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Since | 18.0 |
Overview ¶
The metadata on primitives is a “grab bag” of useful settings, such as:
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Visibility and draw mode.
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For what types of render the prim is used.
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Bookkeeping information such as references to files on disk.
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How primitives are traversed.
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Space where studios or tools can store their own arbitrary per-prim data.
Tips ¶
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This node will only author a bit of metadata if the corresponding parameter has its checkbox turned on. If the checkbox for a parameter is off, the node will not change any existing metadata corresponding to that parameter.
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You can easily switch the draw mode of primitives in the scene using the controls in the Scene Graph Tree pane. The controls in the pane modify an in-memory “view layer” that is not saved to disk, so they are more useful for working interactively.
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Proxy Primitive, Card Geometry, Card Color, the card Textures, Asset Identifier, Asset Name, Asset Version, Asset Dependencies, and Icon can all use the following local variables to get a per-prim value:
@numprim
The total number of primitives being modified by this node.
@prim
Index of the primitive being modified. This value goes from
0
to@numprim-1
.@primpath
The path of the primitive being modified.
@primname
The last token in the primpath
-
A python expression can use
hou.lvar('primpath')
to get the path and from there get the USD prim from which further information can be retrieved, for instancepwd().input(0).stage().GetPrimAtPath(hou.lvar('primpath')).GetPrimStack()[-1].layer.identifier
Parameters ¶
Primitives
The primitive(s) the node should operate on. You can drag primitives from the scene graph tree pane into this textbox to add their paths, or click the Reselect button beside the text box to select the primitives in the viewer, or ⌃ Ctrl-click the Reselect button to choose prims from a pop-up tree window. You can also use primitive patterns for advanced matching, including matching all prims in a collection (using /path/to/prim.collection:‹name›
).
Note
This parameter needs to be exposed in order for the transform handles to be context-aware. Without it, the handles may not be positioned properly.
Type
Set the primitive’s type. Changing the type of an existing primitive can lead to unexpected results, as all existing attributes on the primitive will remain, and not all attributes have any meaning or the same meaning in a different primitive type. However this capability can be invaluable in performing low level corrections to scenes that may have been authored incorrectly.
Specifier
Set the primitive’s specifier in the active layer. Note that this may not change the composed specifier for the primitive, depending on whether a different specifier is already set in another layer. In particular, an Over
specifier opinion is weaker than any other specifier opinion, even if the other opinion is on a weaker layer.
Purpose
Set the primitive’s purpose. Purposes are a way to control what gets rendered. The viewer/renderer only shows primitives tagged with one of a specified set of purposes.
Default
No set purpose, rendered by default.
Render
Should be used to tag high-resolution geometry that should appear in final renders.
Proxy
Should be used to tag faster/cheaper/lower-resolution proxy geometry. This may be used for test renders.
Guide
Should be used to tag “guide geometry” that should appear in an interactive viewer but not a rendered image. For example, collision geometry for a simulation.
If you set up purposes on your primitives, then you can control visibility of all primitives with the same purpose at render time by setting what purposes are visible in the render settings.
Note
If you set a primitive to have a Render purpose, there should be a corresponding prim with its purpose set to “Proxy”, and on the “Render” prim you should set the Proxy primitive (below) to the path of the “Proxy” prim.
Proxy Primitive
For a primitive with Render Purpose, this metadata holds the path to the primitive with Proxy purpose which corresponds to this render primitive.
Kind
See Kinds and the model hierarchy for an explanation of kinds and how they should be used. To maintain a proper model hierarchy, you should apply a kind to any prim whose descendants contain geometry.
None
Mark this prim as not having a kind.
Assembly
Mark this prim as an “important” group of models (for example, if a prop is made up of smaller moving parts, the top level of the prop would be an Assembly, and the sub-parts would be Groups and/or Components).
Group
Mark this prim as a group of models.
Component
Mark this prim as a “leaf” model.
