Converts from byte
index_ within the this to line and X position.
(X position is measured from the left edge of the line)
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), or
location to store resulting position within line (%PANGO_SCALE units per device unit), or