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. No changes should be made to the line.
Retrieves a particular line from a PangoLayout. This is a faster alternative to pango_layout_get_line(), but the user is not expected to modify the contents of the line (glyphs, glyph widths, etc.). Since 1.16