space_sim

A from-scratch space-sim renderer in C++20. Runs at 60fps on Metal, boots in milliseconds, no engine.

"The whole point of programming used to be how satisfying it felt. I'm trying to remember." — probably

Screenshot

Purple-and-green nebula, plasma sun with fresnel limb-brightening, corona + god rays, volumetric gas shell, 12 000 parallax-dust specks, bloom post-process, procedural lens flare, all driven by a seed string you typed at the command line.

Build & Run

cmake -S . -B build
cmake --build build -j
./build/new_privateer

That's it. It works on any macOS with a Metal GPU.

# Try different stars (hot-swap with 1..6 at runtime too):
./build/new_privateer --star blue
./build/new_privateer --star red    --seed sector_4774
./build/new_privateer --star purple --seed troy_rich

Controls

key	action
mouse	look (pointer captured FPS-style)
right-click	toggle pointer capture
W / S	throttle forward / reverse
A / D	strafe left / right
Space / L-Shift	thrust up / down
Tab (hold)	cruise engine — 10× thrust + FOV widen
X	full brake
1..6	swap star (yellow / blue / red / green / orange / purple)
Esc ×2	quit (double-tap within 1s)

Generate your own skybox

# Any string is a valid seed. Presets: --rich / --sparse / --wild.
tools/gen_skybox.sh my_cool_system --rich

# Pick specific nebula colors:
tools/gen_skybox.sh purple_haze --rich --nebula-colors "0.55,0.15,0.85;0.2,0.75,0.3"

./build/new_privateer --seed my_cool_system

Requires skyboxgen built next to this repo (or set SKYBOXGEN=/path/to/skyboxgen).

What's in here

Layer	Lines	Notes
Procedural skybox cubemap	skybox.{h,cpp} + skybox.glsl	loads 6 PNGs, flips faces to match D3D/Metal convention, draws with CLAMP_TO_EDGE so seams don't bleed
6-DOF flight + cruise engine	camera.{h,cpp}	exponential damping, smooth cruise windup/windown, FOV widens on engage
Plasma sun	sun.{cpp,glsl}	animated fBM granulation, limb-brightening (not darkening — stars are optically thick emitters)
Gas shell	sun_gas.{cpp,glsl}	noise-ring billboard that hugs the silhouette, breaks the hard sphere boundary
Corona + god rays	sun_corona.{cpp} + sun_glow.glsl	procedural sunbeams, aspect-corrected anamorphic streaks
Stellar presets	star_presets.{h,cpp}	6 "star types" differing in color, granulation contrast, flow speed, corona size
Parallax dust	dust.{cpp,glsl}	12 k GL_POINTS, wrapped in the vertex shader to feel infinite
Bloom + lens-flare post	postprocess*.cpp + post_*.glsl	two-pass separable gaussian at quarter-res, procedural flare tracking sun NDC
On-screen HUD	sokol_debugtext	speed / mode / distance / position / controls

Total ≈ 1 700 lines of project code. No engine, no ECS, no asset pipeline.

Toolchain

Layer	Tool	Why
Language	C++20	matches skyboxgen
Build	CMake 3.20+	boring, universal
Window/Input	sokol_app	Metal on Mac, GL/D3D elsewhere
Renderer	sokol_gfx	modern command-buffer API
Text HUD	sokol_debugtext	6 built-in bitmap fonts
Images	stb_image	one header, zero config
Math	HandmadeMath	vec/mat/quat, single header
Shaders	GLSL → sokol-shdc → MSL/SPIR-V/HLSL	write once, run everywhere

All dependencies live as single-header files in third_party/. No package manager, no submodules, no vcpkg.json.

Layout

.
├── src/                C++ sources
├── shaders/            GLSL (cross-compiled to MSL/SPIR-V/HLSL at build time)
├── assets/skybox/troy/ Default skybox (generated reference)
├── third_party/        single-header libs + sokol-shdc binary
├── tools/              shell helpers: gen_skybox.sh, ...
└── CMakeLists.txt

Roadmap

• Procedural skybox (seed → 6 PNGs) with color + nebula tuning
• Mouselook camera, 6-DOF flight, cruise engine
• Plasma sun with corona, gas shell, god rays, stellar presets
• Parallax dust
• Bloom + procedural lens flare
• On-screen HUD
• Asteroid field (instanced, LOD billboards at distance)
• Mesh loader (glTF) + a placeholder ship
• Volumetric nebula gas clouds (raymarched 3D noise)
• Audio (sokol_audio — engine whoosh, ambient drone)
• HUD overlays, targeting, weapons
• Missions, factions, trade, the actual game

Credits

• Andre Weissflog for sokol — the spine of this whole project.
• Sean Barrett for stb_image and forever reminding us what a good header looks like.
• Chris Roberts & the Digital Anvil team for Freelancer (2003), which is still the benchmark 22 years later.

License

MIT. See LICENSE if you see one — otherwise assume MIT and go wild.