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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. The Edit mode has two variations. Edit will not modify primitives which have a
houdini:editable attribute set to
false. Force edit will modify a primitive regardless of the existence or value of this attribute. This attribute can be set on a primitive using the Configure Primitives LOP.
Parameters that correspond to a USD attribute have a pop-up menu to the left that controls how the node authors the attribute.
In addition to that, any connectable USD attributes (i.e., the ones in the
inputs: namespace) will have menu items that allow disconnecting them from their sources.
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.)
Deletes the attribute input connection to its source. Input connections take precedence over attribute values, so disconnecting an input allows the attribute value to take effect.
Ignore this parameter, don’t create or change the attribute in any way.
You will usually set the dome light to project a texture (environment map), such as a generic sky dome, or an IBL light probe (mirror-ball) reading taken on set.
If you use a cube map, it must be a vertical cross.
If you use a latitude-longitude map, you use should follow the OpenEXR specification for these kinds of environment maps. The following is from the OpenEXR documentation:
The environment is projected onto the image using polar coordinates (latitude and longitude). A pixel’s x coordinate corresponds to its longitude, and the y coordinate corresponds to its latitude. Pixel (dataWindow.min.x, dataWindow.min.y) has latitude +pi/2 and longitude +pi; pixel (dataWindow.max.x, dataWindow.max.y) has latitude -pi/2 and longitude -pi.
In 3D space, latitudes -pi/2 and +pi/2 correspond to the negative and positive y direction. Latitude 0, longitude 0 points into positive z direction; and latitude 0, longitude pi/2 points into positive x direction.
The size of the data window should be 2*N by N pixels (width by height), where N can be any integer greater than 0.
Whether this node should create new prims, or edit existing prims. In addition, the
Force Edit option can be chosen to cause this node to ignore the
houdini:editable attribute on prims, and always edit the specified attributes. This is in contrast to the
Edit mode which will trigger a warning and not set attributes on prims with the
houdini:editable attribute set to
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.
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.
If the Specifier is
Over, this parameter will cause some ancestor primitives to be authored with a specifier of
Class. This makes it easy to create an
Define within a
Class without having to use two separate nodes. When the Specifier is
Class, this parameter is disabled because the entire primitive hierarchy is already authored as
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.
File path to the texture file to use as an environment map.
How the spherical environment is encoded in the texture image. The default,
Automatic, tries to guess.
Optional light filter primitives that should be applied to this light.
Optional portal geometry prim(s) to use to guide light sampling.
When this is on, objects hit by this light will cast shadows (subject to shadow masks).
Tints the color of shadows cast by this light. Changing this from black (
0, 0, 0) is a non-physical “tweak”.
The near distance at which shadow falloff begins.
The default value (-1) indicates no falloff.
A gamma (i.e., exponential) control over shadow strength with linear distance within the falloff zone (between Falloff and Distance.
The maximum distance to check for objects shadowing this light. The default is
-1, meaning no limit. Setting this may speed up rendering if you know all objects you want shadowed are within a certain distance.
Outside this radius, the light will have no effect.
Controls whether multiple importance sampling will sample from the BSDF, the light, or both the BSDF and light.
This is the per-light sampling quality. Increasing the quality will add additional samples for this light source, improving the sampling quality of this light relative to other light sources.
Force Uniform Sampling
When using the light tree for rendering, Karma will try to put any light source that’s compatible into the tree. This option can force a light to be excluded from the tree and subject to uniform sampling, which can sometimes yield an improved sampling quality the light at the expense of speed.
The category identifier used to select this light source for illumination.
Maximum HDRI Size
If an environment map is larger than this resolution, it will be scaled down when performing texture analysis. If the map has some very small, very bright values, this filtering may affect how sampling of the environment map is performed.