feat: StepDetector

move StepDetector from lockstep android to libpasada

pasada-lib/include/ssf_filter.h

@@ -52,6 +52,8 @@ public:
     SsfStepDetector(size_t len_refr);
     double filter(double val);
     double peek_threshold();
+
+    static size_t initial_samples();
 };
 
 /**

pasada-lib/include/step_detector.h

@@ -0,0 +1,52 @@
+//
+// Created by david on 15.03.2026.
+//
+
+#ifndef PASADASUPERPROJECT_STEP_DETECTOR_H
+#define PASADASUPERPROJECT_STEP_DETECTOR_H
+
+#include "iir_filter.h"
+#include "ssf_filter.h"
+#include <vector>
+
+class StepListener {
+public:
+    virtual ~StepListener() {}
+    virtual void playBeat() = 0;
+};
+
+/**
+ * Step detector from accelerometer signal.
+ *
+ * Settling time is 3.0 sec (defined in SsfStepDetector.LEN_INIT),
+ * no steps are detected before.
+ */
+class StepDetector {
+protected:
+    StepListener *listener;
+    IirFilter f_highpass;
+    Filt f_neg;
+    SsfFilter f_ssf;
+    SsfStepDetector f_ssd;
+    RunningQualityFilter f_sqi;
+
+    bool debug;
+    std::vector<double> buf_ssd;
+    std::vector<double> buf_sqi;
+    std::vector<double> buf_out;
+
+public:
+    StepDetector(StepListener *listener, bool debug = false);
+    void filter(std::vector<float> values);
+    std::vector<double> getBufSsd();
+    std::vector<double> getBufSqi();
+    std::vector<double> getBufOut();
+
+    /**
+     * Prime the filters using the given input signal.
+     * Used for debugging (non-realtime processing) to align the signal.
+     */
+    void primeFilters(std::vector<double> sig);
+};
+
+#endif //PASADASUPERPROJECT_STEP_DETECTOR_H