Reflectivity settings for viewing angle
Many kinds of material reflect differently depending on the angle you view them from; for example, looking directly at a flat surface might show little or no reflection, but viewing the surface at an oblique angle might clearly show reflections. This effect is also called Fresnel.
Use the Reflectivity menu to determine if reflectivity varies by angle viewed:
Depends on the viewing angle - Reflections are stronger on areas of the surface viewed edge-on and weaker on areas of the surface viewed directly on. Adjust this effect using the reflectivity graph.
Is constant across the surface - The brightness of reflections is constant across the surface (the default). The other reflectivity controls are disabled.
The mathematical function that relates the angle of view to the amount of reflection is called a "Fresnel function", and it is uses three parameters: Bias, Scale, and Power. The fourth parameter, Max, stops the amount of reflectivity from ever going above a certain number.
The formula is: reflectivity = bias + (scale * (1.0 - cos(view angle))**power)). You can try typing in these values directly, or use the reflectivity graph to change the Fresnel function. As you change the curve on the graph, the look of the material updates in the view.
Change the reflectivity by clicking and moving the handles. The left side of the graph shows how reflective the material is when viewed directly ("at center"). The right side shows you how reflective the material is when viewed on an oblique angle ("at edge").