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The Constraint Offset CHOP applies a transformation to revert the effect of a constraint. To do so, it needs to keep a pose of the object before the constraint was applied and the original evaluation of the constraint. Given these two poses, an offset transformation is built and applied during evaluation.
The Update Offset button evaluates the node’s inputs and writes the result on the node’s parameters.
The Clear Offset button reverts the parameters back to an identity matrix.
Blend weight of the contribution of the offset.
Rotation channels typically don’t blend well when treated as Euler angles, and straight linear blending can result in flips and odd rotations. Instead, shortest path blending can be used to properly blend orientations represented by Euler rotation angles.
Rotation channels are blended like any other channel.
Two inputs are blended using shortest path rotation blending.
Define which of the transform components (TX,TY,TZ,RX,RY,RZ,SX,SY,SZ) to blend.
Define which of the transform components (TX,TY,TZ,RX,RY,RZ,SX,SY,SZ) contribute to the offset.
The alignment option to use.
Extend to Min/Max
Find the earliest start and latest end, and extend all inputs to that range using the extend conditions.
Stretch to Min/Max
Find the earliest start and latest end, and stretch every channel’s start and end to that range.
Shift to Minimum
Find the earliest start and shift all channels so they all start at that index. All channels are extended to the length of the longest one.
Shift to Maximum
Find the latest end and shift all channels so they all end at that index. Extend all channels to the length of the longest one.
Shift to First Interval
Shift all channels to the start of the first channel and sample all inputs using the first input’s range.
Trim to First Interval
Trim all channels to first channel’s range.
Stretch to First Interval
Stretch all channels to the first channel’s range.
Trim to Smallest Interval
Trim all channels to the smallest start/end interval. The start and end values may not come from the same channel.
Stretch to Smallest Interval
Stretch all channels to the smallest start/end interval. The start and end values may not come from the same channel.
Specifies the range of data to generate.
Use Full Animation Range
All of the animated range.
Use Current Frame
Only the sample at the current frame.
The range is specified from the Start and End parameters.
Use Value Animation
The range is taken from range of keys available in the evaluated Value parameters.
The start time of the channel range.
The end time of the channel range.
The sample rate of the CHOP.
Number of Threads
The number of separate threads to use to evaluate the channel samples. The default is no threading.
Since Houdini evaluates the VEX program for each sample in the input geometry, it can benefit greatly from threading on a multi-processor or multi-core machine when the CHOP nodes have many samples.
Some of these parameters may not be available on all CHOP nodes.
To determine which channels get affected, some CHOPs have a scope string. Patterns can be used in the scope, for example
* (match all), and
? (match single character).
The following are examples of possible channel name matching options:
Matches a single channel name.
chan3 tx ty tz
Matches four channel names, separated by spaces.
Matches each channel that starts with
Matches each channel that has
foot in it.
? matches a single character.
t? matches two-character channels starting with t.
Matches number ranges giving
[xyz]matches three characters, giving channels
Sample Rate Match
The Sample Rate Match Options handle cases where multiple input CHOPs’ sample rates are different.
Resample At First Input’s Rate
Use rate of first input to resample others.
Resample At Maximum Rate
Resample to highest sample rate.
Resample At Minimum Rate
Resample to the lowest sample rate.
Error if Rates Differ
Does not accept conflicting sample rates.
The units for which time parameters are specified.
For example, you can specify the amount of time a lag should last for in seconds (default), frames (at the Houdini FPS), or samples (in the CHOP’s sample rate).
When you change the Units parameter, it does not convert the existing parameters to the new units.
Time Slicing is a feature which boosts cooking performance and reduces memory usage. Traditionally, CHOPs calculate the channel over its entire frame range. If the channel does need to be evaluated every frame, then cooking the entire range of the channel is unnecessary. It is more efficient to calculate only the fraction of the channel that is needed. This fraction is known as a Time Slice.
Causes the memory consumed by a CHOP to be released after it is cooked and the data passed to the next CHOP.
The Export prefix is prepended to CHOP channel names to determine where to export to.
For example, if the CHOP channel was named
geo1:tx, and the prefix was
/obj, the channel would be exported to
You can leave the Export Prefix blank, but then your CHOP track names need to be absolute paths, such as
Every CHOP has this option. Each CHOP gets a default color assigned for display in the Graph port, but you can override the color in the Common page under Graph Color. There are 36 RGB color combinations in the Palette.
Graph Color Step
When the graph displays the animation curves and a CHOP has two or more channels, this defines the difference in color from one channel to the next, giving a rainbow spectrum of colors.
The following examples include this node.
The first example shows a LookAt constraint with a global Y axis up vector. The second example shows a LookAt constraint with its up vector driven by an object. The third example shows a LookAt constraint applied with Keep Position turned on. The CHOP Offset node, after the constraint, makes the object keep its orientation when the constraint is applied. You can use the LookAt Shelf Tool to recreate the examples.