relative to a particular lines first character
the standard custom layer context pointer
the id of the view who's layout will be measured
the line number of the line that serves as the relative starting point of the measurement
the absolute byte index of the position to query
the relative index, based at the first character of the base line, of the character that is closest to spanning the query position on success, when the view exists and contains the base line and query position, zero otherwise
Line numbers are 1 based.
Equivalent to calling the buffer related function of the same name by deriving the buffer, width, and face from the view.