VisRTX is an experimental, scientific visualization-focused implementation of the Khronos ANARI standard, and is developed by the HPC Visualization Developer Technology team at NVIDIA.

VisRTX is designed to track ongoing developments of the ANARI standard and provide usable extensions where possible. Prospective backend implementors of ANARI are encouraged to use VisRTX as a much more complete example of a GPU-accelerated, ray tracing based implementation of ANARI.

Note that the ANARI implementation of VisRTX is a complete rewrite from previous versions. Please refer to the v0.1.6 release of VisRTX for the previous implementation.

Please do not hesitate to provide feedback by opening an issue!

VisRTX is supported on both Linux and Windows.

Building VisRTX requires the following:

• CMake 3.17+
• C++17 compiler
• NVIDIA Driver 495+
• CUDA 11.3.1+
• OptiX 7.4+
• ANARI-SDK 0.7.0

Building VisRTX is done through invoking CMake on the source directory from a stand alone build directory. This might look like

mkdir build && cd build
cmake -DCMAKE_INSTALL_PREFIX=path/to/desired/install /path/to/visrtx/source
make
make install

The OptiX and ANARI-SDK dependencies can be found via placing their installation locations on CMAKE_PREFIX_PATH, either as an environment variable or a CMake variable.

The build will result in a single libanari_library_visrtx library that will install to ${CMAKE_INSTALL_PREFIX}/lib, and is usable with any ANARI app if either it is installed to the same location as the ANARI-SDK or libanari_library_visrtx is placed on LD_LIBRARY_PATH respectively.

VisRTX comes with a simple, single-file tutorial application that show how to use VisRTX through the ANARI API. It is always enabled as it only requires the ANARI SDK and compiles very quickly.

VisRTX also comes with an optional interactive example application that gives application developers a sense of what VisRTX has to offer. To enable the interactive example, simply turn on the VISRTX_BUILD_INTERACTIVE_EXAMPLE option in your local CMake build. This can be done with adding -DVISRTX_BUILD_INTERACTIVE_EXAMPLE=ON to the CMake command above, or done with either of the interactive CMake programs (ccmake or cmake-gui).

The interactive example requires GLFW as an additional dependency.

The following sections describes details of VisRTX's ANARI completeness, provided extensions, and known missing extensions to add in the future.

In addition to standard ANARI_KHR extensions, the following vendor extensions are also implemented in the visrtx device. Note that all vendor extensions are subject to change

This vendor extension indicates that raw CUDA GPU buffers from frame objects can be mapped for applications which are already using CUDA. The following additional channels can be mapped:

• "colorGPU"
• "depthGPU"

GPU pointers returned by anariMapFrame() are device pointers intended to be kept on the device. Applications which desire to copy data from the device back to the host should instead map the ordinary color and depth channels.

This vendor extension indicates that additional attribute indexing is available for the triangle geometry subtype. Specifically, the following additional index arrays will be interpreted if set on the geometry:

• vertex.color.index
• vertex.normal.index
• vertex.attribute0.index
• vertex.attribute1.index
• vertex.attribute2.index
• vertex.attribute3.index

Each of these arrays must be of type UINT32_VEC3 and is indexed per-triangle on the geometry where each component indexes into the corresponding index array that matches. For example, vertex.color.index for primitive 0 (first triangle) will load values from vertex.color accordingly. For every .index array present, the matching vertex array must also be present. All index values must be within the size of the corresponding vertex array it accesses.

The following section describes what additional parameters and properties can be used on various ANARI objects.

The device itself can take a single INT32 parameter "cudaDevice" to select which CUDA GPU should be used for rendering. Once this value has been set and the implementation has initialized CUDA for itself, then changing this to another value will be ignored (a warning will tell you this if it happens). The device will initialize CUDA for itself if any object gets created from the device.

The following properties are available to query on ANARIFrame:

The numSamples property is the lower bound of pixel samples taken when the checkerboard renderer parameter (see below) is enabled because not every pixel will have the same number of samples accumulated.

The nextFrameReset property can give the application feedback for when accumulation is about to reset in the next frame. When the property is queried and the current frame is complete, all committed objects since the last rendering operation will be internally updated (may be expensive).

The following extensions are not yet implemented by VisRTX:

• Light: spot, instancing
• Camera: omnidirectional, stereo rendering
• Sampler: image3D
• Frame: variance property
• Core extensions:
  • ANARI_KHR_FRAME_COMPLETION_CALLBACK
  • ANARI_KHR_DEVICE_SYNCHRONIZATION
  • ANARI_KHR_TRANSFORMATION_MOTION_BLUR

For any found bugs in extensions that are implemented, please open an issue!