mental ray for Maya offers all the features traditionally expected of photorealistic rendering and includes functionality not found in most rendering software.
mental ray for Maya allows interactive and batch mental ray rendering from within the Maya user interface. With the help of built-in shaders supporting almost any effect available in Maya, mental ray for Maya allows the rendering of scenes created within Maya or their export into the mental images file format (.mi).
(For detailed information on the mental ray standalone application, see the mental ray reference User Manual and the mental ray Shaders Guide, available from the Maya help.)
After you load the mental ray plug-in (and select mental ray as the renderer), the Render menu lists available menu items for mental ray for Maya. As well, the Attribute Editor contains a mental ray section in which you can edit attributes that are used exclusively when rendering with mental ray for Maya.
To load the mental ray for Maya plug-in, see the note in Select a renderer.
The IFF image support in mental ray permits both color and depth information written into a single file. This requires the proper parameters to be set in the Render Settings (Depth Channel [Z Depth] in the File Output section must be turned on).
mental ray for Maya can also be used in Maya as a file exporter. When you export a Maya scene file to the proprietary mental images (.mi) file type, the file export simply writes a .mi file to disk with the given name. Additional options are available in the user interface to control ASCII or binary mode export and file-pre-frame creation for animations.
See Exporting .mi files.
Maya supports three types of geometry: polygonal (Polygon Mesh), free-form objects (NURBS curves/surfaces), and subdivision surfaces.
The native Maya and mental ray renderers may produce different results in certain situations. For more details, see mental ray for Maya renders look different than Maya renders .
A shading group in Maya defines the material, volume, and displacement shaders, along with the list of lights used in the illumination calculation for renderable objects. Such a shading group can directly be translated into a .mi material.
For more information on mental ray for Maya shaders, see mental ray for Maya shaders.
Global illumination, Caustics, Final Gather, and HDRI
For information and procedures, see Indirect (global) vs. direct illumination in the Lighting guide.
mental ray for Maya can render with Global illumination, the technique used to capture indirect illumination (the natural phenomenon where light bounces off anything in its path until it is completely absorbed).
mental ray can render with Caustics, the light effects that caused by specular reflected or refracted light, like the shimmering light at the bottom of a pool of water.
mental ray for Maya can render with Final gather (a method of global illumination) to create very (or purely) diffuse scenes where the indirect illumination changes slowly.
Direct light with mental ray for Maya Area Lights
The main purpose of area light sources is to generate more realistic lighting, resulting in soft shadows. This is achieved by using one of four primitives (rectangles, discs, spheres, and cylinders) as light sources with nonzero area.
For more information about mental ray for Maya areas lights, see Default lighting in Maya in the Lighting guide.
mental ray for Maya supports both host and network parallel rendering. It renders identical output on all common and widely-used platforms. For network rendering, it performs best in a client-server setup, where it takes care of load balancing and network communication reduction.
For information on mental ray for Maya network rendering, see mental ray network rendering: Satellite and Standalone.
When rendering animation files or previewing animations inside Maya, mental ray for Maya exploits incremental changes. This means it determines if scene elements actually have changed between frames and just processes those changes, thus accelerating the render cycle. The check is based on Maya information and includes both geometry (plus instances) and shading nodes. If no changes are detected, the corresponding object or shader is not updated in subsequent frames and appear animated.
Incremental changes are not used if animations are exported as file per frame.
mental ray object rendering flags
You can control how particular objects contribute to certain rendering stages by setting per-object rendering flags in the object’s Attribute Editor.
For information about mental ray for Maya motion blur, see mental ray for Maya motion blur.
(For mental ray advanced users only.)
The Custom Text Editor can be used to create and attach custom text to certain scene entities. This replaces the internally created .mi output with the custom text. Using the Custom Text Editor you can integrate custom mental ray shaders into Maya.
To use the Custom Text Editor, see Custom mental ray text.
mental ray for Maya checks and reads special custom attributes on certain Maya nodes and uses them for customized scene processing. Additionally, it adds its own custom nodes to Maya for convenient handling of mental ray extensions.
All of these customizations are located in the Custom Entities section of the Render Settings window. For descriptions of the mental ray for Maya Custom Entities attributes, see Render Settings: mental ray tabs, Options tab.
It is, however, enabled for the .mi file export to create customized scene files for external rendering.
mental ray for Maya supports a method to produce custom text in the output stream written to the .mi file. This is for text-only integration of custom mental ray shaders within Maya; it allows for the creation of special-purpose Maya nodes that hold customized mental images (mi) text.
mental ray for Maya checks Maya polygonal meshes for additional dynamic (custom) attributes that supply per vertex data. This data is exported as additional mental ray texture spaces for shader access.
For more information about custom vertex data, see Custom vertex data.
Error handling and diagnostics
mental ray for Maya checks for errors in a Maya scene and recognizes various operating system errors. You can use diagnostics to help you diagnose issues with samples and photon maps.
For more information on mental ray for Maya diagnostics, see mental ray for Maya error handling and diagnostics.
mental ray specific image formats
The following image formats are unique to the mental ray renderer.
The following is true when rendering to a format other than Maya IFF or RLA. If rendering to Maya IFF or RLA, all channels RGBAZ are written to one file. For all other image formats, when the Depth Channel (Z depth) option is enabled in the mental ray Render Settings, mental ray will write out a separate image file containing depth information. Z-depth is now written out in IFF format and rendered to a separate file that has “Depth” as a suffix to the image name, for example, imageDepth.#.iff.
Hyperthreading can slow down mental ray rendering
The mental ray IPR and the Auto Render Threads option in Render > Render Current Frame > 
and Render > Batch Render > do not distinguish between dual core CPU's and hyperthreading. Therefore, these options report all virtual CPU's as available
threads.
Workaround 1: Turn hyperthreading off.
Workaround 2 (for Auto Render Threads option): Turn off Auto Render Threads and reduce the number of threads by 1/2.
mental ray for Maya does not support the following Maya rendering features:
Unsupported File Texture Formats
The following file texture formats are currently unsupported by mental ray for Maya:
(TIFF,CIN,GIF) For these unsupported file formats, Maya's imgcvt image conversion tool can be used to convert the files to a supported format such as IFF or RGB. For a complete list of file texture types supported by mental ray, see the mental ray for Maya reference guide.
(BOT) There is currently no workaround that will allow Maya BOT files to be used in conjunction with mental ray for Maya. mental ray does support its own memory-mapped map file texture format, however. Standard image files can be converted to this format using the imf_copy command:
imf_copy -p <filename>.rgb <filename>.map
See the Rendering with mental ray Handbook for a full description of memory-mapped textures in mental ray.
