TControl.GetScrollSize

AvailableSize is passed in so the control can take this into account. However, the control is not required to return a size that is smaller than the available size. This function should only be called after the control has been inserted into a properly rooted control hierarchy for which the properties of the applicable rendering device are fully available (IsBoundToLayout). This ensures that resources like fonts can be used properly in size calculations.

The value returned from this function can differ from the value returned from GetPreferredSize. GetScrollSize should return the exact extent over which a scroll panel should scroll this control.