Category Archives: Tips

Updating MtoA 1.2.7.3 with Arnold 4.2.14.0

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MtoA 1.2.7.3 ships with Arnold 4.2.13.

If you want to take advantage of the improvements in Arnold 4.2.14.0 (like the increase  in the maximum number of threads from 128 to 256), here’s what you need to do:

  • Download  Arnold 4.2.14.0 and extract the archive
  • Replace Arnold (libai.so, ai.dll, libai.dylib), kick, and maketx in the MtoA bin folder with the versions from the Arnold 4.2.14.0 download
  • Replace the Arnold Python bindings in  the MtoA scripts/arnold folder with the Python bindings from the Arnold python/arnold folder. For example, replace this folder: 
       C:\solidangle\mtoadeploy\2016-1.2.7.3\scripts\arnold

    with the python\arnold folder from the Arnold 4.2.14.0 download. For example:

       C:\solidangle\arnold\Arnold-4.2.14.0-windows\python\arnold

You must update the Arnold Python bindings, otherwise MtoA won’t load. That’s because Arnold 4.2.14.0 included a number of API changes, including the removal of some API (like AiLicenseSetServer). The older Python bindings still refer to the removed API, so there will be Python errors that prevent MtoA from loading.

[Arnold] Understanding the texture cache

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Arnold uses the OpenImageIO texture cache. From the OIIO Programmer Documentation:

In short, if you have an application that will need to read pixels from many large image files, you can rely on ImageCache to manage all the resources for you. It is reasonable to access thousands of image files totalling hundreds of GB of pixels, efficiently and using a memory footprint on the order of 50 MB.

So, if you’re using tx files (tiled and mipmapped textures), then Arnold can read tiles as required, and use the texture cache to keep memory usage under control.

The reason we don’t read all the textures at once is that many of our customers have (literally) 100+GB of textures, so we use a texture cache that constantly loads small bits of texture data as required, and unloads old data.

By default, the size of the texture cache is 2048KB (as of Arnold 4.2.13.0). The size of the texture cache is set in the Arnold Render Settings.

Max Cache Size
The maximum amount of memory to be used for texture caching. Arnold uses a tile-based cache with a LRU (Least Recently Used) type algorithm, where the least recently used tiles are discarded when the texture caches is full.

Note If we get an error reading a texture, we mark that texture as bad and we never try to read it again. This makes the renderer a lot faster when you have a missing texture, since we won’t ask the file server millions of times to read from a nonexistent file. But in a transient network error case, one bad experience and the rest of your render has the texture missing.

[MtoA] Switching between multiple versions of MtoA

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start_menu_mtoa

If, like me, you need to switch between different versions of MtoA, here’s a recipe for setting that up.

First, you have to install multiple versions. As you probably already know, the MtoA installer always wants to uninstall first. I take care of that by zapping the Uninstall registry entry with this command:

reg delete "HKCU\Software\Microsoft\Windows\CurrentVersion\Uninstall\MtoA2016" /f

Then I run the MtoA installer and install in a folder with the version name, like this:
C:\solidangle\mtoadeploy\2016-1.2.7.3

I start Maya with a batch file that creates a symbolic link named “C:\solidangle\mtoadeploy\2016” that links to the version of MtoA I want to use:

rmdir C:\solidangle\mtoadeploy\2016
mklink /D C:\solidangle\mtoadeploy\2016 C:\solidangle\mtoadeploy\2016-1.2.7.3
rem mklink /D C:\solidangle\mtoadeploy\2016 C:\solidangle\mtoadeploy\2016-1.2.2.0

set RLM_DEBUG=arnold
start "" "C:\Program Files\Autodesk\Maya2016\bin\maya.exe" %* -log %TEMP%\maya.log

My batch file also adds the location of my custom mtoa.mod to MAYA_MODULE_PATH. My custom mtoa.mod points to “C:\solidangle\mtoadeploy\2016”, and handles all versions of Maya:

