Hair

Important

Conversion to particle hair is broken in Blender 2.80. Hopefully it will come back later.

• Hair Color:
• Resize Hair: Change the number of hair vertices so all strands have the same number, and hence belong to the same particle system.
• Hair Length: The number of hair vertices, if hair is resized.
• Resize In Blocks:  Change the number of hair vertices to a multiple of ten. This results in a moderate number of particle systems and fairly uniform vertex density.
• Sparsity: Ignore some hairs if this number exceeds one.
• Skull Group: Create a vertex group on the human called Skull. The hair is attached to it when the head moves.
• All: Add all vertices to the Skull group.
• Top: Only add the top-most vertex (maximal z-coordinate) to the Skull group.
• None: Don't create a Skull group.
• Make Hair: Convert the selected, hair mesh to particle hair of the active, human mesh. To avoid confusion, the meshes are listed right below.
• Hair: The hair mesh.
• Human: The human mesh.
• Update Hair:
• Color Hair: Assign the Hair Color to the hair particles to give the hair a new color.
• Connect Hair:
• Add Pinning Group: This button is useful for simulation of mesh hair. Add a vertex group which can be used as a pinning group in a cloth simulation. The four parameters below control the vertex weights.
• Pin X0:
• Pin X1:
• Pin W0:
• Pin W1:

The DAZ importer can convert certain types of mesh hair to particles. It only works if the hair solely consists of stripes, whose UV coordinates are arranged vertically. Fortunately, most hair meshes in DAZ Studio are made in this way.

Here we have moved Ana's hair to a separate layer. The hair mesh consists of many disconnected pieces, which are of two types. The actual hairs are narrow bands with UVs arranged vertically, and a skull with a different type of UV coordinates.

We need to separate the skull from the rest of the mesh. In edit mode, select a skull vertex and hit ctrl-L to select all connected vertices. Then hit P and separate the selection to a new mesh.

There are now two meshes. Hair consists solely of bands with vertical UVs. This is the mesh that we will convert to particle hair.

We renamed the other mesh to Skull and changed the color to brown to distinguish it from the hair.The color is not important because it will not be visible in renders.

Select the character mesh, and then shift-select the Hair to make it active. Use the default settings and press Make Hair. After a slight delay Ana has particle hair, and the character mesh hair can be hidden or deleted.

Since it can be difficult to remember which mesh to select first, the hair and human meshes are listed below the button, so we can easily detect if the meshes have been selected in the wrong order.

The character mesh now has particle systems. In fact, it has many of them, called Hair-32, Hair-33 etc. Due to limitations in Blender's hair system, all hairs in a certain particle system must have the same number of vertices. Since the number of vertices is the same as the length of the stripe in the original mesh hair, a different particle systems are created for each stripe length. The number of segments is one less.

The Skull Group option was set to Top when we pressed Make Hair. The particle density is controlled by the Skull group, which consists of a single vertex located at the top of the head.

The reason for this choice is that the hair should follow the head bone when posed, and it is very likely that the uppermost vertex is only influenced by the head bone. We can verify that the hair moves correctly by bending the neck.

In Particle Edit mode we can highlight the vertices belonging to the Hair-32 particle system.

Because the character mesh has so many particle systems, it is quite tedious to edit parameters, because the changes must be repeated for each particle system. The DAZ importer has a tool that makes it possible to make the changes only once. Make the changes in one particle system and then hit the Update Hair button to transfer the changes to the others.

Unfortunately, Blender's particle system is quite brittle, and sometimes (most of the times, actually), all updated particle systems disappear from the viewport, although they can still be selected in the properties window. Work is underway to solve this problem.

The options of the Hair-33 system now reflects the changes made in the Hair-32 system.

The hair color was determined by the Hair Color selector at the top of the Hair section, but we can change it afterwards. Change the same Hair Color selector and press the Color Hair button. Ana now has blue hair.

Alternatively, we can grow hair on the Skull mesh instead of the character mesh. We have also changed some options:

• Hair Color. It is set to some light yellow, to mimic the color of the original mesh hair.
• Resize Hair. A single particle system will be created, and the hairs will be rescaled to fit.
• Hair Length. The number of hair vertices in the single particle system.
• Sparsity. It is usually not necessary to create hairs for each stripe in the mesh hair, because we can add children to the particle hair afterwards. If Sparsity = n, only every n:th hair will be added to the particle system.
• Skull Group. Because the entire skull mesh moves rigidly with the head, we can add all vertices to the Skull group.

With Skull selected and Hair active, now press Make Hair.

A single particle system is created, and all hairs belong to it. The particle system name is Hair-20 (from the Hair Length variable) and it has nineteen segments. We don't want the skull to be visible in renders, so turn the Emitter option off. It is on by default because if we had grown hair on the character mesh we would want it to be visible.

The vertex density varies depending on whether the original stripe was short (short distance between vertices) or long (long distance). This is a consequence of rescaling the hairs. An advantage is that we only have a single particle system to vary the parameters in, so there is no need to use the Update Hair button.

Here is Ana after the number of children has been cranked up, in the viewport and rendered.

All vertices in the Skull mesh belongs to the Skull vertex group with weight one. This works fine because the entire skull moves rigidly with the head.

Finally we explore some addition settings in the Hair section.

• Hair Color. Set to almost black.
• Resize in Blocks. If Resize Hair is turned off many particle systems are created, and if it is turned on the hairs are heavily resized. As a compromize with can resize the hairs in blocks of ten. All hairs with between 75 and 84 vertices will resized to belong to the system Hair-80 with eighty vertices. This keeps the number of particle systems down while not affecting the hair density very much.
• Sparsity. Only every fourth hair is kept.
• Skull Group. Set to None, so density is not controlled by any vertex group.

Hit Make Hair again.

There are now only a few particle systems (six of them, in fact), and they contain many hairs each.

Hair density is not controlled by any vertex group, but posing still works since the skull moves rigidly.

The last part of the Hair section is a utility for mesh hair. When doing cloth simulations we often want part of the mesh not to move, whereas other parts should move more or less. The extent to which a certain vertex is pinned down is controlled by a vertex group.

Select the hair mesh (the scalp should already be separated as another object) with the default settings, and press Add Pinning Group. A new vertex group called HairPinning is created. The weight assignments can be seen in Weight Paint mode.

The parameters Pin X0, Pin X1, Pin W0 and Pin W1 affect the weight assignment according to the graph above.

If the default weight assignment was not satisfactory, we simply change the parameters and press Add Pinning Group again. The HairPin group is now updated with new weights.