Switch bars positions based on the sign of the contribution

Author: xjules

src/ert/gui/plotting/ert_plots/waterfall.py

@@ -140,12 +140,16 @@ def _plot_waterfall(
         width=0.7,
     )
 
-    # Connector lines between bars
+    # Connector lines between bars, at the running total after each bar
+    # (bottom of bar for negative contributions, top otherwise)
     for i in range(n_bars - 1):
-        top_i = bottoms[i] + heights[i]
+        if types[i] == "contribution" and values[i] < 0:
+            level_i = bottoms[i]
+        else:
+            level_i = bottoms[i] + heights[i]
         ax.plot(
             [x[i] + 0.35, x[i + 1] - 0.35],
-            [top_i, top_i],
+            [level_i, level_i],
             color="grey",
             linewidth=0.6,
             linestyle="--",