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This CHOP creates vibrations influenced by the input channels, as if a mass was attached to a spring.
It acts as if, for every channel, there is a mass at the end of a spring, affected by a distance from the actual position (the output of the channel at the previous frame) to the desired position (the input channel at the current frame). When the distance (output - input) is zero, there is no force and therefore no movement.
Alternately, when Input Effect is force, the input is used as a force on the spring/mass, and the CHOP reacts to this force plus the force of the spring/mass. In this case, the mass would always stabilize at value
0 if the input is a force of
The Damping acts to make the spring system lose energy, so that higher damping makes everything come to rest sooner.
Its behavior is best understood by feeding it a CHOP that steps from one constant value to another in sequence, then playing with the constants.
A number describing how strong the spring is. Larger spring constants produce higher frequency oscillations.
The mass of the object on the end of the spring. Higher masses will produce lower frequency oscillations, have higher amplitudes, and be more resistant to damping.
The amount of damping (resistance) applied to the spring action. Higher damping causes oscillations to die off more quickly.
Determines whether the input channel(s) represents a position or a force.
Initial Conditions From Channel
If on, the initial position and velocity are calculated from the values at the beginning of the channel.
The initial position of the mass attached to the spring.
The initial velocity of the mass attached to the spring.
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 current channel number (0 to NC-1).
The total number of channels.