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procedure TForm1.Button1Click(Sender: TObject);
var
DCanvas: TCanvas;
DHandle: HWND;
begin
DHandle:=GetDC(0);
if DHandle<>0 then
begin
   try
     DCanvas:=TCanvas.Create;
     try
       DCanvas.Handle:=DHandle;
       DCanvas.Pen.Color:=clRed;
       DCanvas.Font.Size:=72;
       DCanvas.Brush.Style:=bsClear;
       DCanvas.MoveTo(0,0);
       DCanvas.LineTo(500,500);
finally
       DCanvas.Free;
     end;
    finally
      if ReleaseDc(0, DHandle)<>1 then
        RaiseLastOSError;
    end;
end
else
   RaiseLastOSError;
end;