There are basically four ways to create custom properties. All these methods are valid, and which method you use depends on the purpose of your CustomProperty:
Using the Interactive Tools in Softimage
Using the On-the-Fly Approach
Creating an instance of a Self-installing CustomProperty Plug-in (recommended for persistent data)
Creating an instance of a CustomProperty defined in a SPDL file (supported for shaders, deprecated for other persistent-data plug-ins)
You can create custom property sets and pages from the user interface under the Animate
CreateParameter menu. These are persisted in the scene but are not available to other scenes unless you explicitly save them as a preset.
Using the interactive tools is a great way to learn about custom property sets and to prototype, but you need to create an instance of a Self-installing CustomProperty Plug-in if you want a more sophisticated toolset.
For more information about using the interactive tools, see the Softimage user guide.
You can create custom property sets and pages from a script or C++ API custom command using the basic SIAddProp and SIAddCustomParameter commands or the more sophisticated CustomProperty or CustomProperty, PPG or PPG or PPG, and PPGLayout or PPGLayout objects.
If you are using a custom property set as a temporary dialog box, it is easy to create it on the fly and delete it afterwards. Any parameter data you create as part of this custom property set persists for the duration of the scene or until you explicitly delete it. However, you may need to install it as a Self-installing CustomProperty Plug-in in either of these two situations:
If you want to reuse the same custom property in another scene.
If you quit Softimage and then re-start it the layout for your custom property set is gone, even though the data contained in the custom properties is still there. If you inspect the property set the parameters all appear, but with no Logic (no buttons, since they are not associated with any parameters), and no special controls (such as Combo boxes).
On-the-Fly properties are defined directly on their owners in the implementation code, whereas self-installing custom properties are defined, installed, and then applied on their owner using the SceneItem.AddProperty method.
Self-installing CustomProperty Plug-in
The Autodesk Softimage SDK provides a rich toolset to define a self-installing custom property plug-in (sometimes called a plug-in-based CustomProperty). The custom property sets can be built in much the same way as the On-the-Fly properties; however, they are applied as if there is a preset defined on the system (using the SceneItem.AddProperty or SceneItem::AddProperty method) and are available to other scenes after the plug-in is installed.
CustomProperty defined in a SPDL file
You can use the SceneItem.AddProperty or SceneItem::AddProperty method to apply a custom property defined in an installed SPDL file in the same way as you apply a self-installing custom property. However, defining the property set and property page layout is not as easy and is more error-prone than using the object model.
Using a SPDL file is no longer the recommended approach, but is being maintained for backwards compatibility. Creating a Self-installing CustomProperty Plug-in is the recommended approach.