Collidoscope

#pragma once 

namespace collidoscope {

/* 

 * An ASR envelope with linear shape. It is modeled after the STK envelope classes.

 * The tick() method advances the computation of the envelope one sample and returns the computed sample

 * The class is templated for the type of the samples that each tick of the envelope produces. 

 *

 * Client classes can set/get the current state of the envelope with the

 * respective getter/setter methods

 *

 */

template <typename T>

class EnvASR

{

public:

    /** Possible states of the envelope. Idle means the envelope ouputs 0 */

    enum class State {

        eAttack,

        eSustain,

        eRelease,

        eIdle // before attack after release  

    };

    EnvASR( T sustainLevel, T attackTime, T releaseTime, std::size_t sampleRate ) :

        mSustainLevel( sustainLevel ),

        mState( State::eIdle ),

        mValue( 0 )

    {

        if ( attackTime <= 0 )

            attackTime = T( 0.001 );

        if ( releaseTime <= 0 )

            releaseTime = T( 0.001 );

        mAttackRate =  T( 1.0 ) / (attackTime * sampleRate);

        mReleaseRate = T( 1.0 ) / (releaseTime * sampleRate);

    }

    /** Produces one sample worth of envelope */

    T tick()

    {

        switch ( mState )

        {

        case State::eIdle: {

            mValue = 0;

        };

            break;

        case State::eAttack: {

            mValue += mAttackRate;

            if ( mValue >= mSustainLevel ){

                mValue = mSustainLevel;

                mState = State::eSustain;

            }

        };

            break;

        case State::eRelease:

            mValue -= mReleaseRate;

            if ( mValue <= 0 ){

                mValue = 0;

                mState = State::eIdle;

            }

            break;

        default:

            break;

        }

        return mValue;

    }

    State getState() const

    {

        return mState;

    }

    void setState( State state )

    {

        mState = state;

    }

private:

    T mSustainLevel;

    T mAttackRate;

    T mReleaseRate;

    // output

    T mValue;

    State mState;

};

}