mental ray’s GPU accelerated GI engine prototype

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)

Mosque - mental ray 3.12 GI GPU diffuse

                                                                                            Autodesk Maya scene courtesy Lee Anderson, environment from openfootage

 

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)

mosque_fg_auto

 

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)

Medieval - mental ray 3.12 GI GPU diffuse

                                                                                                                                             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)

Medieval - mental ray 3.12 CPU

 

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.

 

max-screenshot

Script Download

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

 

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

mental ray for Maya 2015 SP2

mentalray for Maya 2015 SP2 is now available and provides important fixes around XGen hair rendering, layering shaders, massive assembly scenes, native IBL and more. Here’s a short list of fixes that come with the new mental ray 3.12.1.16 and the new version of the mental ray plugin.
Please, consult the mental ray and the Maya 2015 SP1 and SP2 release notes for the complete list.

  • XGen
    The performance of the XGen hair shader has been significantly improved for scenes with dense hair.
  • Layering shaders (Mila)
    Several fixes in the shaders and the UI – namely, possible crash with subsurface scattering initialization, possible NaN values and a too bright contribution of the user IBL environment shader in glossy components, reordering layers with bump or weight connection.
  • Binary Maya file compatibility with Maya 2014 restored
    Some mental ray shader nodes saved in .mb files were not compatible between 2014 and 2015. This is now fixed.
  • GI GPU
    Improved performance of the GPU and multi-CPU rendering, and added support for NVIDIA Maxwell GPUs.
  • Large scene with assemblies
    Fixed possible crash when rendering large scenes with multiple assemblies exceeding physical memory.
  • Native environment lighting
    IPR now automatically updates when changing the new “emit light” features which control the native environment lighting. Fixed brightness difference in IPR versus Render Current Frame.

Happy rendering,

Julia