public virtual void get_preferred_height (float for_width, out float min_height_p, out float natural_height_p)
Computes the requested minimum and natural heights for an actor, or if they are already computed, returns the cached values.
An actor may not get its request - depending on the layout manager that's in effect.
A request should not incorporate the actor's scale or anchor point; those transformations do not affect layout, only rendering.
available width to assume in computing desired height, or a negative value to indicate that no width is defined
return location for minimum height, or
return location for natural height, or