Rendering a contour image in mental ray for Maya has been a nice way to show wireframes on an object. In Maya 2016 the usual method has become somewhat hidden, so I thought I would post a brief update on how to do that.
1) Create a black surface shader and apply it to your geometry
2) In the hypershade, access the shading group (e.g. surfaceShader1SG) and open the mental ray tab in the Attribute Editor (or Hypershade property editor!)
3) Under Contours, check Enable Contour Rendering and adjust the other options as you like
4) In the render settings, make sure mental ray is selected, and go to the Configuration tab
5) Check "Show Advanced Settings" and find the Contours section at the bottom
6) Check "Enable Contour Rendering" and increase the Over-Sample to something like 3
7) Under the "Draw By Property Difference" section, check "Around all poly faces"
Not quite done... you might see a Warning: Contour Rendering is not supported with Unified sampling
8) Go to the Quality tab and check "Show Advanced Settings"
9) Expand the Legacy Options section at the bottom and choose Sampling Mode: Legacy Sampling Mode
Hit render! *phew*
Note that if you are rendering beauty passes or other things, you probably want to use the original Unified Sampling and just create layer overrides for the contour settings. Also make sure that you have unchecked both "Around all poly faces" and "Enable Contour Rendering" for these non-contour passes/layers/renders, because I have had the filter settings be set to Box (1, 1) in the background without my knowledge due to "incompatibility with contour rendering". Just something to be cautious about; not sure if they may have fixed that in this version.
Thanks for reading,