A program for modelling a two dimensional galaxy based on the density wave theory. This repository contains the source code for an article at beltoforion.de about simulating a galaxy with the density wave theory.
For more details please read the articles:
- https://beltoforion.de/en/spiral_galaxy_renderer [english]
- https://beltoforion.de/de/rendern_von_spiralgalaxien [german]
A typescript implementation of this code is available here:
An online demo of the typescript version can be viewed here:
The output of the C++ version is virtually the same.
Here is a selection of galaxies created by the algorithm:
The project is built with CMake (3.16+) and a C++17 compiler. It depends on
SDL2, SDL2_ttf, GLEW and OpenGL. Dear ImGui is
fetched automatically by CMake, and glm is bundled in
dependencies/.
Install the dependencies:
- Linux (Debian/Ubuntu):
sudo apt install cmake libsdl2-dev libsdl2-ttf-dev libglew-dev - macOS (Homebrew):
brew install cmake sdl2 sdl2_ttf glew - Windows (vcpkg):
vcpkg install sdl2 sdl2-ttf glewand configure with the vcpkg toolchain file.
Then configure and build:
cmake -S . -B build
cmake --build build
The executable is written to build/ and the assets/ folder (fonts) is copied next to it, so run
it from there:
cd build
./galaxy_renderer
To stage a portable copy (binary + assets + presets) in dist/:
cmake --build build --target dist
On Linux, to additionally package that into a self-contained dist/Galaxy_Renderer-x86_64.AppImage
(fetches linuxdeploy on first run):
cmake --build build --target appimage
With the MinGW-w64 toolchain installed (sudo apt install g++-mingw-w64-x86-64), a portable
Windows build (exe + DLLs + assets + presets) can be staged in dist/windows/ with:
./packaging/build-windows.sh
Windows builds of SDL2/SDL2_ttf and the GLEW sources are downloaded automatically on first run and
cached in dependencies/windows/.
All parameters can be edited live through a Dear ImGui control panel (sliders, checkboxes,
combo boxes and buttons). Press [F1] to show or hide the panel. The classic keyboard shortcuts
still work as well (e.g. [F2] axis, [F3] dust, [+]/[-] zoom, [Space] pause, the numeric
keypad for the predefined galaxies).
Galaxy configurations are stored as plain text files. The presets shipped with the application live
in the presets/ folder next to the executable; your own saves go to the per-user data directory
(~/.local/share/beltoforion/GalaxyRenderer/presets/ on Linux,
%APPDATA%\beltoforion\GalaxyRenderer\presets\ on Windows). A user preset with the same name
overrides a shipped one. Presets can be selected, saved and overwritten from the Presets section
of the control panel.
The renderer can export its animation as an H.264 encoded MP4 video. The video is rendered into an offscreen framebuffer whose resolution is independent of the window size, so you can record 4K (or higher) footage on a normal desktop. The raw frames are piped to ffmpeg for encoding, so ffmpeg must be installed and available in the search path.
- Press [F7] (or use the Video Export section of the control panel) to start and stop the
recording. The video is written to a file named
galaxy-YYYYMMDD-HHMMSS.mp4in the current working directory. - The default video resolution is 3840x2160 (4K UHD) at 60 fps. It can be set in the control panel or on the command line:
./galaxy_renderer --video-size 1920x1080 --video-fps 30
Notes:
- One simulation step is recorded per video frame, so the exported video plays back the evolution of the galaxy at a fixed rate independent of how fast your machine renders.
- Text overlays (help screen, axis labels) are not part of the video; use [F2]/[F6] etc. to choose which visual elements (axis, density waves, dust, ...) are included.
- Recording 4K footage is demanding. If recording is slow, this only affects the time it takes to record - the resulting video always plays back smoothly at the selected frame rate.
The renderer requires OpenGL 3.3. On old systems or GPUs whose driver does not advertise it, the Mesa version override may help (Linux):
MESA_GL_VERSION_OVERRIDE=3.3 MESA_GLSL_VERSION_OVERRIDE=330 ./galaxy_renderer