Slope channel node

Calculates the slope (or derivative) of the input channels.

All

Parameters

Example files

See also: Area, Math

This CHOP calculates the slope (or derivative) of the input channels.

If the input CHOP represents position, the slope can be interpreted as speed. By default, the Slope CHOP converts position to speed.

In mathematical terms, the slope is the first derivative of the channel curve. The second and third derivatives can also be calculated. The second derivative can be interpreted as acceleration (and the third derivative could be interpreted as the rate of change in acceleration).

This CHOP can be used in conjunction with the Area CHOP to manipulate speed or acceleration directly. You can calculate the speed or acceleration of a moving object with a Slope CHOP and manipulate it with other CHOPs. Then you can convert the new speed or acceleration curve back to position data with an Area CHOP. You may need to adjust the starting position, since the Slope CHOP removes this information. This can be done with the use of the Constant parameters in the Area CHOP.

The Units option causes the output to be expressed as a change in value per sample, value per frame, or value per second.

Parameters

Slope

Type

The type of slope to calculate.

Slope	Calculates the slope of the channels.
Acceleration	Calculates the acceleration of the channels.
Acceleration of Slope	Calculates the acceleration of the slopes of the channels.

Method

The sample pairs used to calculate the slope.

Use Previous And Current Sample	The current sample and the sample before it are used. This is the only method applicable in realtime applications.
Use Current And Next Sample	The current and the next samples are used.
Use Previous And Next Sample	The previous and the next samples are used, producing slightly more continuous slopes than the other methods.

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.

Example files

Slope

$HFS/houdini/help/examples/nodes/chop/slope/Slope.cmd

Load | Launch

This example demonstrates how the Slope CHOP calculates the slope (or derivative) of the input channels.

If the input CHOP represents position, the slope can be interpreted as speed.

By default, the Slope CHOP converts position to speed.

Usages in other examples

Example name	Example for
FurBallWorkflow	Fur surface node	Load \| Launch
TypesOfDrag	Drag Force dynamics node	Load \| Launch
FluidWireInteraction	Fluid Force dynamics node	Load \| Launch
Chain	RBD Pin Constraint dynamics node	Load \| Launch
Pendulum	RBD Pin Constraint dynamics node	Load \| Launch
grass		Load \| Launch
AnimatedClothPatch	Cloth Solver dynamics node	Load \| Launch
StitchedClothPatches	Cloth Solver dynamics node	Load \| Launch
ClothAttachedDynamic	Cloth Solver dynamics node	Load \| Launch
PinnedClothWind	Cloth Solver dynamics node	Load \| Launch
ClothSpringsBalls	Cloth Solver dynamics node	Load \| Launch
PaddleWheel	RBD Solver dynamics node	Load \| Launch
AnimatedSkin	Wire Glue Constraint dynamics node	Load \| Launch
DampedHinge	RBD Angular Spring Constraint dynamics node	Load \| Launch
ShatterGlass	RBD Glue Object dynamics node	Load \| Launch
DentingWithPops	SOP Solver dynamics node	Load \| Launch
ParticlesAndCloth	Particle Fluid Solver dynamics node	Load \| Launch
Weights	RBD Spring Constraint dynamics node	Load \| Launch
BeadCurtain	Wire Solver dynamics node	Load \| Launch
BendingTree	Wire Solver dynamics node	Load \| Launch
Pendulum	RBD Hinge Constraint dynamics node	Load \| Launch