This CHOP is used for controlling other CHOPs. Its first operation, “Fan Out”, selects one of N output channels based on the input channel’s value. A selected output has a value of 1, and all non-selected outputs have a value of 0. The selection is done by index; the first output channel is index value 0, the second, 1, and so on. If the input value is above N-1 or below 0, the value can be clamped, cycled or ignored.
For example, if the value of the input channel at a certain frame is 4 and the CHOP outputs 8 channels, channel 5 will have a value of 1, and all other channels will have a zero value at that frame.
The input is assumed to have 1 channel which contains integer values; fractions are truncated and extra channels are ignored. The output channels are binary (0 or 1) channels.
The second operation, Fan In, does the opposite: it takes a bunch of binary inputs and produces one channel containing the index of the “on” channel. If more than one input channel is “on”, the first “on” input channel is selected.
Selects either “Fan In” or “Fan Out”.
The names for the output channels that this CHOP creates. This also controls how many output channels are created (one for each name) in Fan Out mode. In Fan In mode, only one channel is created, and its name is the base name (minus the number suffix) of the first input channel.
Determines how to handle input values that are outside the index range (0 to N-1).
If less than 0, clamp to 0, and if greater than N-1, clamp to N-1.
Loop back through the index list.
Set Channels to 0
Don’t select any channels; set every channel to zero.
All Channels Off
For a Fan In operation, when all input channels are off, set the output to -1 or 0.
Set to 0
Selects the first channel.
Set to -1
Doesn’t select any of the channels.
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.