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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.
Using Lag ¶
Parameters ¶
Lag ¶
Method
The method by which lag is applied to the channels.
Lag Value
Up is defined as an increase in values of the input channels, and down is a decrease in values of the inputs.
Lag Amplitude
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.
Lag Magnitude
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.
Lag
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.
Overshoot
Applies overshoot to a channel. The first value is for overshoot while moving up, and the second is for overshoot while moving down.
Clamp Slope
Clamps the slope (or velocity) to lie between the values listed in “Max Slope” below. Slope is expressed as value/Units.
Max Slope
The first value limits the slope when it is rising, and the second value limits the slope when it is decreasing.
Clamp Acceleration
Clamps the acceleration to lie between the values listed in “Max Acceleration” below. Acceleration is expressed as value/(Units*2)
Max Acceleration
The first value limits the acceleration when it is rising, and the second value limits the acceleration when it is decreasing.
Common ¶
Some of these parameters may not be available on all CHOP nodes.
Scope
To determine the channels that are affected, some CHOPs have a scope string. Patterns can be used in Scope, for example *
(match all), and ?
(match single character).
The following are examples of possible channel name matching options:
chan2
Matches a single channel name.
chan3 tx ty tz
Matches four channel names, separated by spaces.
chan*
Matches each channel that starts with chan
.
*foot*
Matches each channel that has foot
in it.
t?
The ?
matches a single character. t?
matches two-character channels starting with t.
blend[3-7:2]
Matches number ranges, giving blend3
, blend5
, and blend7
.
blend[2-3,5,13]
Matches channels blend2
, blend3
, blend5
, blend13
.
t[xyz]
[xyz]
matches three characters, giving channels tx
, ty
and tz
.
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 the rate of the first input to resample the others.
Resample At Maximum Rate
Resample to the highest sample rate.
Resample At Minimum Rate
Resample to the lowest sample rate.
Error if Rates Differ
Does not accept conflicting sample rates.
Units
The units of the time parameters.
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).
Note
When you change the Units parameter, the existing parameters are not converted to the new units.
Time Slice
Time slicing is a feature that boosts cooking performance and reduces memory usage. Traditionally, CHOPs calculate the channel over its entire frame range. If the channel needs 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 the Time Slice.
Unload
Causes the memory consumed by a CHOP to be released after it is cooked, and the data passed to the next CHOP.
Export Prefix
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 /obj/geo1/tx
.
Note
You can leave the Export Prefix blank, but then your CHOP track names need to be absolute paths, such as obj:geo1:tx
.
Graph Color
Every CHOP has this option. Each CHOP gets a default color assigned to it for display in the graph, but you can override the color with the 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.
Locals ¶
I
The current index.
C
The current channel (0 to NC-1).
NC
The total number of channels.
Examples ¶
LagBasic Example for Lag channel node
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.
See also |