std_library_voices.cmajor

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/// std.voices

/**
    This module demonstrates a simple voice-allocation algorithm.

    The way it's structured is that you pass an incoming stream of note events to
    the voice allocator processor, and it redirects them to an array of destination
    processors which each handle a single voice.

    The voice allocators use the channel property of the incoming events to group
    them together, and take care of ensuring that each target voice only receives
    the events from one channel at a time.
*/
namespace std::voices
{
    /** A basic least-recently-used voice allocator.

        If there's an inactive voice, then a new note will be assigned to it,
        otherwise it will steal the least-recently-used active voice. For more
        fancy note-stealing algorithms, you can use this as an example and add
        your own logic!
    */
    processor VoiceAllocator (int numVoices,
                              int MPEMasterChannel = 0)
    {
        //==============================================================================
        input event (std::notes::NoteOn,
                     std::notes::NoteOff,
                     std::notes::PitchBend,
                     std::notes::Slide,
                     std::notes::Pressure,
                     std::notes::Control)    eventIn;

        output event (std::notes::NoteOn,
                      std::notes::NoteOff,
                      std::notes::PitchBend,
                      std::notes::Slide,
                      std::notes::Pressure,
                      std::notes::Control)   voiceEventOut[numVoices];

        //==============================================================================
        event eventIn (std::notes::NoteOn noteOn)
        {
            let oldest = findOldestIndex();

            // send a note-off when stealing a voice
            if (voiceState[oldest].isActive)
                voiceEventOut[oldest] <- std::notes::NoteOff (voiceState[oldest].channel,
                                                              voiceState[oldest].pitch,
                                                              0.0f);

            voiceState[oldest].start (noteOn.channel, noteOn.pitch);

            voiceEventOut[oldest] <- noteOn;
        }

        event eventIn (std::notes::NoteOff noteOff)
        {
            for (wrap<numVoices> i)
            {
                if (voiceState[i].channel == noteOff.channel
                     && voiceState[i].pitch == noteOff.pitch)
                {
                    if (isSustainActive (noteOff.channel))
                    {
                        voiceState[i].isReleasing = true;
                    }
                    else
                    {
                        voiceEventOut[i] <- noteOff;
                        voiceState[i].free();
                    }
                }
            }
        }

        event eventIn (std::notes::PitchBend bend)
        {
            for (wrap<numVoices> i)
                if (voiceState[i].channel == bend.channel)
                    voiceEventOut[i] <- bend;
        }

        event eventIn (std::notes::Pressure pressure)
        {
            for (wrap<numVoices> i)
                if (voiceState[i].channel == pressure.channel)
                    voiceEventOut[i] <- pressure;
        }

        event eventIn (std::notes::Slide slide)
        {
            for (wrap<numVoices> i)
                if (voiceState[i].channel == slide.channel)
                    voiceEventOut[i] <- slide;
        }

        event eventIn (std::notes::Control control)
        {
            if (control.control == 64) // 64 = sustain
            {
                bool isMPEMasterChannel = control.channel == MPEMasterChannel;
                bool sustainActive = control.value >= 0.5f;

                setChannelSustain (control.channel, sustainActive);

                if (isMPEMasterChannel)
                    mpeMasterSustainActive = sustainActive;

                if (! sustainActive)
                {
                    for (wrap<numVoices> i)
                    {
                        if ((isMPEMasterChannel || voiceState[i].channel == control.channel)
                             && voiceState[i].isActive
                             && voiceState[i].isReleasing)
                        {
                            voiceEventOut[i] <- std::notes::NoteOff (voiceState[i].channel,
                                                                     voiceState[i].pitch,
                                                                     0.0f);
                            voiceState[i].free();
                        }
                    }
                }
            }
            else
            {
                for (wrap<numVoices> i)
                    if (voiceState[i].channel == control.channel)
                        voiceEventOut[i] <- control;
            }
        }

        //==============================================================================
        struct VoiceState
        {
            bool isActive, isReleasing;
            int32 channel, age;
            float32 pitch;

            void start (int32 channel, float32 pitch)
            {
                this.isActive     = true;
                this.isReleasing  = false;
                this.channel      = channel;
                this.pitch        = pitch;
                this.age          = ++nextActiveTime;
            }

            void free()
            {
                this.isActive  = false;
                this.age       = ++nextInactiveTime;
            }
        }

        static_assert (numVoices > 0);
        VoiceState[numVoices] voiceState;

        int32 nextActiveTime = 0x70000000, nextInactiveTime = 1;

        bool mpeMasterSustainActive;
        int64 perChannelSustainActive; // one per bit (assumes that channel IDs are <64, and could be made more general)

        bool isSustainActive (int32 channel)
        {
            return mpeMasterSustainActive || (perChannelSustainActive & (1L << channel)) != 0;
        }

        void setChannelSustain (int32 channel, bool active)
        {
            if (active)
                perChannelSustainActive |= (1L << channel);
            else
                perChannelSustainActive &= ~(1L << channel);
        }

        wrap<numVoices> findOldestIndex()
        {
            if const (numVoices == 1)
            {
                return 0;
            }
            else
            {
                wrap<numVoices> index;
                var oldest = voiceState[0].age;

                for (wrap<numVoices> i = 1)
                {
                    let age = voiceState[i].age;

                    if (age < oldest)
                    {
                        index = i;
                        oldest = age;
                    }
                }

                return index;
            }
        }
    }
}