The hair workflow

The Guerilla hair workflow is a solution to render a high (millions+) number of hairs. The Hair procedural duplicates hairs at render time, keeping the complexity at the end of the rendering process. The simulation and the export processes stay light.

The Hair procedural workflow is similar to the User Guide/Procedurals/Fur workflow. It uses the same Library/Procedurals/HairAndFur procedural node, but in the Interpolate Guides mode.

In the hair workflow, the scalp and the guide curves are mandatory. The final fiber curves are interpolated from the input guide curves.

The User Guide/Procedurals/Fur procedural to learn how to use the procedural, link the scalp and the guide curves, bake the implantation. The Library/Procedurals/HairAndFur procedural for all the procedural attributes details.

Our scalp mesh in red, the guide curves and the interpolated hairs.

If you are using Yeti®, you may not need to use the Hair procedural. Yeti® provides a RenderMan® DSO that can be directly used in Guerilla Render. See the TD Guide/Third Party Tools/Yeti sections for details.

Create the Hair node

The Hair node is a procedural geometry node. It acts like a regular mesh node (shaders, sets can be assigned to it using the RenderGraph) but it generates its geometry. It has to be linked to other mesh nodes, like the scalp meshes and the guide curves.

Create a Hair procedural node
  1. Create a Procedurals/Hair node.

The hair interpolation

First Tweaks

Setup the Density and the Selection Radius
  1. Select the Hair procedural and tweak the Hair > Procedural > Density > Density attribute until some hairs are generated.
  2. Fine tune the Hair > Procedural > Guides > Selection Radius attribute to get a nice coverage of the fibers.

First the hair density is adjusted, then the selection radius.

The density in the number of fiber per scalp mesh's surface unit. The 'Selection Radius' is the radius of the circle that selects the guide curves on a scalp position. Add a cut map

Now you probably want to add a cut map to get a clean hair implantation border. To do that, add a Density sub shader texture on the scalp mesh as explained in the User Guide/Procedurals/Fur procedural section.