IParam

Overview

The IParam class represents a plugin parameter in iPlug2. It handles value storage, normalization, display formatting, constraints, and parameter shaping. Parameters are accessed by index and store non-normalized (real) values. Header: IPlug/IPlugParameter.h

IParam values are stored as atomic doubles for thread-safe access. Use Value() to read and Set() to write.

Enumerations

EParamType

Defines the type of parameter.

enum EParamType
{
  kTypeNone,    // Uninitialized
  kTypeBool,    // Boolean (0 or 1)
  kTypeInt,     // Integer
  kTypeEnum,    // Enumerated list
  kTypeDouble   // Double precision floating point
};

EParamUnit

Used by AudioUnit plugins to determine parameter appearance.

enum EParamUnit
{
  kUnitPercentage, kUnitSeconds, kUnitMilliseconds, kUnitSamples,
  kUnitDB, kUnitLinearGain, kUnitPan, kUnitPhase, kUnitDegrees,
  kUnitMeters, kUnitRate, kUnitRatio, kUnitFrequency, kUnitOctaves,
  kUnitCents, kUnitAbsCents, kUnitSemitones, kUnitMIDINote,
  kUnitMIDICtrlNum, kUnitBPM, kUnitBeats, kUnitCustom
};

EDisplayType

Used by AudioUnit plugins to determine parameter mapping.

enum EDisplayType
{
  kDisplayLinear, kDisplayLog, kDisplayExp, kDisplaySquared,
  kDisplaySquareRoot, kDisplayCubed, kDisplayCubeRoot
};

EFlags

Parameter flags for special characteristics.

enum EFlags
{
  kFlagsNone = 0,
  kFlagCannotAutomate = 0x1,  // Parameter is not automatable
  kFlagStepped = 0x2,          // Parameter is stepped/discrete
  kFlagNegateDisplay = 0x4,    // Display as negative value
  kFlagSignDisplay = 0x8,      // Display as signed value
  kFlagMeta = 0x10             // Meta parameter (affects other params)
};

EShapeIDs

enum EShapeIDs
{
  kShapeLinear = 0,
  kShapePowCurve = 1,
  kShapeExponential = 2,
  kShapeUnknown
};

Parameter Shaping

Parameter shapes determine how normalized values (0-1) map to real values.

Shape

Base struct for parameter shaping.

struct Shape
{
  virtual Shape* Clone() const = 0;
  virtual void Init(const IParam& param);
  virtual EDisplayType GetDisplayType() const = 0;
  virtual double NormalizedToValue(double value, const IParam& param) const = 0;
  virtual double ValueToNormalized(double value, const IParam& param) const = 0;
};

ShapeLinear

Linear parameter mapping (default).

struct ShapeLinear : public Shape
{
  double mShape;
};

ShapePowCurve

Power curve shaping for custom response curves.

struct ShapePowCurve : public Shape
{
  ShapePowCurve(double shape);
  double mShape;
};

shape

double

required

Shape exponent. Values < 1 compress low end, > 1 compress high end

// Example: Frequency parameter with power curve
GetParam(kFreq)->InitDouble("Frequency", 1000., 20., 20000., 0.1, "Hz",
                            0, "", IParam::ShapePowCurve(3.0));

ShapeExp

Exponential/logarithmic shaping (ideal for frequency).

struct ShapeExp : public Shape
{
  void Init(const IParam& param) override;
  double mMul = 1.0;
  double mAdd = 1.0;
};

// Example: Exponential frequency parameter
GetParam(kFreq)->InitDouble("Frequency", 1000., 20., 20000., 0.1, "Hz",
                            0, "", IParam::ShapeExp());

Constructor

IParam();

Default constructor. Parameters must be initialized with one of the Init*() methods.

Copy constructor and assignment operator are deleted. Parameters cannot be copied.

Initialization Methods

InitBool

void InitBool(const char* name, bool defaultValue, const char* label = "",
              int flags = 0, const char* group = "",
              const char* offText = "off", const char* onText = "on");

Initialize as a boolean parameter.

name

const char*

required

Parameter name

defaultValue

bool

required

Default value (true/false)

offText

const char*

Display text when value is 0 (default: “off”)

onText

const char*

Display text when value is 1 (default: “on”)

GetParam(kBypass)->InitBool("Bypass", false, "", 0, "", "Disabled", "Enabled");

