If a clean install of MtoA doesn’t work (and the computer does support SSE4.1), then “The specified module could not be found.” usually means there’s a missing dependency. Dependency Walker is a decent, if aging, tool for checking out dependencies, but for leaving no stone unturned, I prefer Process Monitor.
The MtoA plugin (mtoa.mll) depends on a handful of files only. Here’s the log of loaded DLLs for a working MtoA:
Here’s a quick walkthrough (no audio) of how to get a Process Monitor log:
MtoA defines a lot of batch render flags for Arnold. For example, here’s how to set the Arnold log verbosity and enable file logging:
render -s 2 -e 2 ^ -r arnold ^ -ai:lve 2 ^ -ai:ltf true ^ -ai:lfn C:/Users/blairs/Downloads/render.log ^ D:\Projects\maya\Support\scenes\example.ma
First, to use the Arnold batch render flags, you need to use the Maya -r flag to specify that the renderer is arnold (otherwise, you’ll get an “Invalid flag” error).
Then you can use the Arnold batch render flags:
Arnold 5.1 adds operators, which among other things, allow you to override parameters in ass files loaded by procedural nodes.
Here’s a quick example using the brand new MtoA 3.0
I exported some particles from Softimage, loaded them into Maya with an aiStandin (aka an Arnold procedural), and then used a set_parameter operator to scale the radius by 0.5
Note that I connect my operator by setting the Target Operator in the Render Settings.
I can chain two set_parameter operators together, to set the mode and then scale the radius:
You can use kick to render with debug shading. Here’s the flags to use:
Here’s some examples that show how to kick with different types of debug shading (I’ve used the Arnold Render View debug shading modes for these examples)
| Debug shading | kick flags |
| Basic: disable all shaders in the scene, switching to a gray ‘ndoteye’ shader; a very fast shading mode. |
kick -is or kick -is -sm notdoteye |
| Lighting: renders the scene with a white lambert shader |
kick -is -sm lambert |
| Occlusion: use ambient occlusion shading |
kick -is -sm ambocc |
| Wireframe: displays geometry as a wireframe |
kick -is -cm polywire or kick -is -sm ndoteye -cm polywire |
| Normal: visualizes the normal vector (between 0 and 1, in tangent space) |
kick -is -sm flat -cm n |
| UV: displays the coordinates of the primary UV set (red=U, green=V) |
kick -is -sm flat -cm uv |
| Primitive ID: displays random colors based on the per-primitive (triangle, curve) index |
kick -is -sm flat -cm prims |
| Barycentric: displays intra-primitive parametric coordinates (barycentric for triangles, parametric length, and width for curve segments) |
kick -is -sm flat -cm bary |
| Object: displays random colors based on the per-object ID |
kick -is -sm flat -cm obj |
In this case, when the user tried to render after enabling the OptiX denoiser, they got this error:
ERROR | [gpu] OptiX version 0.30.91 is lower than the minimum required version 5.0.0
This was with MtoA 3.0.1, which means Arnold 5.1.1.0
So, that means there is an incompatible version version of the OptiX library on the system, and it’s being loaded instead of the OptiX that ships with MtoA.
I probably could have just checked the PATH setting, but I used Process Monitor to absolutely sure, and I found this:
The problem is that another renderer added itself to the PATH. That’s a bad thing 
The solution? Remove that folder from PATH. Create a batch file or wrapper script to set the required environment when you start Maya to use the other software. Rather like the mtoa module file sets PATH when you start Maya.
NOTE In previous versions of MtoA, this would prevent MtoA from even loading.
There’s two denoisers. Here’s when to use them:
For more info, check the docs
If you want to control object visibility with operator, or the Arnold Python API, or by editing an ASS file, you need to understand Arnold’s visibility parameter.
In the UI, the object visibility options look like a bunch of separate parameters:
but in Arnold, all those options are stored in one visibility parameter.
For example, if an object is visible to the camera (primary visibility), and to transmission (both diffuse and specular), then that’s visibility 13.
Why 13? Because 13 = 1 + 4 + 8
The Arnold visibility parameter tells Arnold the rays to which the object is visible.
Here’s the decimal values for all the different ray types.
To figure out the visibility, just add up the values for the rays you want.
| Ray type | Decimal Value |
| Camera (Primary Visibility) | 1 |
| Shadow (Casts Shadows) | 2 |
| Diffuse transmission | 4 |
| Specular transmission | 8 |
| Volume | 16 |
| Diffuse reflection | 32 |
| Specular reflection | 64 |
| SSS (subsurface) | 128 |
This error means that you are trying to render multiple AOVs into a single file, and the file format (PNG in this example) does not support that.
JPEG, PNG, and TIFF cannot have multiple AOVs in a single file. The AOVs have to be rendered in separate files.
If you get this error, check the Common tab. If you don’t see the <RenderPass> token, then you’re going to get the “more than one output statement was associated with single layer driver” error.
For JPEG, PNG, and TIFF, you need the <RenderPass> token:
Normally, MtoA will automatically add the <RenderPass> token for you. But sometimes Merge AOVs gets enabled for EXRs, and then the Image format is changed to another format, like PNG.
So just switch back to EXR and disable Merge AOVs. Then switch back to the other image format.
You can use use color_correct with alpha_is_luminance enabled, like this:
If you see this warning when you render
Warning: [mtoa] [translator polymesh] ShadingGroup exampleSG has no surfaceShader input
it’s because a shadingEngine node either has nothing connected to the surfaceShader port, or (more likely) it has an unknown node plugged into surfaceShader.
For example, if you load a scene that was set up with a different renderer, and that renderer is not loaded, then you’ll get some “ShadingGroup has no surfaceShader input” warnings.
