.. _sec-zFiber:

zFiber
------

The zFiber node is used to convert a generic tissue to a "muscle" by adding a fiber field.
The fiber field is a user-specified vector field through the volume of the tissue that defines the direction that the muscle will contract.

+---------------------------+--------------------------------------------------------------------------------+
| Attribute                 | Meaning                                                                        |
|                           |                                                                                |
+===========================+================================================================================+
| **envelope**              | Attenuates the excitation of this fiber node.                                  |
+---------------------------+--------------------------------------------------------------------------------+
| **strength**              | Defines the strength of the muscle. This is similar to the Young’s modulus     |
|                           | parameter on the material node.                                                |
|                           | The unit for muscle force is: N/m^2 (Newtons divided by meters squared).       |
+---------------------------+--------------------------------------------------------------------------------+
| **strengthExp**           | The power to which the value of the strength is raised.                        |
+---------------------------+--------------------------------------------------------------------------------+
| **contractionLimit**      | The muscle’s contraction force works to make the muscle this fraction of its   |
|                           | initial length. If this is set to 0.0, the muscle will seek to collapse into   |
|                           | nothing. If this is 0.5, the muscle will seek to be half its initial length. If|
|                           | this is set to 1.0, the muscle will seek to be its initial length.             |
+---------------------------+--------------------------------------------------------------------------------+
| **excitation**            | Controls the amount of muscle contraction. A value of "0.0" is relaxed and     |
|                           | "1.0" is fully contracted.                                                     |
+---------------------------+--------------------------------------------------------------------------------+
| **enableMuscleGrowth**    | Turns muscle growth on/off.                                                    |
+---------------------------+--------------------------------------------------------------------------------+
| **muscleGrowthScale**     | Sets the amount of muscle growth. This is a scaling factor; value must be > 0. |
|                           | Value of 1.0 means no growth. A value > 1.0 (e.g., 1.2, 1.5, etc.) will cause  |
|                           | the muscle to grow perpendicularly to the fiber. Values < 1.0 (e.g., 0.8)      |
|                           | cause shrinkage. This can be used to make the muscle bulkier or leaner.        |
+---------------------------+--------------------------------------------------------------------------------+
| **useLoaForMuscleGrowth** | When on, the muscleGrowthScale is internally multiplied with the line of       |
|                           | action value. This makes it possible to drive muscle growth using line of      |
|                           | action. When off, the muscleGrowthScale value is used directly.                |
+---------------------------+--------------------------------------------------------------------------------+
| **endPoints**             | This attribute is used to author the fiber direction field by painting 1.0     |
|                           | in-points and 0.0 out-points that define a gradient that the fibers will flow  |
|                           | along. Regardless of what is painted, the map is rounded to 0.0, 0.5, and 1.0  |
|                           | before use.                                                                    |
+---------------------------+--------------------------------------------------------------------------------+
| **weights**               | A paintable attribute that is used to scale the effect of the fiber force      |
|                           | through the volume. It allows one to localize the effect of the fiber field to |
|                           | certain parts of the tissue. As in the zMaterial node, if localized fiber      |
|                           | attenuation is required, the tet mesh will need to have enough local detail to |
|                           | support the desired detail in the fiber field.                                 |
+---------------------------+--------------------------------------------------------------------------------+