The following attributes are common to the Environment Fog and Light fog Volumetric materials:
You can control the mask value for individual objects. See Matte Opacity.
Matt Opacity attributes are available for Anisotropic, Blinn, Lambert, Layered Shader, Phong, PhongE, Shading Map and Use Background material types.
Click to display the three Matte Opacity Modes from the drop-down list.
Default Matte Opacity Mode. The Opacity Gain value is used as a gain control on the usual matte value contribution of a material.
A matte channel is first calculated this way— a value of 1.0 for an opaque surface completely covers a pixel, less if it covers part of a pixel. The value is reduced appropriately for transparent objects, and then multiplied by the specified Matte Opacity value.
The Matte Opacity Mode value is also keyable. The Opacity Gain range is from completely transparent to no effect (rendered as usual).
The matte channel for all pixels covered by the object is set to 0 (fully transparent), even if the object is transparent, and regardless of what is behind the object if it is transparent. This creates a black hole where the object is in the image, to knock out the matte. In this mode, the Matte Opacity slider is disabled and its value ignored.
This value behaves in different ways based on which Matte Opacity Mode is selected (Opacity Gain or Solid Matte).
For example, for the Opacity Gain mode, the Matte Opacity slider value indicates the transparent multiplier amount for the alpha channel. The default is 1, which means that any opaque object registers a full alpha value.
If the Matte Opacity value is 1, a 0 alpha value is registered. Any values between 0 and 1 act as a multiplier to the alpha channel value to arrive at a new alpha value.
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