Add passive hair curves

If you discover areas of the model's scalp where there are too few hair curves, you can use the Paint Follicles tool to add more follicles to the hair system. One method of increasing hair density is to add passive hair curves by painting passive follicles. Passive hair curves generate movement by interpolating the behavior of neighboring dynamic curves. Since the Nucleus solver does not need to calculate dynamics for passive curves, they are useful for increasing the curve density of a hair system without affecting the performance of the hair simulation.

In this section of the lesson, you use the Paint Hair Follicles tool to add passive follicles to selected areas of the model's scalp.

To paint hair follicles

1. Rewind the simulation to the start frame.
2. Select the hair system and select nHair > Paint Hair Follicles > .

   The Paint Hair Follicles Settings window appears.

   NoteIf the Tool Settings window appears, close it. You do not use it in this lesson.
3. In the Paint Hair Follicles Settings window, select Edit > Reset.
4. Do the following:
   • Set Paint mode to Create passive follicles.
   • Ensure that Hair system is set to hairSystemShape1.
   • Ensure that Output is set to Paint Effects.
   • Set Follicle density U and Follicle density V to 40.

     Follicle density specifies the number of follicles created in the U and V direction for the selected face.

   • Set Points per hair to 6.
   • Set Hair length to 10.0.

     This ensures the passive curve length matches the existing dynamic curve length.

   
5. Using the paint tool, select the areas of the scalp where there are not dynamic curves.

   As you paint the model surface, the placements of passive follicles are indicated by the blue markers.

   

   To further add density to your hair style, you can further increase the Clump Width.

6. Select the hair system and in the Attribute Editor, click the hairSystemShape1 tab.
7. In the Clump and Hair Shape section, set Clump Width to 0.5.
8. Play the simulation.

   Notice that when you play the hair simulation, the hair appears limp and flat. You can add body to the hair style by setting the Stretch Resistance, Compression Resistance, and Bend Resistance attributes.

To add stiffness and body to the hair

1. Rewind the simulation to the start frame.
2. Select the hair system and in the Attribute Editor, click the hairSystemShape1 tab.
3. In the Dynamics Properties section, set the following:
   • Stretch Resistance: 50
   • Compression Resistance: 20
   • Bend Resistance: 3.0
   
4. Play the simulation.

   The hair style has more body and bounce. To add more stability and stiffness to the hair style, you can apply what it known as a "hairspray" effect. You do this by setting the Start Curve Attract attribute, which specifies the amount dynamic curves maintain the shape and position of the curve Start Position.

5. Rewind the simulation to the start frame.
6. In the Dynamics Properties section, set the following:
   • Start Curve Attract: 0.025
   • Attraction Damp: 0.5

     Setting Attraction Damp decreases the springiness in the hair, resulting in smoother curve motion.

     You can vary the amount of Start Curve Attraction applied along the curve length by setting an Attraction Scale ramp.

7. In the Attraction Scale section, click in the ramp to create additional markers then set the following marker values:

   Marker	Selected Position	Selected Value
   1	0	0.160
   2	0.25	0.5
   3	0.75	0.5
   4	1.0	0.16

8. Play the simulation.

   Notice that the attraction force overpowers gravity and causes the hair to be too stiff and wire-like. To solve this, in the next section of the lesson you change how Nucleus Gravity affects the hair simulation by setting the Space Scale attribute.

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