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[3.0.1] Parameter MIDI Mapping

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How the mapping works between MIDI CCs and parameters.

MIDI Mapping Interface: Vst::IMidiMapping

MIDI controllers are not transmitted directly to a VST component. MIDI as hardware protocol has restrictions that can be avoided in software. Controller data in particular come along with unclear and often ignored semantics. On top of this, they can interfere with regular parameter automation and the host is unaware of what happens in the plug-in when passing MIDI controllers directly.

So any functionality that is to be controlled by MIDI controllers must be exported as regular parameter. The host will transform incoming MIDI controller data using this interface and transmit them as regular parameter change. This allows the host to automate them in the same way as other parameters. CtrlNumber can be a typical MIDI controller value extended to some others values like pitchbend or aftertouch (see ControllerNumbers). If the mapping has changed, the plug-in must call IComponentHandler::restartComponent (kMidiCCAssignmentChanged) to inform the host about this change.


In myeditcontroller.h

class MyEditController: public EditControllerEx1, public IMidiMapping
    tresult PLUGIN_API getMidiControllerAssignment (int32 busIndex, int16 channel, CtrlNumber midiControllerNumber, ParamID& id) SMTG_OVERRIDE;
    OBJ_METHODS (MyEditController, EditControllerEx1)
        DEF_INTERFACE (IMidiMapping)
    END_DEFINE_INTERFACES (MyEditController)
    REFCOUNT_METHODS (MyEditController)

In myeditcontroller.cpp

tresult PLUGIN_API MyEditController::getMidiControllerAssignment (int32 busIndex, int16 midiChannel, CtrlNumber midiControllerNumber, ParamID& tag)
    // for my first Event bus and for MIDI channel 0 and for MIDI CC Volume only
    if (busIndex == 0 && midiChannel == 0 && midiControllerNumber == kCtrlVolume)
        tag = kGainId;
        return kResultTrue;
    return kResultFalse;