Sub-component
Mark this prim as a subordinate part under a Component model.
Fix Kind Hierarchy
Set the kind of all parents of the selected prims so that the hierarchy is correct. Primarily this makes sure all parents of component or group have a kind of assembly or group.
Instanceable
See Instancing for an explanation of instanceable primitives. If a prim is marked as “instanceable”, all duplicates of that prim (and its descendants) are automatically replaced with lightweight references to a single “master” instance. You can still change attributes on instanceable prim (for example, to give each instance its own transform), but you can’t edit any of its descendants.
Apply Draw Mode On This Primitive
Indicates that this prim should be drawn according to the draw mode set on this prim or one of its ancestors. Component prims and prims with unloaded payloads are the normal locations where the draw mode is applied. This attribute allows any other primitive (that is part of a valid model hierarchy) to be the point in the scene graph where the chosen draw mode is applied.
Draw Mode
Controls how the renderer draws geometry under this prim. These options allow you to replace extremely heavy geometry in the viewer with faster, cheaper alternatives. Descendants of this prim will inherit this setting unless they change it.
Note
You can easily switch the draw mode of primitives in the scene using the controls in the Scene Graph Tree pane. The controls in the pane modify an in-memory “view layer” that is not saved to disk, so they are more useful for working interactively. This parameter should not be set here as it will interfere with these controls, however it is useful to temporarily set it to configure the cards.
Full Geometry
Force the geometry to be drawn normally, ignoring any value set on a parent.
Origin Axes
Instead of drawing the geometry, draw a “jack” (three lines along the X, Y, and Z axes) aligned to the geometry’s local space, at its local origin.
Bounding Box
Instead of drawing the geometry, draw a world-space-aligned box representing the bounding box of the geometry.
Textured Cards
Draws rectangular polygons with optional textures within or around the bounding box of this primitive. A variety of other attributes are used to control the appearance of these cards. They may be drawn as a bounding box, or as three cards that meet at the origin. The texture maps for each of the six visible card faces are also controlled though attributes.
Draw Mode Color
Color to draw Origin, Bounds, or if all the card textures are missing
Card Geometry
If Cards Draw Mode is chosen, what kind of Cards to draw
Cross
Draw the texture cards parallel with the box sides and intersecting at the center of the extents
Box
Draw a box the size of the extents with the cards as the sides
From Texture
Use the worldtoscreen metadata of the texture to place the cards at any orientation. Houdini cannot generate these textures.
Sampling Behavior
Cooking this node can generate many USD time samples, rather than just a single time sample at the current time. This can be equivalent to having a Cache LOP following this node, but it will evaluate much faster, and does not cache data from any other nodes. This allows animated data to be authored to USD without introducing a node time dependency which would then cause all following nodes to also be time dependent. This can vastly improve playback performance of some LOP Networks.
In all sampling modes, if a parameter on this node does not vary with time, and does not rely on other time sampled data from the stage, only a single default value will be generated in USD for the corresponding attribute. USD time samples are only generated for parameters that may vary over time.
Sample Current Frame
A single time sample will be generated for the current time.
Sample Frame Range If Input Is Not Time Dependent
If the input to this node is time dependent, this node behaves as if it is in Sample current frame
mode. Otherwise it behaves as if it is in Sample frame range
mode.
Sample Frame Range
The Start/End/Inc parameter is used to generate multiple times at which this node’s parameters are evaluated, and a USD time sample is created for each attribute at each one of these times.
Start/End/Inc
When the Sampling behavior is Sample frame range
, this parameter controls the number and spacing of base time samples to be generated by this node. The default values of this parameter are @fstart
, @fend
, and @finc
. These values correspond to the start, end, and step size of the global Houdini animation settings when interacting with Houdini. When using a ROP node to generate a range of frames, these values correspond to the start, end, and increment values specified on the ROP node being executed. This default ensures that a USD file written to disk will contain time samples for exactly the frame range requested by the ROP (regardless of the Houdini animation settings).
