There are two required files to write plugins for QERadiant : qerplugin.h and qertypes.h. The plugin API is ANSI C. So the easiest way to write plugins for QERadiant is to use C or C++. However it is also possible to use VB, but no examples are provided yet. A QERadiant plugin is a Win32 DLL with a few exports. A sample one is provided in the ZIP version of the SDK in the sampledll directory. It's a project file for Visual C++ 5.0 or later that builds a plugin as a MFC DLL.

1. Read active or selected brushes, remove or create new ones.
   
2. Read points and point lists through the editor.
   
3. Create their own dialog boxes, as any Win32 app.
   

The plugin API should evolve in many ways as new Radiant releases come out. The Half-Life plugin can override the textures, but this feature is not documented yet.

The sampledll files provides a basic framework to write plugins. There are all the exports needed to write a plugin, and one example of brush scanning. For a better understanding of plugin programming, best is to look at the sources of the Rogue plugin, and the sources of MGS.