DarkRoom/docs/windows.md

DarkRoom — A Windows installer from the Linux CI

Satisfies: FR-PLAT-WIN-1 · FR-PLAT-WIN-2 · FR-PLAT-WIN-3 · NFR-COMPAT-2 (a stated channel) Companion to: distribution.md · requirements.md §3.8, §4.4 · android-signing.md

Spec for producing DarkRoom-<version>-x86_64-setup.exe from the same Gitea runner that builds the Arch package and the APK, with no Windows machine in the loop. It names the toolchain, what the tree has to change to compile for the target, what the installer does, how the CI job is shaped, and — because there is no Windows hardware on the runner — exactly how much of the result can be verified before a person double-clicks it.

It is a spec, not a report. Nothing below has been built. Where a claim rests on reading rather than running, it says so, in the same discipline faces.md §2.3 applies to licences: the cheap way to find out is to read first, and the expensive way is at packaging time.

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1. Why this is nearly free, and where it is not

The reason to write this at all is that the tree is closer to Windows than a Linux-only project usually is. The three things that ordinarily make a cross-build to Windows a week of work are all absent:

Usual obstacle	Here
A C image library (libraw, libjpeg-turbo, lcms)	rawler, zune-jpeg, jpeg-encoder, all pure Rust
OpenSSL, or a TLS stack with a system dependency	reqwest on rustls + webpki-roots; ring cross-compiles to the GNU target
A GUI toolkit with a platform-specific build	Slint on winit + wgpu, which already runs the same code on Linux and Android

rusqlite is bundled, so SQLite compiles with whatever C compiler the target has; that is the one place a cross C compiler is required, and it is a package install rather than a port. The inference engine is tract, in Rust, which is what faces.md §3 chose it for — and this is the second time that choice pays: the C++ ONNX Runtime would have needed a prebuilt Windows binary fetched at build time.

Where it is not free is dr-plat and the handful of paths above it, which is exactly where NFR-PORT-1 says platform code should be and where §3 finds it. That the list in §3 is short and every item on it is already behind a cfg is the measure of whether NFR-PORT-3 ("a third platform requires implementing the platform interfaces only") was met. It was, nearly: the gaps are in things that grew above dr-plat — a settings file path, an xdg-open — rather than in the interfaces themselves.

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2. Toolchain: the GNU target, from a container

Two Rust targets can produce a Windows binary from Linux.

Target	Linker	What it needs on the runner	What it costs
x86_64-pc-windows-gnu	MinGW-w64 gcc	gcc-mingw-w64-x86-64 (Debian/Ubuntu), mingw-w64-gcc (Arch) — one apt/pacman install	Binaries link libgcc_s and libwinpthread unless told not to; the SEH unwinder is MinGW's rather than MSVC's; DirectX bindings are less exercised (not used — §2.1)
x86_64-pc-windows-msvc	lld-link via cargo-xwin	The MSVC CRT and Windows SDK headers, fetched from Microsoft's servers by xwin on first use (~1.5 GB, licence-accepted by flag)	A download step in CI that depends on Microsoft keeping those URLs stable, and a licence the runner accepts on the project's behalf

Decision: GNU. It is a package install, it is what rustup target add supports out of the box, and every crate in the dependency graph that carries a C component (ring, libsqlite3-sys, zstd-sys if present) builds against MinGW today. The MSVC route produces a marginally more conventional binary — the same CRT every other Windows application links — and costs a 1.5 GB fetch of Microsoft-licensed headers on every cold CI run. That is the wrong trade for a channel whose users are, for now, the author.

Static-link the MinGW runtime so the installer carries one file rather than three:

# .cargo/config.toml
[target.x86_64-pc-windows-gnu]
linker = "x86_64-w64-mingw32-gcc"
ar = "x86_64-w64-mingw32-gcc-ar"
rustflags = ["-C", "link-args=-static-libgcc -static-libstdc++ -Wl,-Bstatic,--whole-archive -lwinpthread -Wl,--no-whole-archive"]

The winpthread incantation is the well-known one and is stated rather than derived; it is the first thing to check if the resulting .exe complains about a missing libwinpthread-1.dll.

2.1 What the binary reaches at runtime

Nothing the installer has to carry. wgpu opens Vulkan (dr_gpu::new_shared, D1 — Vulkan on both targets, and the shared-device path permits nothing else), and on Windows the Vulkan loader vulkan-1.dll is installed by every GPU vendor's driver. Slint's femtovg renderer finds system fonts through fontdb, so the fontconfig the Linux CI job installs has no Windows counterpart. There is no libxkbcommon, no display-server library: winit speaks Win32 directly.

