Stretch channel node

Preserves the shape of channels and the sampling rate, but resamples the channels into a new interval.

All Parameters Local variables Example files

See also: Resample, Trim, Warp

This CHOP preserves the shape of channels and the sampling rate, but resamples the channels into a new interval. All data in the range is stretched or compressed to the new start and end positions.

Parameters

Stretch

Interpolation

The interpolation method to use when resampling.

No Interpolation

Use the value of the nearest sample.

Linear

Use linear interpolation between samples if CHOP is being lengthened. Averages all samples near the new sample if CHOP is being shortened.

Cubic

Cubically interpolates between samples, for smoother curves than Linear. This method is not recommended for channels with sharp changes.

Pulse Preserve

A linear interpolation that recognizes single sample pulses and preserves their height and one sample width. A pulse is a non-zero value preceded and followed by zero-value samples.

Constant Area

If on, keeps the area under the channel constant by scaling the the values of the channel.

Unit Values

Determines how Start/End parameters are interpreted.

Absolute

The value is the new start/end position.

Relative to Start/End

The value is a shift from the old start/end position.

Start

The CHOP’s new start position.

End

The CHOP’s new end position.

Length Scale

Scales the length of the channel after determining the start/end interval. Good for doubling or halving the length.

Reverse Interval

Reverses the channel so that it plays backwards.

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

C

The current channel (0 to NC-1).

NC

The total number of channels.

Example files

Stretch

$HFS/houdini/help/examples/nodes/chop/stretch/Stretch.cmd

Load | Launch

This example demonstrates how the Stretch CHOP changes the Start and/or End interval. It then resamples the input channel, preserving the shape of the channel. The sample rate remains the same, however, the interval changes.

Usages in other examples

Example name Example for