ui: signal pages honour the signal lock and disable the plot a signal is already on

The per-signal page bypassed the signals lock for the acquire tick and the math
Edit/Delete buttons, and offered "Plot on r" for a plot the signal was already on.
A removed page also let another signal's page show during the close animation.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/ui_signal_page.cpp

@@ -96,6 +96,8 @@ void fill(App& app, const std::string& name, GtkWidget* page) {
   g_object_set_data(G_OBJECT(enable), "udpscope-signal", GSIZE_TO_POINTER(index));
   g_signal_connect(enable, "notify::active", G_CALLBACK(on_signal_switch), &app);
   gtk_widget_set_visible(enable, sig.math || app.waveform_name.empty());
+  // The signal lock is the list's lock too: the page may not do what the locked list refuses.
+  gtk_widget_set_sensitive(enable, unlocked);
   gtk_box_append(GTK_BOX(page), enable);
 
   // Colour.
@@ -137,7 +139,13 @@ void fill(App& app, const std::string& name, GtkWidget* page) {
     GtkWidget* b = text_button(std::to_string(r + 1).c_str(), rows_box);
     tag(b, index);
     g_object_set_data(G_OBJECT(b), "udpscope-row", GINT_TO_POINTER(r));
-    gtk_widget_set_tooltip_text(b, "draw this signal on this plot");
+    // A button for a plot the signal is already on would add it to a second slot there.
+    bool on_this_row = false;
+    for (int slot = 0; slot < RowSet::kSlotsPerRow; ++slot) {
+      if (app.rows->row(r).signal_name[static_cast<std::size_t>(slot)] == sig.name) on_this_row = true;
+    }
+    gtk_widget_set_sensitive(b, !on_this_row);
+    gtk_widget_set_tooltip_text(b, on_this_row ? "already on this plot" : "draw this signal on this plot");
     g_signal_connect(b, "clicked", G_CALLBACK(+[](GtkButton* b, gpointer user) {
                        outlive_the_rebuild(GTK_WIDGET(b));
                        assign_signal_to_row(*static_cast<App*>(user), tagged(b),
@@ -176,10 +184,12 @@ void fill(App& app, const std::string& name, GtkWidget* page) {
   GtkWidget* more = gtk_box_new(GTK_ORIENTATION_HORIZONTAL, 6);
   if (sig.math) {
     GtkWidget* edit = text_button("Edit graph...", more);
+    gtk_widget_set_sensitive(edit, unlocked);
     tag(edit, index);
     g_signal_connect(edit, "clicked", G_CALLBACK(on_math_edit_clicked), &app);
     GtkWidget* del = text_button("Delete", more);
     gtk_widget_add_css_class(del, "destructive-action");
+    gtk_widget_set_sensitive(del, unlocked);
     tag(del, index);
     g_signal_connect(del, "clicked", G_CALLBACK(on_math_delete_clicked), &app);
   } else {
@@ -221,6 +231,11 @@ void signal_pages_sync(App& app) {
   for (auto it = app.signal_pages.begin(); it != app.signal_pages.end();) {
     if (signal_index(app, it->first) == std::string::npos) {
       if (slideover_page(app) == page_id(it->first)) slideover_close(app);
+      // The stack keeps showing the dying page through the close animation; park it on the list so that
+      // removing the page does not let another signal's page take its place for those frames.
+      if (slideover_has_page(app, "signals")) {
+        gtk_stack_set_visible_child_name(GTK_STACK(app.slideover.stack), "signals");
+      }
       slideover_remove_page(app, page_id(it->first));
       it = app.signal_pages.erase(it);
     } else {
@@ -295,12 +310,46 @@ gboolean signal_page_probe(gpointer user) {
     }
   }
 
+  // Start from a signal that is on no plot (the layout may have it somewhere), through the page's own button.
+  auto page_it = a.signal_pages.find(name);
+  if (signal_plotted(a, name) && page_it != a.signal_pages.end()) {
+    GtkWidget* off0 = find_descendant(page_it->second, [](GtkWidget* w) {
+      return is_button_labelled(w, "Remove from plots");
+    });
+    if (off0 != nullptr) g_signal_emit_by_name(off0, "clicked");
+  }
+
   // Plot on row 0 through the function the "Plot on" buttons call, then take it off through the page's own
   // button (outlive_the_rebuild + remove_signal_from_plots + the page's refill).
   const bool assigned = assign_signal_to_row(a, index, 0);
   const int plot_on_row0 = assigned && signal_plotted(a, name) ? 1 : 0;
+
+  // The refilled page disables the button of the plot the signal is now on.
+  int plot_on_row0_disabled = -1;
+  page_it = a.signal_pages.find(name);
+  GtkWidget* rows_box_on = page_it == a.signal_pages.end() ? nullptr : find_descendant(page_it->second, [](GtkWidget* w) {
+    return std::string(gtk_widget_get_name(w)) == "udpscope-plot-on";
+  });
+  if (rows_box_on != nullptr && gtk_widget_get_first_child(rows_box_on) != nullptr) {
+    plot_on_row0_disabled = gtk_widget_get_sensitive(gtk_widget_get_first_child(rows_box_on)) ? 0 : 1;
+  }
+
+  // The signal lock: with it on, the page's acquire tick is insensitive after the sync (the lock change
+  // re-runs it through rebuild_signal_panels); restored afterwards.
+  int locked_enable_sensitive = -1;
+  const bool was_locked = a.signals_locked;
+  a.signals_locked = true;
+  signal_pages_sync(a);
+  page_it = a.signal_pages.find(name);
+  if (page_it != a.signal_pages.end()) {
+    GtkWidget* enable_now = find_descendant(page_it->second, [](GtkWidget* w) { return GTK_IS_CHECK_BUTTON(w); });
+    if (enable_now != nullptr) locked_enable_sensitive = gtk_widget_get_sensitive(enable_now) ? 1 : 0;
+  }
+  a.signals_locked = was_locked;
+  signal_pages_sync(a);
+
   int removed = -1;
-  auto page_it = a.signal_pages.find(name);
+  page_it = a.signal_pages.find(name);
   GtkWidget* off = page_it == a.signal_pages.end()
                        ? nullptr
                        : find_descendant(page_it->second, [](GtkWidget* w) {
@@ -370,9 +419,11 @@ gboolean signal_page_probe(gpointer user) {
   slideover_close(a);
   std::fprintf(stderr,
                "[signalpage] name=%s open=%d pages=%d enable_visible=%d plot_buttons=%d plot_on_row0=%d "
+               "plot_on_row0_disabled=%d locked_enable_sensitive=%d "
                "removed=%d btn_row0=%d back_to_list=%d row_opens=%d pruned=%d rows=%d\n",
-               name.c_str(), open, pages, enable_visible, plot_buttons, plot_on_row0, removed, btn_row0,
-               back_to_list, row_opens, pruned, a.rows->row_count());
+               name.c_str(), open, pages, enable_visible, plot_buttons, plot_on_row0, plot_on_row0_disabled,
+               locked_enable_sensitive, removed, btn_row0, back_to_list, row_opens, pruned,
+               a.rows->row_count());
   return G_SOURCE_REMOVE;
 }