figure: x axes follow the column structure; split rows keep the right gutter on the last cell only

src/render/renderer.cpp

@@ -480,10 +480,11 @@ void Renderer::draw(Figure& figure) {
   // than laying each row out a second time. Nothing draws before this: a row's
   // viewport is the figure's to set.
   //
-  // The figure's one x axis needs no pass of its own: it is the bottom row's own, so
-  // that row stages it in its own strip through `draw_tick_labels()` like any other
-  // plot's axis -- and every row above it reserved no x chrome, which is what keeps
-  // the labels from appearing once per row without a second staging here.
+  // A shared x axis needs no pass of its own: it is the bottom row's own (of a run of rows
+  // with the same columns), so that row stages it in its own strip through
+  // `draw_tick_labels()` like any other plot's axis -- and every row of the run above it
+  // reserved no x chrome, which is what keeps the labels from appearing once per row without
+  // a second staging here. A row whose columns differ stages its own.
   figure.layout();
   for (u32 row = 0; row < rows; ++row) {
     Plot& plot = figure.plot(row);
@@ -878,8 +879,8 @@ void Renderer::draw_tick_labels(const Plot& plot, const PlotLayout& layout) {
   const f32 line_h = font_backend_.height();
 
   // X labels: unless the plot gave its x label strip away -- a row of a `Figure`
-  // that reserves no x chrome, because the figure draws one shared axis in the bottom
-  // row's own strip instead -- in which case it has no strip to put them in and their
+  // that reserves no x chrome, because the row below has the same columns and draws the
+  // axis in its own strip instead -- in which case it has no strip to put them in and their
   // absence is the point. A plot with no strip would otherwise stage its labels just
   // above `axes`' bottom edge, i.e. over its own data. Centred under their tick on the
   // strip's single text line, which is the one rule for a plot's labels and a figure's