A black hole ray tracer written in Haskell. There's an article about this on my homepage. I've also written a theoretical writeup on Schwarzschild geodesics.

• Fast, parallel ray tracing
• Rendering Schwarzschild black holes
• Rendering accretion disks
• Drawing the celestial sphere using a star catalogue
• Bloom effect
• Antialiasing by 4x supersampling for smoother images
• Easy, YAML based configuration
• A simple CLI
• Batch mode and sequence generator for creating animations

It is a tribute to David Bowie, referring to his last album.

Use stack to build this. First clone the repo, then run stack build and follow the instructions given by stack. You should be able to build blackstar on any platform where you can install stack.

Alternatively, one can use plain cabal to build blackstar (although this is not recommended due to the various advantages stack gives over cabal). After cloning this repo, proceed with these commands in the root folder of the project:

cabal update
cabal sandbox init
cabal install --dependencies-only
cabal build

It will take a while to build all the dependencies. Currently, the package is meant to be built with ghc-8.0.1.

This repository includes a star lookup tree (stars.kdt), which has been generated from the PPM star catalog. The prebuilt tree in binary form is included for convenience, but you can also build it yourself. First, remove stars.kdt. Download this archive and extract the file PPM to the root folder of this project. Then run stack exec generate-tree PPM stars.kdt and the tree will be generated and saved.

When doing large or batch renders, it is recommended to build blackstar using GHC's LLVM backend. GHC produces LLVM bytecode and LLVM produces fast native code from GHC's output. In my tests I've noticed ~1.5x speedups.

The LLVM backend isn't used by default since one needs to install (and usually build) a specific version of LLVM separately. Moreover, the build time is significantly higher with LLVM, so one doesn't definitely want to use it while hacking on the code.

To successfully build with LLVM, you need to:

• Download and build LLVM 3.7.1. You can skip the Clang parts. After the build, you should make sure the tools llc and opt are found in your PATH. Notice that these aren't included in the prebuilt LLVM binaries, that's why you'll need to build it.
• Build blackstar with stack build --ghc-options -fllvm. (If you've just built it, run stack clean first to ensure it really gets rebuilt with LLVM.)
• Wait patiently
• Enjoy the result!

When blackstar has been built with stack, you can run it with

stack exec blackstar -- [-p|--preview] [-f|--force] [-o|--output=PATH] [-s|--starmap=PATH] SCENENAME

Notice the two dashes (--) which are required to terminate stack's argument list.

cabal users can run blackstar by executing

cabal run -- [OPTIONS] SCENENAME

in the root folder of the project.

Scenes are defined using YAML config files. Look in the scenes folder for examples. To render the default scene to the directory output, run

stack exec blackstar -- scenes/default.yaml --output output

in the root directory of the project. The --output flag specifies the output directory. By default, blackstar searches for a starmap in the path ./stars.kdt, but a different path can be specified using the --starmap flag.

The rendered files are named scenename.png and scenename-bloomed.png. The --preview flag can be used to render small-sized previews of the scene while adjusting the parameters. The --force flag will cause blackstar to overwrite output images without a prompt.

If a directory is given as the input scene path, blackstar searches non-recursively for YAML files in that directory and tries to render them. The scenes are placed in the specified output directory.

There's also a help text which can be seen by running

stack exec blackstar -- --help
OR
cabal run -- --help

Better images can be achieved by rendering larger than the target size and then scaling down (some antialiasing is achieved). This is called supersampling and is implemented in blackstar. It can be enabled by setting supersampling to true in the YAML config file — see scenes/default-aa.yaml for an example.

Thanks to stack, profiling is incredibly easy. Rebuild blackstar by running

stack build --profile

and then run it with

stack exec blackstar -- scenes/default.yaml -o output +RTS -p

The profile will be generated to blackstar.prof.

As always, there's a plenty of room for improvement. For example:

• Document the animator
• Overall better documentation (wiki pages?)
• Binary releases?
• Preview GUI for planning scenes
• GPU acceleration?
• Arbitrary textures for accretion disk?
• Redshifting of the accretion disk?

Pull requests are welcome! If you find some cool scenes, I'd appreciate if you contributed them to this repository.