Houdini 11 Nodes Channel nodes

Get the state of a chop as it was one frame or time slice ago.

The Feedback CHOP allows you to get the state of a CHOP as it was one frame or time slice ago. This allows you to connect CHOPs in circular loops without incurring the dreaded 'Infinite Recursion' error, because it simply copies its input without cooking it first.

POPs do this inherently, and some CHOPs like Lag and Filter look back in time (iterate) internally to the chop, but sometimes the output of a chain of CHOPs is needed as the input of the same chain one frame later.

For example, if you need the position or speed of an object from a frame ago in order to compute its position, displacement or speed at the current frame, you would select a chop containing those values and feed it into the Feedback CHOP. It will then output it a frame or time slice later.

Since its input is not recooked, it must be forcibly updated by following it with an exported CHOP to a displayed object.

Parameters

Feedback

Output

Specifies how the input should be copied.

Previous Channels at Previous Time

All in the past.

Previous Channels at Current Time

Some at current time.

Last Sample at Current Time

Only last sample at current time.

Delta Time

If on, adds a dt channel whose value is the elapsed time since the last cook. It is expressed in units determined by the Units parameter of the Common page.

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.

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