Contributing to Polykrom

Polykrom is an open-source parametric 3D CAD app written in pure Rust. You sketch on a plane, constrain the sketch, turn profiles into solids, and change a parameter to watch the timeline rebuild. It runs as a desktop app (Windows, Linux), in the browser (wasm + WebGPU/WebGL2), headless from a CLI, and as an MCP server that AI agents can model with.

Help is welcome, whether that’s a one-line fix or owning a whole area. This page covers how to build it, how the code is laid out, the few rules that aren’t negotiable, and where help is needed most.

Polykrom is a fork of SolidCraft. The process below is SolidCraft’s; for Polykrom, open issues and PRs on wckdboy/polykrom, and send fixes that also apply to SolidCraft upstream under its own rules.

Before choosing a task, check the command inventory and roadmap for implemented capabilities and current priorities.

Questions, ideas or want to say what you’re working on? Join the Discord.

Kernel work is paused

We’re evaluating a new geometry kernel. Until that’s decided, please don’t open issues, pull requests or discussions about kernel work: booleans, fillets, chamfers, shell, offsets, sweeps and lofts, threads and holes, STEP/IGES import and export, tessellation, or anything else that changes crates/kernel/. The pinned issue on the tracker explains it. New ones get the kernel-paused label (.github/workflows/kernel-paused.yml) and a maintainer answers them. Crashes and data loss are still taken as issues, and everything outside the kernel carries on as normal.

Get it running (about 10 minutes on a fast machine)

You need stable Rust 1.95 or newer (required by egui/eframe 0.36). For the web build you also need rustup target add wasm32-unknown-unknown and trunk (documentation).

git clone https://github.com/wckdboy/polykrom && cd polykrom
cargo run --release -p solidcraft -- --sample      # desktop app with a sample part
cargo xtask test                                   # unit, engine and UI-scenario tests
cargo xtask ci                                     # everything a PR must pass (see below)

Polykrom is the product, repository, Cargo package and executable name. Build the desktop app with cargo build --release -p solidcraft, or the CLI with cargo build --release -p solidcraft-cli. Run the CLI with cargo run --release -p solidcraft-cli -- commands (or target/release/solidcraft-cli commands after building). The old name appears only in the compatibility shims listed in docs/compatibility.md; don’t add new uses of it.

Web: cd apps/solidcraft-web && trunk serve --release, then open the printed URL (?sample opens the sample part, ?webgl forces WebGL2). Saving and opening files in the browser needs HTTPS or localhost, because it uses the Origin Private File System.

Windows from Linux: cargo xwin build --release --target x86_64-pc-windows-msvc -p solidcraft.

NixOS: nix develop

NixOS has no /usr/lib, so nothing is on LD_LIBRARY_PATH and a plain cargo run finds none of the libraries the app loads at run time: the Wayland ones winit opens the window through, the EGL loader wgpu renders through, and libdbus-1, which rfd’s file dialogs reach xdg-desktop-portal through (a dialog then never appears and the pick returns no path):

ERROR solidcraft: winit EventLoopError: ... The wayland library could not be loaded
ERROR eframe::native::run: Exiting because of error: WGPU error: Failed to create surface for any enabled backend: {}
ERROR rfd::backend::xdg_desktop_portal::portal::libdbus: Can't connect to a portal: libdbus-1.so not found

nix develop (the flake.nix in the repository root) supplies Wayland, X11, EGL, Vulkan-loader and D-Bus runtime libraries. It also exposes the NixOS driver manifests in /run/opengl-driver/share, so Vulkan can discover the system drivers. Enable hardware.graphics.enable on NixOS; other Linux distributions may need a matching nixGL wrapper. The default development shell retains the Rust/C toolchain already on PATH; nix develop .#rust supplies the pinned toolchain and builds in target/nix.

To launch, use nix run .#solidcraft -- --sample. To install the app’s terminal commands, desktop entry and generated icons, use nix profile install .#solidcraft. nix build alone creates a build result; it does not install a launcher in your desktop menu. The installed solidcraft command runs the wrapped app; solidcraft-cli is included as well. See Nix installation and troubleshooting for remote-flake commands, desktop integration and how to distinguish an old executable on PATH.

