We just released a major update of the NVIDIA Mental Ray for Maya plugin, introducing support for the upcoming Volta GPU generation from NVIDIA using CUDA 9. If you are a user of this plugin then you should have received a notification from the NVIDIA taskbar tool. You may also download the latest version from our mental ray for Maya website.
We now introduce: Mental Ray for Maya 2018.
This is the first release of the NVIDIA mental ray plugin for Maya 2018, coupled with the matching NVIDIA mental ray Standalone. For release notes and download locations please visit our forum at Now Available: Mental Ray for Maya 2018.
For those who use mental ray Standalone to render on a remote computer or in a render farm, the creation of a scene file in the proprietary .mi format is a necessary step. Most content creation tools are able to “echo” the full scene into a .mi representation on disk using mental ray’s built-in capability. But mental ray for Maya implements a much more flexible approach with extra functionality to ease render pipeline integration. In this post we would like to take a closer look at some of these features.
The mental ray export options can be opened in Maya’s “Export All” or Export Selected” windows by sliding the separator handle to the left.
Or, click the little options box next to “Export All” or “Export Selected” menu items.
Last but not least, the file export can be triggered and controlled via scripting, like in the Script Editor. We show an example towards the end of this post.
Export Binary vs. Ascii
Similar to Maya’s ascii (.ma) vs. binary (.mb) scene formats, the .mi file can also come in two flavors: ascii or binary. The binary variant is the preferred choice when the precision of the scene data should be retained. The reason is, floating-point numbers are written in a binary form with no loss of bits and precision. Maya’s mental ray export enables binary by default.
That’s perfectly fine if you just like to feed that .mi file to Standalone for final rendering, and not touch it. In a production studio environment this is rarely the case, though. Typically, all the assets (textures, materials, geometry, …) are collected from different sources or departments, and may undergo steps of post-processing and editing before passing to the renderer. The ascii version of the .mi export is often better suited in such situations since it allows simple text editing and easier scripting. On the other hand, it may result in larger file sizes, and can lead to precision problems due to lossy ascii-binary conversions. There are ways to solve that with mental ray for Maya. Let’s take a closer look in the next sections.
The mental ray for Maya export engine can be tuned to use a more exact ascii conversion of extreme values that reside close to the edge of the floating-point precision range. Especially single-precision floating-point data are prone to this problem. Guess what, this is (still) most widely used to represent 3D scene geometry and transformation operations. The standard ascii conversion, which is using a maximum of 6 significant digits for single-precision values (15 digits for double-precision), can be increased up to 9 (or 18, respectively), by creating the following dynamic attributes in your scene prior to export.
Large scene dimensions and hierarchies, but also repetitive use of certain Maya modeling operations, can lead to such extreme values, see hints in the older Autodesk Knowledge Base Article.
Export File Path
A typical .mi scene contains various references to external files, like textures, finalgather maps, or output images. When rendering on a remote machine or in the render farm, the directory path to these files may be totally different than what was used on the exporting machine. Therefore, it is often desirable to not write an absolute file path into the .mi file, but just the relative one rooted at the project directory, or no path at all, and then use mental ray Standalone’s search path configuration on the remote computer to point to the right folders, or shared network drives. For example, using the “-T <path>” command line option, or the _MI_REG_TEXTURE registry value.
The mental ray for Maya export options provide selective control for each type of file.
This section of the export options allows to create .mi files that only contain elements of a certain scene type, like all “textures”, or all “materials”. It translates the full scene as usual but actually writes only the pieces selected in the “filter”. This way it is possible to split up a large scene into more manageable .mi parts that fit together perfectly. Here is an example. It will export three .mi files:
The “textures.mi” file contains just the textures references, all with absolute file path. The “scene.mi” file carries most of the scene data, geometry, lights and materials, and gets compressed to save disk space. Finally, the last one “render.mi” stores the render options, render cameras, and the final render command. Now, the first two .mi files can be included into the last one “render.mi” to create a renderable “master” .mi file, see this .mi snippet:
The resulting .mi file can be given to mental ray Standalone for final rendering. Arrgh, I got a new version of one of the textures last minute! Well, no problem! Just update the “textures.mi” file, no need to touch any of the heavy data. And re-render. Voila!
While this works great in general, it does not help the renderer to load certain scene parts on demand only, like when it is actually “seen” during rendering. That’s where mental ray “assemblies” come into play.
This export option helps to create a valid mental ray “assembly” from a Maya scene. It writes a normal .mi file with a few special properties. A mental ray assembly is used to store a larger part of the scene that belongs together spatially, like a character or a whole building. Normally, it comprises the geometry details of the sub-scene and related local properties like materials.
Such a .mi file can be referenced from a “master” scene “stand-in” bounding box object, which defines the ultimate location and scale in the global space.
In contrast to Maya file references, such an assembly is not loaded or shown in Maya immediately, thus not filling up memory and impacting your modeling operations. Instead, mental ray will load these parts only on demand during rendering, and even unload the piece in case room for other assemblies is needed. This mechanism enables the renderer to handle massive amounts of scene elements more efficiently, and keep memory consumption under control. The resulting rendering is no different to a regular render.
If you like to build a scene that contains huge amounts of similar looking objects that can share the actual assembly geometry, we suggest to use instances of the same assembly rather than copies (!) (which is the default “duplicate” operation in Maya). The placement and scale of the stand-in “proxy” element referencing the assembly determines the final location and size in the final rendering.
This technique of using mental ray assemblies is also available to shader writers and integrators through the programming API. In fact, it is utilized in the mental ray implementation of crowd simulation engines like Massive for Maya, or Maya’s native procedural generator XGen, to handle incredible amount of elements.
