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This CHOP adds lag and overshoot to channels. It can also limit the velocity and acceleration of channels. Lag is an effect that slows down rapid changes in the input channels. Overshoot amplifies the changes in the input channels.
Two values exist for each parameter. For example, in the Lag effect, when the input channel value is rising, the first lag parameter is used, and when the channel value is decreasing, the second lag parameter is used. This can give a quick rise, and a slow fall. But lag up and down are often kept at the same value.
The Spring CHOP provides some similar effects.
The method by which lag is applied to the channels.
Up is defined as an increase in values of the input channels, and down is a decrease in values of the inputs.
Up is defined as an increase in amplitude (moving away from zero) and down is defined as a decrease in amplitude (moving towards zero) of each input channel.
All the input channels are treated as components of one vector, and each operation is applied to the vector as a whole. Only the first parameter in Lag, Overshoot, Clamp Slope and Clamp Acceleration applies in this mode.
Applies a lag to a channel. The first value is for lagging up, and the second is for lagging down. It is approximately the time that the output follows 90% of a change to the input.
Applies overshoot to a channel. The first value is for overshoot while moving up, and the second is for overshoot while moving down.
Clamps the slope (or velocity) to lie between the values listed in “Max Slope” below. Slope is expressed as value/Units.
The first value limits the slope when it is rising, and the second value limits the slope when it is decreasing.
Clamps the acceleration to lie between the values listed in “Max Acceleration” below. Acceleration is expressed as value/(Units*2)
The first value limits the acceleration when it is rising, and the second value limits the acceleration when it is decreasing.
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 index.
The current channel (0 to NC-1).
The total number of channels.
This file demonstrates the Lag CHOP.
The Lag CHOP can apply a lag, or overshoot an input channel. It can also limit the velocity and acceleration of input channels. The result of modifying channels in this way is similar to the effect of the Spring CHOP, yet not as naturalistic.