Provide the interpolated beat position

src/sfizz/BeatClock.cpp

@@ -64,12 +64,6 @@ T BeatClock::dequantize(qbeats_t qbeats)
 }
 
 ///
-BeatClock::BeatClock()
-{
-    setSampleRate(config::defaultSampleRate);
-    setSamplesPerBlock(config::defaultSamplesPerBlock);
-}
-
 void BeatClock::clear()
 {
     beatsPerSecond_ = 2.0;
@@ -99,7 +93,8 @@ void BeatClock::setSampleRate(double sampleRate)
 
 void BeatClock::setSamplesPerBlock(unsigned samplesPerBlock)
 {
-    runningBeat_.resize(samplesPerBlock);
+    runningBeatNumber_.resize(samplesPerBlock);
+    runningBeatPosition_.resize(samplesPerBlock);
     runningBeatsPerBar_.resize(samplesPerBlock);
 }
 
@@ -147,11 +142,11 @@ void BeatClock::setPlaying(unsigned delay, bool playing)
     isPlaying_ = playing;
 }
 
-absl::Span<const int> BeatClock::getRunningBeat()
+absl::Span<const int> BeatClock::getRunningBeatNumber()
 {
     fillBufferUpTo(currentCycleFrames_);
 
-    return absl::MakeConstSpan(runningBeat_.data(), currentCycleFrames_);
+    return absl::MakeConstSpan(runningBeatNumber_.data(), currentCycleFrames_);
 }
 
 absl::Span<const int> BeatClock::getRunningBeatsPerBar()
@@ -163,7 +158,8 @@ absl::Span<const int> BeatClock::getRunningBeatsPerBar()
 
 void BeatClock::fillBufferUpTo(unsigned delay)
 {
-    int *beatData = runningBeat_.data();
+    int *beatNumberData = runningBeatNumber_.data();
+    float *beatNumberPosition = runningBeatPosition_.data();
     int *beatsPerBarData = runningBeatsPerBar_.data();
     unsigned fill = currentCycleFill_;
 
@@ -172,8 +168,10 @@ void BeatClock::fillBufferUpTo(unsigned delay)
         beatsPerBarData[i] = sig.beatsPerBar;
 
     if (!isPlaying_) {
-        for (; fill < delay; ++fill)
-            beatData[fill] = 0;
+        for (; fill < delay; ++fill) {
+            beatNumberData[fill] = 0;
+            beatNumberPosition[fill] = 0;
+        }
         currentCycleFill_ = fill;
         return;
     }
@@ -190,7 +188,9 @@ void BeatClock::fillBufferUpTo(unsigned delay)
         mustApplyHostPos = false;
 
         // quantization to nearest for prevention of rounding errors
-        beatData[fill] = dequantize<int>(quantize(clientPos.toBeats(sig)));
+        double beats = clientPos.toBeats(sig);
+        beatNumberData[fill] = dequantize<int>(quantize(beats));
+        beatNumberPosition[fill] = static_cast<float>(beats);
     }
 
     currentCycleFill_ = fill;

src/sfizz/BeatClock.h

@@ -5,6 +5,7 @@
 // If not, contact the sfizz maintainers at https://github.com/sfztools/sfizz
 
 #pragma once
+#include "Buffer.h"
 #include <absl/types/span.h>
 #include <vector>
 #include <iosfwd>
@@ -73,8 +74,6 @@ struct BBT {
 
 class BeatClock {
 public:
-    BeatClock();
-
     /**
      * @brief Set the sample rate.
      */
@@ -113,8 +112,20 @@ public:
     void setPlaying(unsigned delay, bool playing);
     /**
      * @brief Get the beat number for each frame of the current cycle.
+     *
+     * This signal is quantized to a fixed resolution, such that it never
+     * suffers 1-off errors due to imprecision in the host time position.
      */
-    absl::Span<const int> getRunningBeat();
+    absl::Span<const int> getRunningBeatNumber();
+    /**
+     * @brief Get the beat position for each frame of the current cycle.
+     *
+     * This is a fractional equivalent of the beat number, however the beat
+     * boundaries can be traversed erratically due to approximation errors.
+     * If you need to perform work on exact beat transitions, prefer
+     * `getRunningBeatNumber` instead.
+     */
+    absl::Span<const float> getRunningBeatPosition();
     /**
      * @brief Get the time signature numerator for each frame of the current cycle.
      */
@@ -124,7 +135,7 @@ private:
     void fillBufferUpTo(unsigned delay);
 
 private:
-    double samplePeriod_ = 0;
+    double samplePeriod_ { 1.0 / config::defaultSampleRate };
 
     // quantization
     typedef int64_t qbeats_t;
@@ -150,8 +161,9 @@ private:
     // plugin-side counter
     BBT lastClientPos_;
 
-    std::vector<int> runningBeat_;
-    std::vector<int> runningBeatsPerBar_;
+    Buffer<int> runningBeatNumber_ { config::defaultSamplesPerBlock };
+    Buffer<float> runningBeatPosition_ { config::defaultSamplesPerBlock };
+    Buffer<int> runningBeatsPerBar_ { config::defaultSamplesPerBlock };
 };
 
 } // namespace sfz

src/sfizz/Synth.cpp

@@ -925,7 +925,7 @@ void Synth::renderBlock(AudioSpan<float> buffer) noexcept
     constexpr bool metronomeEnabled = false;
     if (metronomeEnabled) {
         impl.resources_.metronome.processAdding(
-            bc.getRunningBeat().data(), bc.getRunningBeatsPerBar().data(),
+            bc.getRunningBeatNumber().data(), bc.getRunningBeatsPerBar().data(),
             buffer.getChannel(0), buffer.getChannel(1), numFrames);
     }