On this page | |
Since | 18.0 |
Overview ¶
This node manipulates the transforms of a prim so it appears to be parented to another prim somewhere else in the scene graph tree.
You can disable different transform components to get different effects. For example, you can constrain only position (pin constraint), rotations (align constraint), scales (size constraint), or shears.
Solaris constraints ¶
Currently, USD does not support constraints. Parametric constraints are probably antithetical to USD’s design mission of being descriptive, immutable, and idempotent.
As a layer above USD, that generates USD, the LOP network can compute dynamic constraints, and “bake” the results as time samples when it writes the USD to disk.
Tips ¶
-
The Relative Offset option lets you match the target’s translation at a different point on the timeline. For example, if you set the relative offset to
-1
seconds, the source object appears to lag behind the target.
Parameters ¶
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.
Source Type
Whether the source (the thing to be transformed) is a regular primitive, or a point instance. You cannot use a nested point instance as a source.
Source
When Source Type is Primitive, the scene graph path to the prim to use.
Source Instances
When Source Type is Point Instancer, the point instance to use, using /‹path›[‹instance_index›]
syntax (for example, /geometry/instancer[1]
).
Target Source
Where to get the “parent” prim, either the first input or the second input.
Target Type
Whether the “parent” is a regular primitive, or a point instance.
Target
When Target Type is Primitive, the scene graph path to the prim to use.
Target Instance
When Target Type is Point Instancer, the point instance to use, using /‹path›[‹instance_index›]
syntax (for example, /geometry/instancer[1]
).
Hide Target
When Target Source is First Input and Type is Primitive, whether to hide set the path’s visibility to “hidden”.
Import Time
Specify the frame at which the source and/or target geometry are imported into the embedded SOP network to build the constraints.
The default $FF
expression forces the constraint LOP to be time dependent, which is needed when operating on a non time-dependent
network that has time samples driving the source or target primitives.
However, for better performance with a non time-dependent network with no time samples, it is recommended to use a static value instead.
Position
Inherit position (translation) from the target. If this is off, the target does not affect the source object’s position.
Rotation
Inherit rotation from the target. If this is off, the target does not affect the source object’s orientation.
Scale
Inherit scales from the target. If this is off, the target does not affect the source object’s size.
Shear
Inherit shear from the target. If this is off, the target does not affect the source object’s shear.
Relative Offset
Get the target’s transform from a different point in the timeline. You can specify an offset in frames or seconds below.
Maintain Local Offset
When this is on (the default), the object maintains the relative distance between itself and the target, even though it otherwise inherits the target’s position.
Method
When Relative Offset is on, whether to calculate the offset in frames or seconds.
Frame
When Relative Offset is on and Method is By Frame, the relative number of frames ahead or back to get the target’s translation from.
Integer Frames
When Relative Offset is on and Method is By Frame, rounds the given frame number to the nearest integer frame, avoiding fractional frame cooking.
Time
When Relative Offset is on and Method is By Time, the number of seconds ahead or back to get the target’s translation from.
Examples ¶
ParentConstraint Example for Parent Constraint
This example contains a number of various uses for the Parent Constraint LOP.
See also |