This simple script decomposes the value of the Average True Range into a bullish component and a bearish component.
The script supports two plotting methods; Mirrored and Two Lines. If Mirrored is chosen, the indicator plots the bullish component as a positive number, and the bearish component as a negative number. If Two Lines is chosen, the indicator plots two lines, both of positive values. It is the same data, just visualized differently.
Side note: This is very similar to how the strength (average gain) part in the Relative Strength Index calculation works. However, the RSI uses the realized range (close - previous close) rather than true range. If we were to use the bullish component of the ATR as the average bullish gain part in the RSI calculation, and the bearish component of the ATR as the average bearish gain part in the RSI calculation, we would get very similar (but not equal) results to the standard RSI. This shows how the ATR and the RSI are related to each other.