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# 6.1 Rendering Algorithms

If incompatible options are given to mental ray, some of them are overridden to return to a consistent state. In mental ray 1.9.9.20 and higher, including mental ray 2.x, the strategy was changed: instead of re-enabling ray tracing if any other feature such as lenses are used and ray tracing was explicitly turned off, the newer versions do not turn ray tracing back on but change the operation of the feature normally requiring ray tracing. The following features are affected:

- If ray tracing is turned off, lens shaders cannot modify the ray origin and direction. Lens shaders are still useful in this mode because they can modify the color returned by the eye ray, or decide to not sample points in certain directions.

- A new algorithm was introduced in mental ray 2.x that supports fast motion blur in scanline mode. Turning ray tracing off no longer disables motion blurring.

- Similarly, shadow maps were introduced that support shadows in scanline mode. Only opaque shadows are supported in this mode; transparent and transparency-mapped shadows still require ray tracing. Shadow maps do support motion-blurred shadows.