Rendering Basics

Selecting a Renderer

In Applications based on Omniverse Kit, there is usually an option to select between different renderers or renderer modes.

In Omniverse Create, different renderers or renderer modes are available in a drop-down menu in the Viewport:

Screenshot highlighting the render mode dropdown in |create|

In Omniverse View, you can select between Draft, Preview, and Photo modes, where Draft uses the Omniverse RTX Renderer’s RTX – Real-Time mode, while Preview and Photo uses the RTX – Interactive (Path Tracing) mode, and each modify the Render Settings to balance the quality and performance for the desired experience.

Screenshot highlighting the render mode list in View

For information on modifying renderer settings, see Render Settings Overview.

Multi-GPU Rendering

Omniverse RTX Renderer supports multi-GPU rendering.

Multi-GPU rendering is enabled by default if you must have a system with multiple NVIDIA RTX-enabled GPUs and if they are of the same model.

While the GPUs do not need to be of the same model, uneven GPU memory capacity and performance will result in suboptimal utilization. When you use GPUs with different memory capacities, the GPU with the lowest capacity becomes a bottleneck, preventing you from loading a scene that would fit on the memory of the higher-capacity GPU. In such cases, you may have to remove or disable the low-capacity GPU to avoid this limitation. Similarly, a GPU with lower performance will hold back other GPUs. This will be addressed in a future release with an automatic load-balancing.

To enable multi-GPU even when the GPUs are not of the same model, Omniverse Kit must be launched with the following argument:

`--/renderer/multiGpu/enabled=true`

Note

SLI mode is unstable and should be globally disabled in the NVIDIA control panel for multi-GPU. This will be addressed in future releases.

To set the maximum number of GPUs, add the following argument:

`--/renderer/multiGpu/maxGpuCount`

Note

GPU devices that don’t support ray tracing are skipped automatically.

For additional details on Multi-GPU rendering settings see:

Matte Objects

../_images/matte_objects1.png

The Matte Object post-process allows rendering invisible objects which still receive shadows and secondary illumination (reflections, AO, global illumination), usually used in combination with a textured domelight or a backplate.

Matte Object settings are found in the Post Processing render settings.

The post-process must be enabled to render matte objects. For a mesh geometry to be rendered as a matte object, its Matte Object flag must be enabled.

Debug Views

../_images/common_debug_view_heatmap.jpg

Debug Views are available for various purposes. Some are useful to identify potential areas of optimization in the scene’s content, for example heat maps to correlate frame time spent per pixel, or the number of invoked Intersection or Any Hit shaders per pixel.

For more details on Debug Views, see Debug View render settings.

Arbitrary Output Variables (AOV)

../_images/AOV.jpg

RTX – Interactive (Path Tracing) mode can output Arbitrary Output Variables (AOVs) which are data known to the renderer and used to compute illumination. Typically, AOVs contain decomposed lighting information such as:

  • Direction and indirect illumination

  • Reflections and refractions

  • Objects with self illumination

But they can also contain geometric and scene information, such as:

  • Surface position in space

  • Orientation of normals

  • Depth from camera.

As the final image is computed, the intermediate information used during rendering can be optionally written to disk, providing opportunities to modify the final image during compositing and additional insights through 2D analysis. The auxiliary images, called “passes” in Omniverse and “Render Products” in USD, are just named outputs. The AOV data used by the renderer is referred to as a “Render Variable” and defines what is written for each pass.

If the Optix Denoiser is enabled (true by default) the AOVs will be denoised. There is an option to control this in the RTX – Interactive (Path Tracing)’s Denoising settings.

AOV passes can be enabled for previewing in the RTX – Interactive (Path Tracing)’s AOV render settings and then selected in the Debug View render settings.

Multi Matte

../_images/multimatte.png

RTX – Interactive (Path Tracing) mode supports Multi Matte which extends AOV support by enabling rendering masked mesh geometry to AOVs.

Multi Matte settings are found in the RTX – Interactive (Path Tracing)’s Multi Matte render settings.

The Multi Matte channel count defines the total number of channels available, and each is assigned to a Multi Matte AOV’s color channel (red, green, or blue). Each channel has an index, and Mesh geometry with a matching Multi Matte ID index will be rendered to the first Multi Matte AOV channel found with a matching index.

Each of the resulting Multi Matte AOV can be previewed in the Debug View render settings.

Adaptive Sampling

Example of Adaptive Sampling debug view

RTX – Interactive (Path Tracing) mode supports Adaptive Sampling. With Adaptive Sampling, samples are non-uniformly distributed where most beneficial for further convergence, which can result in less noise for the same number of samples and also provides a more consistent noise level across multiple frames.

Adaptive Sampling can be enabled in the RTX – Interactive (Path Tracing)’s render settings, and its Target Error value can be adjusted there as well, which when reached will stop accumulating more samples.

An Adaptive Sampling Error debug view can be selected in the Debug View render settings, which allows visualizing the normalized standard deviation of the Monte Carlo estimator of the pixels: warm colors represent high variance, which indicate that additional samples would lead to improved convergence for those pixels.

Note that currently Movie Capture does not support ending the rendering of a frame earlier when the Target Error threshold has been reached, but it will be supported in a following release.

MDL Texture Formats Accepted

Extension

Format

Description

.bmp

Bitmap Image File

Common image format developed by Microsoft.

.dds

DirectDraw Surface

Microsoft DirectX format for textures and environments.

.exr

OpenEXR

High Dynamic Range format developed by Industrial Light and Magic

.gif

Graphical Interchange Format File

Common color constrained lossless web format developed by CompuServe.

.hdr

High Dynamic Range Image File

High Dynamic Range format developed by Industrial Light and Magic.

.jpeg

Joint Photographic Experts Group

Common “lossy” compressed graphic format.

.jpg

Joint Photographic Experts Group

Common “lossy” compressed graphic format.

.tif

Target Image File Format

Common “lossless” and “lossy” graphic format.

.png

Portable Network Graphics File

Common “lossless” compressed graphics format.

.psd

Adobe Photoshop Document

The native format for Adobe Photoshop documents.

.tga

Truevision Advanced Raster Graphics Adapter

High Quality raster graphic format developed by Avid Technology |