Open topic with navigation

Falloff Map

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

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 using the Falloff Skew Factor as an exponent. OctaneRender^® uses the Skew Factor to interpolate between the spectral shades resulting from the Minimum Value and Maximum Value parameters.

You can use the Falloff Map to control the blending amount of a Mix node. The Mix node can either be Mix Texture or Mix MaterialThe representation of the surface or volume properties of an object..

Falloff Map Parameters:

• 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.

There are three Modes:

1. 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.
   (Skew factor = 1; Direction does not apply)
   
2. 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.
   (Skew factor = 1; Direction x=1)
   

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. (Skew factor = 1; Direction x=1)

Here below you can see the same scene with the Three Modes:

Normal vs. Eye Ray

Normal vs. Vector 90deg

Normal vs. Vector 180deg

Falloff Skew Factor value of 0.1 leads to almost complete coverage by the grazing value regardless of viewing angle, whereas a value of 15 leads to almost complete coverage by the Normal value. This parameter's default setting is 6.

While the index value on Glossy and Specular nodes corresponds to a real world Index of Refraction (IOR) value on dielectric materials like plastic and glass (OctaneRender doesn't yet support metals and Bezier curves), the Falloff node works differently because of this Falloff Skew Factor.

If set to 1, then the value is proportional to the angle between the Normal and the Camera Ray (i.e. if 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.

You can approximate the behaviour of glass with a Skew Factor of 8.0 and a Normal value of 0.034.

You can also use the Falloff Map for other things, like the input for glass opacity. Falloff is useful for car shaders (at 90 degrees, it should have the desired color and in less somewhat darker, but at the same time a bit more reflective), water shaders (tends to be more reflective to low angles of incidence), and fabrics like velvet (tends to become almost white at low angles). It is also useful for some metals to simulate some coating effects.

Figure 1: Image using the falloff node

Figure 2: Image without Falloff

Figure 3: Image with Falloff

Open topic with navigation