Limit channel node

Provides a variety of functions to limit and quantize the input channels.

All

Parameters

Local variables

Example files

See also: Filter

This CHOP provides a variety of functions to limit and quantize the input channels.

Limiting a channel causes all its values to lie within a range. Several different methods are available for limiting:

Off	Do not limit the values.
Clamp	Simply cut the channel value off if it is out of the Maximum/Minimum range, and replace it with the Maximum or Minimum limit value.
Loop	Continue the channel at the other end of the interval.
Zigzag	Mirror the values back inside the interval.

Quantizing a channel value snaps its values to the closest allowable value (the “quantized values”). Quantizing methods are: Floor, Ceiling, and Round.

Quantizing a channel index is like quantizing in time, and acts as a sample and hold mechanism. The channel is sampled at a quantized index, and held at that value until the next quantized index at which time the value takes on the input value at that point.

Parameters

Limit

Type

The limit function to use:

Off	Do not limit the values.
Clamp	Simply cut the channel value off if it is out of the Maximum/Minimum range, and replace it with the Maximum or Minimum limit value.
Loop	Continue the channel at the other end of the interval.
Zigzag	Mirror the values back inside the interval.

Maximum

The maximum value the output channel can have.

Minimum

The minimum value the output channel can have.

Positive Only

Takes the absolute value of the channel, making all negative values positive.

Normalize

Scale and shift the channel so that it lies between -1 and +1.

Quantize

Quantize Value	Selects the quantization method to use: Off, Floor, Ceiling, and Round.
Value Step	The increment between quantized values.
Value Offset	The offset for quantized values, to allow steps to not lie at zero, the default.
Quantize Index	Selects whether to quantize the index relative to the sample 0, or the start index of the CHOP.
Index Step	The increment between quantized indices, in seconds, frames or samples.
Index Offset	The offset for quantized indices.

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

LimitBasic

$HFS/houdini/help/examples/nodes/chop/limit/LimitBasic.cmd

Load | Launch

This example file uses the Limit CHOP both to limit the height and to “quantize” the values of a channel.

By limiting the height the Limit CHOP can keep data values from going to high or from falling to low. To “quantize” the data, the curve is broken into steps rather than a smooth curve.

Usages in other examples

Example name	Example for