double pango_gravity_to_rotation ( PangoGravity gravity )
PangoGravity value to its natural rotation in radians.
pango_matrix_rotate() takes angle in degrees, not radians.
So, to call [method@Pango.Matrix,rotate] with the output of this function
you should multiply it by (180. / G_PI).
Available since: 1.16
Gravity to query, should not be