нужно почитать про Regions 
Region Functions 
CombineRgn 
CreateEllipticRgn 
CreateEllipticRgnIndirect 
CreatePolygonRgn 
CreatePolyPolygonRgn 
CreateRectRgn 
CreateRectRgnIndirect 
CreateRoundRectRgn 
EqualRgn 
ExtCreateRegion 
FillRgn 
FrameRgn 
GetPolyFillMode 
GetRegionData 
GetRgnBox 
InvertRgn 
OffsetRgn 
PaintRgn 
PtInRegion 
RectInRegion 
SetPolyFillMode  
 
GetWindowRgn 
SetWindowRgn 
		
	
		
		
		
		
			
		
		
		
		
	
		
		
	
	
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