InitEnum

void InitEnum(const char* name, int defaultValue, int nEnums,
              const char* label = "", int flags = 0, const char* group = "",
              const char* listItems = nullptr, ...);
              
void InitEnum(const char* name, int defaultValue,
              const std::initializer_list<const char*>& listItems,
              int flags = 0, const char* group = "");

Initialize as an enumerated list parameter.

name

const char*

required

Parameter name

defaultValue

int

required

Default value (0-based index)

nEnums

int

required

Number of enum items (variadic version)

listItems

initializer_list or variadic

required

List of item names

// Using initializer list (preferred)
GetParam(kWaveform)->InitEnum("Waveform", 0,
  {"Sine", "Triangle", "Saw", "Square"}, 0, "Oscillator");

// Using variadic arguments
GetParam(kFilter)->InitEnum("Filter Type", 0, 3, "", 0, "Filter",
  "Low Pass", "High Pass", "Band Pass");

InitInt

void InitInt(const char* name, int defaultValue, int minVal, int maxVal,
             const char* label = "", int flags = 0, const char* group = "");

Initialize as an integer parameter.

GetParam(kVoices)->InitInt("Voices", 8, 1, 32, "", 0, "Polyphony");

InitDouble

void InitDouble(const char* name, double defaultVal, double minVal, double maxVal,
                double step, const char* label = "", int flags = 0,
                const char* group = "",
                const Shape& shape = ShapeLinear(),
                EParamUnit unit = kUnitCustom,
                DisplayFunc displayFunc = nullptr);

Initialize as a double-precision floating point parameter.

name

const char*

required

Parameter name

defaultVal

double

required

Default value

minVal

double

required

Minimum value

maxVal

double

required

Maximum value

step

double

required

Step size (0.01 for 2 decimal places)

label

const char*

Unit suffix (e.g., “dB”, “Hz”, ”%”)

flags

int

Parameter flags (see EFlags)

group

const char*

Parameter group name

shape

const Shape&

Parameter shaping (linear, exponential, power curve)

unit

EParamUnit

AudioUnit unit type

displayFunc

DisplayFunc

Custom display function (lambda)

// Standard gain parameter
GetParam(kGain)->InitDouble("Gain", 0., -70., 12., 0.1, "dB",
                            0, "Levels", IParam::ShapeLinear(), IParam::kUnitDB);

// Frequency with exponential scaling
GetParam(kFreq)->InitDouble("Frequency", 1000., 20., 20000., 0.1, "Hz",
                            0, "Filter", IParam::ShapeExp(), IParam::kUnitFrequency);

Convenience Initialization Methods

InitSeconds

void InitSeconds(const char* name, double defaultVal = 1.,
                 double minVal = 0., double maxVal = 10.,
                 double step = 0.1, int flags = 0,
                 const char* group = "");

InitMilliseconds

void InitMilliseconds(const char* name, double defaultVal = 1.,
                      double minVal = 0., double maxVal = 100.,
                      int flags = 0, const char* group = "");

InitFrequency

void InitFrequency(const char* name, double defaultVal = 1000.,
                   double minVal = 0.1, double maxVal = 10000.,
                   double step = 0.1, int flags = 0,
                   const char* group = "");

InitPitch

void InitPitch(const char* name, int defaultVal = 60,
               int minVal = 0, int maxVal = 128,
               int flags = 0, const char* group = "",
               bool middleCisC4 = false);

InitGain

void InitGain(const char* name, double defaultVal = 0.,
              double minVal = -70., double maxVal = 24.,
              double step = 0.5, int flags = 0,
              const char* group = "");

InitPercentage

void InitPercentage(const char* name, double defaultVal = 0.,
                    double minVal = 0., double maxVal = 100.,
                    int flags = 0, const char* group = "");

InitAngleDegrees

void InitAngleDegrees(const char* name, double defaultVal = 0.,
                      double minVal = 0., double maxVal = 360.,
                      int flags = 0, const char* group = "");

Init

Clone from existing parameter

void Init(const IParam& p, const char* searchStr = "",
          const char* replaceStr = "",
          const char* newGroup = "");

Value Access

Value

double Value() const;

Get the current parameter value (non-normalized, real value).

return

double

Current parameter value (thread-safe atomic read)

Bool

bool Bool() const;

Get parameter value as boolean.

return

bool

true if value >= 0.5, false otherwise

Int

int Int() const;

Get parameter value as integer.

