v-ray rt and gpu rendering

8/13/2019 V-Ray RT and GPU Rendering

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General

Supported hardware and drivers

OpenCL run-time compilation

Choosing which devices to use for rendering

Balancing the GPU load

Supported features on the GPUCommon OpenCL errors

References

General

GPU rendering allows V-Ray RT to perform the raytracing calculations on the GPUs installed in the system,

rather than the CPU. Since GPUs are specifically designed for massively parallel calculations, they can speed

up the rendering process by an order of magnitude.

To enable GPU rendering, select the OpenCL (single kernel)or CUDA (single kernel)value for the Engine

typeparameter in the V-Ray RT settings.

Supported hardware and drivers

V-Ray RT for GPU has two back-ends (or engines). One is based on OpenCL (see the references section

below for more info on OpenCL) and the other one - on the nVidia CUDA platform.

The OpenCL engine should be able to run on any OpenCL-compatible hardware. However, as of the time of

this writing (April 28th, 2012), only the nVidia implementation of OpenCL is sufficiently advanced to run it

properly. For best results, a Fermi- or Kepler-based card with at least 2 GB of video RAM is recommended.

Older cards will work, but performance will be significantly worse. Due to the large amount of RAM needed to

compile the OpenCL code, currently it only works in 64-bit builds of V-Ray RT. It may be possible to run the

OpenCL engine on software CPU implementations of OpenCL from AMD and Intel, however this has not been

thoroughly tested.

The CUDA engine is supported only in 64-bit builds of V-Ray RT for Fermi- and Kepler-based nVidia cards. It

is recommended to use the CUDA engine on nVidia GPUs.

Rendering on multiple GPUs is supported and by default V-Ray RT for GPU will use all available

OpenCL/CUDA devices. See the sections below how to choose devices to run V-Ray RT GPU on.

V-Ray RT for GPU has been tested on a number of graphics cards including:

nVidia GeForce 680 GTX;


nVidia GeForce 590 GTX;nVidia GeForce 570;


nVidia Tesla C2050;

nVidia Quadro 2000M;

If V-Ray RT for GPU cannot find a supported OpenCL/CUDA device on the system, it will silently fall back to

CPU code. To see if the V-Ray render server is really rendering on the GPU, check out its console output.

OpenCL run-time compilation

In general, for portability reasons, OpenCL code is compiled at run-time when a program runs (much like

OpenGL shaders written in GLSL and DirectX shaders written in HLSL), as opposed to CUDA code, which isprecompiled in advance and stored in a binary format inside the program executable. This allows the OpenCL

code to be portable and best optimized for the particular hardware on which it runs. The downside is that the

compilation may take a while, depending on the OpenCL code complexity, number of OpenCL devices in the

system, and the OpenCL compiler and driver versions. Luckily, the binary version of the compiled OpenCL

code can be cached and the re-loaded much faster later on.

ay RT and GPU rendering http://help.chaosgroup.com/vray/help/rt100/render_gpu.htm

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The first time you install V-Ray RT GPU and perform a GPU rendering, V-Ray will compile the OpenCL code

for your hardware. This may take anywhere from 30 seconds to several minutes, depending on the number of

graphics cards and driver version. In the V-Ray RT render server console window you will see something like

this:

[ 2010/ Sep/ 6| 21: 05: 44] Runni ng RTEngi ne[ 2010/ Sep/ 6| 21: 05: 44] I ni t i al i zi ng OpenCL render er ( si ngl e ker nel ver si on) . . .[ 2010/ Sep/ 6| 21: 05: 44] Number of OpenCL devi ces f ound: 1

[ 2010/ Sep/ 6| 21: 05: 44] OpenCL devi ce l i st :[ 2010/ Sep/ 6| 21: 05: 44] Devi ce 0: GeFor ce GTX 480[ 2010/ Sep/ 6| 21: 05: 44] VRAY_OPENCL_DEVI CES envi r onment var i abl e not speci f i ed;usi ng al l avai l abl e devi ces[ 2010/ Sep/ 6| 21: 05: 44] cl _nv_compi l er_opt i ons support ed![ 2010/ Sep/ 6| 21: 05: 44] Bui l di ng OpenCL t r ace pr ogr am. . .[ 2010/ Sep/ 6| 21: 06: 34] OpenCL pr ogr ambui l t i n 49. 156 s

The resulting compiled binary code is cached to disk in the temporary folder for the current user. On

subsequent runs, the compilation phase is skipped and the code is loaded directly from the disk:

[ 2010/ Sep/ 6| 21: 46: 54] Bui l di ng OpenCL t r ace pr ogr am. . .

