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A RenderVar is a custom variable computed by the renderer and/or shaders. The usual case for computing a render var is to include it in a render product as an AOV (an extra data plane in the output image).
This node creates a prim which specifies the source of the data (a shader output or light path expression). It also allows encoding (generally renderer-specific) parameters that configure the renderer to compute the variable.
Creating vs. editing prims
This node belongs to a class of nodes that create or edit USD prims directly. These nodes operate in Create mode or Edit mode. This is controlled by a Create primitives checkbox or a Create/Edit popup menu. In create mode, the node creates new prims. In edit mode, the node changes the attributes on an existing prim.
Parameters that correspond to a USD attribute have a pop-up menu to the left that controls how the node authors the attribute.
Pop-up menu item
Set or Create
Sets the attribute to the given value, whether it previously existed or not.
Set If Exists
Only set the attribute to the given value if it previously existed.
Use this mode to make sure an attribute is only set on primitives of the correct type. For example, only
Makes the attribute appear to not exist, so it takes on its default value. (If the attribute doesn’t already exist on the prim, this does nothing.)
Ignore this parameter, don’t create or change the attribute in any way.
Pixar’s specification calls for all RenderSettings, RenderVar, and RenderProduct prims to be under
/Renderin the scene graph tree (so the render pipeline isn’t required to traverse the entire tree looking for them).
See Pixar’s render settings proposal for more information.
Whether this node should create new prims, or edit existing prims.
In create mode, this lets you control where in the scene graph to create the prim(s).
The default is usually
/$OS. This creates a primitive at the root level with the same name as the node (for example,
/tube1). This is a useful default for preventing naming conflicts, but terrible for organization. You should try to remember to change the Primitive path to a better value when you create prims.
For example, instead of naming models after the node that created them, you might want to name them after the geometry inside, and organize them under a
The "Create primitives" section contains basic controls for how to create the new prim(s).
In edit mode, the node has a Primitive pattern parameter. This lets you specify the prim(s) the node should operate on. You can click the select button beside the text box to select the primitives from the scene graph tree. You can also use primitive patterns for advanced matching, including matching all prims in a collection.
Initialize Parameters For Edit
In edit mode, changes the state of all control menu parameters to
Do Nothing, so that this node will not apply any changes. Also grabs the current values of each property from the first Primitives match, and sets the values of the corresponding parameters to match. This means that changing any parameter’s control menu to
Set or Create mode will set the property to its current value, making it easier to apply changes to an existing value rather than setting a brand new value.
This section only appears when the node is creating primitives.
If you want to create a new cube primitive at
/world/objects/cube1on an empty stage: Set Primitive Specifier to "Define", and the Parent Primitive Type to "Xform".
If you want to override the radius of a sphere at
/world/objects/sphere1: Set Primitive Specifier to "Over", and the Parent Primitive Type to None. This makes sure the primitive types of any existing ancestor prims are not be modified by this node.
The number of primitives to create.
Set all created prims to have this kind.
Parent Primitive Type
If any parents of a path in Primitive paths do not exist, this node will automatically create them. In this case, it will create parent nodes of this type.
The USD operator to use when creating the new prims.
Authors a completely new prim. Use this if you want to create a brand new prim or replace an existing prim.
Authors an override of an existing prim. Attributes not explicitly authored on this prim will get their values from the existing prim on the lower layer.
Define a primitive class. This is usually not necessary unless you are doing deep USD magic.
The USD data type of the render variable.
When saving to OpenEXR files, the data type is used to determine the channel names. For example, if the data type is
color3f, the channel names will be
B, while if the data type is
normal3f, the channel names will be
Where to get the render variable contents. See Source type below.
The renderer should look for an output with this name as the computed value for the RenderVar.
How to interpret the Source name parameter.
Pass the source name directly to the renderer. This assumes the renderer knows how to interpret the source name string. This is the default.
The Source name is the name of primvar.
Some renderers may use this to ensure that the primvar is provided to the renderer. Other renderers may require that a suitable material network be provided, in which case this is simply an advisory setting.
The Source name is a Light Path Expression.
(Some renderers may accept extensions to the OSL Light Path Expression syntax, which will necessarily be non-portable.)
Currently not implemented. In the future, USD may provide for a portable list of baseline rendervars, such as camera depth, that would be implemented by all renderers.
The name of the AOV in the output image that stores the data from this rendervar.
The data format that should be used when saving this image plane to the output file.
EXR Channel Prefix
When saving to OpenEXR files, this is used as the prefix for channel names. For single value channels, this value will be used as the channel name. For example, for a normal AOV, if the prefix is
nml, the channels will be named
Whether the render buffer should be multisampled.
The initial value to fill the buffer with before rendering. Usually this is
0, however for example for
Pz you might set it to
When rendering with Karma, specify a pixel filter to run on the buffer. See Karma pixel filters.