the index of a line, which must be between 0 and pango_layout_get_line_count(layout) - 1, inclusive.
the requested PangoLayoutLine, or NULL if the index is out of range. This layout line can be ref'ed and retained, but will become invalid if changes are made to the PangoLayout.
Retrieves a particular line from a PangoLayout. Use the faster pango_layout_get_line_readonly() if you do not plan to modify the contents of the line (glyphs, glyph widths, etc.).