Displacement shading with the mental ray renderer is similar to Displacement mapping of standard materials. One advantage of using mental ray displacement is that the additional polygons of displaced surfaces are stored only in the mental ray scene database, not in your 3ds Max scene, so they do not increase the memory requirements of your scene, except at render time. This can be a big improvement in performance over displacement mapping with standard materials and the scanline renderer.
To add displacement to a mental ray rendering:
Preferences. Go to the mental ray panel, and turn on Enable Mental Ray Extensions.
(Render Setup).
If the active renderer is not already the mental ray renderer, go to the Common panel, and on the Assign Renderer rollout, click the “...” button for the Production renderer. A Choose Renderer dialog is displayed. Highlight “mental ray Renderer” in the list, and then click OK.
Open the Material Editor.
the lock button to unlock the Displacement component. Click the shader button (“None”) and use the Browser to assign a displacement
shader to the surface.
Another technique would be to use the mental ray material, and assign a shader to the Displacement component. (If you are using the mental ray material, you don't need to first unlock the Displacement component.)
