the byte index of a grapheme within the layout
an integer indicating the edge of the grapheme to retrieve the position of. If > 0, the trailing edge of the grapheme, if 0, the leading of the grapheme
location to store resulting line index. (which will between 0 and pango_layout_get_line_count(layout) - 1)
location to store resulting position within line (PANGO_SCALE units per device unit)
Converts from byte index_ within the layout to line and X position.
The X position is measured from the left edge of the line.