Module waterfall 

Waterfall (bridge) chart: geom_waterfall. Each step is a bar floating from the previous running total; total bars rise from 0. Bars are coloured through the fill scale on the stat’s direction column (Increase / Decrease / Total), and thin connectors join each bar’s end to the next bar.

Structs

GeomWaterfall

Waterfall chart. Map x (the steps, in data order) and y (each step’s change). List subtotal steps in totals (their y is ignored) and set final_total to append a closing total bar.