+ MAYAVERSION:2018 mtoa any C:\solidangle\mtoadeploy\2018
PATH +:= bin
MAYA_CUSTOM_TEMPLATE_PATH +:= scripts/mtoa/ui/templates
MAYA_SCRIPT_PATH +:= scripts/mtoa/mel
MAYA_RENDER_DESC_PATH +:= 
+ MAYAVERSION:2017 mtoa any C:\solidangle\mtoadeploy\2017
PATH +:= bin
MAYA_RENDER_DESC_PATH +:=
MAYA_CUSTOM_TEMPLATE_PATH +:= scripts/mtoa/ui/templates
MAYA_SCRIPT_PATH +:= scripts/mtoa/mel
+ MAYAVERSION:2016 mtoa any C:\solidangle\mtoadeploy\2016
PATH +:= bin
MAYA_CUSTOM_TEMPLATE_PATH +:= scripts/mtoa/ui/templates
+ MAYAVERSION:2015 mtoa any C:\solidangle\mtoadeploy\2015
PATH +:= bin
MAYA_CUSTOM_TEMPLATE_PATH +:= scripts/mtoa/ui/templates
+ MAYAVERSION:2014 mtoa any C:\solidangle\mtoadeploy\2014
PATH +:= bin
+ MAYAVERSION:2013 mtoa any C:\solidangle\mtoadeploy\2013
PATH +:= bin

 

[Arnold] Overriding parameters of nodes created by a standin

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A common question is “how can I override the subdivision/displacement of the nodes in a standin?”

The standard answer is: “you can’t”. A standin is an Arnold procedural node, and you can override only the parameters supported by the procedural node, which do not include subdivision or displacement.

But…here’s how to do with the [deprecated] override back door. The override node allows you set a parameter value on a specific node. So if a standin loads an ASS file with a polymesh named “tRexShape”, then you can override tRexShape.subdiv_iterations like this:

override
{
 tRexShape subdiv_iterations 2
}

So, in Maya, do this:

  • Create a standin that loads an ASS file with the polymesh nodes (in this example, a tRexShape with subdiv_iterations=1).
    trex
  • Create a second standin that loads an ASS file with the override node. Clear the Defer Standin Load check box for this second standin, and your standin will render with the override value for subdiv_iterations.
    trex_override

 

NOTE
override nodes aren’t supported by the Arnold API, and there’s no guarantee that support for override nodes won’t be removed at some point in the future.

[Arnold] Setting up the Standard shader to be energy conserving

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For energy conservation with Diffuse and SSS, you must have Diffuse + SSS <= 1

With Specular, it depends on whether or not Fresnel is enabled:

  • If Fresnel is off, then you must have SSS + specular + diffuse <= 1
  • If Fresnel is on, then you must only have diffuse + SSS <= 1. The shader will mix specular with diffuse and SSS in a way that’s energy conserving.

Ok, that’s the simple case (without diffuse backlighting and refraction). Now let’s add diffuse backlighting and refraction:

For energy conservation with Diffuse and SSS, you must have Diffuse + SSS + backlighting <= 1

With Specular, it depends on whether or not Fresnel is enabled:

  • If Fresnel is off, then you must have specular + (SSS + diffuse + backlighting) <= 1
  • If Fresnel is on, then you must only have diffuse + SSS + backlighting<= 1. The specular and refraction weights can be anywhere between 0 and 1, and the shader will mix everything in a way that’s energy conserving.

[MtoA] Running a silent install on Windows

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On Windows, if MtoA isn’t already installed, then the /S flag will do a silent install:

MtoA-1.2.7.3-2016.exe /S

You can also specify an install location with the /D flag:

MtoA-1.2.7.1-2016.exe /S /D=C:\solidangle\mtoadeploy\2016-1.2.7.1
There’s no help, but I found the /S and /D via Google:

There is no silent install on OSX or Linux.

If another version of MtoA is installed, there will be some pop-up dialogs. You can get around that by doing a silent uninstall, like this:
C:\solidangle\mtoadeploy\2016-1.2.7.1\uninstall.exe /S

or, if you want to keep the existing install around, you could do this:

reg DELETE HKCU\Software\Microsoft\Windows\CurrentVersion\Uninstall\MtoA2016 /f

After you delete that registry key, an MtoA install won’t detect an existing installation, so you get to keep the old install, and install a new version.

