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

For the example shown on the right, VRayFalloff is used in the Diffuse channel of a VRayMtl. The Falloff type is set to Perpendicular/parallel with the falloff Direction set to World Y Axis. Solid Colors ofbright orange and dark green are used for the Front and Side Color parameters.

Front / Side Color – 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 Falloff Type and Falloff Direction.

Falloff Type – Specifies the type of falloff :

Towards/Away – Based on face normal directions. Faces with normals that point in the Falloff Direction generate the Front Color while those facing in the opposite direction (180 degrees off the falloff direction) generate the Side Color. 
Perpendicular/Parallel –Based on face normal directions. Faces with normals that point in the Falloff Direction generate the Front Color while those facing in a perpendicular direction (90 degrees off the falloff direction) generate the Side Color.      
Fresnel –Based on changes to the index of refraction (IOR) over the surface due to Fresnel calculations. Faces with normals that point in the Falloff Direction generate the  Front Color  and those facing in other directions generate varying colors depending on the IOR set by Fresnel Index Of Reflection. 
Distance – Sets the falloff range based on distance from the camera, as specified by Near Distance and Far Distance. 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.

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

Viewing Direction (Camera Z-Axis) – Uses the camera viewing direction. This is the most common selection.
Camera X-Axis / Camera Y-Axis – Uses one of the camera's other axes.
Explicit Dir – Uses the direction specified by the Explicit direction parameter.
Local X-Axis / Local Y-Axis / Local Z-Axis – Uses one of the object's local axes.
World X-Axis / World Y-Axis / World Z-Axis – Uses one of the world axes.

Explicit direction – Specifies the direction for falloff when Falloff Direction is set to Explicit Dir.

Fresnel Index Of Reflection – Defines the IOR (Index of Refraction)when Falloff Type is set to Fresnel.

Near Distance – When Falloff Type is set to Distance, parts of the surface at this distance from the camera will receive the Front Color.

Far Distance – When Falloff Type is set to Distance, parts of the surface at this distance from the camera will receive the Side Color.

Extrapolate – When enabled, the effect continues beyond the range set by Near Distance and Far Distance. Parts of the surface nearer than Near Distance receive the Front Color, while parts farther from the camera than Far Distance receive the Side Color.

Double click – Creates a new point or changes an existing one. 
Left button drag over a point – Moves the point. If several points were selected beforehand, they will move the same amount.
Left button drag over several points – Selects several points. 
Middle button drag over the background – Drags the visible area. If the Shift key is pressed, scales the diagram in the corresponding direction. 
Mouse wheel – Zooms in/out.
Right-click – Displays a drop-down menu where you can add a point, edit or delete a selected point, and fit the entire diagram or gradient into the view. If multiple points are selected, they can be edited simultaneously. 

Invert – Inverts the color values.

Clamp – Clamps the color values.

Alpha From RGB Intensity – Takes the alpha information from the intensity of the RGB.

Output Amount – Determines the alpha multiplier.

RGB Offset – Allows a color offset to the produced RGB values.

RGB Level – Determines the intensity of the falloff effect.

Bump Amount – Defines how much bump is produced.

Enable Color Map – Enables the texture as a color map.

Color Map Red/Green/Blue Parameters

The curve controls here can be used to remap the Red, Green, and Blue channels. For information about curve controls, please see the Mix Curve Parameters section.