mental ray Architectural and Design Visualization Shader Library

112 5 General Utility Shaderscolor is the overall color, and applies both to built in light or light derived from light sources.intensity is the intensity of the “built in” light, i.e. the surface will appear to the camera tohave an intensity of color multiplied by intensity (assuming use lights is off - see below).fg contrib is how much of the light that is visible to FG rays, and refl contrib how muchthat is visible to reflection rays.When use lights is on, the lights listed in the lights array are polled and their intensity(multiplied by the lights multiplier) is added to the output dictated by the intensityparameter; i.e. if L is the output of all lights in the lights list, the final output color ofthe shader is:color ∗ (L ∗ lights multiplier + intensity)When lights eval point is 0,0,0 the intensity of the light is evaluated (with shadows disabled)at the point in 3D space that is being shaded. Since this may vary in an undesirable way fora light that has an IES profile, one can specify an explicit point at which the light color isevaluated. This point is in the coordinate space of the light.5.3.2 Use Cases5.3.2.1 Illumination in GeneralIn the real world every light emitting object is visible, has an area, and emits light from thatarea. When using FG, mental ray will treat any surface that adds light energy into the sceneas if it was a light source. However, to get the best possible quality out of this, one need veryhigh FG settings, with long render times.Light sources in computer graphics can be either point sources or area lights, and the arealights themselves may, or may not, be visible in the rendering. In most cases It is simply moreefficient to use actual light sources:Emitting FG, Not emitting FG, And using a point lightThe image above shows 3 patches that are all using the mia light surface above a checkeredplane. The leftmost patch has it’s fg contrib set to 1.0 (and is hence illuminating the floor),