The methods return rectangles around changed areas.
function IsRectValid(Index: Integer): Boolean;
function GetRect(Index: Integer): TRVMRect;
These methods can be called after calling DetectChanges.
DetectChanges returns the count of these rectangles. Index must be in the range from 0 to count - 1. Not all of these rectangles are valid, ignore rectangles with the indexes where IsRectValid returns False.