src/layout_store.cpp

@@ -611,6 +611,15 @@ bool load_layout(const std::string& path, LayoutState& out) {
         st.rows.back().signals = names;
       } else if (key == "weight") {
         st.rows.back().weight = std::strtod(value.c_str(), nullptr);
+      } else if (key == "row") {
+        try {
+          const int r = std::stoi(value);
+          if (r >= 0) st.rows.back().row = r;
+        } catch (...) {
+        }
+      } else if (key == "width") {
+        const double w = std::strtod(value.c_str(), nullptr);
+        if (w > 0.0) st.rows.back().width = w;
       }
     } else if (section == Section::Math && !st.math.empty()) {
       MathChannel& m = st.math.back();
@@ -784,7 +793,11 @@ bool save_layout(const std::string& path, const LayoutState& state) {
   o << "relative_time = " << (state.relative_time ? "true" : "false") << "\n";
   if (state.capture_packets > 0) o << "capture_packets = " << state.capture_packets << "\n";
   for (const auto& row : state.rows) {
-    o << "\n[[plot]]\nweight = " << row.weight << "\nsignals = [";
+    o << "\n[[plot]]\n";
+    // A row of -1 is a state built without the split (nothing in the app does that now); leaving the
+    // key out keeps it readable as the one-cell-per-row file it is.
+    if (row.row >= 0) o << "row = " << row.row << "\nwidth = " << row.width << "\n";
+    o << "weight = " << row.weight << "\nsignals = [";
     for (std::size_t i = 0; i < row.signals.size(); ++i) {
       if (i != 0) o << ", ";
       o << toml_escape(row.signals[i]);

src/layout_store.hpp

@@ -24,6 +24,13 @@ struct LayoutState {
     /// The row's share of the figure's height, 1 for equal rows. Part of the layout because a sizing a
     /// user dragged is an arrangement, and an arrangement that is not saved is one that is lost.
     double weight = 1.0;
+    /// The figure row this plot sits in; plots of one row are the cells of a horizontal split, in
+    /// order. -1 means the file had no `row` key (a session from before the split), which loads as
+    /// one cell per row.
+    int row = -1;
+    /// This cell's share of its row's width, 1 for equal cells. `weight` is the *row's* and is
+    /// written on every cell of the row; `width` is the cell's own.
+    double width = 1.0;
   };
 
   double window_s = 0.0;  ///< 0 keeps the default window

src/ui_app.hpp

@@ -223,6 +223,9 @@ struct App {
   int dbg_layout_step = 0;
   /// Which step of the split probe runs next (`UDPSCOPE_PROBE_SPLIT_MS`).
   int dbg_split_step = 0;
+  /// The split probe's round trip: the arrangement saved, and the legacy copy of its file.
+  std::string dbg_split_expect;
+  std::string dbg_split_legacy_path;
   /// Which step of the cursors probe runs next (`UDPSCOPE_PROBE_CURSORS_MS`).
   int dbg_cursors_step = 0;
   /// Which step of the fit probe runs next (`UDPSCOPE_PROBE_FIT_MS`).

src/ui_layout.cpp

@@ -30,8 +30,16 @@ LayoutState collect_layout(App& app) {
       row.signals.push_back(r.layer[si] > 0 ? std::string()
                                             : r.signal_name[si]);
     }
+    // The figure row's own weight and this cell's share of the row's width.
+    const int fr = app.rows->figure_row_of(i);
     const std::vector<float>& weights = app.rows->row_weights();
-    if (static_cast<std::size_t>(i) < weights.size()) row.weight = weights[static_cast<std::size_t>(i)];
+    row.row = fr;
+    if (fr >= 0 && static_cast<std::size_t>(fr) < weights.size()) {
+      row.weight = weights[static_cast<std::size_t>(fr)];
+    }
+    const std::vector<float>& cw = app.rows->cell_weights(fr);
+    const int cell = app.rows->cell_of(i);
+    if (cell >= 0 && static_cast<std::size_t>(cell) < cw.size()) row.width = cw[static_cast<std::size_t>(cell)];
     st.rows.push_back(std::move(row));
   }
   for (std::size_t si = 0; si < model.signals().size(); ++si) {
@@ -444,17 +452,67 @@ void apply_layout(App& app, const LayoutState& st) {
 
