Dibujar sobre el escritorio de Windows

[roman]

Un ejemplito, aunque no con lo de Zarco,

Código Delphi [-]
var
  Desktop: TControlCanvas;

begin
  Desktop := TControlCanvas.Create;

  try
    Desktop.Handle := GetDC(0);

    Desktop.Pen.Width := 2;
    Desktop.Pen.Color := clRed;

    Desktop.MoveTo(0, 0);
    Desktop.LineTo(Screen.Width, Screen.Height);

    Desktop.MoveTo(0, Screen.Height);
    Desktop.LineTo(Screen.Width, 0);
  finally
    Desktop.Free
  end;
end;

// Saludos