func doClear(_data)
  fvar(flg)
  flg = '0'
  if(isdef(ColorBuffer))
    flg += '|GL_COLOR_BUFFER_BIT'
  end
  if(isdef(DepthBuffer))
    flg += '|GL_DEPTH_BUFFER_BIT'
  end
  if(isdef(StencilBuffer))
    flg += '|GL_STENCIL_BUFFER_BIT'
  end
  println('glClear(' + flg + ');')
  event(onClear)
end