The XUnionRegion function computes the union of two regions. The XUnionRectWithRegion function updates the destination region from a union of the specified rectangle and the specified source region. The XXorRegion function calculates the difference between the union and intersection of two regions. The XOffsetRegion function moves the specified region by a specified amount. The XShrinkRegion function reduces the specified region by a specified amount.
Positive values shrink the size of the region, and negative values expand the region.