DirectX 12 is deliberately not enabled. wgpu supports it and on Windows would be the conventional choice, but the develop pipeline's compute shaders are written once for Vulkan (NFR-PORT-2) and validated on two Vulkan drivers already; a third backend is a third set of driver behaviours to characterise (NFR-R1's tolerance argument), and no Windows machine that can run this application lacks a Vulkan ICD. The same reasoning that keeps GL out of new_shared keeps DX12 out here. It is one flag away if that turns out to be wrong.

2.2 Where it builds

The same shape as the Android leg: a job container built from a Dockerfile in the tree and pushed to the Gitea registry, tagged by the tree id of its directory so an unrelated push reuses it (android-image.yml already does this and the comment there explains why).

docker/windows/
  Dockerfile        ubuntu + rustup (1.92.0, target x86_64-pc-windows-gnu) + gcc-mingw-w64-x86-64 + nsis + wine64 + osslsigncode
  build.sh          cargo build --release --target x86_64-pc-windows-gnu -p darkroom-desktop
  package.sh        the LFS guard, then makensis

makensis is a Linux binary; NSIS has always been buildable and runnable on POSIX hosts, and Debian ships it as nsis. Wine is in the image for §6, not for the build.

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3. What the tree has to change

Read from the source, not run. Everything here is dr-plat or the thin layer above it — nothing in core/ is touched, which is NFR-PORT-1 holding.

3.1 Already handled

• volumes.rs — card detection reads /proc/mounts and /sys/block under cfg(target_os = "linux") and returns an empty list elsewhere. Windows gets no card detection in this pass; the import flow's path picker still works. (A GetDriveType/DRIVE_REMOVABLE implementation is a screen of code and a follow-up.)
• display.rs — the X11 and Wayland colour-profile readers are cfg(all(unix, not(android))); the fallback is FR-DSP-8's stated one. Windows ICC profiles via GetICMProfile are a follow-up for the same reason.
• desktop_client.rs — the Nextcloud desktop client's Unix socket is cfg(unix). On Windows the client listens on a named pipe (\\.\pipe\...); until that is implemented FR-NC-6c's integration is absent and the app behaves as it does on a Linux machine with no client running.
• secrets.rs — has a PlatformSecretStore for "any platform without an implementation" that returns SecretError::Unavailable on every call. It is loud on purpose, so a Windows build made with no further change compiles, starts, and fails at sign-in with a clear message. §3.2 is what turns that into a working store.
• keyring, x11rb, wayland-* are target-scoped dependencies already, so the Linux-only crates are not even compiled.

3.2 Required before the installer is worth shipping

Ordered by what blocks a first sign-in.

1. Secret store. keyring has a Windows Credential Manager backend; enable its feature under a cfg(windows) target dependency and add the third impl SecretStore for PlatformSecretStore beside the two that exist. The feature's exact name has changed across keyring majors (windows-native in 3.x) and is to be read from the 4.x changelog rather than assumed. FR-NC-2's rule carries over unchanged: Credential Manager is always present on Windows, so there is no degraded mode to state.

2. Paths. FR-PLAT-LIN-1 says XDG, and the code says it in five places by reading XDG_*_HOME and falling back to $HOME/.local/.... On Windows HOME is normally unset, so every one of these degrades to a relative path from the working directory — which for a Start Menu launch is C:\Windows\System32. The fix is one function per kind of directory in dr-plat, with the Windows branch reading %APPDATA% (config; roams) and %LOCALAPPDATA% (data, cache, state; does not), and the five call sites using it:

   Kind	Linux today	Windows
   config (settings.json, accounts)	$XDG_CONFIG_HOME/darkroom — dr_sync::config_dir, settings_store.rs	%APPDATA%\darkroom
   data (catalog, thumbnails, faces)	$XDG_DATA_HOME/darkroom — library::data_root	%LOCALAPPDATA%\darkroom
   state (crash reports, diagnostics)	$XDG_STATE_HOME/darkroom — state.rs, crash.rs	%LOCALAPPDATA%\darkroom\state

   FR-PLAT-WIN-1 states this as the requirement. The catalog and thumbnail formats do not change, so a library directory copied from a Linux machine opens.

3. Face models. library::system_face_models_dirs walks $XDG_DATA_DIRS, which does not exist on Windows. The installer puts the models beside the executable (§5), so the Windows branch returns current_exe().parent().join("models"). The user-directory lookups above it are unchanged, so a hand-placed pair still outranks the installed one, exactly as on Linux.