DBToAmp

double DBToAmp() const;

Convert current value from decibels to linear amplitude.

return

double

Linear gain (approximation of 10^(value/20))

// Example: Apply gain parameter
void ProcessBlock(sample** inputs, sample** outputs, int nFrames)
{
  const double gain = GetParam(kGain)->DBToAmp();
  
  for (int s = 0; s < nFrames; s++)
  {
    outputs[0][s] = inputs[0][s] * gain;
  }
}

GetNormalized

double GetNormalized() const;

Get the current value as normalized (0-1).

Value Modification

Set

void Set(double value);

Set the parameter value (real value). Automatically constrains and steps.

value

double

required

New value (will be clamped to min/max and stepped)

SetNormalized

void SetNormalized(double normalizedValue);

Set the parameter from a normalized value (0-1).

normalizedValue

double

required

Normalized value between 0 and 1

SetString

void SetString(const char* str);

Set parameter value from textual representation.

SetToDefault

void SetToDefault();

Reset parameter to its default value.

SetDefault

void SetDefault(double value);

Change the default value and reset to it.

Value Conversion

ToNormalized

inline double ToNormalized(double nonNormalizedValue) const;

Convert a real value to normalized (0-1).

FromNormalized

inline double FromNormalized(double normalizedValue) const;

Convert a normalized value (0-1) to real value.

Constrain

inline double Constrain(double value) const;

Constrain value to min/max range and apply stepping.

ConstrainNormalized

inline double ConstrainNormalized(double normalizedValue) const;

Constrain a normalized value.

StringToValue

double StringToValue(const char* str) const;

Convert textual representation to value.

Display

GetDisplay

void GetDisplay(WDL_String& display, bool withDisplayText = true) const;
void GetDisplay(double value, bool normalized, WDL_String& display,
                bool withDisplayText = true) const;

Get textual display for current or specified value.

display

WDL_String&

required

Output string

value

double

Value to format (if not using current value)

normalized

bool

If true, value is normalized

withDisplayText

bool

Include custom display texts

GetDisplayWithLabel

void GetDisplayWithLabel(WDL_String& display, bool withDisplayText = true) const;

Get display string with unit label appended.

SetDisplayText

void SetDisplayText(double value, const char* str);

Set custom display text for a specific value.

value

double

required

Value to associate with text

str

const char*

required

Display text

// Example: Show "-inf" for -70dB
GetParam(kGain)->SetDisplayText(-70.0, "-inf");

SetDisplayPrecision

void SetDisplayPrecision(int precision);

Set number of decimal places for display.

SetDisplayFunc

void SetDisplayFunc(DisplayFunc func);

Set custom display function.

// Example: Custom display function
GetParam(kRatio)->SetDisplayFunc([](double value, WDL_String& str) {
  str.SetFormatted(32, "%.2f:1", value);
});

DisplayFunc Type

using DisplayFunc = std::function<void(double, WDL_String&)>;

Display Text Methods

NDisplayTexts

int NDisplayTexts() const;

Get number of display texts

GetDisplayText

const char* GetDisplayText(double value) const;

Get display text for a value

GetDisplayTextAtIdx

const char* GetDisplayTextAtIdx(int idx, double* pValue = nullptr) const;

Get display text by index

MapDisplayText

bool MapDisplayText(const char* str, double* pValue) const;

Get value for display text

Property Accessors

GetName

const char* GetName() const;

Returns the parameter name.

GetLabel

const char* GetLabel() const;

Returns the parameter label (unit suffix).

GetGroup

const char* GetGroup() const;

Returns the parameter group.

SetLabel

void SetLabel(const char* label);

Set the parameter label after creation.

If called after the host queries parameters, the host may not update its display.

Type Information

Type

EParamType Type() const;

Unit

EParamUnit Unit() const;

DisplayType

EDisplayType DisplayType() const;

GetFlags

int GetFlags() const;

Range Information

GetDefault

double GetDefault(bool normalized = false) const;

GetMin

double GetMin() const;

GetMax

double GetMax() const;

GetBounds

void GetBounds(double& lo, double& hi) const;

GetRange

double GetRange() const;

GetStep

double GetStep() const;

Flag Queries

GetCanAutomate

bool GetCanAutomate() const;

GetStepped

bool GetStepped() const;

GetNegateDisplay

bool GetNegateDisplay() const;

GetSignDisplay

bool GetSignDisplay() const;

GetMeta

bool GetMeta() const;

Shape Information

EShapeIDs GetShapeID() const;
double GetShapeValue() const;

Debug Utilities

GetJSON

void GetJSON(WDL_String& json, int idx) const;

Get JSON description of the parameter.