Subframe Sampling
For each primary sample generated by this node, these parameters can cause additional samples to be generated around that primary sample time. This is most often used to ensure that accurate data exists at exactly the camera shutter open and close times, as well as at the primary sample time.
Shutter
Controls the method used to specify the shutter open and close times relative to the primary sample times.
Specify Manually
The Shutter Open/Close parameter values provide exact offset values relative to the primary sample time.
Use Camera Prim
The Camera Prim parameter provides the scene graph path of a camera primitive from which the shutter open and close times are extracted to provide the offset values relative to the primary time sample.
Shutter Open/Close
When Shutter is set to Specify Manually, these two offset values are added to the primary sample time to indicate the shutter open and close times. The open time should be less than or equal to zero, and the close time should be greater than or equal to zero.
Camera Prim
When Shutter is set to Use Camera Prim, this is the scene graph path of a camera prim on the input node’s stage. The shutter open and close attribute values are read from this primitive.
Samples
The number of subframe samples to create for each primary sample. These samples are evenly distributed between the shutter open and close times. Note that such an even distribution may or may not create a sample at exactly the primary sample time.
Always Include Frame Sample
When turned on, forces a sample to be created at exactly the primary sample time. If the Samples value, together with the shutter open and close times, already place a sample at the primary sample time, turning on this option has no effect. Otherwise, this option causes an addition sample to be added. This means that the actual number of samples per primary sample may in fact be one more than the number specified in the Samples parameter.
Visibility
For performance reasons, the options for this attribute are Inherit or Invisible (there is no explicit “Visible” value). This means that when you mark a primitive is marked invisible, all its descendants are made invisible as well.
It can be useful to animate this setting over time, unlike most of the parameters on this node.
Set Extents
Compute any missing extents
or extentsHint
attributes. This information is needed to draw the cards and bounds at the correct size for those draw modes.
Primitives Missing Extents
Only primitives in the pattern which can meaningfully have an extents
or extentHints
attribute, and which do not already have this attribute will calculate and set an extent value.
All Primitives
All primitives in the pattern which can meaningfully have an extents
or extentHints
attribute will calculate and set an extent value.
+X Texture
Texture to draw on the +X side of the box or cross. If missing the -X texture is mirrored. If both are missing then YZ plane is not drawn. This parameter can be animated.
-X Texture
Texture to draw on the -X side of the box or cross. If missing the +X texture is mirrored. If both are missing then YZ plane is not drawn. This parameter can be animated.
+Y Texture
Texture to draw on the +Y side of the box or cross. If missing the -Y texture is mirrored. If both are missing then XZ plane is not drawn. This parameter can be animated.
-Y Texture
Texture to draw on the -Y side of the box or cross. If missing the +Y texture is mirrored. If both are missing then XZ plane is not drawn. This parameter can be animated.
+Z Texture
Texture to draw on the +Z side of the box or cross. If missing the -Z texture is mirrored. If both are missing then XY plane is not drawn. This parameter can be animated.
-Z Texture
Texture to draw on the -Z side of the box or cross. If missing the +Z texture is mirrored. If both are missing then XY plane is not drawn. This parameter can be animated.
Activation
If you turn this off, the primitive has no effect on the scene (for example, a light object will not cast light), it becomes invisible, and behaves as if it has no children.
Asset Identifier
Stores the file path or asset ID of the file this primitive came from. USD does not use this metadata, but it may be useful for internal tools.
Asset Name
A human readable name that may describe the asset. This may be authored by a pipeline/asset management tool. USD does not use this metadata, but it may be useful for internal tools.
Asset Version
For version-controlled assets, the version number of the asset when the scene was authored. This may be authored by a pipeline/asset management tool. USD does not use this metadata, but it may be useful for internal tools.
Asset Dependencies
An optional list of other files that are loaded indirectly by the asset file. This may be authored by a pipeline/asset management tool. USD does not use this metadata, but it may be useful for internal tools.
