refactor: what counts as an event moves into its own evaluator, so a search can ask the same question the trigger asks

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

CMakeLists.txt

@@ -105,6 +105,7 @@ add_executable(udpscope
   src/config.cpp
   src/channel.cpp
   src/model.cpp
+  src/condition.cpp
   src/trigger.cpp
   src/acquisition.cpp
   src/plot_host.cpp

src/condition.cpp

@@ -0,0 +1,49 @@
+// SPDX-License-Identifier: MIT
+// SPDX-FileCopyrightText: 2026 Martino Ferrari
+
+#include "condition.hpp"
+
+namespace udpscope {
+
+void EventDetector::configure(const EventCondition& c) noexcept {
+  if (c == cond_) return;
+  cond_ = c;
+  reset();
+}
+
+void EventDetector::reset() noexcept {
+  have_prev_ = false;
+  prev_ = 0.0;
+}
+
+double EventDetector::feed(double value, double t) noexcept {
+  if (!have_prev_) {
+    prev_ = value;
+    have_prev_ = true;
+    return kNoEvent;
+  }
+  double event = kNoEvent;
+  switch (cond_.type) {
+    case TriggerType::Edge:
+      event = feed_edge(value, t);
+      break;
+    case TriggerType::PulseWidth:
+    case TriggerType::Window:
+    case TriggerType::Dropout:
+      break;  // implemented in the tasks that add their panel rows
+  }
+  // After the handler: every crossing test above reads `prev_` as the previous sample.
+  prev_ = value;
+  return event;
+}
+
+double EventDetector::feed_edge(double value, double t) noexcept {
+  const bool up = crossed_up(value);
+  const bool down = crossed_down(value);
+  const bool fired = (cond_.edge == TriggerEdge::Rising && up) ||
+                     (cond_.edge == TriggerEdge::Falling && down) ||
+                     (cond_.edge == TriggerEdge::Both && (up || down));
+  return fired ? t : kNoEvent;
+}
+
+}  // namespace udpscope

src/condition.hpp

@@ -0,0 +1,91 @@
+// SPDX-License-Identifier: MIT
+// SPDX-FileCopyrightText: 2026 Martino Ferrari
+
+#pragma once
+
+#include <limits>
+
+namespace udpscope {
+
+/// Which way through a level counts. Shared by every condition type: for `Window` it is
+/// the direction through the *band* (into it, out of it, or either), and for `Dropout` it
+/// selects which crossings count as the signal still being alive.
+///
+/// It lives here rather than in `trigger.hpp` because the buffer search needs the
+/// evaluator without the engine's arming state.
+enum class TriggerEdge { Rising, Falling, Both };
+
+/// What shape in the signal counts as an event.
+enum class TriggerType { Edge, PulseWidth, Window, Dropout };
+
+/// How a measured pulse width is compared with the condition's bounds. `Less` is the
+/// glitch trigger: "a pulse shorter than it should be".
+enum class WidthCmp { Less, Greater, Within, Outside };
+
+/// Everything that decides whether a sample is an event. No arming, no capture window:
+/// those belong to `TriggerConfig`.
+struct EventCondition {
+  TriggerType type = TriggerType::Edge;
+  double level = 0.0;
+  double level2 = 0.0;               ///< Window: the band's other edge. Ignored otherwise.
+  TriggerEdge edge = TriggerEdge::Rising;
+  WidthCmp cmp = WidthCmp::Greater;  ///< PulseWidth only.
+  double width_s = 1.0e-3;           ///< PulseWidth only.
+  double width2_s = 2.0e-3;          ///< PulseWidth, Within/Outside only.
+  double timeout_s = 1.0e-3;         ///< Dropout only.
+
+  bool operator==(const EventCondition& o) const noexcept {
+    return type == o.type && level == o.level && level2 == o.level2 && edge == o.edge &&
+           cmp == o.cmp && width_s == o.width_s && width2_s == o.width2_s &&
+           timeout_s == o.timeout_s;
+  }
+  bool operator!=(const EventCondition& o) const noexcept { return !(*this == o); }
+};
+
+/// The event condition's state machine: one sample in, an event time or nothing out.
+///
+/// It holds no arming state and no capture state -- that is `TriggerEngine`'s job -- which
+/// is what lets the buffer search run the *same* evaluator over retained samples and get
+/// the answers the live trigger would have given.
+///
+/// Every condition but `Edge` is sequential: a pulse's width is only known at its closing
+/// edge, and a dropout is a measured absence. Callers must therefore feed it **every**
+/// sample in stream order, including samples they intend to ignore; a gap is a pulse it can
+/// never close.
+class EventDetector {
+ public:
+  /// What `feed()` returns when the sample is not an event.
+  static constexpr double kNoEvent = std::numeric_limits<double>::quiet_NaN();
+
+  /// Re-applying the same condition is a no-op, deliberately: the producer calls this on
+  /// every packet, and resetting there would restart the machine before any pulse could
+  /// close. A genuinely different condition resets, because its state means nothing.
+  void configure(const EventCondition& c) noexcept;
+  void reset() noexcept;
+
+  /// One sample, in stream order. Returns the event's own stream time, or `kNoEvent`.
+  ///
+  /// There is no finite-value check: a NaN sample is benign here (every comparison against
+  /// it is false, so it cannot fire), and rejecting one would leave `prev_` at the last good
+  /// value and let the sample *after* the NaN fire a crossing that today cannot happen.
+  double feed(double value, double t) noexcept;
+
+  double last_value() const noexcept { return prev_; }
+  bool have_last() const noexcept { return have_prev_; }
+  const EventCondition& condition() const noexcept { return cond_; }
+
+ private:
+  bool crossed_up(double v) const noexcept {
+    return prev_ < cond_.level && v >= cond_.level;
+  }
+  bool crossed_down(double v) const noexcept {
+    return prev_ > cond_.level && v <= cond_.level;
+  }
+  double feed_edge(double value, double t) noexcept;
+
+  EventCondition cond_{};
+  bool have_prev_ = false;
+  double prev_ = 0.0;
+};
+
+}  // namespace udpscope

