The Rasterizer

Location:

The Render Manager > mental ray (Global Renderer)
The Render Manager > (expand a pass) > mental ray
Set a current pass and choose Render > Render > Renderer Options from the Render toolbar.
Tab: Rendering
Options: Aliasing (Raytracing & Scanline Only) [Properties Reference]

The Rasterizer accelerates motion blur rendering for complex scenes containing a lot of moving objects. The Rasterizer produces high-quality blurs in a fraction of the time that it would take to render raytraced motion blur. It works by subdividing object surfaces into increasingly smaller triangles. Once the surface is subdivided, the triangles are drawn on screen, according to the number of samples that you specify.

NoteThe Rasterizer does not have a noticeable effect on particle rendering.

To render motion blur with the rasterizer

Select Rasterizer from the Primary Rays Type options.
Set the Motion Steps sampling options.

Rasterizer Performance

The rasterizer should be used for scenes that do not require raytraced effects. Keep in mind, however, that each shading sample has the ability to trace reflected and refracted rays. Once a ray is shot, much of the time and memory savings you get from using the rasterizer could be quickly consumed by BSP tree calculations and object loading.

For this reason, you should avoid features that trigger rays to be traced (as described in the table below):

Feature	Type of Ray	Description
Reflection/refraction	Eye rays	Surface shaders may reflect or refract. Turn Ray Tracing off or reduce Raytracing Depth to 0, 0, 0. Note that custom shaders may override these settings. Environment maps will still work for reflections when raytracing is disabled.
Raytraced shadows	Shadow rays	Use shadow maps to produce transparent shadows without raytracing.
Final gathering	Final gathering rays	For each final gathering point, multiple final gathering rays are cast back into the scene.
Photon tracing (global illumination and caustics)	Photon rays	Photons trace forward from the light source, and require the same structures as raytracing.
Ray-bending lens shaders	Eye rays	Both the regular scanline algorithm and the rasterizer require a straight primary eye ray. Ray-bending lens shaders may cause artifacts.