fix(plot): a figure row's strip shows labels and title independently, and the shared axis is the bottom row's strip

src/render/renderer.cpp

@@ -364,27 +364,22 @@ void Renderer::draw(Figure& figure) {
   for (u32 row = 0; row < rows; ++row) prepare_plot(figure.plot(row));
 
   // The figure's one layout for the frame. It hands every row its rect and its
-  // x-label policy, advances the link groups, and lays every row out against its own
+  // x-strip mode, advances the link groups, and lays every row out against its own
   // rect -- which is why the rows below are drawn with the layout it produced rather
   // than laying each row out a second time. Nothing draws before this: a row's
   // viewport is the figure's to set.
-  const FigureLayout& layout = figure.layout();
+  //
+  // 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.
+  figure.layout();
   for (u32 row = 0; row < rows; ++row) {
     Plot& plot = figure.plot(row);
     // The layout the figure just computed, read through the non-recomputing
     // overload -- the one layout of this frame, not a second derivation of it.
     draw_plot(plot, static_cast<const Plot&>(plot).layout());
   }
-
-  // The figure's one shared x axis, staged last so it joins the frame's single text
-  // flush: the labels of the last row's x axes, in the strip the figure measured
-  // under it. The rows reserved no strip of their own for them (see
-  // `Plot::set_x_label_strip()`), which is what keeps one set of labels from being
-  // drawn once per row; with the figure set to label every row, there is no shared
-  // strip and each row drew its own above.
-  if (rows != 0u && figure.x_labels_only_on_bottom() && layout.x_axis_strip.h > 0.0f) {
-    draw_x_tick_labels(figure.plot(rows - 1u), layout.x_axis_strip);
-  }
   flush_text();
 }
 
@@ -654,32 +649,29 @@ void Renderer::draw_axis_lines(const Plot& plot) {
   }
 }
 
-void Renderer::draw_x_tick_labels(const Plot& plot, const Rect& strip) {
-  // Centred under their tick, on the strip's single text line -- the one rule for a
-  // plot's own label strip and for the strip a figure shares out under its last row.
-  // A plot that reserved no strip of its own hands its labels to the figure, which
-  // is why this takes the rect rather than reading the layout it came from.
-  const f32 line_h = font_backend_.height();
-  for (u32 i = 0; i < plot.x_axis_count(); ++i) {
-    const Transform transform = plot.x_transform(i);
-    for (const Tick& tick : plot.x_axis(i).ticks) {
-      if (!tick.major || tick.label.empty()) continue;
-      const f32 width = font_backend_.measure(tick.label.c_str());
-      stage_text({static_cast<f32>(transform.to_screen_x(tick.value)) - 0.5f * width,
-                  strip.y + 0.5f * (strip.h - line_h)},
-                 tick.label.c_str());
-    }
-  }
-}
-
 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`
-  // whose figure drew one shared axis 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.
-  if (plot.x_label_strip()) draw_x_tick_labels(plot, layout.x_label_area);
+  // 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
+  // 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
+  // shared axis alike -- the figure's axis is drawn by this same pass, in the bottom
+  // row's own `x_label_area`.
+  if (x_strip_has_labels(plot.x_strip_mode())) {
+    for (u32 i = 0; i < plot.x_axis_count(); ++i) {
+      const Transform transform = plot.x_transform(i);
+      for (const Tick& tick : plot.x_axis(i).ticks) {
+        if (!tick.major || tick.label.empty()) continue;
+        const f32 width = font_backend_.measure(tick.label.c_str());
+        stage_text({static_cast<f32>(transform.to_screen_x(tick.value)) - 0.5f * width,
+                    layout.x_label_area.y + 0.5f * (layout.x_label_area.h - line_h)},
+                   tick.label.c_str());
+      }
+    }
+  }
 
   // Y labels: right-aligned in their strip, centred on the tick and pulled back
   // inside the strip at the two extremes (a label centred on the top tick would