src/trigger.cpp

@@ -4,6 +4,7 @@
 #include "trigger.hpp"
 
 #include <algorithm>
+#include <cmath>
 
 namespace udpscope {
 
@@ -20,8 +21,10 @@ void TriggerEngine::configure(const TriggerConfig& cfg, const std::string& chann
   post_seconds_ = post_seconds > 0.0 ? post_seconds : 0.0;
   pre_seconds_ = pre_seconds > 0.0 ? pre_seconds : 0.0;
   oldest_s_ = oldest_s;
+  // A no-op unless the condition actually changed: this runs on every packet.
+  detector_.configure(cfg_.condition);
   if (channel_changed) {
-    have_prev_ = false;
+    detector_.reset();
     pending_ = false;
     post_accum_count_ = 0;
   }
@@ -32,23 +35,21 @@ void TriggerEngine::arm(double now_s) noexcept {
   pending_ = false;
   post_accum_count_ = 0.0;
   holdoff_until_s_ = now_s;
-  have_prev_ = false;
+  detector_.reset();
 }
 
 bool TriggerEngine::process(double value, double now_s) noexcept {
   if (!cfg_.enabled || !armed_ || cfg_.channel < 0) return false;
 
-  // Hold-off: settled, waiting for the next edge.
+  // The detector is fed **first and unconditionally**, on every sample the engine sees --
-  if (!pending_ && now_s < holdoff_until_s_) {
+  // including during the hold-off and during an open capture, where its answer is thrown
-    prev_ = value;
+  // away. It is a sequential machine: a pulse whose opening edge fell in a skipped stretch
-    have_prev_ = true;
+  // can never be closed, and the symptom would be a width condition that silently stops
-    last_t_s_ = now_s;
+  // firing after the first hold-off.
-    return false;
+  const double event_t = detector_.feed(value, now_s);
-  }
 
