This repository describes an extension to the PBRT implementation of the Stochastic Progressive Photon Mapper (SPPM) that allows it to visualize the light generated by superluminal particles (i.e., particles traveling faster than the speed of light of the medium), typically known as Cherenkov radiation.

In practice, this extension adds a new kind of area light source, called a "particle" light. This light first emits one or more particles during the scene pre-processing stage that are later sampled during rendering of the scene.

Note that this light source has only been tested for SPPM and will not work as expected in any other setting.

A few example scenes based on the Cornell box has been provided: They are available in the scene directory.

The project can be built in the same way as PBRT (as listed below), it is however recommended to enable the PBRT_FLOAT_AS_DOUBLE configuration options as some quantities (such as wavelengths) might be very small and can be clamped to zero in some cases depending on the scene and can thus trigger asserts throughout the code-base.

Additionally, to properly visualize the color of the Cherenkov radiation, make sure to enable PBRT_SAMPLED_SPECTRUM.

To check out pbrt together with all dependencies, be sure to use the --recursive flag when cloning the repository, i.e.

$ git clone --recursive https://github.com/mmp/pbrt-v3/

If you accidentally already cloned pbrt without this flag (or to update an pbrt source tree after a new submodule has been added, run the following command to also fetch the dependencies:

$ git submodule update --init --recursive

pbrt uses cmake for its build system. On Linux and OS X, cmake is available via most package management systems. To get cmake for Windows, or to build it from source, see the cmake downloads page. Once you have cmake, the next step depends on your operating system.

Create a new directory for the build, change to that directory, and run cmake [path to pbrt-v3]. A Makefile will be created in the current directory. Next, run make to build pbrt, the obj2pbrt and imgtool utilities, and an executable that runs pbrt's unit tests. Depending on the number of cores in your system, you will probably want to supply make with the -j parameter to specify the number of compilation jobs to run in parallel (e.g. make -j8).

By default, the makefiles that are created that will compile an optimized release build of pbrt. These builds give the highest performance when rendering, but many runtime checks are disabled in these builds and optimized builds are generally difficult to trace in a debugger.

To build a debug version of pbrt, set the CMAKE_BUILD_TYPE flag to Debug when you run cmake to create build files to make a debug build. To do so, provide cmake with the argument -DCMAKE_BUILD_TYPE=Debug and build pbrt using the resulting makefiles. (You may want to keep two build directories, one for release builds and one for debug builds, so that you don't need to switch back and forth.)

Debug versions of the system run much more slowly than release builds. Therefore, in order to avoid surprisingly slow renders when debugging support isn't desired, debug versions of pbrt print a banner message indicating that they were built for debugging at startup time.

To make an Xcode project on OS X, run cmake -G Xcode [path to pbrt-v3]. A PBRT-V3.xcodeproj project file that can be opened in Xcode. Note that the default build settings have an optimization level of "None"; you'll almost certainly want to choose "Faster" or "Fastest".

On Windows, first point the cmake GUI at the directory with pbrt's source code. Create a separate directory to hold the result of the build (potentially just a directory named "build" inside the pbrt-v3 directory) and set that for "Where to build the binaries" in the GUI.

Next, click "Configure". Note that you will want to choose the "Win64" generator for your MSVC installation unless you have a clear reason to need a 32-bit build of pbrt. Once cmake has finished the configuration step, click "Generate"; when that's done, there will be a "PBRT-V3.sln" file in the build directory you specified. Open that up in MSVC and you're ready to go.

There are two configuration settings that must be set when configuring the build. The first controls whether pbrt uses 32-bit or 64-bit values for floating-point computation, and the second controls whether tristimulus RGB values or sampled spectral values are used for rendering. (Both of these aren't amenable to being chosen at runtime, but must be determined at compile time for efficiency). The cmake configuration variables PBRT_FLOAT_AS_DOUBLE and PBRT_SAMPLED_SPECTRUM configure them, respectively.

If you're using a GUI version of cmake, those settings should be available in the list of configuration variables; set them as desired before choosing 'Generate'.

With command-line cmake, their values can be specified when you cmake via -DPBRT_FLOAT_AS_DOUBLE=1, for example.

• The pbrt website has general information about both the Physically Based Rendering* book as well as many other resources for pbrt. As of October 2018, the full text of the book is now available online, for free.
• There is a pbrt Google Groups mailing list that can be a helpful resource.
• Please see the User's Guide for more information about how to check out and build the system as well as various additional information about working with pbrt.
• Should you find a bug in pbrt, please report it in the bug tracker.
• Please report any errors you find in the Physically Based Rendering book to [email protected].