mental ray for Maya rendering limitations

This section contains information about the unsupported features, software limitations and workarounds, as well as some tips for this version of mental ray for Maya.

Unsupported features

Keyframing or set driven keyframing on the RGB components of a ramp shader’s colorEntryList (the list of colors that comprise the ramp shader) are unsupported.
postprocessing effects: Paint Effects, light glow, optical effects, and 2d motion blur
Field Rendering
The -hardware_echo flag is not supported through the command line.

Known limitations

The following lists the software limitations and workarounds for this version of mental ray for Maya.

mental ray impacted by Hyperthreading

Intel CPUs offer hyperthreading as a feature to simulate additional logical processors which are actually running on a single physical CPU. This feature is intended to accelerate applications which make use of additional processors for parallel execution like mental ray. However, since hyperthreads are not able to deliver a performance gain like a physical processor but only about 15-25%, the performance increase may be small or not visible.

Disable “Auto Render Threads” and set the number of render threads manually.

Volume method for fur rendering does not produce shadows

In the Fur Render Settings (Fur > Fur Render Settings) if you set the Fur Shader to Volume the fur does not render with shadows if the scene uses shadow maps.

Use raytraced shadows.
Set the Fur Shader to Hair Primitive and re-render the scene.

Shadow method is set to Simple by default; simple shadows are not compatible with volume effects

The Shadow Method in the Render Settings window: mental ray tab is set to Simple by default. Simple shadows are not compatible with volume effects such as fluids, volume fur, particles and volume shaders and therefore may not render shadow volume effects correctly.

Intersecting fluids show artifacts in mental ray rendering

Intersecting volume effects such as fluids, particle clouds and volumetric lights may cause artifacts in mental ray rendering. For example, the bounding box may show in the rendered image.

Render each volume effect via a separate layer and composite the layers into a final image.

Material swatches do not update during mental ray IPR

When rendering in mental ray IPR, material swatches in the Hypershade and Attribute Editor do not update with adjustments.

mental ray contour shaders are not compatible large images

mental ray contour shaders cannot handle large images with high resolution (for example, >6K).

Contour rendering artifacts (on Mac OS X)

Exporting to .mi with dynamics

Manually run up the scene to the current frame and export
Use batch export to .mi

Depth map shadow quality with Rapid scanline rendering

The quality of depth map shadows with Rapid scanline rendering is decreased compared to the quality of depth map shadows and default scanline rendering.

In the Attribute Editor (light shape node), in the mental ray > Shadow Maps section, increase the number of Samples.

Advanced filtering and file textures

Scenes that contain custom shaders for volume effects or environment shader may not render correctly with advanced filtering (quadratic, quartic, etc.) for file textures.

Custom mental ray shaders and importing or referencing

Imported or referenced Maya 5.0 files containing mental ray shaders, with color, scalar, or texture parameters, do not correctly convert in the current release of Maya. You may notice shaders becoming disconnected.

Open the Maya 5.0 scene file in Maya Interactive, and save it. Then import or reference the file in the current release of Maya.

Maya's environment shaders do not work well with IBL

IBL provides UV coordinates to the attached shading network, but Maya’s environment shaders do not base their calculations on UVs. Maya environments are supported with final gather-based IBL, but photon and light emission are unsupported.

IBL node with primary visibility off ignores camera environment settings

Adding an IBL node to your scene with primary visibility turned off results in a black background regardless of your camera environment settings.

Create a geometry sphere and apply an HDR image to it. Turn off the primary visibility. Now, you can change the environment color of your camera.

Lightlinking is not obeyed when baking vertex color with IBL

Lightlinking appears to be ignored when vertex baking is used with IBL. This is not a problem with the baking. Instead, the hardware display needs to be adjusted.

Under the mesh node, and under the Mesh Component Display section, set Display Color Channel to None.

Partial creases rendering as full creases

Partial creases of subdivision surfaces are not supported in this version of mental ray for Maya. They will be rendered as full creases.

Depth map shadows and particle rendering

Directional light does not work well with Photons

Rendering final gather in a scene created using Maya version 7.0 or earlier

Artifacts much like polka dots may appear when you use Maya 8.5 to render scenes with final gather that was created using Maya version 7.0 or earlier.

Add global illumination to your scene. Lower the final gather trace by turning the Secondary Diffuse Bounces control off and on. You can find the Secondary Diffuse Bounces control in the Render Settings window, mental ray tab, under the Final Gathering Options in the Final Gathering section.

Workaround 2: Use this workflow to obtain the exact same render results as you did with Maya 7.0

Switch back to compatibility with the mental ray 3.4 final gather algorithm using the following command:

Warning messages appear when importing scene files in Hypershade

When importing scene files containing mental ray nodes, you may see warning messages such as:

// Warning: 'Draft.message' is already connected to 'mentalrayItemsList.options'. //

These warning messages, about pre-existing connections between mental ray related node, are harmless and can be safely ignored.