4. Opening the sign-in URL. launch_ui.rs shells out to xdg-open. Windows wants ShellExecuteW with the open verb, or cmd /C start "" <url>; the open crate does the cfg for every platform and is the conventional answer. Android has its own Intent path already, so this is the third branch of a function that already has two.

5. std::os::unix uses outside a cfg. diagnostics.rs and presets.rs use PermissionsExt for mode bits on written files. Most are inside #[cfg(unix)] blocks already; the first cross-compile will name any that are not, and the fix is a cfg rather than a Windows ACL equivalent — the files in question are the user's own.

6. The executable's identity. Windows takes the icon and the version block from a resource compiled into the .exe, not from a .desktop file. A build.rs in darkroom-desktop using winresource (which invokes MinGW's windres when cross-compiling) embeds ui/dr-ui/ui/app-icon.png converted to .ico, the version from CARGO_PKG_VERSION, and the product name. This is the fourth place the identifier lives (distribution.md §1's "one identifier, four places" becomes five), and tools/set-version.sh does not need to learn it: the resource reads the version cargo already knows.

Everything in this list is cfg(windows) code in dr-plat or a call-site switch in dr-ui, and none of it touches the image core, the catalog schema, or the edit pipeline. That is the NFR-PORT-3 test, and it should be stated in the commit that closes the list whether it passed.

3.3 Explicitly not in this pass

• MIME/file-type registration — FR-PLAT-LIN-1's .desktop MIME entries have a registry equivalent (HKCU\Software\Classes\.cr2 etc.). Not until the application opens a file from the command line usefully, which main.rs accepts but the launch flow does not yet act on.
• High-DPI declaration — winit sets per-monitor-v2 awareness through its manifest by default. Verified in winit's source, not on a monitor; if text is blurry on a 150% display this is the first suspect.
• Card detection, ICC profiles, the desktop-client pipe — §3.1's three follow-ups.
• A GL or DX12 fallback — §2.1. A machine without Vulkan gets the library and no develop path, which is what it gets on Linux too.

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4. The build script

docker/windows/build.sh, in the shape of the Android one and with the same rules:

cargo build --release --target x86_64-pc-windows-gnu -p darkroom-desktop

Release only, with CARGO_TARGET_DIR inside the workspace so the CI cache key (windows-${{ hashFiles('**/Cargo.lock') }}) covers it. The whole workspace is not built for the target: darkroom-android cannot be, and the examples that need a display or a catalog on disk have nothing to run against. cargo clippy --target x86_64-pc-windows-gnu -p darkroom-desktop is worth running in the same job, because the cfg(windows) branches from §3 are otherwise never linted — the Linux job cannot see them.

Not cargo test --target x86_64-pc-windows-gnu: the test binaries would be Windows executables, and running them means Wine. §6 does that for exactly one binary, deliberately.

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5. The installer

packaging/windows/darkroom.nsi, compiled by makensis on the runner into DarkRoom-<version>-x86_64-setup.exe. package.sh passes the version in (/DVERSION=…, from tools/set-version.sh's single source, the workspace Cargo.toml) and refuses to run if any models/face/*.onnx is smaller than 100 KB — the LFS-pointer guard every other packager carries, for the reason distribution.md §1 gives.

5.1 Per-user, not per-machine

Install to $LOCALAPPDATA\Programs\DarkRoom, register the uninstaller under HKCU\Software\Microsoft\Windows\CurrentVersion\Uninstall\DarkRoom, RequestExecutionLevel user. No UAC prompt, no Program Files, no writes outside the user's profile. This is the shape VS Code's "User Installer" and most Electron applications use, and it is right for this project for two reasons: an unsigned installer that also asks for administrator rights is the most alarming thing Windows can show a user (§5.4), and a per-user install means the application's own data directories (§3.2) and its binaries are governed by the same account, which is what NFR-SEC-5's "the user's own hardware" means on a shared machine.

5.2 What it puts on disk

$LOCALAPPDATA\Programs\DarkRoom\
  darkroom.exe
  models\
    scrfd_500m_640.onnx   scrfd_2.5g_640.onnx   scrfd_10g_640.onnx   arcface_mbf_b1.onnx
    yolo26s-sem-ade20k.onnx   yolo26s-sem-ade20k.classes.json   categories.txt
  LICENSE
  uninstall.exe

Plus a Start Menu shortcut, and nothing on the desktop unless the user ticks it. The models are the same seven files the APK bundles and the PKGBUILD installs; models\ beside the executable is where §3.2's lookup finds them. The face weights carry the research-only grant that faces.md §2 records, and this channel changes nothing about that: the installer is for the author's own machines until §2.2a's caveat is resolved, exactly as the APK is.

