using "SetWindowRgn" you can create much more than round/eclipse Mask

instead of a Handle from CreateEllipticRgn()

hRgn := CreateEllipticRgn(nLeftRect,nTopRect,nRightRect,nBottomRect)

you also can assign a Array with a RECT() Structure

AADD(aRegion,{116,29,124,30})

! Note : Coordinate must close lines at Start / End

as you see Mask is transparency. we can use it on ever Control which have a Handle ( o:getHWND() )

this Sample use a Bitmap on o:DrawingArea od a Dialog without Titlebar
as i use oDlg as Parent all get transparent except those Region i want to show Bitmap