How the code is laid out

The architecture page has the layer table. The short version:

• crates/geom: vectors, planes, meshes, measures.
• crates/sketch: our own constraint solver, plus profile finding.
• crates/kernel: the B-rep kernel boundary. It wraps truck, and it’s the only crate allowed to touch truck. Fillets, chamfers, shell/offset, Delete Face, Split Face, STEP/IGES read and write, and face provenance are our own code here. Patched copies of three truck crates live in vendor/ and are excluded from our fmt/clippy rules.
• crates/doc: the document. It holds parameters and expressions, the feature timeline and its incremental rebuild, components and occurrences, joints, appearances, and persistent naming.
• crates/io: design files and mesh formats (3MF, STL, OBJ).
• crates/engine: the session and the command registry. Everything the user can do is a command, and the toolbar, dialogs, scripts, CLI, control channel and MCP all run the same commands.
• crates/ui-egui: the desktop/web front end (egui + wgpu). It’s swappable; nothing below it depends on egui.
• crates/mcp, apps/solidcraft, apps/solidcraft-cli, apps/solidcraft-web.

cargo xtask layers fails the build if a lower layer depends on a higher one.

Rules that aren’t negotiable

1. Independent. Polykrom is independent. Behaviour is designed from public documentation, general CAD conventions and user feedback. Reference tests use analytic values and open-source tools. We don’t drive, script, automate or extract data from commercial CAD products, and we never copy another product’s code, icons, artwork, help text, tooltips, templates or materials. Command ids are our own (solid.fillet).
2. No GPL/LGPL/AGPL code, not even reading it. That rules out OpenCASCADE, FreeCAD (including planegcs), SolveSpace, CadQuery/OCP, LibreCAD and QCAD. Polykrom is MIT OR Apache-2.0, and its solver and blends are written from the maths. (Running an open-source application to get reference values for a test is fine; reading its source is not.) Permissive dependencies are fine. Note which one you’re adding and why in the PR. THIRD-PARTY-LICENSES.txt lists it once the change lands: the Generated files workflow rewrites it on main. Nightly/manual CI also scans advisories, bans and sources with cargo-deny; see the local command and coverage limits.
3. Every asset is original or openly licensed and has a row in ATTRIBUTION.md. Icons are drawn in code (crates/ui-egui/src/icons.rs). cargo xtask assets enforces this.
4. Never crash. People trust a CAD app with their work.
   • Non-test code never uses unwrap, expect, panic! or indexing on input-derived data. There’s no unsafe outside apps/solidcraft/src/open_documents.rs (macOS file-open events), apps/solidcraft/src/native_crash.rs (Windows native crash capture) and crates/threedx-client/src/macos.rs (the 3Dconnexion driver’s client API on macOS), and the compiler denies it.
   • An unsupported case returns an error (“not supported yet: …”); it never panics.
   • Every call into truck goes through solidcraft_kernel::guard.
   • Every crash fix comes with a regression test.
5. Everything is a command, with a test. A new feature means a CommandSpec in crates/engine/src/cmd/, engine tests that measure the result (volume, area, face/edge/vertex counts against a value you can derive), and for UI work a scenario (below).
6. One set of camera controls. Every page or canvas that shows a view (the modelling viewport, the Render preview, and any new page such as a flat pattern or drawing) calls navigation::handle (crates/ui-egui/src/navigation.rs) for its camera input, with NavCaps saying whether it can orbit (off for flat 2D pages) and pick. New canvases must use navigation::handle; never read drags, the wheel or pinch to move the camera yourself. The hand_rolled_camera_input_is_rejected test fails if a page does.

Labels, parameter docs, messages and docs use the terms in the glossary: one term for each idea. A change that adds a new idea adds its term there.

AGENTS.md has the long form of these rules. It’s written for AI agents, but it’s the most complete description of the house style.

Tests

A geometry change that changes the robustness goldens re-records them in the same pull request: ROBUSTNESS_GOLDENS_BLESS="why it changed" cargo test --profile ci -p solidcraft-engine --lib robustness_goldens:: (see docs/robustness.md); CI runs every seed on pull requests that touch geometry. docs/mutation-testing.md shows how to find kernel behaviour these black-box suites miss.

UI scenarios drive the real app headless: start a tool, click a plane or a sketch point, press keys, then assert on the result.

