File content as of revision 0:c5e94349541f:

/*
 * ADSR Type Envelope Class
 *
 * 2018.06.28
 *
 */
 
#ifndef _ENVELOPE_ADSR_H_
#define _ENVELOPE_ADSR_H_

class EnvelopeADSR
{
private:
    enum EnvelopeState {
        ST_ATTACK,
        ST_DECAY,
        ST_SUSTAIN,
        ST_RELEASE
    };

public:
    EnvelopeADSR()
    {
        count = 0;
        amplitude = 0;
        setADSR(0, 0, 0.0f, 0);
    }
    
    void setADSR(int _attack, int _decay, float _sustain, int _release)
    {
        attack = _attack;
        decay = _decay;
        sustain = _sustain;
        release = _release;

        if (attack != 0) {
            attackRatio = 1.0f / attack;
        } 
        else {
            attackRatio = 0.0f;
        }
        if (decay != 0) {
            decayRatio = -(1.0f - sustain) / decay;
        }
        else {
            decayRatio = 0.0f;
        }
        if (release != 0) {
            releaseRatio = -sustain / release;
        }
        else {
            releaseRatio = 0.0f;
        }
    }
    
    void gateOn()
    {
        isGateOn = true;
        count = 0;
        amplitude = 0.0f;
        state = ST_ATTACK;
    }

    void gateOff()
    {
        isGateOn = false;
        state = ST_RELEASE;
    }

    float getAmplitude()
    {
        return amplitude;
    }

    long getCount()
    {
        return count;
    }

    int getState()
    {
        return state;
    }
    
    float tick()
    {
        float currentAmplitude = amplitude;

        switch (state) {
        case ST_ATTACK:
            amplitude += attackRatio;
            break;
        case ST_DECAY:
            amplitude += decayRatio;
            break;
        case ST_SUSTAIN:
            // do nothing
            break;
        case ST_RELEASE:
            amplitude += releaseRatio;
            break;
        }

        // Limiter
        if (amplitude < 0.0f) {
            amplitude = 0.0f;
        }
        else if (amplitude > 1.0f) {
            amplitude = 1.0f;
        }

        count++;
        if (count < attack) {
            state = ST_ATTACK;
        } else if (count < attack + decay) {
            state = ST_DECAY;
        } else if (isGateOn) {
            state = ST_SUSTAIN;
        }
        
        return currentAmplitude;
    }

private:
    int attack;
    int decay;
    float sustain;
    int release;
    
    float attackRatio;
    float decayRatio;
    float releaseRatio;
    
    long count;
    bool isGateOn;
    EnvelopeState state;
    
    float amplitude;
};

#endif //_ENVELOPE_ADSR_H_