-  if (!have_prev_) {
+  // Hold-off: settled, waiting for the next event.
-    prev_ = value;
+  if (!pending_ && now_s < holdoff_until_s_) {
-    have_prev_ = true;
     last_t_s_ = now_s;
     return false;
   }
@@ -60,7 +61,6 @@ bool TriggerEngine::process(double value, double now_s) noexcept {
     // past it. Time, not a sample count: `now_s` is the same clock the x axis reads,
     // so the capture covers exactly the requested span whatever the cadence is.
     ++post_accum_count_;
-    prev_ = value;
     if (now_s - pending_start_s_ >= post_seconds_) {
       pending_ = false;
       post_accum_count_ = 0;
@@ -74,33 +74,28 @@ bool TriggerEngine::process(double value, double now_s) noexcept {
     return false;
   }
 
-  // Edge detection against the level.
+  if (!std::isfinite(event_t)) return false;
-  const bool crossed_up = prev_ < cfg_.level && value >= cfg_.level;
-  const bool crossed_down = prev_ > cfg_.level && value <= cfg_.level;
-  const bool fired = (cfg_.edge == TriggerEdge::Rising && crossed_up) ||
-                     (cfg_.edge == TriggerEdge::Falling && crossed_down) ||
-                     (cfg_.edge == TriggerEdge::Both && (crossed_up || crossed_down));
-  prev_ = value;
-  if (!fired) return false;
 
-  // The pre-trigger window has to already be behind this edge, or the capture opens
+  // The pre-trigger window has to already be behind the event, or the capture opens on a
-  // on a half-filled pre window and the event is short on its left side -- the plot
+  // half-filled pre window and the event is short on its left side -- the plot then shows a
-  // then shows a window that is correctly sized but only partly drawn. The buffer
+  // window that is correctly sized but only partly drawn. The buffer fills whether or not the
-  // fills whether or not the trigger is armed, so this normally passes on the first
+  // trigger is armed, so this normally passes on the first event; it only bites just after a
-  // edge; it only bites just after a rebuild (a CONFIG, or enabling the signal),
+  // rebuild (a CONFIG, or enabling the signal), when the history genuinely is not there yet.
-  // when the history genuinely is not there yet.
+  //
-  if (now_s - oldest_s_ < pre_seconds_) return false;
+  // Measured from the *event's own* time, not from `now_s`: for a qualified condition the two
+  // differ (a pulse is reported at its closing edge), and the pre window belongs to the event.
+  if (event_t - oldest_s_ < pre_seconds_) return false;
 
-  // The edge's own time, which is what a trigger marker marks: the latch itself
+  // The event's own time, which is what a trigger marker marks: the latch itself may happen
-  // may happen a post-window later.
+  // a post-window later.
-  last_trigger_s_ = now_s;
+  last_trigger_s_ = event_t;
 
-  // The edge always opens a capture; there is no "latch on the edge itself" case.
+  // The event always opens a capture; there is no "latch on the event itself" case.
   // A zero-length post window latches on the very next sample, which is the least a
   // capture can hold, and every longer window is just more samples -- no conversion
   // from seconds to a sample count, so no conversion to get wrong.
   pending_ = true;
-  pending_start_s_ = now_s;
+  pending_start_s_ = event_t;
   post_accum_count_ = 0;
   return false;
 }

src/trigger.hpp

@@ -6,10 +6,9 @@
 #include <cstdint>
 #include <string>
 
-namespace udpscope {
+#include "condition.hpp"
 
-/// Which way the trigger signal crosses the level.
+namespace udpscope {
-enum class TriggerEdge { Rising, Falling, Both };
 
 /// How an armed trigger re-arms after it fired.
 enum class TriggerMode { Normal, Single };
@@ -24,8 +23,10 @@ struct TriggerConfig {
   bool enabled = false;          ///< trigger mode on/off (toolbar).
   bool armed = false;            ///< arm/disarm button.
   int channel = -1;              ///< index into ScopeModel::channels(), -1 = none.
-  double level = 0.0;
+  /// What counts as an event on that channel: the level and edge, and for the qualified
-  TriggerEdge edge = TriggerEdge::Rising;
+  /// shapes the width, band or timeout as well. The engine does not interpret it -- it
+  /// hands it to an `EventDetector`.
+  EventCondition condition{};
   double pretrigger_pct = 50.0;  ///< share of the buffer shown before the event.
   double holdoff_s = 0.010;      ///< default from the spec.
   TriggerMode mode = TriggerMode::Normal;
@@ -92,8 +93,8 @@ class TriggerEngine {
   /// pre-trigger window an edge needs before it may open a capture.
   double history() const noexcept { return last_t_s_ - oldest_s_; }
   double pre_seconds() const noexcept { return pre_seconds_; }
-  double last_value() const noexcept { return prev_; }
+  double last_value() const noexcept { return detector_.last_value(); }
-  bool have_last() const noexcept { return have_prev_; }
+  bool have_last() const noexcept { return detector_.have_last(); }
   double last_t() const noexcept { return last_t_s_; }
   double holdoff_until() const noexcept { return holdoff_until_s_; }
 
@@ -107,8 +108,9 @@ class TriggerEngine {
   TriggerConfig cfg_{};
   std::string channel_name_;  ///< the trigger channel's stable identity (see `configure`).
   bool armed_ = false;
-  bool have_prev_ = false;
+  /// What an event *is*. The engine owns when one may open a capture; this owns whether
-  double prev_ = 0.0;
+  /// the sample is one at all.
+  EventDetector detector_{};
   bool pending_ = false;      ///< an edge was seen; collecting the post window
   double pending_start_s_ = 0.0;
   double holdoff_until_s_ = 0.0;

src/ui.cpp

@@ -1609,10 +1609,10 @@ void publish_trigger_fields(App* app) {
   {
     std::lock_guard<std::mutex> lock(app->model->mutex());
     TriggerConfig& tc = app->model->trigger();
-    tc.level = level;
+    tc.condition.level = level;
     tc.pretrigger_pct = pre;
     tc.holdoff_s = holdoff;
-    tc.edge = edge == 0 ? TriggerEdge::Rising
+    tc.condition.edge = edge == 0 ? TriggerEdge::Rising
                         : edge == 1 ? TriggerEdge::Falling
                                     : TriggerEdge::Both;
     tc.mode = mode == 0 ? TriggerMode::Normal : TriggerMode::Single;
@@ -2050,7 +2050,7 @@ void rebuild_trigger_signals(App& app) {
     if (std::isfinite(sig.range_min) && std::isfinite(sig.range_max) &&
         sig.range_max > sig.range_min) {
       const double mid = 0.5 * (sig.range_min + sig.range_max);
-      tc.level = mid;
+      tc.condition.level = mid;
       gtk_spin_button_set_value(GTK_SPIN_BUTTON(app.trigger_level_spin), mid);
     }
   }
@@ -6344,7 +6344,7 @@ gboolean tick(gpointer user) {
     span_s = model.partition().span_s;
     time_stride = model.partition().time_stride;
     const int chan = model.trigger().channel;
-    trigger_level = model.trigger().level;
+    trigger_level = model.trigger().condition.level;
     if (chan >= 0 && chan < static_cast<int>(model.channel_count())) {
       trigger_name = model.channels()[static_cast<std::size_t>(chan)].name;
     }
@@ -8270,7 +8270,8 @@ gboolean trigrenum_probe(gpointer user) {
                  "holdoff=%.4f level=%.4g edge=%d mode=%d enabled=%d armed=%d ch=%d "
                  "channels=%zu\n",
                  a->rows->time_window(), a->model->event_span(), tc.pretrigger_pct,
-                 tc.post_span_s(a->model->event_span()), tc.holdoff_s, tc.level, int(tc.edge),
+                 tc.post_span_s(a->model->event_span()), tc.holdoff_s, tc.condition.level,
+                 int(tc.condition.edge),
                  int(tc.mode), int(tc.enabled), int(tc.armed), tc.channel,
                  a->model->channel_count());
   }
@@ -8295,7 +8296,7 @@ gboolean fields_probe(gpointer user) {
   std::lock_guard<std::mutex> lock(a->model->mutex());
   std::fprintf(stderr, "[fields-probe] mode=%u edge=%u published mode=%d edge=%d capturing=%d\n",
                gtk_drop_down_get_selected(mode), gtk_drop_down_get_selected(edge),
-               int(a->model->trigger().mode), int(a->model->trigger().edge),
+               int(a->model->trigger().mode), int(a->model->trigger().condition.edge),
                int(a->model->trigger_pending()));
   std::fflush(stderr);
   return G_SOURCE_REMOVE;