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The MtlWrapper node provides inputs for controlling various material properties. Some correspond to parameters in the section below.

base_material – Specifies the material that the additional wrapper properties are applied to.

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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 generates zDepth, velocity, extra tex and multi matte render element for matte objects. When this check box is disabled V-Ray does not generate any render elements for matte objects.

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.

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 a primary engine. You can safely use that with matte surfaces as secondary engines.

Shadow Tint  – 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.

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 will appear a matte object to itself and will not be able to "see" the refractions on the other side).

Matte For Secondary Rays – Normally the base material is used when an object with a MtlWrapper is seen through reflections/refractions. This option controls whether the MtlWrapper shows the base material or environment when seen through secondary rays (e.g. reflections/refractions).

Disable – The base material is used when the MtlWrapper is seen through reflections/refractions.
Without Projection Mapping – The environment is seen through reflections/refractions.
With Projection Mapping – The environment is seen through refrlections/refractions with projection mapping to increase the realism.

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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 will not be blended. This can be useful to prevent light leaks between objects of vastly different illumination.

Trace Depth – Specifies the number of times a ray can be reflected. Scenes with lots of reflective and refractive surfaces may require higher values to look correct. A value of -1 specifies this option is controlled by the global Render Settings.

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