implement the FFT deques also for math channels, add an "input overrun" indication

src/ui/Application.cpp

@@ -334,16 +334,20 @@ void Application::processAudio() {
                     wfInfo.push_back({c.x, c.y, c.z,
                                       ui_.channelEnabled[ch % kMaxChannels]});
                 }
-                // Math channels only available for the latest spectrum;
-                // include them only on the last iteration.
-                if (si == histSz - 1) {
-                    for (size_t mi = 0; mi < mathChannels.size(); ++mi) {
-                        if (mathChannels[mi].enabled && mathChannels[mi].waterfall &&
-                            mi < mathSpectra.size()) {
-                            const auto& c = mathChannels[mi].color;
+                // Math channels: use their own waterfall history.
+                for (size_t mi = 0; mi < mathChannels.size(); ++mi) {
+                    if (mathChannels[mi].enabled && mathChannels[mi].waterfall &&
+                        mi < mathSpectra.size()) {
+                        const auto& c = mathChannels[mi].color;
+                        const auto& mHist = audio_.mathWaterfallHistory(static_cast<int>(mi));
+                        int mHistSz = static_cast<int>(mHist.size());
+                        int mIdx = std::max(0, mHistSz - (histSz - si));
+                        if (mIdx < mHistSz) {
+                            wfSpectra.push_back(mHist[mIdx]);
+                        } else {
                             wfSpectra.push_back(mathSpectra[mi]);
-                            wfInfo.push_back({c[0], c[1], c[2], true});
                         }
+                        wfInfo.push_back({c[0], c[1], c[2], true});
                     }
                 }
                 waterfall_.pushLineMulti(wfSpectra, wfInfo, ui_.minDB, ui_.maxDB);

src/ui/ControlPanel.cpp

@@ -95,6 +95,23 @@ void ControlPanel::render(AudioEngine& audio, UIState& ui,
             ImGui::GetWindowDrawList()->AddText({tx, ty}, IM_COL32(255, 255, 255, 220), overlayText);
             if (ImGui::IsItemHovered()) ImGui::SetTooltip("Overlap");
         }
+
+        // Overrun indicator
+        {
+            int overruns = audio.overrunCount();
+            float now = static_cast<float>(ImGui::GetTime());
+            if (overruns > lastOverrunCount_) {
+                lastOverrunCount_ = overruns;
+                lastOverrunTime_ = now;
+            }
+            if (overruns > 0 && (now - lastOverrunTime_) < 3.0f) {
+                ImGui::TextColored({1.0f, 0.4f, 0.4f, 1.0f},
+                                   "Input overrun: %d FFTs", overruns);
+            } else if (overruns > 0) {
+                audio.resetOverrunCount();
+                lastOverrunCount_ = 0;
+            }
+        }
     }
 
     // ── Display ──

src/ui/ControlPanel.h

@@ -45,6 +45,10 @@ private:
     bool needsSave_   = false;
     bool needsUpdate_ = false;
 
+    // Overrun display
+    int   lastOverrunCount_ = 0;
+    float lastOverrunTime_  = 0.0f;  // ImGui time of last overrun
+
     void flagSave()   { needsSave_ = true; }
     void flagUpdate() { needsUpdate_ = true; }
 };