Where to get and try the alSurface shader

The shader is currently available for download in our Guithub:

https://github.com/ChaosGroup/vray_al_surface/releases

Installation for 3ds Max 

Copy the .dlt file for your 3ds Max version to the [maxroot]\plugins\vrayplugins folder.

Usage in 3ds Max 

The material is called VRayALMtl.

Installation for Maya

Windows 

Copy the file vray_BRDFAlSurface.dll to the folder with the rest of the V-Ray plugins (f.e. C:\program files\autodesk\maya2016\vray\vrayplugins)

OR

Add the path to the vray_BRDFAlSurface.dll to the environment variables VRAY_FOR_MAYA2016_PLUGINS_x64 and VRAY_PLUGINS_x64

Linux 

Copy the file libvray_BRDFAlSurface.so to the folder with the rest of the V-Ray plugins (f.e. /usr/autodesk/maya2016/vray/vrayplugins)

OR

Add the path to the libvray_BRDFAlSurface.so file to the environment variables VRAY_FOR_MAYA2016_PLUGINS_x64 and VRAY_PLUGINS_x64

Usage in Maya

You can create the new material from Create > V-Ray > Create from V-Ray plugin > BRDF material. From that list select BRDFALSurface.

最大的区别是什么？简单弱智高效，下面是原文

Here is a breakdown of those differences:

Diffuse: 

VRay Skin Mtl: Diffuse and Sub-Surface color are actually two different maps and they are blended together by the diffuse amount.

alSurface: Diffuse and Sub-Surface color are actually driven by the same map and there is a SSS mix that controls how much that surface is effected by the subsurface scattering versus how much is driven by the Lambertian diffuse.

Sub-Surface Scattering:

VRay Skin Mtl: There is a 3 level depth sub surface which is equally blended together. It also uses a standard dipole model for the SSS.

alSurface: This also has a 3 level depth for the SSS but has weight controls on each one. It also offers several SSS modes. Vlado has implemented two of them for the V-Ray version of the alSurface shader. Diffusion, which preserves more detailed compared to the standard dipole model, and Directional, which allows for an approximation of Single Scatter maps for even greater detail preservation.

Specular:

VRay Skin Mtl: This uses a two lobe specular model with a sharp and broad reflection. It also uses Phong as the reflective BRDF. This model proved to work well in many situations, but at glancing angles, based on the way that it would cut out the SSS, could cause darkening. This is because the Fresnel effect is computed as a function of the angle between the viewing direction and the surface normal, ignoring the directions from which lights illuminate the surfaces.

alSurface: This model also uses a two lobe specular model. However, instead of using a smooth BRDF like Phong or Blinn, it uses a microfacet one. The Fresnel effect is computed as part of the BRDF calculations (a.k.a. “glossy Fresnel”) and takes into account the viewing direction, the surface normal, and the light directions. The user has a choice between GGX and Beckmann BRDF models. Based on the nature of the micro faceting, it can avoid the darkening effect at the glancing angles through retro-reflection. Additionally it does not cover the SSS at the same glancing angles.

Other notable differences:

The IOR values that are used for the Fresnel are different in both shaders based on how the fresnel calculation is made.  Therefore, if the user used a same value for both shaders, the alSurface shader would appear more reflective.

The VRay Skin Mtl uses glossiness, so high values are more shinny, the alSurface shader uses roughness so high values are more diffuse. So if a map is used for one it needs to be reversed if it is being applied to the other.

The VRay Skin Mtl blends in diffuse, meaning a value of 1 is 100% diffuse. The alSurface shader blends in SSS meaning that a value of 1 is 100% SSS. If a map is used, such as a Single Scatter Map, the map would have to be reversed before it can be applied.