[
  {"start": "sketch.create"},
  {"click": {"plane": "XY"}},
  {"start": "sketch.rectangle.two_point"},
  {"click": {"sketch": [0, 0]}},
  {"click": {"sketch": [40, 30]}},
  {"expect": {"errors": 0}}
]

A new .json file in that folder is picked up automatically. To record a bug before it’s fixed, put {"pending": "why"} in the scenario, and remove it in the PR that fixes the bug.

A failing test without its fix can’t merge as-is: it would turn main’s CI red for everyone. Either include the fix in the same PR, or mark the test #[ignore = "fails until #123 is fixed"] (it can then merge right away), and remove that line in the PR that fixes the bug.

Use the ci profile. CI runs the tests with --profile ci: light optimisation, line tables, no LTO, and debug assertions off (truck has debug-only assertions that reject valid geometry). It builds several times faster than --release. If a test fails only in a plain debug build, say so in the PR. cargo xtask test builds the tests with it and then runs every test binary at once (cargo test runs them one after another); arguments after -- go to each binary, e.g. cargo xtask test -- shell. Tests run beside each other on a busy machine, so a test must not depend on wall-clock timing.

Ready pull requests test what they touch. CI maps changed files to workspace packages and runs Clippy, the test build and tests for those and their dependents. The package selector and CI workflow define which changes require native checks; documentation, packaging, other-workflow and bot-script-only changes run the repository checks only, on pull requests and on main. Workspace-wide changes, merge-queue groups, nightly runs and Run workflow select the full workspace. A push to main reuses a successful merge-queue run for the same commit, and runs only the repository checks when no code changed since the last push to main that passed; otherwise it runs the full suite. Doc tests, reference tests and the Windows jobs run on main and nightly only.

CI shards the tests. One job builds them into a cargo-nextest archive; two shards run on pull requests and four during full validation. Every test runs in its own process: don’t rely on state left by another test. Pull requests skip a few heavy tests (one to twelve minutes each), which run in full validation (the merge queue, nightly, manual runs and pushes to main not already tested by the queue). Check that validation after merging. They are listed in .config/nextest.toml and the testing page:

• solidcraft-engine: tests::hostile_params_never_panic, everything in tests::robustness and the seeds of tests::robustness_goldens (seed_00 … seed_95; pull requests that change the kernel, truck or the goldens run all but the slowest, SLOW_SEEDS in ci.yml), pattern_suppress_tests::enclosure_arc_extinction_keeps_a_real_sharp_inner_lip_after_resize_and_reopen, pattern_suppress_tests::enclosure_datums_follow_wall_height_and_board_depth_with_material_proofs, cmd::plastic::tests::enclosure_snap_fit_follows_resized_front_wall, the atomic_commands contract tests
• solidcraft-kernel: tests::boolean_identity_on_tangent_primitives, tspline::tests::hostile_tsplines_never_panic, and the boolean_props property tests (these run only in the nightly “Property tests” job: their inputs are random, so main skips them too)
• solidcraft-ui-egui scenarios: acceptance_sensor_enclosure

The action matrix tries every ordinary action on every face, edge, vertex and body of a corpus of designs against a checked-in ratchet (docs/action-matrix.md). A pull request that makes an action pass should record it with cargo xtask action-matrix --bless; one that makes a passing action fail fails the sample every CI run checks.

The reference tests live in tests/oracle/, each a recipe.json in our own format with an expected.json beside it. Polykrom rebuilds the recipe and compares body count, volume, area, centre of mass and bounding box (and, where there is a reference.stl, the surface itself). Expected values are either worked out in closed form (tools/oracle-analytic/) or computed by building the same recipe in FreeCAD, run as a separate program (tools/freecad-oracle/); each file says which. The generated reference test report has the current case count and results. The reference-test CI job runs cargo xtask oracle during full validation; pull-request runs skip it. A case that fails because of a known bug names its issue in expected.json ("known_failure": "#123"); never change an expected value to match Polykrom’s output.

Changing the design file format

A design file says which format it is in ("format": "solidcraft/N"). If your change saves something new in a design (a field, a feature type, a new kind of name), or makes older designs mean something else, it needs a format change. Add one file, and edit nothing shared:

1. Create crates/doc/src/format/pending/<what-it-is>.rs (lowercase, dashes). Start it with a //! note: what is saved, what older designs get without it, and that the last release asks for an update instead of meeting it.
2. If older designs must be rewritten as they open, put pub fn step(v: &mut Value) -> crate::Result<()> in the same file. Pending steps run in file-name order, after the older formats’ steps.
3. Don’t touch FORMAT, JSON_STEPS, the history in crates/doc/src/format.rs, another change’s file, or any v<N>/ folder: those are fixed once released.

