This page provides some details on the settings available for the utility Material Wrapper in V-Ray.
Base material – Specifies the actual surface material.
The options from this rollout are inactive when the render engine is set to V-Ray CUDA.
Use Irradiance Map – When enabled, the Irradiance Map approximates diffuse indirect illumination for the material. If this is off, brute force GI is used. You can use this for objects in the scene which have small details and are not approximated very well by the Irradiance Map.
Generate GI – Controls the GI generated by the material.
Generate GI Multiplier – A multiplier for the amount GI generated by the material.
Receive GI – Controls the GI received by the material.
Receive GI Multiplier – A multiplier for the amount GI received by the material.
Subdivs Mult. – A multiplier for the subdivisions of all secondary ray tracing done for the particular surface.
Generate caustics – When disabled, the material does not generate caustics.
Receive caustics – When disabled, the material does not receive caustics.
Caustics multiplier – Determines the effect of caustics on the material.
When using the V-Ray CUDA engine, only the Matte Surface, Alpha Contribution, Generate Render Elements and Shadows options are active from this rollout.
Matte surface – Makes the material appear as a matte material, which shows the background, instead of the base material, when viewed directly. Note that the base material is still used for things like GI, caustics, reflections etc.
Alpha contribution – Determines the appearance of the object in the alpha channel of the rendered image. A value of 1.0 means the alpha channel is derived from the transparency of the base material. A value of 0.0 means the object does not appear in the alpha channel at all and shows the alpha of the objects behind it. A value of -1.0 means that the transparency of the base material cuts out from the alpha of the objects behind. Matte objects are typically given an alpha contribution of -1.0. Note that this option is independent of the Matte surface option (i.e. a surface can have an alpha contribution of -1.0 without being a matte surface).
Generate Render Elements – When enabled, V-Ray will generate zDepth, velocity, extra tex and multi matte render element for matte objects. When this checkbox is disabled V-Ray does not generate any render elements for matte objects.
Shadows – When enabled, makes shadow visible on the matte surface.
Affect alpha – When enabled, makes shadows affect the alpha contribution of the matte surface. Areas in perfect shadow produce white alpha, while completely unoccluded areas produce black alpha. Note that GI shadows (from skylight) are also computed, however GI shadows on matte objects are not supported by the light cache GI engine, when used as primary engine. You can safely use it with matte surfaces as secondary engines.
Shadow Tint Color – An optional tint for the shadows on the matte surface.
Shadow Brightness – An optional brightness parameter for the shadows on the matte surface. A value of 0.0 makes the shadows completely invisible, while a value of 1.0 show the full shadows.
Reflection Amount – Shows the reflections from the base material.
Refraction Amount – Shows the refractions from the base material.
GI amount – Determines the amount of GI shadows.
No GI on other mattes – Causes the object to appear as a matte object in reflections, refractions, GI etc for other matte objects. Note that if this is on, refractions for the matte object might not be calculated (the object appears a matte object to itself and is not able to "see" the refractions on the other side).
Matte for all secondary rays – Normally the base material is used when an object with a VRayMtlWrapper is seen through reflections/refractions. Turn this option on, if you want the VRayMtlWrapper to show the environment when seen through reflections/refractions. V-Ray can also do projection mapping to increase the realism.
This option is not active when using the V-Ray CUDA engine.
GI surface ID – This number can be used to prevent the blending of light cache samples across different surfaces. If two objects have different GI surface IDs, the light cache samples of the two objects are not blended. This can be useful to prevent light leaks between objects of vastly different illumination.