Ior and Ior Out - Index of refraction, determined by the physical properties of the material. It goes from 0 (air) to 2.4 (diamond) and behond. I have not found out what the difference in setting Ior Out with a value different from 1 is. Our scene will use a Ior of 1.3.

Ignore Normals - Set it if the model is poorly done to avoid problems with strange normals.

Phong Coefficient - Set it greater than 0 if you want a fake highlight event though the correct calculations wouldn't result in one. The higher the value (100 or more) the more visible and defined the highlight is. Personally, I don't like the result, so I leave it to 0.

Lights - If left blank, all lights in the scene will contribute to the shader's calculations. Alternatively, link one or more lights' message to this field to use only those.


Parti Volume

Stands for participating media and it is used to simulate materials like fog, smoke and, in our case, fire. Do the following:

1. Assign a parti volume as MR volume shader.
2. Assign a parti volume photon material as MR volume photon shader.

Mode: When 0, the entire object is filled with the volumetric media. When 1, it is filled only partially.

Height: When Mode is 1, it specifies up to what height the volumetric medium fills the object. Example: height = 0.5


Scatter: The color of the medium.

Extintion: The density of the medium. 0 is vacuum (no volumetric material). Example: extintion = 1


R, G1, G2: These parameters account for eventual particles dispersed in the medium. If G1 = G2 = 0, the particles are too fine to influence light scattering, and R is uninfluential. Otherwise, it is suggested to use G1 with negative values for back scattering, and G2 with positive values for forward scattering. G1 has weight R and G2 has weight 1-R. G Values close to 1 approximate an almost solid volumetric material. Since our fire is homogeneous, all three values will be 0.

R = 1, G1 = -1, G2 = 1 R = 0, G1 = -1, G2 = 1 (only back scatter) (only front scatter)

Nonuniform: Values between 0 (uniform) and 1 (least uniform). Example: nonuniform = 1


Min/Max Step Length: Used with the nonuniform setting, the smaller the Min Step and larger the Max Step, the more marked the nonuniformity will be.

Min = 0.5	Min = 3.0	Min = 0.5
Max = 5.0	Max = 5.0	Max =10

Light Distance: Used in conjunction with an area light. Tells how far from the area light you will have the highest sampling.

Min Level: Optimizes how photons are stored.

No Global Illumination When Direct: Optimizes calculations when the light that directly illuminates the volume isn't involved in Global Illumination.