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iPlug2 is a cross-platform C++ audio plugin framework that provides a powerful abstraction layer for creating audio plugins across multiple formats and platforms.

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Architecture

The framework consists of two main components:

IPlug

Core plugin abstraction layer for DSP, parameters, and state management

IGraphics

Optional GUI toolkit with multiple backends (NanoVG, Skia)

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Supported Formats

iPlug2 generates plugins for all major formats:
  • CLAP - Modern cross-platform format
  • VST3 - Steinberg’s VST3 standard
  • AUv2/AUv3 - Apple Audio Units (macOS/iOS)
  • AAX - Avid Pro Tools format
  • Standalone App - Desktop application
  • WAM - WebAssembly audio modules
  • VST2 - Legacy format (deprecated)

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Platform Support

  • macOS (x86-64, ARM64)
  • Windows (x86-32, x86-64, ARM64)
  • Linux (via CLAP/VST3)

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Core Classes

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Plugin Base Classes

// Main plugin classes you'll interact with
class IPluginBase      // Parameters, presets, state serialization
class IPlugProcessor   // Audio processing, MIDI, channel I/O
class Plugin           // Combined base class (IPluginBase + IPlugProcessor)

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Key Components

Parameters

IParam - Type-safe parameters with ranges, shapes, and display functions

Presets

IPreset - Factory presets and state management

Processor

Audio processing and channel configuration

MIDI

IMidiMsg and ISysEx for MIDI handling

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Plugin Structure

Every iPlug2 plugin consists of three main files:
1

config.h

Compile-time configuration defining plugin properties:
#define PLUG_NAME "MyPlugin"
#define PLUG_MFR "MyCompany"
#define PLUG_CHANNEL_IO "1-1 2-2"  // Mono and stereo
#define PLUG_TYPE 0                 // 0=Effect, 1=Instrument, 2=MIDI Effect
#define PLUG_DOES_MIDI_IN 0
#define PLUG_LATENCY 0
2

Plugin.h

Plugin class declaration with parameter enums:
enum EParams {
  kGain = 0,
  kFrequency,
  kNumParams
};

class MyPlugin : public iplug::Plugin {
public:
  MyPlugin(const InstanceInfo& info);
  void ProcessBlock(sample** inputs, sample** outputs, int nFrames) override;
};
3

Plugin.cpp

Implementation with parameter initialization and DSP:
MyPlugin::MyPlugin(const InstanceInfo& info)
: Plugin(info, MakeConfig(kNumParams, kNumPresets))
{
  GetParam(kGain)->InitDouble("Gain", 0., -70., 12., 0.1, "dB");
  GetParam(kFrequency)->InitFrequency("Frequency", 1000., 20., 20000.);
}

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Basic Example

Here’s a simple gain plugin from the IPlugEffect example:
IPlugEffect.cpp
#include "IPlugEffect.h"

IPlugEffect::IPlugEffect(const InstanceInfo& info)
: iplug::Plugin(info, MakeConfig(kNumParams, kNumPresets))
{
  // Initialize parameter: name, default, min, max, step, label
  GetParam(kGain)->InitDouble("Gain", 0., 0., 100.0, 0.01, "%");
}

void IPlugEffect::ProcessBlock(sample** inputs, sample** outputs, int nFrames)
{
  const double gain = GetParam(kGain)->Value() / 100.;
  const int nChans = NOutChansConnected();
  
  for (int s = 0; s < nFrames; s++) {
    for (int c = 0; c < nChans; c++) {
      outputs[c][s] = inputs[c][s] * gain;
    }
  }
}

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Realtime Safety

ProcessBlock() runs on the high-priority audio thread. Never perform blocking operations:
  • ❌ File I/O
  • ❌ Memory allocation
  • ❌ Lock acquisition (use lock-free structures)
  • ❌ System calls
  • ✅ Only realtime-safe DSP operations

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Code Style

iPlug2 follows these conventions: 
// Member variables
mSampleRate     // m prefix
pData           // p prefix for pointers

// Methods
ProcessBlock()  // Public methods: PascalCase
_HelperMethod() // Internal methods: underscore prefix

// Formatting
2-space indentation (no tabs)
Unix line endings

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Next Steps

Plugin Base

Learn about plugin properties, state management, and presets

Audio Processing

Understand ProcessBlock and channel I/O configuration

Parameters

Deep dive into the IParam system

MIDI

Handle MIDI messages and SysEx

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Resources

API Documentation

Complete API reference

GitHub Wiki

Guides and tutorials