Following are the functions used with regions:
CombineRgn
CreateEllipticRgn
CreateEllipticRgnIndirect
CreatePolygonRgn
CreatePolyPolygonRgn
CreateRectRgn
CreateRectRgnIndirect
CreateRoundRectRgn
EqualRgn
ExtCreateRegion
FillRgn
FrameRgn
GetPolyFillMode
GetRgnBox
GetRegionData
InvertRgn
OffsetRgn
PaintRgn
PtInRegion
RectInRegion
SetPolyFillMode