V-Ray has its own matte system. You can control matte properties either on an object level through the VrayObjectProperties node, or on a material level through the special VRayMtlWrapper material. Matte Surface – Enabling this option turns the object into a matte object. This means that the object is not directly visible in the scene; instead, the background color is shown in its place. However, the object appears normally in reflections/refractions and generates indirect illumination based on its actual material.
Alpha contribution – Controls how the object appears in the alpha channel. Note that an object doesn't have to be a matte object for this setting to work - the alpha contribution can be changed regardless of whether the object is matte or not. A value of 1.0 means that the object will appear normally in the alpha channel. E.g. if the object is opaque, the alpha is white; if the object is fully transparent, it will not influence the alpha channel at all. A value of 0.0 means that the object, regardless of its actual opacity, will not be present in the alpha channel, although it will be present as normal in the RGB channel. A value of -1.0 means that the object's alpha is cut out from the alpha of the objects behind it. E.g. if the object is fully opaque, its alpha will be black and will be blocking the alpha of the objects behind it, whereas if the object is fully transparent, it will not influence the alpha at all. Note that turning an object into a matte object does not change its appearance in the alpha channel. You need to explicitly change its alpha contribution.This can be mapped by a texture. V-Ray GPU works with a value of either 1 or -1. Shadows – When enabled, the matte object receives shadows. 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 – Specifies the color of the shadows. 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 – If the material of the object is a reflective V-Ray material, this controls how much of the reflection is visible on the matte object. V-Ray GPU always renders this parameter with a value of 1. Refraction amount – If the material of the object is a refractive V-Ray material, this controls how much of the refraction is visible on the matte object. V-Ray GPU always renders this parameter with a value of 1. GI amount – Controls how much of the indirect illumination received by the object is visible on the matte. V-Ray GPU always renders this parameter with a value of 0. No GI On Other Mattes – When enabled, causes the object to appear as a matte object in reflections, refractions, GI, etc. for other matte objects. Note that if this is enabled, refractions for the matte object might not be calculated. (The object appears as 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 Secondary Rays – Normally the base material is used when an object with a VRayMtlWrapper is seen through reflections/refractions. Enable this option, 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. |