Adding Plugins to the CMT Library

The CMT LADSPA plugin collection is written in C++ and uses a little additional sophistication to make plugin writing easier. This document describes how to add a new plugin to the toolkit.

CMT plugins interpret LADSPA_Handle entities as pointers to objects derived from the CMT_PluginInstance class. Plugin instance structures are defined by subclassing this, so writing a descendent of CMT_PluginInstance is the first thing to do. The CMT library provides its own implementation of connect_port(), cleanup() and a templated form of instantiate() (see CMT_Instantiate<>()). These calls assume that any instantiation or cleanup mechanisms required will be written in the constructor or destructor of the class.

When writing a plugin module, an initialisation function should be included. To ensure this is called, add a call to the initialise_modules() function in descriptor.cpp. The module should also be added to the makefile.

Your initialisation function should construct new CMT_Desctiptor plugin descriptor structures and pass them to registerNewPluginDescriptor(). The CMT_Descriptor is directly descended from LADSPA_Descriptor but provides constructor, destructor and addPort() methods.

All plugins need unique IDs. During development, use values between 1 and 1000. When the plugin is ready, please request an ID from Please also add a brief description of your module to plugins.html.

In practice, CMT plugin writing is probably best learned by example. For a simple case, see the mixer.cpp module. This defines a SimpleMixer class to handle instance data, a runSimpleMixer() function for use with it and a mixer_descriptor() function to provide a description of the plugin to the CMT core. The mixer_descriptor() function is declared and referenced in the descriptor.cpp module. Additional information is available in cmt.h and ladspa.h.

CMT plugins are licenced under GPL version 2. Please read and understand this license before submitting plugins to the library.

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