The Application Programming Interface (API).

Creating user interface for a plugin (adding menu buttons etc.)

EQUINOX-3D uses the platform-independent GUI library, called EGUI.
This library is capable of creating menus, dialog boxes etc.
The most common GUI element you will need is probably a menu or ToolPanel button that activates a function in your plugin.

 MyButton = EGUI_AddPushButton("Tool->Transform", "Origin to ctr",
	    '\0', NULL, NULL, 
	    "Move Model's local origin to the center of its Objects",
	     _OriginToCenter, (EPointer)0);

The above call will add a button to the "Transform" folder of the ToolPanel, labeled "Origin to ctr".
"Move Model's local origin to\nthe center of its geometries" is the tool-tip (bubble help) that will appear around the button if the user rests the pointer on the button for a few seconds. Note that the '\n' (new line) code is accepted in strings.

 void _OriginToCenter(EguiItem LItem, EPointer LClientData,
                         EPointer LCallData)
 {
 .
 .
 }