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Tutorials

ospTutorial

A minimal working example demonstrating how to use OSPRay can be found at apps/tutorials/ospTutorial.c¹.

An example of building ospTutorial.c with CMake can be found in apps/tutorials/ospTutorialFindospray/.

To build the tutorial on Linux, build it in a build directory with

gcc -std=c99 ../apps/ospTutorial/ospTutorial.c \
-I ../ospray/include -L . -lospray -Wl,-rpath,. -o ospTutorial

On Windows build it can be build manually in a “build_directory\$Configuration” directory with

cl ..\..\apps\ospTutorial\ospTutorial.c -I ..\..\ospray\include -I ..\.. ospray.lib

Running ospTutorial will create two images of two triangles, rendered with the Scientific Visualization renderer with full Ambient Occlusion. The first image firstFrame.ppm shows the result after one call to ospRenderFrame – jagged edges and noise in the shadow can be seen. Calling ospRenderFrame multiple times enables progressive refinement, resulting in antialiased edges and converged shadows, shown after ten frames in the second image accumulatedFrames.ppm.

ospExamples

Apart from tutorials, OSPRay comes with a C++ app called ospExamples which is an elaborate easy-to-use tutorial, with a single interface to try various OSPRay features. It is aimed at providing users with multiple simple scenes composed of basic geometry types, lights, volumes etc. to get started with OSPRay quickly.

ospExamples app runs a GLFWOSPRayWindow instance that manages instances of the camera, framebuffer, renderer and other OSPRay objects necessary to render an interactive scene. The scene is rendered on a GLFW window with an imgui GUI controls panel for the user to manipulate the scene at runtime.

The application is located in apps/ospExamples/ directory and can be built with CMake. It can be run from the build directory via:

./ospExamples <command-line-parameter>

The command line parameter is optional however.

Scenes

Different scenes can be selected from the scenes dropdown and each scene corresponds to an instance of a special detail::Builder struct. Example builders are located in apps/common/ospray_testing/builders/. These builders provide a usage guide for the OSPRay scene hierarchy and OSPRay API in the form of cpp wrappers. They instantiate and manage objects for the specific scene like cpp::Geometry, cpp::Volume, cpp::Light etc.

The detail::Builder base struct is mostly responsible for setting up OSPRay world and objects common in all scenes (for example lighting and ground plane), which can be conveniently overridden in the derived builders.

Renderer

This app comes with four renderer options: scivis, pathtracer, ao and debug. The app provides some common rendering controls like pixelSamples and other more specific to the renderer type like aoSamples for the scivis and ao renderer or maxPathLength for the pathtracer.

The sun-sky lighting can be used in a sample scene by enabling the renderSunSky option of the pathtracer renderer. It allows the user to change turbidity and sunDirection.

ospMPIDistribTutorial

A minimal working example demonstrating how to use OSPRay for rendering distributed data can be found at modules/mpi/tutorials/ospMPIDistribTutorial.c².

The compilation process via CMake is the similar to apps/tutorials/ospTutorialFindospray/, with the addition of finding and linking MPI.

To build the tutorial on Linux, build it in a build directory with

mpicc -std=c99 ../modules/mpi/tutorials/ospMPIDistribTutorial.c \
-I ../ospray/include -L . -lospray -Wl,-rpath,. -o ospMPIDistribTutorial

On Windows build it can be build manually in a “build_directory\$Configuration” directory with

cl ..\..\modules\mpi\tutorials\ospMPIDistribTutorial.c -I ..\..\ospray\include -I ..\.. ospray.lib

The MPI module does not need to be linked explicitly, as it is loaded as a module at runtime.

ospMPIDistribTutorialSpheres and ospMPIDistribTutorialVolume

The spheres and volume distributed tutorials are built as part of the MPI tutorials when building OSPRay with the MPI module and tutorials enabled. These tutorials demonstrate using OSPRay to render distributed data sets where each rank owns some subregion of the data, and displaying the output in an interactive window. The domain is distributed in a grid among the processes, each of which will generate a subset of the data corresponding to its subdomain.

In ospMPIDistribTutorialSpheres, each process generates a set of spheres within its assigned domain. The spheres are colored from dark to light blue, where lighter colors correspond to higher ranks.

In ospMPIDistribTutorialVolume, each process generates a subbrick of volume data, which is colored by its rank.

ospMPIDistribTutorialPartialRepl

The partially replicated MPI tutorial demonstrates how to use OSPRay’s distributed rendering capabilities to render data sets that are partially replicated among the processes. Each pair of ranks generates the same volume brick, allowing them to subdivide the rendering workload between themselves. For example, when run with two ranks, each will generate the same brick and be responsible for rendering half of the image tiles it projects to. When run with four ranks, the pairs of ranks 0,1 and 2,3 will generate the same data and divide the rendering workload for that data among themselves.

The image work subdivision happens automatically, based on which ranks specify the same bounding box for their data, as demonstrated in the tutorial.

The partially replicated distribution is useful to support load-balanced rendering of data sets that are too large to be fully replicated among the processes, but are small enough to be partially replicated among them.

ospMPIDistribTutorialReplicated

The replicated MPI tutorial demonstrates how OSPRay’s distributed rendering capabilities can be used to render data sets that are fully replicated among the ranks with advanced illumination effects. In this case, although the processes are run MPI parallel, each rank specifies the exact same data. OSPRay’s MPI parallel renderer will detect that the data is replicated in this case and use the same image-parallel rendering algorithms employed in the MPI offload rendering configuration to render the data. This image-parallel rendering algorithm supports all rendering configurations that are used in local rendering, e.g., path tracing, to provide high-quality images.

The replicated MPI tutorial supports the same scenes and parameters as the ospExamples app described above.

This mode can be useful when high-quality rendering is desired and it is possible to copy the entire data set on to each rank, or to accelerate loading of a large model by leveraging a parallel file system.