Asset Info Count
Additional named values to associate with the asset info dictionary on these prims or properties. Set the number of items to set/edit, or use the plus and minus buttons to add or remove items.
Asset Info Name
For each item of asset info, the name of the item.
Asset Info Type
For each item of asset info, the data type of the value.
String
The value is stored as a single string.
String Array
The value is parsed into an array of substring, respecting quotes to group space separated words into a single substring.
Token
Like a string, but represented as a USD Token, which generally should not contain spaces. Using this specific data type may be necessary to match scripts or tools later in your pipeline.
Token Array
Like a string array, but because USD Tokens generally aren’t expected to have spaces, the string is parsed into tokens using a simpler algorithm which ignores quotes and always splits the string where there is whitespace.
Float
The value is stored as a floating point number.
Integer
The value is stored as a whole integer value.
Boolean
The value is stored as a True or False value.
Asset Info Value
For each item of asset info, the value to associate with the name.
(Behind the scenes there are several different parameters (assetinfostrvalue‹n›
, assetinfofloatvalue‹n›
, assetinfointvalue‹n›
, assetinfoboolvalue‹n›
) all labeled Asset info value, with the visible one controlled by the Asset info type value. This may be relevant if you are using expressions or scripting these values.)
Icon
A path to an icon or image file that should be associated with the selected primitives in the Scene Graph Tree. This icon path is stored in a the primitive’s custom data dictionary.
Allow LOPs to Edit This Primitive
Applies a Houdini-specific attribute to the primitive which controls whether Edit Properties LOP node are allowed to modify this primitive. Disallowing the editing of a particular primitive can be used to prevent accidental modifications of cameras or other critical scene elements. Note that this toggle does not affect all edits of this primitive in LOPs, only the Edit Properties type LOP nodes respect this attribute.
Allow Viewport Selection of This Primitive
Applies a Houdini-specific attribute to the primitive which controls whether or not the primitive can be selected in the viewport. Setting this attribute on a primitive also affects all descendants of the primitive that do not specify their own explicit value for this attribute.
Hide Primitive In Scene Graph Trees
Sets the hidden
USD metadata to the primitive which controls whether or not this primitive (and its descendants) should be visible in the scene graph tree pane. Primitives tagged as hidden will still be visible in the viewport unless the primitive is also marked as invisible or inactive. Note that the scene graph tree pane provides an option to ignore this attribute (primarily for debugging purposes).
Apply API Schemas
See schemas for an explanation of API schemas. Primitives automatically keep a record of which API schemas have been “applied” to them. This parameter allows to list additional API schemas to apply to this primitive.
Custom Data Count
The metadata of every prim and property contains a dictionary for use by software packages and/or studios to store custom data. You can set or edit multiple custom key-value pairs here. Set the number of items to set/edit, or use the plus and minus buttons to add or remove items.
Custom Data Name
For each item of custom data, the name of the item.
Custom Data Type
For each item of custom data, the data type of the value.
String
The value is stored as a single string.
String Array
The value is parsed into an array of substring, respecting quotes to group space separated words into a single substring.
Token
Like a string, but represented as a USD Token, which generally should not contain spaces. Using this specific data type may be necessary to match scripts or tools later in your pipeline.
Token Array
Like a string array, but because USD Tokens generally aren’t expected to have spaces, the string is parsed into tokens using a simpler algorithm which ignores quotes and always splits the string where there is whitespace.
Float
The value is stored as a floating point number.
Integer
The value is stored as a whole integer value.
Boolean
The value is stored as a True or False value.
Custom Data Value
For each item of custom data, the value to associate with the name.
(Behind the scenes there are several different parameters (customdatastrvalue‹n›
, customdatafloatvalue‹n›
, customdataintvalue‹n›
, customdataboolvalue‹n›
) all labeled Custom data value, with the visible one controlled by the Custom data type value. This may be relevant if you are using expressions or scripting these values.)
See also |