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V-Ray Falloff produces a gradient texture based on the angular falloff of the the surface of the geometry to which the texture is applied. The resulting map can simulate the falloff of opacity, reflection, and refraction for surfaces where these properties vary depending on the surface's angle to the camera, such as curved glass or water.

To create the texture, V-Ray Falloff starts with two colors, usually black and white. Placement of these colors on the surface is based on the Falloff Type and Direction Type selected. The remainder of the map is generated as a gradient between these two colors, with a gradual falloff between the colors.

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The TexGrid node provides inputs for controlling various texture properties. They correspond to parameters in the section below.

Type – Specifies the type of falloff:

Towards/Away – Based on face normal directions. Faces with normals that point in the Direction Type generate Color 1 while those facing in the opposite direction (180 degrees off the falloff direction) generate Color 2. 
Perpendicular/Parallel – Based on face normal directions. Faces with normals that point in the Direction Type generate the Color 1 while those facing in a perpendicular direction (90 degrees off the falloff direction) generate the Color 2.
Fresnel – Based on changes to the index of refraction (IOR) over the surface due to Fresnel calculations. Faces with normals that point in the Direction Type generate the Color 1 and those facing in other directions generate varying colors depending on the IOR set by Fresnel Ior. 
Distance Blend – Sets the falloff range based on distance from the camera, as specified by Distance Near and Distance Far. This option is useful for generating a Z-depth type of map when rendering a very large object such as terrain, where the Falloff Map can be used as a mask to dim distant details. For more information, see the Distance Falloff Type example below.

Direction Type – Specifies the falloff direction to be used by the Falloff Type.

Color 1/2 – Sets the extreme ends of the range of colors for the Falloff Map's gradient. The specific placement of these colors on the surface is determined by Type and Direction Type.

Use Blend Input – Enables the Blend Input parameter for controlling the blending.

Blend Input – Specifies the final blending amount that is taken from the texture.

Use Blend Curve – Enables the Blend Curve for controlling the blending.

Falloff Curve – Allows the user to specify the falloff curve using the curve tools.

View Z/View X/View Y – Uses the camera viewing direction. This is the most common selection.
Explicit – Uses the direction specified by the Explicit Direction parameter.
Local X/ Local Y / Local Z – Uses one of the object's local axes.
World X / World Y/ World Z – Uses one of the world axes.

Default Color – Specifies the color when there are no valid UVW coordinates.

Mult – Specifies a strength multiplier for the texture color.

Offset – Color corrects the texture by adding the the RGB color values specified here to the RGB color values in the texture.

Invert – When enabled, inverts the resulting texture color.

Source – Specifies where the alpha channel is drawn from.

Alpha – Alpha channel is drawn from the texture.
Color – Alpha is generated from pixel intensity.
Opaque – Alpha channel is fully opaque.

Use – Differentiate between textures exported from different applications. You can choose between Color Intensity (3ds Max) and Color Luminance (Maya).

Mult – Specifies a multiplier for the texture alpha.

Offset – Specifies an additional offset for the texture alpha.

Invert – When enabled and Invert from Color Tweaks is also enabled, the resulting texture alpha is inverted as well.