Houdini 21.0 Nodes Geometry nodes

Muscle Tension Lines Activate geometry node

Calculates activation values for tension lines based on the position of the animated bones and the settings specified on the node.

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Since 21.0

This node sets the activation value for the incoming muscle tension lines. The default attribute is muscletension. With the multi parameter interface, you can set different activation settings for different lines or group of lines. When connected to the third input of the Muscle Flex SOP, it removes the need to set Activation Ratios on the Muscle Flex SOP.

Tip

This node gives you more control over muscle activation than the Muscle Flex SOP as there are multiple parameters to set instead of one per tension line on Muscle Flex. It is also simpler than the Muscle Flex Activation Ratio interface, as activation settings for multiple lines can be set at once instead of having one parameter per tension line. Furthermore, using lines instead of muscles to preview the activation values is faster to cook.

State

Muscle Tension Lines Activate state hotkeys

In the viewport, the Muscle Tension Lines Activate SOP state is similar to a selection state. Select one or multiple tension lines and then press Enter to make them your current selection. Scrub the timeline slider in the playback bar to any frame and then perform an action on your current selection.

Hotkeys

Action

Press A

Add New: Adds a new Activation multi parameter for the currently selected tension line(s) in the viewport state.

Press I

Invert Activation: Toggles the Activate when Extended (Invert Activation) parameter for the currently selected tension line(s).

Press N

Set Min from Current: Sets the value of Active Length Min to the current (for that frame) length ratio of the first currently selected line.

Press M

Set Max from Current: Sets the value of Max to the current (for that frame) length ratio of the first currently selected line.

Press ⇧ Shift + N

Set Min if Min: Sets the value of Active Length Min to the current (for that frame) length ratio of the first currently selected line if it’s smaller than the current value.

Press ⇧ Shift + M

Set Max if Max: Sets the value of Max to the current (for that frame) length ratio of the first currently selected line if it’s larger than the current value.

Tip

If you select a line and press Enter, the multi parameter tab containing that line will be selected, if it already exists.

Parameters

Activation Attribute Name

Specifies the name of the attribute that stores all the muscle activation settings, muscletension is the attribute expected by the Muscle Flex SOP.

Activation

Number of Groups

The number of groups of tensionlines to apply unique activation settings to.

Enable

Turn off to bypass this multi parameter instance without having to delete it.

Group

The lines to apply the activation settings for this instance. Using the autoflex_id attribute will ensure that settings remain applied to the correct lines if the line count or order changes.

Group Label

When specified, used as the label for the multi parameter tab. This is useful to stay organized in the node and has no downstream effect.

Active Length Min

The length ratio for the specified line(s), below which the line will be considered fully active or fully inactive if Activate when Extended (Invert Activation) is on. Activation for length values between Active Length Min and Active Length Max will be fit between fully active and fully inactive with the falloff determined by the Falloff Bias or Inactive to Active Falloff.

Set Min From Current Length

Sets the value of Active Length Min to the current (for that frame) length ratio of the first selected line for that tab. Pressing N in the viewport has the same effect.

Max

The length ratio for the specified line(s), above which the line will be considered fully inactive or fully active if Activate when Extended (Invert Activation) is on. Activation for length values between Active Length Min and Active Length Max will be fit between fully active and fully inactive with the falloff determined by the Falloff Bias or Inactive to Active Falloff.

Set Max From Current Length

Sets the value of Max to the current (for that frame) length ratio of the first selected line for that tab. Pressing M in the viewport has the same effect.

Mapping

Activate when Extended (Invert Activation)

When on, lines will be fully active when longer than Max, and fully inactive when shorter than Active Length Min. Between Active Length Min and Max, the activation value will increase as the line gets longer. This is off by default and has the opposite effect as described above. Press I in the viewport to toggle this on or off.

Use Ramp for Falloff

Use a ramp to control the falloff from inactive to active instead of with a single Falloff Bias parameter.

Falloff Bias

The exponent of the function that maps the transition in length between Active Length Min and Max from active 1 to inactive 0. The higher the value, the snappier the activation will appear.

Inactive to Active Falloff

Gives more control over the transition from inactive (left side) to active (right side). The default setting of Activate when Extended is off, the inactive side corresponds to the Max while the active side corresponds to Active Length Min.

Note

If the leftmost point at position 0 has a non-zero value, then the line will never be fully inactive. If the rightmost point at position 1 has a value less than one, then the line will never be fully active.

Strip Prefix from Tab Labels

Removes anything preceding the first _ in the autoflex_id name in the Group field from the multi parameter tab label to save space.

Symmetry

Mirror Activation Settings

Apply the same settings for activation to the corresponding named line on the mirrored side. The output activation values of the two lines are independent, but the criteria for activation are the same.

Allow Bidirectional Mirror

Mirror the settings to the opposite of the specified line, regardless of if the line is on the __from_ _side or to side.

From Prefix

Specifies the name prefix for your autoflex_id values. For example, a value of L_ if your autoflex_id values are L_gastro, or L_extensor, and so on.

To Prefix

Specifies the name prefix that will indicate the opposite side of the From Prefix in all of the autoflex_id values for the mirrored tension lines. For example, if the parameter value for From Prefix is L_, then your To Prefix parameter value should be R_ for R_gastro, or R_extensor, and so on.

Deformation

Deform Lines if Second Input Connected

Deform the lines with the animated bones from the second input, if connected.

Bone Rest Attribute

The name of the attribute that contains the rest position values of the bones, typically tpose.

Display

Isolate Current Tab Selection

Only display the thick activation lines for the currently selected multiparm tab.

Display Bone Geometry

Display the Bone Geometry from the second input in the viewport.

Bone Geometry Color

The red, green, blue, and alpha (opacity) of the bones displayed in the viewport.

Display Activation Attribute

Display the activation attribute specified in Activation Attribute Name as a color on the thick lines. Grey is fully inactive and red is fully active.

Copy Activation Colour to Selection Lines

Copy the activation visualization colour from the thick activation lines to the thin selection lines.

Hide Mirrored Side

Hide the thick activation lines with a name starting with To Prefix.

Display Width

Sets the width of the tension lines in the viewport.

Random ID Seed

The seed for the random colour used on the selection lines and their corresponding text labels.

Inputs

Input 1

Muscle tension lines (autoflex_id).

Input 2

Animation bone geometry.

Outputs

Output 1

Mucle tension lines with animated muscletension or specified Activation Attribute Name.

See also

Geometry nodes