Foreach channel node

Divides the input channels into groups, cooking the contained network for each group.

See also: For

Foreach is a specialized subnet which processes its channels in small groups, by cooking the contained network multiple times for each group. This makes processing of hundreds of particles or objects much easier to manage since the network only needs to be designed to handle a single object.

By specifying a channel group pattern, the channels of input 1 are sorted into groups. Each group is processed by the subnet without the other channels. The channel names within the subnet have the channel group name removed from them, so that they are always consistently named. The subnet may manipulate the channels in any way, by adding, modifying, renaming or removing channels. The remaining channels at the output of the subnet are added to the Foreach node’s output channels by reintegrating the channel group name back into them.

The subnet contains a For node, 4 subnet inputs, and an Output node. The For node contains the channels of the currently processed channel group. The first subnet input contains all the channels that are being iterated over, in case collision detection or some other inter-group relationship needs to be performed. The other 3 subnet inputs allow for constant input to the subnet.

The output node is a convenience. The Foreach draws its output from the node with the Audio flag set.

The current loop iteration can be queried from the For CHOP’s 'Current Loop Index' parameter using a ch() expression.

Note	Channels that are not assigned to a channel group will not be processed or present in the output.

Parameters

Foreach

Channel Group

A set of patterns which describe the members of the channel groups. A wildcard '*' is used to indicate the varying part of the channel name. A channel group is formed by the channels that match the patterns when '*' is replaced by the channel group name.

For example, a pattern of 'leg*:tx leg*:ty leg*:tz' would create a channel group called '4' when leg4:tx, leg4:ty and leg4:tz are in the channels of input 1.

Note	The channel group does not need to be numeric. The match pattern could be ':tx :ty *:tz', giving a channel group of 'leg4' in the above example.

Channel Indexing

The channel group name is stripped out of the channels inside the subnet so that the channel names remain constant within the loop. When these channels are added to the Foreach CHOP, their names are combined with the channel group name to create a unique name for every channel in the channel group.

Append	The channel group name is appended to the channel name.
Replace Token	A text string is used to identify where the channel name should be inserted into the channel name.
Insert at First Separator	The channel group is inserted before the first : or / separator in the channel name.
Insert at Last Separator	The channel group is inserted before the last : or / separator in the channel name.

Group Token

The token being replaced when the Channel Indexing mode is Replace. It should be a text string that isn’t going to naturally occur in your channels (ie, 't'). Each of the output channels inside the Foreach CHOP should contain this token somewhere in their name (ie, handIDX:tx, for a token of IDX).

Renumber From

If enabled, the channel group name is ignored and replaced with a number starting at the specified index, increasing by 1 for each loop.

Preview Groups

If enabled, only the specified channel groups are processed. This allows for a quick preview of a fraction of the groups.

Debug Group

If enabled, the specified channel group is processed last. This leaves the contained subnet in the state that cooked this channel group, so that problems can be investigated and debugged. This only works for a single channel group.

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.

Usages in other examples

Example name	Example for