the text for the run
the number of bytes (not characters) in text.
the analysis information return from pango_itemize()
the byte index within text
whether we should compute the result for the beginning (FALSE) or end (TRUE) of the character.
location to store result. out
Converts from character position to x position. (X position is measured from the left edge of the run). Character positions are computed by dividing up each cluster into equal portions.