3DM

A web app that generates and renders complex 3D fractals in real time using GPU raymarching on WebGPU.

The fractal is rendered entirely on the GPU: a single fragment shader sphere-traces a distance-estimated Mandelbulb, shades the hit with an orbit-trap palette, ray-marched soft shadows and ambient occlusion, and composites under an egui control panel. The CPU only owns the camera and the parameter set.

3DM rendering a detailed Mandelbulb scene

3DM is in an early development phase, not ready for use.

Milestone 2 — the hybrid formula stack.

A fractal is an ordered stack of formulas, each applied inside a single escape-time iteration over a chosen range of iterations. The distance estimator is generated from the stack (src/render/codegen.rs) and the compiled pipeline is cached per stack structure, so parameter and iteration-range edits never trigger a shader rebuild — only adding, removing or reordering formulas does.

Formulas: Mandelbulb, Juliabulb, Mandelbox, Sierpinski (kaleidoscopic IFS) and a Rotate transform. Up to six slots.

Working:

• Hybrid formula stacks with per-formula parameters and iteration ranges
• Automatic choice of logarithmic vs linear distance estimator, with an override
• Sphere tracing with a pixel-sized, distance-adaptive hit threshold, so detail holds at any zoom instead of dissolving as you approach the surface
• Orbit / pan / dolly camera, with a reduced-quality preview while dragging
• Cosine-palette colouring driven by the orbit trap, soft shadows, AO, specular, glow and distance fog — all live
• Headless PNG rendering (examples/still.rs)
• Debug views that render one shading term on its own

Escape-time formulas (Mandelbulb, Juliabulb) produce a distance estimate close to the true distance. Folding formulas (Mandelbox, Sierpinski) produce a valid lower bound that can underestimate by two orders of magnitude.

Anything that compares against a distance therefore has to be told how loose the estimate is, or it silently misbehaves on half the formulas. de_tightness() in fractal.wgsl samples this at the shading point and scales the shadow march by it. Without that correction the folding fractals report their own surface as occluding and render black — which they did.

Not built yet: presets and project files, animation, more formulas.

A WebGPU browser — recent Chrome or Edge, or Safari 26+. There is no WebGL fallback; the renderer is too shader-heavy for one to be worth maintaining.

Development server with hot reload:

trunk serve

Then open http://127.0.0.1:8080.

Production build into dist/:

./build-release.sh

dist/ is a static bundle — serve it from anywhere. Enable gzip or brotli on the server; the wasm is ~6.9 MB raw but ~2.7 MB gzipped.

The app also builds natively, which is the fastest way to iterate on the renderer without a browser in the loop:

cargo run

Renders one frame straight to a PNG with no window and no browser — useful over SSH, in CI, and for checking shader changes:

cargo run --example still -- out.png 1920 1200

It takes a demo stack as a fourth argument — mandelbulb, juliabulb, mandelbox, sierpinski, hybrid or rotbox:

cargo run --example still -- box.png 1280 800 mandelbox

DM3_ISOLATE disables one shading term at a time, which is how the issue above was narrowed down. Values: flat, noao, nofog, noglow, noshadow, amb0, amb1, safede, bigbail, grey, softk.

DM3_ISOLATE=amb0 cargo run --example still -- direct.png 640 480 mandelbox

Production runs on Fly.io as app 3dm in yyz, serving the static bundle from a Caddy container.

fly deploy

The Dockerfile builds the wasm from source, runs wasm-opt -Oz over it, and precompresses everything with gzip and brotli so Caddy can serve .br/.gz directly instead of compressing per request. Content-hashed assets are cached forever; index.html is always revalidated so a deploy takes effect immediately.

Machines auto-stop when idle (min_machines_running = 0) — a static bundle has no state to lose, so there is nothing to pay for between visits. force_https is on because WebGPU only works in a secure context; the app is dead over plain HTTP.

Useful checks:

fly logs
fly status
fly open

Every colour in params.rs is linear, not sRGB. A background of 0.005 is near-black on screen, not a dark grey. The shader applies the sRGB transfer curve itself only when the surface format is linear (encode_srgb), since a *Srgb surface format has the hardware do it.

• Trunk's built-in wasm-opt step fails against Homebrew's binaryen, so index.html sets data-wasm-opt="0" and build-release.sh runs wasm-opt itself. --no-sri goes with it, because rewriting the wasm after Trunk has hashed it would break sub-resource integrity.
• Do not set strip = true in the release profile: the resulting wasm fails binaryen's validator.

Copyright (c) 2026 Andre Paquette

3DM is licensed under the GNU General Public License v3.0 or later — see LICENSE.

The fractal formulas are derived from Mandelbulber2 (© Mandelbulber Team, GPL-3.0), whose OpenCL formula sources are translated to WGSL by tools/mb2-transpile. That makes 3DM a derivative work, which is why it carries the same licence.

Practical consequence: the web build ships a .wasm to every visitor, and that counts as distribution. If you deploy 3DM publicly you must offer the corresponding source to your users. Keeping the repository public, and linked from the app, satisfies this.