Creating Phenomena

The basis for building and attaching Maya shading graphs is the Maya utility node Mentalray Phenomenon, also referred to as Phenomenizer node (Maya node type: mentalrayPhenomenon). It allows you to attach Maya shading graphs easily, and automatically generates the required input attributes on the Phenomenon node. It also provides access to all the advanced mental ray Phenomenon options. The full phenomenon description can be exported to a .mi file for later use.

Phenomenon Options

All Phenomenon options are available in the Attribute Editor of the node grouped under the Options tab. These include version number, apply flags, and requirements. For more information, see Phenomenon in the mental ray reference guide.

Workflow in Maya

To build your phenomenon in Maya

1. Build the initial Phenomenon as follows:
   • Create a Phenomenizer node (In the Hypershade, select Create > mental ray Miscellaneous).
   • Create a mental ray render node intended as the Phenomenonroot. The output of this node determines the output attributes of the whole Phenomenon.
   • Shift-drag the node onto the Phenomenizer node. The Connection Editor opens with the two nodes selected.
   • Connect the message attribute of the node to the Phenomenizerroot attribute. You may need to select Left/Right Display > Show Hidden to see the message attribute.
     Note

     Upon connecting the root node of the Phenomenizer, all additional output (read-only) attributes of that node are also dynamically added to the Phenomenizer node as output. They are considered fields of the final output parameter struct of the Phenomenon.

2. Build the shading graph content
   • Create and connect new nodes to the root node as driving nodes.
   • Set input attributes of those nodes to the desired constant values if they are not going to be exposed as interface parameters.
3. Build the Phenomenon interface

   Create input parameters for the Phenomenon from input attributes of any content node by drag-dropping the Phenomenizer onto the desired node, and then connecting an interface array element to the desired attribute.

   Note

   • Upon connecting an interface element, the attribute behind that plug is dynamically copied to the Phenomenizer, and can be connected to other nodes. Unlike the root attribute (there can only be one root), more than one connection may originate from a single interface element. The Phenomenizer checks if new connections are compatible with the existing dynamic attribute. If not, the connection is refused and an error message is reported.
   • When disconnecting interface elements or the root attribute, the corresponding dynamic attributes are also deleted.

To export the phenomenon to a .mi file

1. Select the Phenomenon node in Maya.
2. Select File > Export Selection >
   • Set File type to mentalRay
   • Turn on Export selected items only
   • Select the filters Factory shaders, and Phenomenizers.
3. Click the Export Selection button.

General Rules

• Mental ray phenomena are considered closed. Shaders inside phenomena must not connect directly to the outer shading graph. Instead, they must pass through the Phenomenon interface.
• mental ray does not support connections to whole parameter struct but only to individual fields. Therefore, interface elements can only be connected to atomic data types (boolean, integer, float, double, and so forth) and compounds with three numeric children (vectors or colors). The mental ray tags are represented as message attributes. Any other type of connection is rejected. Root nodes, however, can have any type of (even compound) result attributes.
• Use of the Connection Editor with the Phenomenizer is encouraged. The Hypershade workflow is somewhat restricted. It does not allow you to connect interface elements to compound plugs and array elements. Furthermore, dynamic attributes may not show up in the UI.
• Save your scene (or shading graph) regularly. The Phenomenon workflow introduces cyclic dependencies into the Maya dependency graph, with the potential to cause problems.

Limitation

• Attribute naming conflicts are not resolved automatically. When connecting a new interface element to an attribute, the name of that attribute is used as the new name of the corresponding interface attribute. If such a name exists already in the interface, the attribute creation fails. If necessary, rename the attributes in the interface before establishing new interface connections.