The V-Ray Mtl Wrapper can be used to specify additional surface properties per material. See the How to Turn an Object Into a Shadow Catcher tutorial to see how you can use it to make an object a shadow catcher.
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Input Sockets
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This section lists input sockets that are not found in the Properties tab but only as inputs for the node.
Base material – Specifies the actual surface material.
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Matte
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properties
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Matte
surface
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
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). V-Ray GPU works with a value of either 1 or -1.
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 the 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 shows the full shadows.
Reflection Amount – Shows the reflections from the base material.V-Ray GPU always renders this parameter with a value of 1.
Refraction Amount – Shows the refractions from the base material.V-Ray GPU always renders this parameter with a value of 1.
GI
amount
Amount – Determines the amount of GI shadows. V-Ray GPU always renders this parameter with a value of 0.
No GI
on other mattes
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).Not available with V-Ray GPU.
Matte
for sec
For Sec.
rays
Rays– Normally, the base material is used when an object with a
VRayMtlWrapper
Mtl Wrapper is seen through reflections/refractions. Turn this option on if you want the V-Ray Mtl Wrapper to show the environment when seen through reflections/refractions. V-Ray can also do projection mapping to increase the realism.
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Additional
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surface properties
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The options from this rollout are not supported on V-Ray GPU.
Use
irradiance map
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 that have small details and are not approximated very well by the Irradiance Map.
Use
Generate GI – Controls the GI generated by the material.
Generate GI
mul
Mult.
–
– A multiplier for the amount of GI generated by the material.
Use
Receive GI – Controls the GI received by the material.
ReceiveGI
mult
Mult. – A multiplier for the amount GI received by the material.
Use
Generate Caustics – When disabled, the material does not generate caustics.
Generated
caustics mult
Caustics Mult. – A multiplier for the caustics generated by the material.
Use
Receive
caustics
Caustics – When disabled, the material does not receive caustics.
Received
caustics mult
Caustics Mult. – A multiplier for the received caustics by the material.
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Miscellaneous
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GI surface 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 Surface IDs, the light cache samples of the two objects are not blended. This can be useful for preventing light leaks between objects of vastly different illumination.