 

[C4DtoA] Understanding shaders and AOVs

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Arnold takes care of writing the built-in AOVs like N, P, Pref, A, and the all-important beauty. But it’s shaders that write to AOVs like direct_diffuse. That’s why something like this is not going to give you what you might expect in the AOVs:

layer_colors

layer_color doesn’t write to AOVs, so you won’t see the layered result in an AOV like direct_diffuse. standard does write to the direct_diffuse AOV (and others), but in this setup, you have multiple standards and they end up overwriting each other, so you get just the last standard output in the AOVs.

It’s better practice to avoid having multiple standard nodes in a single material; instead, layer the maps that go into the standard parameters like the diffuse and specular colors.

Or you could use a node like mix, or the third-party alLayer, which support AOVs. You can tell if a node writes AOVs by looking at its Attribute Editor: there’s usually a tab or list where you can change the names of the AOV outputs.

mix_aovs

[MtoA] Use any mesh for a standin

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MtoA 1.2.7.0 includes an enhancement (“standin as attribute group”) that allows you to use any mesh as a standin. So instead of the aiStandin node, you can have a proxy geometry to represent your standin.

For example, here’s a mesh shape that loads an animated ASS sequence exported from Softimage:

procedural_mesh_transslator
Note that in the shape Attribute Editor, the Arnold Translator is set to procedural.

This feature uses the mesh bounding from Maya, so it’s possible your standin maybe clipped. You can work around this either by disabling Defer Procedural Load, or by using the User Options to set the procedural min and max (for example: min -1 -1 -1 max 1 1 1).

Hat tip: Alf

[Arnold] Setting core affinity aka pinning threads

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Instead of setting the core affinity yourself, you should let Arnold do it. By default, Arnold pins threads (sets the affinity) if you use more than half the cores on the machine.

If you really must set affinity yourself, you can use the Override User Options to set options.pin_threads to off.

BUT you can also limit the number of threads Arnold uses: in the Render Settings, System tab, clear the Autodetect Threads check box and then set the number of threads. For example, you could limit Arnold to six threads, and limiting the threads is probably a better approach, since you won’t end up with multiple render threads running on the same core, which can be bad for performance. This way, you wouldn’t need to set the affinity at all.

See Also:

  • As of Arnold 4.2.3.0, options.pin_threads works on Windows too.
  • Thread affinity was added in Arnold 4.0.8.0.
    From the Arnold release notes:    Threads can now be pinned to cores on Linux. This can improve scalability in modern machines with 16 or 24+ threads and, in the case of ray acceleration structure builds, it can occasionally result in as much as a 3x speedup when all the cores are being used (which is the default in Arnold, options.threads = 0 or -t 0 in kick). The default setting is auto where thread pinning is only enabled if more than half the logical cores are being used.
    This can also be manually set to always on or off by setting the new global option options.pin_threads to on, off, or auto. Note that, if client code, for instance a custom shader, spawns their own threads manually (with pthread_create or similar), these threads will inherit the same thread affinity, which totally breaks the point of spawning threads; in these situations they can either set options.pin_threads to off or they can create their threads with the Arnold API AiThreadCreate() which will un-pin the created thread. (#2733)
  • pin_threads
    Arnold can pin threads on linux and Windows so they don’t jump between multiple processors. This can improve scalability in modern machines multiple processors. It can be set to off, on or auto. By default is set to auto, meaning that if the number of threads is more than half the number of logical cores on the machine, arnold will pin the threads.
  • Adjustable thread priority in OS X: OS X now allows for options.thread_priority to adjust the priority of the render threads. It defaults to lowest, which is lower than the system default that was previously being used. Previously this option only existed in Windows.

[MtoA] Adding user data to standin instances

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The standard way to add user data to an Arnold node is to add an mtoa_constant attribute to the shape node in Maya. MtoA translates the mtoa_constant attributes to user data, so you can use shaders like AiUserDataColor.

Instances in Maya, however, don’t have their own shape node: they all share the shape node of the original object. So you can’t use an mtoa_constant attribute on the shape to get different user data for each instance.

But you can use override sets to get user data on instances. Put the instances in a set, and then add the mtoa_constant as an override attribute.

set_overrides

Then each instance in the set will get that user data.

Another way to add user data to instances is with the particle instancer: you can add per-particle attributes, and then list them in the Arnold > Export Attributes text box. MtoA translates all those attributes to user data on the particle instances.