Maya: Mental Ray: Notes on using DGS and non-DGS Shaders with GI and FG

 

These tenative ideas are taken from two tutorials* on DGS shaders found in the Mental Ray Forum on HighEnd3D.com. None of it is tested yet in a serious way, but some preliminary tests in simple scenes are encouraging.

 

1. On lights

a. physical lights - Custom shaders

1. Surpress all Maya shaders

2. plugin mr physical light

b. light caustics and global illumination

1. emit photons

2. set photon color to match physical light color

3. set photon intensity to match physical light intensity

(suppose physical light is R 1000, G 1000, B 1000,
then photon color is R 1, G 1, B 1 with intensity = 1000)

2. On DGS material

a. create base material, choose lambert, blinn, etc depending on desired
display behavior in OpenGL

b. in Shading Group for base material, assign DGS Material and DGS Photon Material

c. Check Suppress all Maya shaders.

d. DGS Settings

1. DGS diffuse (total scattering)
DGS Glossy (scattering in a direction)
DGS Specular (reflection, no scattering)
DGS Shiny affects blurring or non-blurring of Glossy

a. no Glossy value, then shiny has no effect

b. small shiny - more bluring, i.e, very small values makes glossy act like diffuse

c. large shiny - less bluring, i.e., large shiny values makes
glossy act like specular

d. DGS Shiny U or Shiny V - when set disable simple shiny

2. DGS Diffuse, Glossy, and Specular when added together should not execeed 1 (less than 1 and light is absorbed) - physical limits - see tutorials

e. DGS Photon Material settings

1. Should match DGS Material Settings (do this manually)

f. Light linking is required only for Direct Illumination, ie, for DGS Material and not DGS Photon Material (which is indirect illumination). In Maya 6, if no lights are linked to the DGS Material, then Maya automatically links all lights to DGS Material at render time.

3. On non DGS Materials

a. do NOT check Suppress All Maya shaders in Shading Group custom Shaders section

b. assign DGS Photon Shader (not DGS material)

1. Match diffuse color

2. Try to match non-DGS material Specular to DGS Photon Glossy or Specular.

A tight specular on non-DGS material suggests adjusting the specular on the DGS material. A loose specular on the non-DGS material suggests adjusting glossy on DGS material

* for tutorials see highend3d.com, mental ray forum, look for posts on "A Full Explanation of DGS Shaders" and "A full tutorial for DGS shaders " by ickyptang.