mtlsh_shader

Shader Family: Surface Material

Multiple Outputs: Color

Related mental ray shader: misss_fast_shader_x

This is a Softimage spdl-based version of the mental ray component shader used in the SSS shader compounds.

The mtlsh_shader is the workhorse shader that does the actual scattering. It is highly modular and works with several input shaders that provide the actual contribution for the various layers through the bump, diffuse_illum, and specular_illum input ports. This shader can even be cascaded into itself (again using the diffuse_illum port) for multi-layer scattering (this is exactly how Fast Simple (misss) works). The mtlsh_shader layers the results from the input shaders with the scattered light from the lightmap and then presents the final shaded result.

NoteNote that fast subsurface scattering effects are not included in the maps generated by the RenderMap tool.

Diffuse

Color	Defines the color of the diffuse illumination component. This is normally driven by the object's main surface texture.
Weight	Controls the weight of the Diffuse illumination component when it is blended with the other components (ambient, scattering, etc.).

Scattering

Front

Color	Controls the color for the front surface scattering. The front surface is the side of the object facing the camera, and so front surface scattering is most visible when that side is well lit.
Weight	Controls the weight of the front scattering surface when it is blended with the other lighting components (back scattering, diffuse, etc.).
Radius	Controls the distance that light scatters along the front surface. This value is measured in scene units, but is divided by the Scale value on the Advanced Settings tab.

Back

Color	Controls the color for the back surface scattering (the light going through the object). The Back surface is the side facing away from the camera. Back scattering is most visible when the object is backlit to some extent, or when light passes directly through the object.
Weight	Controls the weight of the back scattering when it is blended with the other lighting components (front scattering, diffuse, etc.).
Radius	Controls the distance that light scatters along the back surface. This value is measured in scene units, but is divided by the Scale value on the Advanced Settings tab. Normally, the back scattering radius should be set to the same value as the back scattering Depth parameter.
Depth	Controls the back scatter depth. The higher the value, the more deeply light is scattered within the object. In effect, raising the depth makes the object appear more translucent when backlit. Generally speaking, higher depth values require an increased number of lightmap samples in order to remove speckling in the rendered image. Normally, the back scattering depth should be set to the same value as the back scattering Radius parameter.

Controls

Sample Falloff	Defines the falloff profile for light scattered along the radius. Higher values cause a sharper falloff. Lower values cause a smoother falloff but cause the scatter distance to appear shorter, though you can increase the Radius value to compensate. For high values (1.0 to 10.0), almost all samples within the scatter radius are weighted equally. For low values (0.1 to 1.0), the samples near the edge of the scatter radius are weighted as less.
Lightmap Samples	Specifies the number of lightmap samples considered by each rendered ray. Generally, this should be set to a power of two (16, 32, 64, 128, etc.). Subtle scattering effects typically require few samples. However, as you begin to increase the front and back scattering radii, or the back scattering depth, you will need to increase the number of samples to avoid speckling in the rendered image.
Scale	A simple utility function that allows a linear division of all distances. Since scattering is distance dependent, loading a material designed for a model made in inches will not work on a model where the unit is meters, and vice versa. Use this option as the conversion factor for scale.
Use Screen Compositing for Colors	When enabled, screen compositing is used. When adding together the contribution of many layers of light, it is very easy to quickly blow out and overexpose into white, but the human eye is inherently nonlinear and perceives intensities in a different way. This option allows you to use what is known in many compositing applications as a screen transfer mode between the layers, which yields a softer, more pleasing result. When disabled, normal addition is used. If rendering in a high dynamic range, and a proper tone-operator is applied in the final output stage already compressing the final luminance, it is best to disable this option. If not, enable it for a more pleasing result.
Output Only Subsurface Scattering Components	Use for debugging and testing or for preparing for external compositing. When enabled, only the scattered contribution is shown.

Render Tree Usage

This shader can be connected into multiple copies of itself via its diffuse_illum port for multi-layer scattering, but the final destination is usually to have its result output port connected to the Material node's Surface input port.