The Falloff Map texture controls material blending, depending on the viewing angle of the material's geometry (figure 1).


Falloff Map

Figure 1: The Falloff Map texture used to control the blending of two RGB Color nodes connected to a Mix Texture node


Falloff Map Parameters

Modes - The angle between the eye ray and the shading normal is mapped from (0, 90) to (0, 1). For values larger than 1, the Falloff node does a gamma correction by using the Falloff Skew Factor as an exponent. Falloff Skew Factor interpolates between the spectral shades resulting from the Minimum and Maximum values, which in figure 1 are based on the first and second inputs of the Mix node.

  • Normal vs. Eye Ray - This is the default mode where OctaneRender® calculates the falloff from the angle between the Surface Normal and the Eye Ray. This mode is often used for reflections. The Falloff color range affects faces directly in front of the view, and gradually falls at angled faces towards the sides as it falls away from the straight-on viewing angle. The Falloff Direction parameter does not apply.
  • Normal vs. Vector 90deg - OctaneRender® calculates the falloff from the angle between the Surface Normal and the specified direction vector, maxing out at 90 degrees. This is similar to the default mode, except that it maintains the effect of the color range according to the Falloff Direction parameter.
  • Normal vs. Vector 180deg - OctaneRender® calculates the falloff from the angle between the Surface Normal and the specified direction vector, maxing out at 180 degrees. This provides a wider color range from the minimum to the maximum values, and maintains the effect of the color range according to the Falloff Direction parameter.

Apply Bump/Normal Map - If enabled, the shading normal, which includes bump/normal mapping, will be used to calculate the falloff. If disabled, the smooth normal, which does not include bump/normal mapping, will be used instead. 

Minimum Value - The visible material on the surface facing the camera. A value of 0 displays the material connected to Material pin 2, and a value of 1 displays the material connected to Material pin 1.

Maximum Value - Determines what material displays towards the grazing angles. A value of 0 displays the material connected to Material pin 2, and a value of 1 displays the material connected to Material pin 1.

Falloff Skew Factor - Balances the Normal and Grazing angles' influence. Low values result in stronger Grazing angle influence - any textures that the Maximum Value controls cover more surface. High values result in stronger Normal angle influence - any textures that the Minimum Value controls cover more surface. While the index value on other material nodes corresponds to a real-world Index of Refraction (IOR) value on dielectric materials like plastic and glass, the Falloff Map node works differently because of the Falloff Skew Factor. If set to 1, the value is proportional to the angle between the normal and the camera ray. For example, if the view angle is 45°, then the value is 0.5. If the value is larger than 1, then it applies a power curve to the angle. If the value is smaller than 1, then it inverts the skew factor, and mirrors the power curve.

  • falloff ≤ 1 : y = x falloff
  • falloff ≥ 1 : y = 1 – (1 – x) (1 / falloff )

Falloff Direction - This is used by the Normal vs. Vector 90deg and Normal vs. Vector 180deg modes. For most materials, the Fresnel effect (the default mode) is often correct, while falloff direction applies for exceptional cases, which can adjust relative to the camera. Changing the object rotation will not change the falloff direction orientation.

Figure 2: Falloff Direction curves


The Falloff Map can be used for other things, like the input for glass opacity. Falloff is useful for car shaders, water shaders, and fabrics like velvet. It is also useful for some metals to simulate coating effects (figure 3).


Falloff Map

Figure 3: Car shader example