feat: add skeleton TempoController

app/src/main/cpp/TempoController.cpp

@@ -0,0 +1,50 @@
+//
+// Created by david on 14.06.2026.
+//
+
+#include "TempoController.h"
+
+TempoController::TempoController(std::atomic<bool> *have_stretch_factor, std::atomic<double> *stretch_factor) :
+    have_stretch_factor(have_stretch_factor),
+    stretch_factor(stretch_factor),
+    lastBeatT(0.0),
+    lastStepT(0.0)
+{
+    this->have_stretch_factor->store(false);
+    this->stretch_factor->store(1.0);
+}
+
+void TempoController::reset(std::vector<double> beatTimes) {
+    std::lock_guard<std::mutex> lock(mMutex);
+    beatTimesSec.assign(beatTimes.begin(), beatTimes.end());
+    lastBeatT = (0.0);
+    lastStepT = (0.0);
+}
+
+void TempoController::resume() {}
+void TempoController::pause() {}
+
+void TempoController::seekTo(double oldMarkerPosSec, double newMarkerPosSec) {
+    std::lock_guard<std::mutex> lock(mMutex);
+    double dt = newMarkerPosSec - oldMarkerPosSec;
+    lastBeatT += dt;
+    lastStepT += dt;
+}
+
+/**
+ * must be thread-safe since these are called from different threads
+ * @param t marker position in sec of original music time
+ */
+void TempoController::onBeat(double t) {
+    std::lock_guard<std::mutex> lock(mMutex);
+    lastBeatT = t;
+}
+
+/**
+ * must be thread-safe since these are called from different threads
+ * @param t time in sec of accelerometer timebase
+ */
+void TempoController::onStep(double t) {
+    std::lock_guard<std::mutex> lock(mMutex);
+    lastStepT = t;
+}