Create nHair on a surface

To have nHair that collides with a surface, such as character's head or body geometry, the hair system must be created on polygonal surfaces. When you create an nHair system, you can choose to place the hair follicles according to the object's UV set map, or you can assign hair to selected polygon faces. For this tutorial, you select faces on a polygon model and assign hair to these locations.

In this section of the lesson, you create hair on a polygon model. You also convert the head model to a passive collision object so that it collides with the hair.

To create nHair on the model's surface

1. In the scene, select the female head model.
2. In the Toolbox, click the Paint Selection Tool icon.
   

   You use the Paint Selection Tool to select polygon faces.

3. In the scene, -click the head mesh and select Face from the marking menu that appears.
4. Paint-select the faces on the scalp region of the head to specify the area of nHair placement

   To resize the paint selection brush, press b and drag the left mouse button.

   
5. Select nHair > Create Hair > .

   The Create Hair Options window appears.

6. In the Create Hair Options window, select Edit > Reset Settings.
7. Set the following:
   • Output:Paint Effects
   • Turn on At selected surface points/faces.
   • Hairs Per Clump: 1
   • Ensure that Dynamic is turned on.
   • Points per hair: 12

     This sets the number of segments per hair. More segments are needed to make long hair look natural or to create complex short hairstyles. As you increase the number of segments, you decrease the performance (speed) of the simulation.

   • Length: 10.

     This value is relative to the world space units.

   
8. Click Create Hairs.

   The hair is attached to the selected polygon faces of the model's scalp region. Notice that the first frame displays the hair curves sticking out normal to the polygon surface. This is the Start Position of the hair. You should only edit the hair curves while nHair is in the Start Position. You can also see red markers on the polygon surface, indicating the placement of the dynamics curve follicles.

   

   In the Outliner, the following new nodes appear:

   • The hairSystem node provides all the attributes that modify the entire hair system. Throughout this tutorial, you adjust these attributes to affect the appearance and behavior of you nHair.
   • The hairSystemFollicle node carries attributes that only affect the selected follicle.
   • The pfHair node carries attributes that affect the Paint Effects strokes of you hair system.
   • The nucleus node is the Maya Nucleus solver node, which provides the attributes affecting the nucleus1 solver system, including internal forces.
   
9. Play the simulation.

   The curves react to the force of Nucleus gravity and begin to fall to a natural state. During any simulated frame, the hair is in its dynamic position, known as the Current Position.

   Notice that instead of colliding with the head model, the hair curves continue to fall and penetrate the model's surface. This occurs because the model is not a Nucleus object. nHair only collides with other Nucleus objects, such as nCloth, nParticles and passive collision objects that are assigned to the same solver. In the next step, you convert the head model to a passive collision object.

   

To create a passive collision object

1. Rewind the simulation.
2. In the Toolbox, click the Select Tool.
3. In the scene, -click the head mesh and select Object Mode from the marking menu that appears.
4. Select the head model then select nMesh > Create Passive Collider.

   The head model is converted to passive collision object and a new nRigid node appears in the Outliner.

5. Play the simulation.
   

   The hairs curves now collide with the head model surface similar to the way real hair makes contact with a person's head, face, and neck.

   In the next section of the lesson, you modify nHair attributes to increase the hair thickness and add curl to make it look more realistic.