Momentum-Apps/sound_engine/sound_engine_adsr.c

#include "sound_engine_adsr.h"

int32_t sound_engine_cycle_and_output_adsr(int32_t input, SoundEngine *eng, SoundEngineADSR *adsr, uint16_t *flags)
{
    switch (adsr->envelope_state)
    {
        case ATTACK:
        {
            adsr->envelope += adsr->envelope_speed;

            if (adsr->envelope >= MAX_ADSR)
            {
                adsr->envelope_state = DECAY;
                adsr->envelope = MAX_ADSR;

                adsr->envelope_speed = envspd(eng, adsr->d);
            }

            break;
        }

        case DECAY:
        {
            if (adsr->envelope > ((uint32_t)adsr->s << 17) + adsr->envelope_speed)
            {
                adsr->envelope -= adsr->envelope_speed;
            }

            else
            {
                adsr->envelope = (uint32_t)adsr->s << 17;
                adsr->envelope_state = (adsr->s == 0) ? RELEASE : SUSTAIN;

                adsr->envelope_speed = envspd(eng, adsr->r);
            }

            break;
        }

        case SUSTAIN:
        case DONE:
        {
            break;
        }

        case RELEASE:
        {
            if (adsr->envelope > adsr->envelope_speed)
            {
                adsr->envelope -= adsr->envelope_speed;
            }

            else
            {
                adsr->envelope_state = DONE;
                *flags &= ~SE_ENABLE_GATE;
                adsr->envelope = 0;
            }

            break;
        }
    }

    return (int32_t)((int32_t)input * (int32_t)(adsr->envelope >> 10) / (int32_t)(MAX_ADSR >> 10) * (int32_t)adsr->volume / (int32_t)MAX_ADSR_VOLUME);
}