Or: how to fix the node “xgen_procedural” is not installed problem.
For example, suppose you want to render XGen hair in CINEMA 4D on macOS.
export DYLD_LIBRARY_PATH=/Applications/Autodesk/maya2018/plug-ins/xgen/lib:/Applications/Autodesk/maya2018/Maya.app/Contents/MacOS
One of the strange thing about supporting Arnold at Autodesk is that you have to be a guru-level licensing expert on Autodesk licensing (not RLM, but Autodesk licensing).
In this case, Maya 2019 would silently fail at startup. Sometimes you’d see the splash screen, but then that would just disappear.
ERROR: checkoutLicense: Failed to authorize license
JsProductLicenseFact.loadSelectedProductInfoKey - Unable to get selected product key due to unknown problem.
TIP All these log files are in the Temp folder.
Process Monitor confirmed that the ProductInformation.pit file was missing:
ProductInformation.pit is an all-important file used by the licensing infrastructure. Every Autodesk product must be registered in that pit file.
If ProductInformation.pit is missing, or corrupted, then everything stops working.
For Arnold itself, you can ignore that message. Unless you have an Arnold license.
Couldn't register Arnold renderer in Maya PIT file (error while parsing .pit file). Please contact support@solidangle.com.
For Maya, that message is a symptom of a problem with your Maya install: the Maya installation is not creating all the required files on your system.
If you finish the install (you can install without MtoA if you want), and then try to start Maya and nothing happens, then the ProductInformation.pit file is missing or corrupt.
The Maya install should create this file:
C:\ProgramData\Autodesk\Adlm\ProductInformation.pit
If there is any problem with that file, Maya (and any other Autodesk software) will not start.
Arnold will still render, but it won’t be able to use any Arnold license.
If that file does exist on your system, delete it.
Then remove all Autodesk software, and install Maya again (without MtoA)
You can install MtoA later (go to arnoldrenderer.com/arnold/download to get the latest MtoA).
If you still have problems with the Maya installation, log on to your Autodesk account to contact the Autodesk support team, or go to the Install and Licensing Autodesk forum at https://forums.autodesk.com/t5/installation-licensing/bd-p/24
Monthly, annual, and 3-year single-user subscriptions of Arnold 6 are now available on the Autodesk e-store
No more license servers! With a new single-user subscription, you just sign in with your Autodesk ID.
You can use the wireframe shader to drive the opacity of a standard_surface.
The wireframe shader itself doesn’t support opacity, and neither do the flat, utility, and ambient_occlusion shaders. They are all color shaders (RGB). In Arnold, only shaders that return closures can support opacity.
In the more general case, where the opacity isn’t coming from the same shader, you can use the emission for the color:
Arnold 6.0.2 includes a new string_replace that lets you do find and replace on string parameters.
For example, I got an ass procedural file from a user, but I didn’t get the textures. Normally I would just enable ignore textures, but this time I used string_replace to replace all textures with my trusty-old-Softimage noicon pic.
Controllable auto-instancing on ASS procedurals: You can now disable the default automatic instantiation of procedurals pointing at the same ASS file with the
Arnold 6.0.2 release notes https://docs.arnoldrenderer.com/x/1gGvBgauto_instancingparameter on each procedural or by theprocedural_auto_instancingoption. This workaround is sometimes useful when overriding procedural parameters with operators.
So, what’s all that mean?
It means that if you load the same ass file many times, Arnold will load the ass file just one time, and then automatically create instances of that. For example, if I load an ass file three times, I will get two instances.
In previous versions, this was known as the procedural cache, and it was a global option. Now it’s called auto_instancing and you can set it on each procedural node (aka aiStandin in Maya).
In general, you want auto instancing, because instancing is more efficient than loading the same ass file over and over. But if you’re using operators to apply different looks to the same procedural, you need to turn off auto instancing. Otherwise all the procedurals will have the same look (because they all be instances of the same one procedural).
For example, with auto instancing on, I get this, even though I’ve assigned different looks to each procedural (standin):
I can also tell from the Arnold log that I’m getting instances. Note that 2 are reused
| --------------------------------------------------------- | ass file cache | unique (loaded from disk) 1 (33.33%) | reused (found in cache) 2 (66.67%) | total referenced .ass files 3 (100.00%) | ---------------------------------------------------------
If I turn off auto instancing (in the procedural parameters)
then I get three different looks
In the Arnold log, that looks like this (0 reused means 0 instances)
| --------------------------------------------------------- | ass file cache | unique (loaded from disk) 1 (100.00%) | reused (found in cache) 0 (0.00%) | total referenced .ass files 1 (100.00%) | ---------------------------------------------------------
This is actually pretty cool…you can use an operator to update file paths before an ASS file or ABC file is loaded, then use another operator to touch the geometry loaded by that procedural.
For example, suppose at render time you want to replace trex_proxy.abc with trex.abc. You can easily do that with a string replace operator:
And that all happens before the abc file is loaded.
We can see this in the Arnold log (Debug verbosity). First the string replace operator is applied; then after the abc file is loaded, a set parameter operator is applied to the nodes loaded from the abc file.
| initializing 16 nodes … | [operators] init op: 'aiStringReplace1' | [operators] cook op: 'aiStringReplace1' | node: '/aiStandIn/aiStandInShape' | [proc] /aiStandIn/aiStandInShape: loaded 1 nodes (1 objects, 0 shaders) | [operators] init op: 'TRex:tRexShape_aiSetParameter1' | [operators] cook op: 'TRex:tRexShape_aiSetParameter1' | node: '/TRex:tRex/TRex:tRexShape'
The Arnold API reference is now available online at docs.arnoldrenderer.com/api/latest