A warning dialog box also appears when these warnings occur. If you are importing many files and wish to avoid manually closing the warning dialog box for every file, you may want to use the file command with -prompt false.

Tearing off mental ray for Maya Render menu may crash Maya

If you tear off the Maya Render menu, then load the mental ray for Maya plug-in and tear off the mental ray for Maya Render menu, Maya may crash.

mental ray for Maya crashes or won’t load when a firewall is active

Firewall software may block command ports. When you load mental ray for Maya, your firewall prompts you if you want "to allow the Maya application to access the internet: IP 127.0.0.1 port 1333." If you select no, Maya instantly exits without a warning or error message. If you select yes, mental ray for Maya starts up as expected.

If you are using any firewall software, you will need to give permission to Maya to communicate on port 1333 in order for mental ray for Maya to work correctly.

Missing Motion Blur

When rendering with motion blur, sometimes parts of deforming geometry will fail to blur. This is because sometimes, during animation, Maya creates incompatible changes to vital mesh data (number and order of vertices, normals, uv indices, polygons). You need to ensure a consistent tessellation for mental ray.

Custom Text Does Not Work for Interactive Renders

The Custom Text feature is intended for use only with the mental ray standalone renderer. To correctly render a scene containing shader/object modifications made using Custom Text, the scene must first be exported to .mi format, then rendered with the standalone product.

Unsupported File Texture Formats

The following file texture formats are currently unsupported by mental ray for Maya:

AVI files
Maya BOT files
certain variants of the TIFF format (those with LZW compression, including those generated by the Maya renderer)
Cineon CIN files
DDS files
EPS files
GIF files
IFF16 files
Wavefront-alpha files

(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 Rendering with mental ray Handbook.

(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:

See the Rendering with mental ray Handbook for a full description of memory-mapped textures in mental ray.

3D Paint issues with mental ray for Maya

When painting a texture with 3D Paint, mental ray for Maya will not pick up new paint strokes automatically.

Save either the texture being painted or the entire scene before rendering with mental ray to ensure that all strokes are rendered correctly.

mental ray images folder

By default, mental ray batch rendered images used to go to mentalRay/images folder of the project. As a result of the design changes in Maya 7 that made all renderers more consistent, any such images are now being saved to the images folder under the project.

mental ray for Maya transfer maps limitation

bake a Maya transfer map with the .tif or .dds file format, and
you choose the Connect maps to shader option,

then, when you bake a mental ray transfer map for a second time, mental ray generates an error.

mental ray does not understand the DDS format or the LZW compressed TIF format.

Use a mental ray friendly file format for your Maya transfer map, for example, EXR.
Assign a different material to the source surface before baking your mental ray transfer map for the second time.
Unselect the Connect maps to Shader option.

mental ray for Maya transfer Maps custom shaders limitation

When creating a Custom Map, Transfer Maps does not support baking Contour shaders or Geometry shaders to texture. Only Material shaders (shaders listed under the Materials section of the mental ray tab in the Create Render Node window) can be baked to texture. Ensure that your custom shader is recognized as a material shader in Maya.

Removal of Zpic support

The Softimage Depth (Zpic) file format is no longer supported for mental ray for Maya rendering.

mental ray IPR fails to remove default light

If you start mental ray IPR on a scene that does not contain lights, IPR correctly uses the default light. However, IPR fails to remove this default light after you add a new light.

Turn off Enable Default Light in the Render Settings window: Common tab before starting IPR.

mental ray satellite rendering limitations

Uninstall mental ray satellite for previous versions before installing new mental ray satellite

The mental ray satellite for Maya packages have the same name. Therefore, you must manually uninstall previous versions of mental ray satellite before installing the current version of mental ray satellite. On Mac OS X, you need to use the mental ray satellite uninstaller in the mental ray satellite folder to properly uninstall this product. If you delete the mental ray satellite folder, port and machine associations may not be updated properly once you install the latest version of mental ray satellite.

Compatibility issues

Due to a number of changes between mental ray satellite for previous versions of Maya and the current mental ray satellite, there are incompatibilities with using a master (with the current release of Maya) with slaves using a previous version of Maya.

Use master and slave machines with the same version of Maya (for example, Maya 8.5 or Maya 8.0).

mental ray for Maya rendering tips

Rendering Color and Z-depth

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 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.

Depth map shadow settings and volumes (like light fog)

To cast shadows into volumes you have to increase the number of volumes samples in the "Render Stats" section of the shape node ("coneShape1"). This is standard procedure for ray trace shadows. mental ray requires you to do the same thing for Dmap shadows. To eliminate Dmap shadow artifacts on the cone boundary try increasing "Samples" in the mental ray "Shadow Map" section of the light shape node.