That’s all. The build counts the files: while any are pending it writes the next format number, which no release reads, so a release refuses a design that has your change instead of losing it. A file also lists the pending changes it has (format_pending), so a later development build runs only the steps that file is missing. Two pull requests that each add a change merge without a conflict. crates/doc/src/format/pending/README.md has an example.

At release time the maintainer runs scripts/fold-format-pending.sh, which moves the pending files into crates/doc/src/format/v<N>/ and fixes that number for good (see docs/releasing.md). Never add a file to a v<N>/ folder afterwards.

Lists many changes add to

Some files gain an item in many pull requests at once. They are kept so that two changes that each add an item only meet when their items are neighbours, which spares everyone a conflict and a fresh CI run:

• Message catalogs (assets/locales/*.json): one message per line, sorted by id. Add your message anywhere and run cargo xtask lists --fix; cargo xtask lists (in cargo xtask ci and the Lists workflow) fails on an unsorted catalog or an id that appears twice.
• mod lines: one per line, in the sorted group they belong to (cargo fmt keeps each group sorted). Add a new module into the existing group, not as a new group at the end.
• Languages (crates/ui-egui/src/i18n.rs): one per line, English first, then by id (a test checks it).
• Generated files: THIRD-PARTY-LICENSES.txt and docs/features.md are rewritten on main after each merge by the Generated files workflow (cargo xtask licences, cargo xtask features). Don’t regenerate or edit them in a pull request.
• Design format: one file per change, never an edit to a shared number (above).

Sending a change

1. Work is tracked in GitHub issues, labelled by area (area:kernel, area:sketch, area:doc, area:ui, area:infra). For anything bigger than a bug fix that has no issue yet, open one first. Claim the issue with a draft PR before you start, so two people don’t build the same thing:
   • Check nobody has it: gh pr list -R tangency-labs/solidcraft --state open --search "#N".
   • Branch from the latest main, commit git commit --allow-empty -m "claim: #N", push, and open a draft PR titled <summary> (#N), e.g. Fillet: variable radius along a chain (#123).
   • The lowest-numbered open PR for an issue wins. If yours lost, close it (or offer to help on the other one).
   • The bot records the claim when the PR is opened: it assigns you, adds in progress and says so on the issue. It reads #N in the PR title and Fixes #N in the body. If someone already holds the issue, or an older open PR references it, it says so on your PR instead.
   • Want to stake a claim before you have a branch? Comment /claim on the issue (below).
   • Push work in progress at least daily. A draft with no pushes for 72 hours may be taken over: comment on it first, then open your own claim.
   • Mark the PR ready for review when it is done.
2. Branch from main and keep the PR to one topic.
3. Run cargo xtask ci before pushing. It runs fmt, the asset, licence and layer checks, clippy (-D warnings), then the tests with the wasm build check alongside. A PR has to pass it. Heavy CI runs after review: a pull request gets the formatting and repository checks and a quick compile (cargo check) when you push. Once a maintainer has reviewed it they add the approved-for-ci label when the PR is ready to merge, which runs the full CI (build, tests, goldens, Clippy); every push after that runs the full set again. Maintainers merge approved PRs in groups by area, so PRs that touch the same code meet a conflict at most once.
4. Reference the issue (Fixes #12). In the PR, say what you tested and how. For geometry work, include the measured numbers (and the expected ones).

Commenting /claim assigns you, adds the in progress label, and replies with its automatic cleanup deadline. It frees a claim with no linked PR after 72 hours, or a claim with a PR after 14 days without pushes. These automatic cleanup deadlines are separate from the daily progress and 72-hour takeover policy above. A draft PR that references the issue claims it the same way. /unclaim releases the bot claim early (only you or a maintainer can). Issues a maintainer has taken are never freed automatically.

Help reviewers see what the words mean. For observable CAD, UI or model behavior, please include actual descriptive screenshots or a short recording in the issue or PR. This evidence is required for changes or bugs that can be demonstrated in the app, including kernel, geometry, assembly and backend work. Coding agents should run a small reproduction and capture the evidence themselves; please don’t ask a human for evidence the agent can produce. Show the actual failure or result, preferably before and after, with brief steps and expected/actual behavior. An arrow or annotation can help identify the detail that matters.

