public void set_line_spacing (float factor)
Sets a factor for line spacing.
Typical values are: 0, 1, 1.5, 2. The default values is 0.
factor is non-zero, lines are placed so that
baseline2 = baseline1 + factor * height2
where height2 is the line height of the second line (as determined by the font(s)). In this case, the spacing set with set_spacing is ignored.
factor is zero, spacing is applied as before.
the new line spacing factor