The 3Delight Hair shader is a physically plausible shader that renders hair and fur using a Monte-Carlo simulation. A Monte-Carolo simulation explores the different light paths inside a medium (in this case, a clump of hair) to produce an image.
An interesting aspect of hair rendering is that all the intricate visual details seen in hair stem from the scattering of light in a multitude of hair strands and is not due to the complexity of a single hair strand. This seemingly simple observation explains why so many complex shaders are not successful at relaying the feeling of realistic hair. This includes the widely used shaders based on the Marschner model.
Example renders of blond, red and dark hair. Note the glow caused by light scattering inside blond and red hair. Also note how black hair has All theses features necessitate proper simulation of light scattering in hair clumps. | |||
Before explaining the the parameters of the shader in detail, let's explain some details that would seem strange at first:
- There is no diffuse term. Most shaders have an add-hoc diffuse term to approximate the soft look of hair. The soft look in hair is caused by light scattering and is not related to a diffuse BRDF. This scattering is properly simulated by the 3Delight Hair shader.
- The is no primary/secondary highlight parameters. As is the case for diffuse, these parameters are an approximation to directly relfected light and to light that has been reflected after bouncing twice inside a hair strand.
- No control over directly reflected color. Directly reflected color from hair and fur is always white.
- There are no "glint" parameters. This visual feature is caused by caustics inside each strand. Depending on hair roughness, light gets periodically concentrated in some areas of each hair strand and this cause the so-called glint.
Parameters
Output Variables