Plugins SDK
The Plugins SDK (software development kit) is for using C/C++ to make your own plugin functions and controls for use with Xojo.
Plugins can be created for use by all project types.
You find the full Plugin SDK documentation located in you Xojo installation here: Extras/PluginsSDK
The folder contains code and documentation in the following folders:
Documentation: Contains the SDK documentation in HTML format.
Examples: Example projects illustrating how to make Xojo plug-ins.
Glue Code: C++ code you must add to your plug-in projects.
Includes: Included by the glue code (and most likely by your own plug-in code as well).
There is also a Plugins channel in the forum to discuss the creation of Xojo plugins: Xojo Forum Plugins SDK Channel