Filter.ixx

module;

#include <algorithm>

export module megasynth.filter;

export class Filter {
public:
  enum Mode {
    LOW_PASS = 0,
    HIGH_PASS,
    BAND_PASS,
    kNumModes
  };

  double process(double inputValue);

  inline void setCutoff(double cutoff) {
    this->cutoff = cutoff;
    calculateFeedbackAmount();
  }

  inline void setResonance(double resonance)
  {
    this->resonance = resonance;
    calculateFeedbackAmount();
  }

  inline void setCutoffMod(double cutoffMod) {
    this->cutoffMod = cutoffMod;
    calculateFeedbackAmount();
  }

  inline void setFilterMode(Mode mode) { this->mode = mode; }

  void reset() {
    buf1 = buf2 = buf3 = buf0 = 0.0;
  }

private:
  double cutoff = 0.99;
  double resonance = 0.0;
  double cutoffMod = 0.0;

  Mode mode = Mode::LOW_PASS;
  double feedbackAmount = 0.0;
  double buf0 = 0.0;
  double buf1 = 0.0;
  double buf2 = 0.0;
  double buf3 = 0.0;

  inline void calculateFeedbackAmount() {
    feedbackAmount = resonance + resonance / (1.0 - getCalculatedCutoff());
  }

  inline double getCalculatedCutoff() const {
    return std::clamp(cutoff + cutoffMod, 0.01, 0.99);
  }

};