[ 2010/ Sep/ 6| 21: 46: 54] OpenCL pr ogr ambui l t i n 0. 016 s

Such run-time compilation is not required by the CUDA engine and it will start rendering right away.

Choosing which devices to use for rendering

You may not want to use all available OpenCL/CUDA devices for rendering, especially if you have multiple

GPUs and you want to leave one of them free for working on the user interface. To do this, you can use the

supplied GUI tool, which you can find in Start Menu > Programs > Chaos Group > V-Ray RT Adv for 3ds

Max > Select OpenCL devices for V-Ray RT :

After changing tis option, you need to restart the V-Ray RT render server (if it is running) for the changes to

take effect. If the V-Ray RT render server is running as a Windows service, you may need to stop it from the

Services applet in the Control Panel.

Note that the tool determines the devices to use for both CUDA and OpenCL rendering.

Balancing the GPU load


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If you have only one GPU on your system, you may find that the user interface becomes sluggish and

unresponsive while V-Ray RT is rendering on the GPU. To alleviate this problem, reduce the Rays per pixel

and/or the Ray bundle sizeparameters in the Performance section of the V-Ray RT renderer settings in the

3ds Max Render Setup dialog. For example, you can try values like 128/8or 128/4. This will break up the data

passed to the GPU into smaller chunks, so that the user interface requests can be processed faster. Note

however, that this will reduce the rendering speed. Turn on the statistics display to check the difference in

render speed and to find the optimal settings for your system.

Supported features on the GPU

On the GPU, V-Ray uses a simplified version of the V-Ray renderer, which supports only a sub-set of all

features of the CPU code. The features listed below are supported; anything else will likely not work.

Geometry

Triangle meshes and VRayProxy objects are supported. Instancing is also supported - see the Instancing and

Forest Prosupport page.

Lights

Note that even for supported lights, only a sub-set of the light parameters are implemented.

Standard lights: omni, spot, directional;

Photometric lights with web profiles;

VRayLight: rectangle lights with textures, sphere and mesh lights without textures; dome light with

textures (for image based lighting or IBL);

VRaySun;

VRayIESlights with web profiles.

Materials

VRayMtl material: diffuse color, (glossy) reflections, refractions, opacity, bump mapping, Fresnel

reflections;

Multi/sub-object material;VRayLightMtlmaterial (without the direct illumination options);

VRayBlendMtlmaterial (without the additive mode option);

Textures

Bitmap textures, the Falloffmap, the VRayHDRI the VRaySky maps are supported. Other procedural

textures (Checker, Noiseetc.) are supported by baking them, provided that they have Explicit UVW mapping

type. If the Resize textures for GPUoption is turned on, then all textures uploaded to the GPU are resampled

to a resolution specified by the GPU texture sizeparameter in the V-Ray RT settings in the Render Setup

dialog. The Mix and ColorCorrectiontextures are also supported.

Cameras

Standard perspective views; depth of field is not supported for these views;

VRayPhysicalCamerawith support for depth of field and bokeh effects;

Stereoscopic rendering is fully supported on the GPU.

Environment mapping

Only the background texture from the Environment dialog is supported and used for background, GI,

reflections and refractions. Only spherical, mirror ball and angular environment mapping types are supported.

Motion blur

Motion blur is supported, provided that the Motion bluroption in V-Ray RT is enabled and motion blur isenabled in the production renderer or through a physical camera.

Common OpenCL errors


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Below is a list of some common OpenCL errors that you may get in the V-Ray RT render server console:

Err or - 4 at l i ne XXX, i n f i l e . / src/ ocl _tr acedevi ce. cpp ! ! !

This errors means that there is not enough VRAM on the GPU to complete the rendering. You can try one or

more of the following to fix the error:

Reduce the "GPU texture size" parameter in the V-Ray RT settings;

Reduce the "Ray bundle size" and/or "Rays per pixel" parameters in the V-Ray RT settings;

Reduce the amount of geometry in the scene.

References

The official OpenCL web site: http://www.khronos.org/opencl/

The nVidia CUDA developer zone: https://developer.nvidia.com/category/zone/cuda-zone


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v-ray rt and gpu rendering

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