improved perfs and event management

src/ui_layout.cpp

@@ -284,18 +284,38 @@ void apply_layout(App& app, const LayoutState& st) {
   ScopeModel& model = *app.model;
   const auto& signals = model.signals();
 
-  // The session's own state first: enabling is what starts acquisition, and a math channel's
-  // *name* is only a signal once its graph is installed -- a row that holds one would otherwise be
-  // skipped as a name the stream no longer has.
+  // The window before anything structural. Nothing is enabled yet, so there are no channels
+  // to plan for and this only *records* the span -- but it is the span every plan below is
+  // then made with, so the `apply_time_window()` at the end of this function finds the
+  // decimation already right and re-plans nothing. Stated last, as it used to be, it moved
+  // the stride and bought a second full allocation of the buffer after the data was already
+  // flowing into the first.
+  if (st.window_s > 0.0) model.set_target_span(st.window_s);
+
+  // The math graph before the enables, because a math channel's *name* is only a signal once
+  // its graph is installed -- a row that holds one would otherwise be skipped as a name the
+  // stream no longer has -- and because installing it while nothing is enabled is the one
+  // ordering in which it does not pay for a buffer of its own. `signals` is a reference to
+  // the model's own vector, so the synthetic entries this appends are visible below.
+  app.math = st.math;
+  apply_math_channels(app);
+
+  // What the session had on, collected and enabled **once**, at the end of this function.
+  // Each enable re-plans the partition, and a re-plan allocates -- and so touches -- the whole
+  // of `--buffer-mb`: seven signals one at a time is seven allocations before a single sample
+  // is kept, which is the ten seconds of blank window a large buffer used to start with. The
+  // math channels are not collected here: their enable state is the session's `math` and
+  // `set_math_channels()` has already restored it, so listing them again could turn on one
+  // the user saved off.
+  std::vector<std::size_t> wanted;
+  wanted.reserve(st.enabled.size());
   for (const std::string& name : st.enabled) {
     for (std::size_t si = 0; si < signals.size(); ++si) {
       if (signals[si].name != name || signals[si].math) continue;
-      model.set_signal_enabled(si, true);
+      wanted.push_back(si);
       break;
     }
   }
-  app.math = st.math;
-  apply_math_channels(app);
   app.measures = st.measures;
   app.measure_stats_on = st.measure_stats;
   app.updating_panels = true;
@@ -341,12 +361,18 @@ void apply_layout(App& app, const LayoutState& st) {
         // Enabling is what starts acquisition (a loaded plot nobody acquires would
         // come back blank), and it is what a drop does for the signal it places.
         app.rows->assign(i, slot, name, name, signal_color_index(signals, si));
-        model.set_signal_enabled(si, true);
+        wanted.push_back(si);
         ++slot;
         break;
       }
     }
   }
+  // The one structural change of a restored session: everything the file had on, and
+  // everything its rows placed, in a single re-plan. Enabling is what starts acquisition (a
+  // loaded plot nobody acquires would come back blank), and it is what a drop does for the
+  // signal it places -- so a row holding a signal the `enabled` list did not name is enabled
+  // here, by having been collected above.
+  model.set_signals_enabled(wanted, true);
 
   for (const auto& cal : st.calibration) {
     for (std::size_t si = 0; si < signals.size(); ++si) {