PrintDetails

void PrintDetails() const;

Print parameter details to debug console (debug builds only).

Example Usage

enum EParams
{
  kGain,
  kFreq,
  kResonance,
  kFilterType,
  kBypass,
  kNumParams
};

class MyPlugin : public iplug::Plugin
{
public:
  MyPlugin(const iplug::InstanceInfo& info)
  : Plugin(info, MakeConfig(kNumParams, 1))
  {
    // Gain parameter with dB scaling
    GetParam(kGain)->InitGain("Gain", 0., -70., 12., 0.5, 0, "Levels");
    GetParam(kGain)->SetDisplayText(-70.0, "-inf");
    
    // Frequency with exponential scaling
    GetParam(kFreq)->InitFrequency("Cutoff", 1000., 20., 20000., 0.1, 0, "Filter");
    
    // Resonance percentage
    GetParam(kResonance)->InitPercentage("Resonance", 50., 0., 100., 0, "Filter");
    
    // Filter type enum
    GetParam(kFilterType)->InitEnum("Type", 0,
      {"Low Pass", "High Pass", "Band Pass", "Notch"},
      0, "Filter");
    
    // Bypass bool
    GetParam(kBypass)->InitBool("Bypass", false);
  }
  
  void OnParamChange(int paramIdx) override
  {
    switch (paramIdx)
    {
      case kGain:
      {
        double gainDB = GetParam(kGain)->Value();
        double gainLin = GetParam(kGain)->DBToAmp();
        DBGMSG("Gain changed: %.2f dB = %.4f linear\n", gainDB, gainLin);
        break;
      }
      
      case kFreq:
      case kResonance:
      {
        double freq = GetParam(kFreq)->Value();
        double res = GetParam(kResonance)->Value() / 100.0;
        mFilter.SetCutoff(freq, GetSampleRate());
        mFilter.SetResonance(res);
        break;
      }
      
      case kFilterType:
      {
        int type = GetParam(kFilterType)->Int();
        mFilter.SetType(static_cast<FilterType>(type));
        break;
      }
    }
  }
};

​Overview

​Enumerations

​EParamType

​EParamUnit

​EDisplayType

​EFlags

​EShapeIDs

​Parameter Shaping

​Shape

​ShapeLinear

​ShapePowCurve

​ShapeExp

​Constructor

​IParam

​Initialization Methods

​InitBool

​InitEnum

​InitInt

​InitDouble

​Convenience Initialization Methods

InitSeconds

InitMilliseconds

InitFrequency

InitPitch

InitGain

InitPercentage

InitAngleDegrees

Init

​Value Access

​Value

​Bool

​Int

​DBToAmp

​GetNormalized

​Value Modification

​Set

​SetNormalized

​SetString

​SetToDefault

​SetDefault

​Value Conversion

​ToNormalized

​FromNormalized

​Constrain

​ConstrainNormalized

​StringToValue

​Display

​GetDisplay

​GetDisplayWithLabel

​SetDisplayText

​SetDisplayPrecision

​SetDisplayFunc

​DisplayFunc Type

​Display Text Methods

NDisplayTexts

GetDisplayText

GetDisplayTextAtIdx

MapDisplayText

​Property Accessors

​GetName

​GetLabel

​GetGroup

​SetLabel

​Type Information

Type

Unit

DisplayType

GetFlags

​Range Information

GetDefault

GetMin

GetMax

GetBounds

GetRange

GetStep

​Flag Queries

GetCanAutomate

GetStepped

GetNegateDisplay

GetSignDisplay

Overview

Enumerations

EParamType

EParamUnit

EDisplayType

EFlags

EShapeIDs

Parameter Shaping

Shape

ShapeLinear

ShapePowCurve

ShapeExp

Constructor

IParam

Initialization Methods

InitBool

InitEnum

InitInt

InitDouble

Convenience Initialization Methods

Value Access

Value

Bool

Int

DBToAmp

GetNormalized

Value Modification

Set

SetNormalized

SetString

SetToDefault

SetDefault

Value Conversion

ToNormalized

FromNormalized

Constrain

ConstrainNormalized

StringToValue

Display

GetDisplay

GetDisplayWithLabel

SetDisplayText

SetDisplayPrecision

SetDisplayFunc

DisplayFunc Type

Display Text Methods

Property Accessors

GetName

GetLabel

GetGroup

SetLabel

Type Information

Range Information

Flag Queries

Shape Information

Debug Utilities

GetJSON

PrintDetails

Example Usage

See Also