Flowcharts and Mermaid diagrams cannot replace evidence of visible behavior. Diagrams are useful for architectural reasoning when actual screenshots cannot illustrate the point. Changes with no useful observable behavior do not need screenshot or video evidence. Use a small example without private designs or sensitive details; attach the media or link to an accessible recording rather than committing generated review artifacts.

Keep an eye on your PR’s status, but don’t push to it only to catch up with main (no merge of main, no Update branch button, no rebase for that alone): every push restarts the whole CI run for everyone waiting behind it, and main‘s own run catches what lands in between. When you push a change anyway, or GitHub reports a conflict, rebase onto the latest main (push your branch with --force-with-lease) or merge main in once, and resolve conflicts without losing others’ changes. Don’t re-run CI on an unchanged commit either: a real failure fails again. Re-run only a job that runner trouble cancelled, with “Re-run failed jobs”. While a task remains active, follow an open PR through its status changes; at handoff, clearly identify anything still awaiting merge.

Much of Polykrom so far was written by AI coding agents (Claude) working in parallel, each owning one area, with a human setting direction and reporting bugs. Their working notes are in AGENTS.md. Human contributors are just as welcome. Use whatever tools you like, as long as the change meets the rules above.

Labels and triage

The triage bot labels every new issue and PR (.github/workflows/triage.yml). It only adds labels; correct them freely and it won’t put them back.

• PRs get area:* from the paths they change (crates/kernel and crates/geom → area:kernel, crates/ui-egui and the apps → area:ui, .github/, scripts/, docs/ → area:infra, and so on).
• Issues get bug (in-app reports and the bug template), enhancement (feature requests), priority:P1 for crashes, and an area:* from the title or the reported command. Until it has a priority, an issue carries needs-triage; setting a priority removes it.
• Maintainers comment /triage area:kernel P1 (any existing label; P0–P3 for a priority, which replaces the old one; -label removes one) to sort an issue or PR.
• Short bug reports without steps to reproduce get needs-info and one comment asking for the steps (and the version, when it’s missing). An app report that arrived empty is asked to paste the report the app copied to the clipboard. The reporter’s reply, or an edit that adds the steps, removes the label; an issue that stays in needs-info for 14 days is closed, and can be reopened any time. Feature requests, app reports with their details, and maintainers’ issues are never asked.
• needs-triage is the queue: open issues with it.

Where help is wanted most

Kernel speed (slow fillets, booleans, STEP): please don’t rewrite the current kernel code for speed; it is being replaced by solidcore (progress). Report slow cases with a file under the kernel-perf label, and put kernel effort into solidcore instead. See #1597.

See the help wanted and good first issue labels. In order of how much they’d help users:

1. Fillet and blend robustness. Fillets are our own code (truck has no fillet operation). Constant, variable-radius and chord fillets work, and so do corners where fillets of different radii meet, including three rounds meeting at a vertex. Next are setback corners, fillets along curved edges between curved faces, and fillets that consume neighbouring faces.
2. Boolean robustness. A random-design fuzzer currently gets about half of its designs through without a kernel error. Each failing seed is a reproducible bug.
3. Drawings, CAM and mesh tools. These are out of scope for now (see ROADMAP.md), but anyone who wants to own one is welcome.

Updating the generated feature list

After adding or renaming commands, run cargo xtask features. The registry is the source of truth for docs/features.md; do not hand-edit the generated rows. The generator sorts commands by ID and omits global and per-section counters, so additions to unrelated areas no longer rewrite shared summary lines.

If two branches still conflict in this file (for example, adjacent additions in the same area), first resolve the command registry and source conflicts, then run cargo xtask features again and stage the regenerated file. Do not use Git’s union merge driver: it can silently retain stale or duplicate command rows. The generator tests cover stable ordering and additions that leave existing lines unchanged. The initial switch to sorted rows is a one-time larger diff.

Licence

By contributing you agree that your contribution is licensed as MIT OR Apache-2.0, like the rest of Polykrom. Polykrom isn’t affiliated with any CAD vendor; product names are trademarks of their owners (see NOTICE).