3Delight Extension Attributes in Custom Nodes

3Delight for Maya defines groups of extension attributes that can be added to any user-defined node type. The grouping follows the types of Maya built-in nodes for which 3Delight for Maya adds some extension attributes. Once the attributes are added to a user-defined node type, that node's Attribute Editor template will automatically display the same group of gadgets as what is defined for Maya built-in nodes.

To list the available attribute groups, use this command:

delightExtensionAttr -listGroups;

To add groups of extension attributes to a node type:

// Adds the common light extension attributes
delightExtensionAttr -nodeType "myCustomAreaLight" "light";
 
// Adds the arealight-specific extension attributes
delightExtensionAttr -nodeType "myCustomAreaLight" "areaLight";

Adding the extension attributes at the right moment

One issue with custom shapes using 3Delight Extension Attributes is that the custom shape is defined in a plug-in, and it requires extension attributes defined in another plug-in, 3Delight for Maya. This can cause issues when opening scenes - if the custom shape plugin is loaded and initialized before 3Delight for Maya is loaded, it will not be able to define the extension attributes on the custom shapes, and Maya will throw errors for each scene file statement setting a custom shape's extension attribute value.

One way to avoid this problem is to define a callback on the MSceneMessage::kAfterPluginLoad event. The callback calls a simple MEL procedure that adds the extension attributes on the node, if 3Delight for Maya is already loaded. Here is how to do it:

1. In your plug-in, define the callback function: 

   static void afterPluginLoadCallback(const MStringArray& i_strings, void* i_data)
   {
   	// This will be called once per plug-in loaded by the scene file, so
   	// avoid executing the command again after it successfully added the
   	// extension attributes.
   	//
       static int attributesAdded = 0;
       if(attributesAdded == 0)
       {
           MString cmd("addExtensionAttributes;");
           MGlobal::executeCommand(cmd, attributesAdded);
       }
   }

2. Create a "addExtensionAttributes.mel" file, and define the MEL procedure that adds the extension attributes: 

   // Adds 3Delight extension attributes on "myCustomAreaLight".
   // Returns 1 if the 3Delight Extension Attributes were added successfully
   //
   global proc int addExtensionAttributes()
   {
   	if(exists("delightExtensionAttr"))
   	{
   		delightExtensionAttr -nodeType "apiMesh" -addGroup "displacementShader";
       	return 1;
   	}
   	
   	return 0;
   }

3. Register the callback somewhere in your plug-in's initialize() function: 

   MStatus status;
   MSceneMessage sceneMessage;
   sceneMessage.addStringArrayCallback(MSceneMessage::kAfterPluginLoad, afterPluginLoadCallback, NULL, &status);

Maya appears to execute the MSceneMessage::kAfterPluginLoad callback after the initialize() function is ran, so the above example will make Maya call afterPluginLoadCallback() once right after your plug-in is initialized, and once after each plug-in required by the scene is loaded. You are thus sure to get afterPluginLoadCallback() called at some point after 3Delight for Maya has been loaded.

It is not recommended to use the procedure passed to MFnPlugin::registerUI() to add extension attributes as it is ran only once, and it is not guaranteed that at the time it is ran, 3Delight for Maya has been loaded.