unbound waterfall scrolling -- prevent low FPS from limiting the speed

src/audio/AudioEngine.cpp

@@ -2,6 +2,7 @@
 #include "audio/FileSource.h"
 
 #include <algorithm>
+#include <chrono>
 #include <cmath>
 #include <cstdio>
 #include <cstring>
@@ -157,19 +158,38 @@ int AudioEngine::processAudio() {
     if (hopFrames < 1) hopFrames = 1;
     audioBuf_.resize(hopFrames * channels);
 
-    constexpr int kMaxSpectraPerFrame = 8;
+    // Drain all available audio so the scroll rate is independent of the
+    // display refresh rate (vsync).  Real-time sources self-limit via their
+    // ring buffer; file sources are capped to wall-clock time so playback
+    // runs at 1× speed regardless of frame rate.
+
+    // For file sources, compute how many samples correspond to elapsed time.
+    size_t fileSampleCap = SIZE_MAX;  // unlimited for real-time
+    if (!audioSource_->isRealTime()) {
+        using Clock = std::chrono::steady_clock;
+        static Clock::time_point lastFileTime = Clock::now();
+        auto now = Clock::now();
+        double elapsed = std::chrono::duration<double>(now - lastFileTime).count();
+        lastFileTime = now;
+        // Clamp elapsed to avoid huge bursts after pauses or stalls.
+        if (elapsed > 0.1) elapsed = 0.1;
+        fileSampleCap = static_cast<size_t>(elapsed * settings_.sampleRate) + 1;
+    }
 
     // Process primary source.
     int spectraThisFrame = 0;
-    while (spectraThisFrame < kMaxSpectraPerFrame) {
+    size_t samplesRead = 0;
+    for (;;) {
+        if (samplesRead >= fileSampleCap) break;
         size_t framesRead = audioSource_->read(audioBuf_.data(), hopFrames);
         if (framesRead == 0) break;
+        samplesRead += framesRead;
         analyzer_.pushSamples(audioBuf_.data(), framesRead);
         if (analyzer_.hasNewSpectrum())
             ++spectraThisFrame;
     }
 
-    // Process extra devices independently.
+    // Process extra devices independently (always real-time).
     for (auto& ed : extraDevices_) {
         int edCh = ed->source->channels();
         const auto& edSettings = ed->analyzer.settings();
@@ -177,13 +197,10 @@ int AudioEngine::processAudio() {
         if (edHop < 1) edHop = 1;
         ed->audioBuf.resize(edHop * edCh);
 
-        int edSpectra = 0;
+        for (;;) {
-        while (edSpectra < kMaxSpectraPerFrame) {
             size_t framesRead = ed->source->read(ed->audioBuf.data(), edHop);
             if (framesRead == 0) break;
             ed->analyzer.pushSamples(ed->audioBuf.data(), framesRead);
-            if (ed->analyzer.hasNewSpectrum())
-                ++edSpectra;
         }
     }
 
@@ -226,6 +243,18 @@ const std::vector<float>& AudioEngine::getSpectrum(int globalCh) const {
     return analyzer_.channelSpectrum(0);
 }
 
+const std::deque<std::vector<float>>& AudioEngine::getWaterfallHistory(int globalCh) const {
+    int n = analyzer_.numSpectra();
+    if (globalCh < n) return analyzer_.waterfallHistory(globalCh);
+    globalCh -= n;
+    for (auto& ed : extraDevices_) {
+        int en = ed->analyzer.numSpectra();
+        if (globalCh < en) return ed->analyzer.waterfallHistory(globalCh);
+        globalCh -= en;
+    }
+    return analyzer_.waterfallHistory(0);
+}
+
 const std::vector<std::complex<float>>& AudioEngine::getComplex(int globalCh) const {
     int n = analyzer_.numSpectra();
     if (globalCh < n) return analyzer_.channelComplex(globalCh);

src/audio/AudioEngine.h

@@ -42,6 +42,7 @@ public:
     // ── Unified channel view across all analyzers ──
     int totalNumSpectra() const;
     const std::vector<float>& getSpectrum(int globalCh) const;
+    const std::deque<std::vector<float>>& getWaterfallHistory(int globalCh) const;
     const std::vector<std::complex<float>>& getComplex(int globalCh) const;
     const char* getDeviceName(int globalCh) const;
     int spectrumSize() const { return analyzer_.spectrumSize(); }

src/ui/Application.cpp

@@ -312,16 +312,31 @@ void Application::processAudio() {
         const auto& mathChannels = audio_.mathChannels();
         const auto& mathSpectra  = audio_.mathSpectra();
 
+        // Push ALL new spectra to the waterfall so that the scroll rate
+        // is determined by the audio sample rate, not the display refresh.
         if (ui_.waterfallMultiCh && nSpec > 1) {
+            // For multi-channel: replay the last spectraThisFrame entries
+            // from channel 0's history to get per-step data.  Other
+            // channels have the same count of new entries.
+            const auto& hist0 = audio_.getWaterfallHistory(0);
+            int histSz = static_cast<int>(hist0.size());
+            int start = std::max(0, histSz - spectraThisFrame);
+
+            for (int si = start; si < histSz; ++si) {
                 std::vector<std::vector<float>> wfSpectra;
                 std::vector<WaterfallChannelInfo> wfInfo;
 
                 for (int ch = 0; ch < nSpec; ++ch) {
                     const auto& c = ui_.channelColors[ch % kMaxChannels];
-                wfSpectra.push_back(audio_.getSpectrum(ch));
+                    const auto& hist = audio_.getWaterfallHistory(ch);
+                    int idx = std::max(0, static_cast<int>(hist.size()) - (histSz - si));
+                    wfSpectra.push_back(hist[idx]);
                     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()) {
@@ -330,10 +345,16 @@ void Application::processAudio() {
                             wfInfo.push_back({c[0], c[1], c[2], true});
                         }
                     }
+                }
                 waterfall_.pushLineMulti(wfSpectra, wfInfo, ui_.minDB, ui_.maxDB);
+            }
         } else {
             int wfCh = std::clamp(ui_.waterfallChannel, 0, nSpec - 1);
-            waterfall_.pushLine(audio_.getSpectrum(wfCh), ui_.minDB, ui_.maxDB);
+            const auto& hist = audio_.getWaterfallHistory(wfCh);
+            int histSz = static_cast<int>(hist.size());
+            int start = std::max(0, histSz - spectraThisFrame);
+            for (int si = start; si < histSz; ++si)
+                waterfall_.pushLine(hist[si], ui_.minDB, ui_.maxDB);
         }
         int curCh = std::clamp(ui_.waterfallChannel, 0, nSpec - 1);
         cursors_.update(audio_.getSpectrum(curCh),