RelativeCCSender.hpp

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#pragma once
 
#include <Control_Surface/Control_Surface_Class.hpp>
 
#include <Arduino.h> // for constrain
 
BEGIN_CS_NAMESPACE
 
/// The encoding to use for relative control change value.
enum relativeCCmode {
    /**
     * @brief    Encode negative MIDI CC values as 7-bit two's complement.
     *
     * | Encoded  | Value | 
     * |---------:|------:|
     * | 000'0000 | 0     |
     * | 000'0001 | +1    |
     * | 011'1111 | +63   |
     * | 100'0000 | -64   |
     * | 100'0001 | -63   |
     * | 111'1111 | -1    |
     */
    TWOS_COMPLEMENT,
    /** 
     * @brief   Encode negative MIDI CC values by adding a fixed offset of 
     *          @f$ 2^6 = 64 @f$.
     *
     * | Encoded  | Value | 
     * |---------:|------:|
     * | 000'0000 | -64   |
     * | 000'0001 | -63   |
     * | 011'1111 | -1    |
     * | 100'0000 | 0     |
     * | 100'0001 | +1    |
     * | 111'1111 | +63   |
     */
    BINARY_OFFSET,
    /**
     * @brief   Encode negative MIDI CC values by using the most significant bit
     *          as a sign bit, and the six least significant bits as the 
     *          absolute value.
     *
     * | Encoded  | Value | 
     * |---------:|------:|
     * | 000'0000 | +0    |
     * | 000'0001 | 1     |
     * | 011'1111 | 63    |
     * | 100'0000 | -0    |
     * | 100'0001 | -1    |
     * | 111'1111 | -63   |
     */
    SIGN_MAGNITUDE,
    /// First relative mode in Reaper.
    REAPER_RELATIVE_1 = TWOS_COMPLEMENT,
    /// Second relative mode in Reaper.
    REAPER_RELATIVE_2 = BINARY_OFFSET,
    /// Third relative mode in Reaper.
    REAPER_RELATIVE_3 = SIGN_MAGNITUDE,
    /// Relative mode in Tracktion.
    TRACKTION_RELATIVE = TWOS_COMPLEMENT,
    /// Relative mode used by the Mackie Control Universal protocol.
    MACKIE_CONTROL_RELATIVE = SIGN_MAGNITUDE,
};
 
class RelativeCCSender {
  public:
    /** Convert an 8-bit two's complement integer to a 7-bit two's complement
     *  integer. */
    static uint8_t toTwosComplement7bit(int8_t value) { return value & 0x7F; }
    /** Convert an 8-bit two's complement integer to a 7-bit integer with a
     *  binary offset of 64. In other words, a value of 0 corresponds to -64,
     *  a value of 64 corresponds to 0, and a value of 127 corresponds to 63. */
    static uint8_t toBinaryOffset7bit(int8_t value) { return value + 64; }
    /** Convert an 8-bit two's complement integer to 7-bit sign-magnitude
     *  format. */
    static uint8_t toSignedMagnitude7bit(int8_t value) {
        uint8_t mask = value >> 7;
        uint8_t abs = (value + mask) ^ mask;
        uint8_t sign = mask & 0b01000000;
        return (abs & 0b00111111) | sign;
    }
    /** Convert an 8-bit two's complement integer to a 7-bit value to send over
     *  MIDI. */
    static uint8_t mapRelativeCC(int8_t value) {
        switch (mode) {
            case TWOS_COMPLEMENT: return toTwosComplement7bit(value);
            case BINARY_OFFSET: return toBinaryOffset7bit(value);
            case SIGN_MAGNITUDE: return toSignedMagnitude7bit(value);
            default: return 0; // Keeps the compiler happy
        }
    }
 
    static void send(long delta, MIDICNChannelAddress address) {
        while (delta != 0) {
            // Constrain relative movement to +/-15 for
            // Mackie Control Universal compatibility
            long thisDelta = constrain(delta, -15, 15);
            uint8_t msgVal = mapRelativeCC(thisDelta);
            // send a Control Change MIDI event
            Control_Surface.MIDI().sendCC(address, msgVal);
            delta -= thisDelta;
        }
    }
 
    static void setMode(relativeCCmode mode) { RelativeCCSender::mode = mode; }
 
  private:
    static relativeCCmode mode;
};
 
END_CS_NAMESPACE