/ VST Home / Technical Documentation

[3.7.0] Parameter Function Name

On this page:

Introduction

Edit controller component interface extension: Vst::IParameterFunctionName.

This interface allows the host to get a parameter associated to a specific meaning (a functionName) for a given unit. The host can use this information, for example, for drawing a Gain Reduction meter in its own UI. In order to get the plain value of this parameter, the host should use the IEditController::normalizedParamToPlain. The host can automatically map parameters to dedicated UI controls, such as the wet-dry mix knob or the Randomize button.

Example

In mycontroller.h

//------------------------------------------------------------------------
// here an example of how a VST 3 plug-in could support this IParameterFunctionName interface.
// we need to define somewhere the iids:
  
//in MyController class declaration
class MyController : public Vst::EditController, public Vst::IParameterFunctionName
{
    // ...
    tresult PLUGIN_API getParameterIDFromFunctionName (UnitID unitID, FIDString functionName,
                                                    Vst::ParamID& paramID) override;
    // ...
  
    OBJ_METHODS (MyController, Vst::EditController)
    DEFINE_INTERFACES
        // ...
        DEF_INTERFACE (Vst::IParameterFunctionName)
    END_DEFINE_INTERFACES (Vst::EditController)
    //...
}

In mycontroller.cpp

#include "pluginterfaces/vst/ivstparameterfunctionname.h"
 
namespace Steinberg {
    namespace Vst {
        DEF_CLASS_IID (IParameterFunctionName)
    }
}
  
//------------------------------------------------------------------------
tresult PLUGIN_API MyController::getParameterIDFromFunctionName (UnitID unitID, FIDString functionName,
                                                                 Vst::ParamID& paramID)
{
    using namespace Vst;
  
    paramID = kNoParamId;
  
    if (unitID == kRootUnitId && FIDStringsEqual (functionName, kCompGainReduction))
        paramID = kMyGainReductionId;
  
    return (paramID != kNoParamId) ? kResultOk : kResultFalse;
}

Example of host implementation

if (auto functionName = Steinberg::U::cast<Vst::IParameterFunctionName> (mEditController->getIEditController ())
{
    Vst::ParamID paramID;
    if (functionName->getParameterIDFromFunctionName (Vst::FunctionNameType::kCompGainReduction, paramID) == kResultTrue)
    {
        // paramID could be cached for performance issue
        Vst::ParamValue norm = mEditController->getIEditController ()->getParamNormalized (paramID);
        Vst::ParamValue plain = mEditController->getIEditController ()->normalizedParamToPlain (paramID, norm);
        // plain is something like -6 (-6dB)
    }
}