Lag channel node

Adds lag and overshoot to channels.

All Parameters Local variables Example files

See also: Spring

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

  1. Select the object that will lag.

  2. Click the Lag tool on the Modify tab of the shelf.

  3. Select the object whose animation the “lagging” object will follow and press Enter .

    The parameters of the Lag CHOP will pop up.

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 avaiable on all CHOP nodes.

Scope

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:

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.

r[xyz]

Matches channels rx, ry and rz.

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 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.

Units

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).

Note

When you change the Units parameter, it does not convert the existing parameters to the new units.

Time Slice

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.

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 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.

Local variables

I

The current index.

C

The current channel (0 to NC-1).

NC

The total number of channels.

Example files

LagBasic

$HFS/houdini/help/examples/nodes/chop/lag/LagBasic.cmd

Load | Launch

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.

Usages in other examples

Example name Example for
BlobbySphere

Channel surface node

Load | Launch