code: func CaptureScreen(args ...int) C.MMBitmapRef {
  	var x, y, w, h C.size_t
  
  	if len(args) > 3 {
  		x = C.size_t(args[0])
  		y = C.size_t(args[1])
  		w = C.size_t(args[2])
  		h = C.size_t(args[3])
  	} else {
  		x = 0
  		y = 0
  		// Get screen size.
  		var displaySize C.MMSize
  		displaySize = C.getMainDisplaySize()
  		w = displaySize.width
  		h = displaySize.height
  	}
  
  	bit := C.capture_screen(x, y, w, h)
  	return bit
  }
docs: // CaptureScreen capture the screen return bitmap(c struct),
  // use `defer robotgo.FreeBitmap(bitmap)` to free the bitmap
  //
  // robotgo.CaptureScreen(x, y, w, h int)