Autodesk 3ds Max 2015 and Autodesk Maya 2015 ship with mental ray 3.12 which includes a prototype of our new global illumination engine accelerated by the GPU.  We encourage our 3ds Max and Maya users to try it out. Your feedback will help us in making this a big step forward into the future of rendering with mental ray. While the current version is in prototype status and not yet feature complete, we are constantly improving the algorithms and adding new features. Your input is most welcome in this process.

The key idea of the new GI engine is full and exact simulation of the lighting interactions in a scene. This way, we overcome drawbacks from caching techniques and interpolation, and make mental ray more interactive and predictable. The brute-force raytracing approach is accelerated on CUDA capable NVIDIA GPUs making it particularly attractive in this set-up. Its result gets combined seamlessly and automatically with the primary rendering done on the CPU. This ensures full compatibility with existing custom shaders, which do not need to be touched in order to take benefit of the new GI engine.

The following Maya scene is rendered using the new GPU GI prototype in 11 min 34 sec (2 x Quad-core Xeon E5620 @ 2.4 GHz in hyper-threading, 8 GB RAM, Quadro K5000)

For comparison, this image is rendered with the classical finalgather automatic mode in 20 min 52 sec (2 x Quad-core Xeon E5620 @ 2.4 GHz in hyper-threading, 8 GB RAM, Quadro K5000)

In the current version, the GI GPU mode considers diffuse-diffuse bounces only, similar to what final gathering typically computes.  In fact, if this mode is enabled without setting further parameters then finalgather settings are used to derive reasonable default  parameters to render towards the same quality. If certain prominent ray tracing effects like mirror reflections or transparent  windows are not used in a scene then the fastest diffuse mode is best suited. For current limitations, see below.

The following image is rendered with the GI prototype in diffuse mode in 37 minutes (Core i7-3930K (6 cores), 16 GB RAM, Quadro K5000)

                                                                                                                                             Autodesk 3dsMax scene courtesy David Ferreira

The following 3dsMax scene is rendered on the CPU with finalgather force in 13 hours (Core i7-3930K (6 cores), 16 GB RAM, Quadro K5000)

The GI GPU mode can be enabled and controlled with scene options or on the command line of the standalone mental ray. We also provide scripts for Maya and 3dsMax that provide a simple GUI for enabling GI GPU (see screenshot). Please, note, that this is by no means how we envision it to be integrated in the applications. It’s rather to provide easy access to users that would like to test the prototype.

Script Download

The scripts to easily enable and access the GI GPU prototype can be downloaded directly from us here:

• Autodesk Maya MEL Script
• Autodesk 3dsMax Script

Current limitations

GI GPU transfers the scene geometry, presampled shader data, and some constant amount of buffer memory onto the GPU. Textures are not needed on the GPU. In the case that the GPU memory is not sufficient, there is an equivalent CPU mode. The new GI engine can still be used but the GPU acceleration must be disabled (uncheck the ‘Use GPU’ checkbox). There is also an absolute limit of 25 million triangles.

For GI GPU to be effective, finalgather must be turned on. Some features are not yet supported: distorting lens shaders, motion blur, particles, volume shaders, camera clipping planes, progressive rendering. There is only limited support for scattering shaders, emissive materials, and hair rendering.

Before testing GI GPU, we recommend to install a recent version of the NVIDIA graphic card driver.

Feedback and discussion

We would like to hear your feedback and see your renderings using this prototype.  Please join our NVIDIA Advanced Rendering forum, if you have not already, and send us your comments and discuss the mental ray GI GPU prototype.  The dedicated mental ray GI GPU Prototype forum topic here

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.

BTW,
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:

> ray -reload

Happy rendering,
Steffen