   int rows = static_cast<int>(st.rows.size());
   if (rows > RowSet::kMaxRows) rows = RowSet::kMaxRows;
-  if (rows > 0) app.rows->set_row_count(rows);
+
+  // The arrangement. A file that names a figure row for every plot (`row = ...`) carries a horizontal
+  // split; one that names none -- every session written before the split -- is one cell per row, which
+  // is what it was. A `row` sequence that cannot be a layout (hand-edited, truncated, from a build
+  // with other limits) is not a reason to refuse the file: it loads as the old shape, with the signals
+  // where they were.
+  std::vector<int> cells_per_row;
+  {
+    bool all_rows = !st.rows.empty() && st.rows.size() <= static_cast<std::size_t>(RowSet::kMaxRows);
+    int prev = -1;
+    for (const LayoutState::Row& r : st.rows) {
+      if (!all_rows) break;
+      if (r.row < 0 || r.row < prev || r.row > prev + 1 || (prev < 0 && r.row != 0)) {
+        all_rows = false;
+      } else if (r.row != prev) {
+        cells_per_row.push_back(1);
+      } else if (++cells_per_row.back() > RowSet::kMaxCellsPerRow) {
+        all_rows = false;
+      }
+      prev = r.row;
+    }
+    if (!all_rows) cells_per_row.clear();
+  }
+  const bool split_file = !cells_per_row.empty();
+  if (split_file) {
+    app.rows->set_cells_per_row(cells_per_row);
+  } else if (rows > 0) {
+    app.rows->set_row_count(rows);
+  }
 
   // The rows' shares of the height come from the same file as their signals: a sizing a user dragged is
   // an arrangement, and the layout is where an arrangement lives. Absent from an older file, the weights
-  // are all 1 -- equal rows -- which is what such a file was saved with.
+  // are all 1 -- equal rows -- which is what such a file was saved with. The weight is the *figure row's*
+  // and is written on every cell of it; the row's first cell is the one read.
   {
     std::vector<float> weights;
     weights.reserve(st.rows.size());
-    for (const LayoutState::Row& wr : st.rows) weights.push_back(static_cast<float>(wr.weight));
+    if (split_file) {
+      std::size_t at = 0;
+      for (const int n : cells_per_row) {
+        weights.push_back(static_cast<float>(st.rows[at].weight));
+        at += static_cast<std::size_t>(n);
+      }
+    } else {
+      for (const LayoutState::Row& wr : st.rows) weights.push_back(static_cast<float>(wr.weight));
+    }
     app.rows->set_row_weights(std::move(weights));
   }
+  // The cells' shares of a split row's width, after the arrangement (which resets them).
+  if (split_file) {
+    std::size_t at = 0;
+    for (std::size_t fr = 0; fr < cells_per_row.size(); ++fr) {
+      const std::size_t n = static_cast<std::size_t>(cells_per_row[fr]);
+      if (n >= 2) {
+        std::vector<float> widths;
+        for (std::size_t c = 0; c < n; ++c) widths.push_back(static_cast<float>(st.rows[at + c].width));
+        app.rows->set_cell_weights(static_cast<int>(fr), std::move(widths));
+      }
+      at += n;
+    }
+  }
   for (int i = 0; i < rows; ++i) {
     int slot = 0;
     for (const std::string& name : st.rows[static_cast<std::size_t>(i)].signals) {

src/ui_probe.cpp

@@ -18,6 +18,7 @@
 #include <cmath>
 #include <cstdio>
 #include <cstring>
+#include <fstream>
 #include <tuple>
 
 namespace udpscope {
@@ -3900,6 +3901,34 @@ void split_probe_report(App& a, const char* tag) {
 }
 
 namespace {
+/// The arrangement and what is in it, as one comparable string: per figure row its weight, per cell
+/// its width share and its traces. Weights are read back as stored, so a load is compared with a save
+/// to the precision the file keeps (`%.4f`).
+std::string split_probe_shape(const RowSet& rs) {
+  std::string out;
+  char buf[48];
+  for (int fr = 0; fr < rs.figure_row_count(); ++fr) {
+    const std::vector<float>& rw = rs.row_weights();
+    const std::vector<float>& cw = rs.cell_weights(fr);
+    std::snprintf(buf, sizeof(buf), "%sr%d(h=%.4f)", fr == 0 ? "" : " ", fr,
+                  static_cast<std::size_t>(fr) < rw.size() ? static_cast<double>(rw[static_cast<std::size_t>(fr)]) : 1.0);
+    out += buf;
+    const int first = rs.first_plot_of_row(fr);
+    for (int k = 0; k < rs.cells_in_row(fr); ++k) {
+      std::snprintf(buf, sizeof(buf), "[w=%.4f:", static_cast<std::size_t>(k) < cw.size() ? static_cast<double>(cw[static_cast<std::size_t>(k)]) : 1.0);
+      out += buf;
+      bool any = false;
+      for (const std::string& n : rs.row(first + k).signal_name) {
+        if (n.empty()) continue;
+        out += (any ? "," : "") + n;
+        any = true;
+      }
+      out += any ? "]" : "-]";
+    }
+  }
+  return out;
+}
+
 /// After any structural change: the new figure is the area's, and the frame tick re-lays it out.
 void split_probe_restructured(App& a) {
   if (a.area != nullptr) a.area->set_figure(&a.rows->figure());
@@ -4002,8 +4031,95 @@ gboolean split_probe_step(gpointer user) {
       split_probe_restructured(*a);
       split_probe_next(*a);
       break;
-    default:
+    case 6: {
       split_probe_report(*a, "remove");
+      // The session round trip, through the real entry points. Plot 0 alone on row 0, plots 1 and 2 side
+      // by side on row 1, each cell holding a different trace, row 0 at twice row 1's height and the
+      // split row at 3:1.
+      rs.set_cells_per_row({1, 2});
+      split_probe_clear_all(*a);
+      for (int p = 0; p < 3; ++p) split_probe_assign(*a, p, static_cast<std::size_t>(p));
+      rs.set_row_weights({2.0f, 1.0f});
+      rs.set_cell_weights(1, {3.0f, 1.0f});
+      a->dbg_split_expect = split_probe_shape(rs);
+      const LayoutState saved = collect_layout(*a);
+      const std::string path = std::string(g_get_tmp_dir()) + "/udpscope-split-probe.toml";
+      const bool wrote = save_layout(path, saved);
+      // Back to the plain arrangement, so a load that did nothing cannot pass.
+      rs.set_cells_per_row({1});
+      split_probe_clear_all(*a);
+      LayoutState loaded;
+      const bool read = load_layout(path, loaded);
+      // The same file with its `row`/`width` lines stripped: a session from before the split.
+      std::string legacy_path = path + ".legacy";
+      {
+        std::ifstream in(path);
+        std::ofstream out(legacy_path);
+        std::string line;
+        while (std::getline(in, line)) {
+          if (line.rfind("row = ", 0) == 0 || line.rfind("width = ", 0) == 0) continue;
+          out << line << "\n";
+        }
+      }
+      a->dbg_split_legacy_path = legacy_path;
+      std::remove(path.c_str());
+      if (read) apply_layout(*a, loaded);
+      std::fprintf(stderr, "[split-probe] roundtrip-io    wrote=%d read=%d plots_in_file=%zu\n",
+                   wrote ? 1 : 0, read ? 1 : 0, loaded.rows.size());
+      split_probe_restructured(*a);
+      split_probe_next(*a);
+      break;
+    }
+    case 7: {
+      split_probe_report(*a, "roundtrip");
+      const std::string now = split_probe_shape(rs);
+      std::fprintf(stderr, "[split-probe] roundtrip       rt=%d expect=%s got=%s\n",
+                   now == a->dbg_split_expect ? 1 : 0, a->dbg_split_expect.c_str(), now.c_str());
+      rs.set_cells_per_row({1});
+      split_probe_clear_all(*a);
+      LayoutState loaded;
+      const bool read = load_layout(a->dbg_split_legacy_path, loaded);
+      std::remove(a->dbg_split_legacy_path.c_str());
+      int rows_unset = 1;
+      for (const LayoutState::Row& r : loaded.rows) {
+        if (r.row != -1) rows_unset = 0;
+      }
+      if (read) apply_layout(*a, loaded);
+      std::fprintf(stderr, "[split-probe] legacy-io       read=%d plots_in_file=%zu row_unset=%d\n",
+                   read ? 1 : 0, loaded.rows.size(), rows_unset);
+      split_probe_restructured(*a);
+      split_probe_next(*a);
+      break;
+    }
+    case 8: {
+      split_probe_report(*a, "legacy");
+      // A `row` sequence that cannot be a layout loads as one cell per row rather than refusing the
+      // file: five cells in one row (over the cap), a gap, a row that goes back, and one that does not
+      // start at 0.
+      const LayoutState base = collect_layout(*a);
+      const std::vector<std::vector<int>> bad = {{0, 0, 0, 0, 0}, {0, 2, 2}, {0, 1, 0}, {1, 1, 2}};
+      std::string out;
+      int ok = 1;
+      for (const std::vector<int>& seq : bad) {
+        LayoutState st = base;
+        st.rows.clear();
+        for (const int r : seq) {
+          LayoutState::Row row = base.rows[0];
+          row.row = r;
+          st.rows.push_back(row);
+        }
+        apply_layout(*a, st);
+        const bool one_each = rs.figure_row_count() == static_cast<int>(seq.size()) &&
+                              rs.row_count() == static_cast<int>(seq.size());
+        if (!one_each) ok = 0;
+        out += (out.empty() ? "" : " ") + std::to_string(rs.figure_row_count()) + "/" +
+               std::to_string(rs.row_count());
+      }
+      std::fprintf(stderr, "[split-probe] invalid-rows    ok=%d frows/plots=[%s]\n", ok, out.c_str());
+      split_probe_restructured(*a);
+      break;
+    }
+    default:
       break;
   }
   return G_SOURCE_REMOVE;