emWin手册上是这么说的:
Additional information
The given data value is added to the data object. If the data object is full, that
means it contains as many data items as specified in parameter MaxNumItems during
the creation, it first shifts the data items by one before adding the new value. So the
first data item is shifted out when adding a data item to a full object.
The value 0x7FFF can be used to handle invalid data values. These values are
excluded when drawing the graph. The following screenshot shows a graph with 2
gaps of invalid data: