Cut out an area of the screen

[Natter]

Sorry, it's hard to choose from the context.

here is such window
procedure Plg_Dlg
local oBrh
private oPlg

DEFINE BRUSH oBru

DEFINE DIALOG oPlg PIXEL STYLE nOR(WS_POPUP) BRUSH oBru TRANSPARENT
ACTIVATE DIALOG oPlg
return

I draw on it
oPlg:Line()
oPlg:PolyPolygon(GetDc(oPlg:hWnd),..)
and etc.

Then I want to erase the painting.