property OnCalcContentBounds: TOnCalcContentBoundsEvent read FOnCalcContentBounds write FOnCalcContentBounds;
The event handler of this event is called to calculate the ContentBounds rectangle bounding all controls in the scrolling region.
The event handler of this event is called from DoRealign. At first DoRealign calls DoCalcContentBounds to calculate the ContentBounds rectangle. Then, if the OnCalcContentBounds event handler is defined, then DoRealign calls this event handler and passes into it the calculated content bounding rectangle for additional calculations.