The DRAW_HISTOGRAM2 drawing style is used for plotting the values of two indicator's buffers as a histogram. The indicator plots the vertical section for each bar between the Open and Close prices.
The DRAW_HISTOGRAM2 drawing style can be used for a drawing in a separate window and main chart window. It doesn't plot empty values, the empty indicator values must be specified explicitly. Two data buffers are needed for the DRAW_HISTOGRAM2 style. The color, width and style of the histogram changed randomly each N ticks. In the OnInit() function, it chooses a day of the week (invisible_day), the indicator values of the bars of this week day will be filled with empty values (PLOT_EMPTY_VALUE=0):
See also: The Drawing Styles in MQL5.