(warning) Please see the Set Up V-Ray RT GPU page in addition to the FAQ. If you are unable to find an answer to a question you have on this page, please contact Chaos Group Support for further help.

 

Frequently Asked Questions


 Which features are supported on the GPU?

The code base for V-Ray RT GPU differs from the code base for the CPU engine. The GPU code base is optimized for GPU hardware and supports a subset of the features of CPU rendering. For a complete list of supported features, please see the V-Ray RT Supported Features page.

 Can I choose which devices are used for GPU rendering?

Yes. See the RT GPU setup section for instructions on how to do this.

 Why does my UI become sluggish when I use V-Ray RT GPU?
  • If you have multiple GPUs, you can speed up screen refresh time by removing the GPU used for monitor/viewport redraw from the devices that RT GPU uses for rendering.
  • If you have only one GPU on your system, you could try reducing the value for Rays per pixel and/or Ray bundle size in the Performance section under the V-Ray RT tab in the Render Setup dialog. This will break up the data passed to the GPU into smaller chunks so that user interface requests can be processed faster. However, this might reduce rendering speed. Enable Show statistics to check the difference in render speed (GPU utilization) and to help find the optimal settings for your system.
  • The Low GPU thread priority parameter was designed to help with this issue. Turn it on in the V-Ray RT tab in the Render Setup window.

 

V-Ray will display a warning if the GPU used for monitoring is participating in the rendering process.

 How can I reduce network bandwidth when using RT GPU in a heavy DR setup?

If you use many GPUs in DR nodes you might find that the network develops a bottleneck at some point due to the GPUs producing data very fast. To increase the size of the workload chunks that are being given to the DR nodes and help reduce the communication between the client and the servers, increase the Ray bundle size and Rays per pixel parameters in the Performance section under the V-Ray RT tab in the Render Setup dialog. Try values like 192/32 or 256/64.

 How do I check the memory usage on the GPU and how do I reduce the GPU memory needed for my scene?

You can use free 3rd party tools like MSI Afterburner and EVGA Precision to monitor both GPU memory usage and utilization.

RT GPU also reports how much memory it uses for textures/geometry/light cache/etc in the V-Ray log. If you enable the Show statistics checkbox from the RT settings, the memory usage information will be printed in the VFB itself as well.

 How do I setup RT GPU as my production renderer? What are the differences between Active Shade mode and Production mode?

You can set it by selecting V-Ray RT from the Renderer dropdown when the Target drop-down is set to Production Rendering Mode from the top of the Render Setup window, or also by adjusting the selected renderer to V-Ray RT in the Production setting found in the Assign Renderer rollout at the bottom of the Common tab. The main differences are, you will lose the interactivity of the Active Shade, but you will be able to render animations, and V-Ray will calculate and use Light Cache for RT GPU GI calculations if it has been set as primary or secondary GI engine.

(warning)  When using RT GPU as the Production renderer with Max noise as the render threshold, please set a value for Max paths/pixel (to something like 10,000) to avoid long render times. The default value for Max paths/pixel is set to 10,000.

 How do I use Light Cache with RT GPU?

If you use RT GPU as a Production and you have selected Light Cache as primary or secondary GI engine, V-Ray will calculate and use the Light Cache for the RT GPU GI calculations. If you run RT GPU in Active Shade, V-Ray will always use Brute Force for primary and secondary GI engines, unless you load your Light Cache from a file. The reason for that is that the Light Cache is view dependent, and recalculating it every time the camera changes its position in Active Shade doesn't make much sense.

 Why do the bump maps look different?

All procedural textures are supported for RT GPU bump maps if attached through a Color2Bump map in the Bump slot of the material editor. Because the RT GPU is a very different engine, the bump map itself can look a bit different compared to V-Ray Adv.

 How to do Stereo Rendering using RT GPU?

In Render Setup > V-Ray RT tab > Stereo mode - choose your desired mode. VRayStereoscopic helper is not supported in V-Ray RT.

 Why doesn't my displacement / hair / etc. show up in ActiveShade mode?

There are global switches that turn them off in ActiveShade. Check the switches to enabled rendering of those in ActiveShade mode. In Production mode, these are enabled by default.

 

 How can I check which devices on my system can be used for GPU rendering? Why my devices is not listed?

Check the list of devices in the RT GPU settings tab. Keep in mind that in certain setups 3DS Max will not recognize some of the devices. If you don't see your device on the list there (the list is empty), try to uncheck the In process checkbox. This will make V-Ray run as a separate process, working around the limitation. If this does not help as well and you have already updated to the latest drivers, please contact Chaos Group Support.

If 3ds Max doesn't properly recognize the devices, V-Ray will automatically turn off the "In process" rendering and show warnings in the VFB and in the log.


 

 

 Why is the GPU rendering not many times faster than the CPU rendering?

The difference in render speeds depends on the video cards and the CPUs that are compared, as well as on the scenes used as benchmarks. It is normal to achieve a big speed boost with the GPUs compared to the CPU with some scenes and to have comparable performance with others. If you, however, consider that this might be a bug, please contact Chaos Group Support.

 Can I use multiple systems with GPU devices to speed up my rendering?

Yes, you can speed up your rendering using DR on multiple systems with CUDA/OpenCL enabled devices.

Keep in mind that if some Windows drivers may have limitations and may not be able to use GPUs if there is no monitor attached to the machine or you are logged in via Remote Desktop. Check the GPU vendor documentation for more information.

 Can V-Ray RT GPU be used as production render?

Yes, within its limitations.

 Can V-Ray RT be used with Motion Blur?

Yes. Note that V-Ray RT rendering supports motion blurred frames that are integer numbers only. Make sure the starting frame of your render is an integer number for motion blur to work correctly. For example, starting the render from frame 0 will produce correct motion blur, but starting from frame 1.25 will produce incorrect motion blur.

 Why doesn't V-Ray RT GPU render my matte objects properly?

If you're trying to use matte materials in situations like making a shadow catcher, V-Ray RT in GPU mode will not render objects with matte properties correctly unless the Elements Active checkbox is enabled under the Render Elements tab of the Render Setup window.