We hope these tips will help you in your daily work.
BTW, there are more possibilities to tweak .mi file export even further (“text boxes”). But they are rarely used, and would justify another blog post in case there is interest. Just let us know.
you love to stay on your Mac and use mental ray for Maya?
No problem, since Maya offers the same Qt user interface and experience like on Windows or Linux. Maya scene files and mental ray .mi files that have been generated on other platforms can simply be used on the Mac. Even the configuration files, “Maya.env” and “maya.rayrc”, work identically. All true, but…
Several things are different. For example, the unique use of Mac specific keyboard shortcuts is puzzling, like in the “open scene” window. Switching to the “OS native” file dialog is possible in the Maya preferences. Although it might even be more confusing to use Qt and non-Qt side by side.
What about mental ray ? Well, it is only dependent on the underlying Unix basis “Darwin” with its stable and standardized interfaces. That keeps it quite independent from frequent Mac OS X updates, which typically just touch the application levels of the operating system.
Normally. But the most recent “Mavericks” update of OS X, version 10.9, seem to have changed some multi-threading behavior of the kernel. mental ray is obviously also affected, and shows unexpected interruptions, or even gets blocked completely during rendering. Our developers are currently diving into it, to come up with a solution as soon as possible.
Here is another little annoyance:
The message log for mental ray preview rendering has disappeared a few Mac OS X versions back, also due to a system change that handles console output. The batch rendering is not affected since it writes the messages to a file. There is a workaround for preview rendering, though, using mental ray for Maya’s built-in log facility that works separately to the system log. It can be enabled on the Maya command line like this (also useful for a Shelf button):
Mayatomr -preview -log
It will create a file with the fixed name “mentalray.log”, typically residing in the last opened scene file directory. Double-clicking on the file in the Mac Finder will open the Console App, giving a similar experience to the message display on other platforms. If you enable the Console preference “bring log window to front” it will pop up automatically with each mental ray rendering of that scene using the -log command.
Today we are happy to announce that our NVIDIA mental ray® Standalone software is now directly available from us at NVIDIA. mental ray Standalone is a command line software necessary for large distributed rendering processes typically on render farms. With a purchase from NVIDIA you receive the current and previous versions of mental ray. This includes immediate access to a private forum with direct support from our development teams. Upgrades of the initial license purchase includes one year of maintenance as well.
Prices start at $695 per license and discounts for large quantities are given. For full details of the pricing and product information visit mental ray Standalone webpage
Recently, we were asked about a not-so-well-known feature to help rendering heavy scenes with mental ray inside Maya, or 3ds Max.
You may skip the introduction and jump down to the setting at the end of this article. For those who are into details, here is a little background.
As you might know, mental ray is based on the concept of “loading on demand”, which helps to cope with huge amounts of data that won’t ever fit into the available memory at once. Buying more memory for your rendering machine will help, but, at the same time, your scene size and texture needs have grown again. Well, typically you should not notice since mental ray takes care of handling these cases automatically. It delays all operations that are memory exhausting or expensive to compute to the latest point in time, and only executes them when really needed to render the current pixel. That is true for scene data, when loading elements from an assembly or Alembic archive, but also for textures, reading and decoding only those textures needed, possibly even keeping just pieces of it in memory, so-called “tiles“. Most importantly, the tessellation of source geometry into triangle data is done on demand only, absolutely critical when working with very detailed displacement. Finally, this mental ray machinery of demand loading is also exposed to shader writers.
Let’s look at mental ray for Maya and its use of this technique for scene translation. Normally, if you do a preview render in Maya (like “Render Current Frame“), the whole scene will be converted to the mental ray database before the actual rendering starts, often referred to as the “translation” step. This will include every scene element independent of its contribution to the rendering of the frame or animation. What is usually OK for most scenarios, might become a bottleneck in extreme situations with many large pieces of geometry or several big chunks of hair, especially if they are not really actively involved when rendering the current view. Like in the example below (a quickly painted cityscape in Maya, but you get the idea)
The usual answer to this problem would be: create a mental ray assembly for those scene parts and reference that in your master scene. But, there is an easier way right from within Maya:
Enable “Render Settings > Options > Translation > Performance > Export Objects On Demand“, as marked below.
What is it doing ?
It does not pre-translate geometry before rendering starts, as it usually does, but delays it to rendering time. The translation just creates so-called “placeholders” – basically bounding boxes around the pieces of geometry – that will trigger execution of the actual translation only when a ray hits that box (or a certain feature is requesting the actual geometry). Because translation becomes very fast it finishes almost unnoticed, so that the Maya progress bar typically starts with “mental ray rendering…” . Leaving the “threshold” setting at 0 (zero) will cause all objects to be demand-loaded, even if tiny. That may be inefficient. Increasing this to a higher number, only those objects with its number of points/vertices beyond the value will be considered for demand loading, the rest gets pre-translated.
Please remember, that in a ray tracing or global illumination context all the objects may be demand-translated immediately anyway even if out of sight! In that case there may be no real benefit using this mode. And, this translation mode has a certain runtime overhead attached to it, so it may pay off only in certain cases, and only with an appropriately chosen threshold.
This setting is saved with your scene. That means, it will also work with “Maya Batch”.
You are working with 3ds Max ? The same feature is available here too, enabled with “Render Setup > Processing > Translator Options > Memory Options > Use Placeholder Objects“, as shown below.
Just give it a try, and leave a comment if you find it useful.
the mental ray Standalone has a similar feature if bounding boxes are given in the .mi file. It is enabled on the command line with: