peak trace: initial work

src/ui/Application.cpp

@@ -994,7 +994,7 @@ void Application::renderWaterfallPanel() {
 
         measurements_.drawWaterfall(specDisplay_, wfPosX_, wfPosY_, wfSizeX_, wfSizeY_,
                                      settings_.sampleRate, settings_.isIQ, freqScale_,
-                                     viewLo_, viewHi_);
+                                     viewLo_, viewHi_, screenRows, analyzer_.spectrumSize());
 
         // ── Mouse interaction: zoom, pan & hover on waterfall ──
         ImGuiIO& io = ImGui::GetIO();

src/ui/Measurements.cpp

@@ -70,6 +70,14 @@ void Measurements::update(const std::vector<float>& spectrumDB,
         globalPeak_.bin = bin;
         globalPeak_.dB = *it;
         globalPeak_.freq = binToFreq(bin, sampleRate, isIQ, fftSize);
+
+        // Push into peak history circular buffer
+        constexpr int kMaxHistory = 4096;
+        if (static_cast<int>(peakHistBins_.size()) < kMaxHistory)
+            peakHistBins_.resize(kMaxHistory, -1);
+        peakHistIdx_ = (peakHistIdx_ + 1) % kMaxHistory;
+        peakHistBins_[peakHistIdx_] = bin;
+        if (peakHistLen_ < kMaxHistory) ++peakHistLen_;
     }
 
     if (!enabled) { peaks_.clear(); return; }
@@ -154,11 +162,47 @@ void Measurements::draw(const SpectrumDisplay& specDisplay,
 void Measurements::drawWaterfall(const SpectrumDisplay& specDisplay,
                                   float posX, float posY, float sizeX, float sizeY,
                                   double sampleRate, bool isIQ, FreqScale freqScale,
-                                  float viewLo, float viewHi) const {
-    if (!enabled || !showOnWaterfall || peaks_.empty()) return;
-
+                                  float viewLo, float viewHi,
+                                  int screenRows, int spectrumSize) const {
     ImDrawList* dl = ImGui::GetWindowDrawList();
 
+    // Peak trace: red squiggly line showing peak frequency history
+    if (showPeakTrace && peakHistLen_ > 1 && screenRows > 1 && spectrumSize > 0) {
+        int histSize = static_cast<int>(peakHistBins_.size());
+        int count = std::min(screenRows, peakHistLen_);
+        ImU32 traceCol = IM_COL32(255, 30, 30, 200);
+
+        // Convert bin index to screen X via normalized frequency fraction
+        auto binToX = [&](int bin) -> float {
+            float frac = (static_cast<float>(bin) + 0.5f) / spectrumSize;
+            // Map through view range
+            float viewFrac = (frac - viewLo) / (viewHi - viewLo);
+            return posX + viewFrac * sizeX;
+        };
+
+        // Walk from newest (bottom) to oldest (top)
+        float prevX = 0, prevY = 0;
+        bool havePrev = false;
+        for (int i = 0; i < count; ++i) {
+            int idx = (peakHistIdx_ - i + histSize) % histSize;
+            int bin = peakHistBins_[idx];
+            if (bin < 0) break;
+
+            // Y: i=0 is newest (bottom), i=count-1 is oldest (top)
+            float y = posY + sizeY - (static_cast<float>(i) + 0.5f) / screenRows * sizeY;
+            float x = binToX(bin);
+
+            if (havePrev) {
+                dl->AddLine({prevX, prevY}, {x, y}, traceCol, 3.0f);
+            }
+            prevX = x;
+            prevY = y;
+            havePrev = true;
+        }
+    }
+
+    // Vertical markers at current peak positions
+    if (enabled && showOnWaterfall && !peaks_.empty()) {
         auto peakColor = [](int idx) -> ImU32 {
             if (idx == 0) return IM_COL32(255, 80, 80, 120);
             return IM_COL32(255, 140, 60, 80);
@@ -174,8 +218,10 @@ void Measurements::drawWaterfall(const SpectrumDisplay& specDisplay,
             dl->AddLine({x, posY}, {x, posY + sizeY}, col, thickness);
         }
     }
+}
 
 void Measurements::drawPanel() {
+    ImGui::Checkbox("Peak trace", &showPeakTrace);
     if (!enabled) return;
 
     ImGui::SetNextItemWidth(-1);

src/ui/Measurements.h

@@ -25,11 +25,12 @@ public:
               float minDB, float maxDB,
               float viewLo, float viewHi) const;
 
-    // Draw vertical markers on the waterfall panel.
+    // Draw vertical markers and peak trace on the waterfall panel.
     void drawWaterfall(const SpectrumDisplay& specDisplay,
                        float posX, float posY, float sizeX, float sizeY,
                        double sampleRate, bool isIQ, FreqScale freqScale,
-                       float viewLo, float viewHi) const;
+                       float viewLo, float viewHi,
+                       int screenRows, int spectrumSize) const;
 
     // Draw sidebar panel (ImGui widgets).
     void drawPanel();
@@ -44,11 +45,17 @@ public:
     float peakThreshold = -120.0f; // ignore peaks below this dB
     bool showOnSpectrum = true;   // draw markers on spectrum
     bool showOnWaterfall = false; // draw vertical lines on waterfall
+    bool showPeakTrace  = false;  // draw peak history curve on waterfall
 
 private:
     PeakInfo globalPeak_;             // always-tracked highest peak
     std::vector<PeakInfo> peaks_;
 
+    // Peak history for waterfall trace (circular buffer, newest at peakHistIdx_)
+    std::vector<int> peakHistBins_;   // bin index per waterfall line
+    int              peakHistIdx_ = 0;
+    int              peakHistLen_ = 0; // how many entries are valid
+
     // Find top-N peaks with minimum bin separation.
     void findPeaks(const std::vector<float>& spectrumDB, int maxN,
                    int minDist, float threshold);