5.3 Uninstall

Removes the install directory, the shortcut and the registry key. Does not touch %LOCALAPPDATA%\darkroom or %APPDATA%\darkroom — the catalog, the thumbnails, the face index, the settings. An uninstaller that deletes a library index the user spent two hours building is the kind of destructive default FR-CULL-12 and NFR-SEC-5's "disabling deletes nothing" both argue against. The uninstaller says so on its one page, and names the two directories so a user who does want them gone knows where they are.

5.4 Signing, and the warning that results from not doing it

An unsigned installer triggers SmartScreen's "Windows protected your PC" interstitial, dismissable through "More info → Run anyway". Signing needs an Authenticode certificate, which is paid and identity-verified; from Linux the signing itself is osslsigncode, which is why it is in the container image, but there is no certificate to give it. This spec ships unsigned and the release notes say what the interstitial looks like. An OV certificate is a cost decision to make if this channel ever has a user who is not the author; an EV one buys instant reputation and costs a hardware token. Neither is a build problem.

The APK went through the same sequence — android-signing.md records a debug-signed build becoming a release-signed one when it mattered — and this channel should be allowed to do the same.

5.5 What NSIS is chosen over

WiX produces an MSI, which is what enterprise deployment tooling wants and what nobody deploying a photo editor to their own laptop cares about; its Linux story is wixl from msitools, which is real but thinly used. Inno Setup runs only under Wine. NSIS is scriptable in plain text, builds natively on Linux, produces a single self-contained .exe, and the script for §5.2 is under a hundred lines. It is the conventional answer for exactly this situation.

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6. Verifying without Windows

This is the part to be honest about. The runner has no Windows, no GPU it can hand to a Windows process, and no display. What can be checked, in increasing cost and decreasing certainty:

Check	How	What it proves
It links	the build succeeds	Every cfg(windows) branch compiles; no unix-only symbol leaked past a cfg
It is a Windows executable	file darkroom.exe reports PE32+; x86_64-w64-mingw32-objdump -p lists the DLLs it imports and none are MinGW's	The static-runtime flags in §2 held
It starts	wine64 darkroom.exe --version exits 0 and prints the version	The CRT, the resource block and main are sound; paths in §3.2 resolve (Wine sets LOCALAPPDATA)
The installer runs	wine64 DarkRoom-setup.exe /S then the install directory exists with the eight files, and wine64 uninstall.exe /S removes it	The NSIS script's file list, sections and uninstaller are right
It draws a window	xvfb-run wine64 darkroom.exe with SLINT_WGPU_CPU and a lavapipe ICD exposed through winevulkan	That Slint's winit backend initialises on Win32 — and this is where the chain gets long enough that a failure says more about Wine than about DarkRoom

The first four are the CI gate. The fifth is worth trying once by hand and not putting in CI: it needs winevulkan to find a host ICD, xvfb, and a Wine prefix warmed up in the container, and every one of those is a moving part that has nothing to do with whether the application works on Windows.

--version does not exist yet — main.rs takes paths and nothing else — and it is added for this, because a smoke test needs an exit that does not open a window. It is two lines.

What none of this proves: that wgpu opens a Vulkan device on a real driver, that a 6000-px render completes, that fonts are found, that the secret store round-trips. Those are a person with a Windows machine, once per release, until there is a Windows runner — and a self-hosted Windows act_runner is how that would be done, not a cloud service. The release notes for the first build say which of these were checked and on what.

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7. The CI job

A fourth leg of build-and-test.yml, beside desktop, Android and traceability:

  windows-image:
    uses: ./.gitea/workflows/windows-image.yml     # same shape as android-image.yml

  windows:
    runs-on: linux/amd64
    name: Windows (x86_64, cross)
    needs: windows-image
    container:
      image: gitea.tourolle.paris/dtourolle/darkroom-windows:latest
    steps:
      - checkout, LFS pull                           # copied from the desktop leg
      - cache: ~/.cargo, target                      # key: windows-${{ hashFiles('**/Cargo.lock') }}
      - docker/windows/build.sh                      # cargo build + clippy, --target x86_64-pc-windows-gnu
      - smoke: file, objdump, wine64 --version       # §6 rows 1–3
      - docker/windows/package.sh                    # LFS guard, makensis
      - smoke: wine64 setup.exe /S; ls; uninstall    # §6 row 4
      - upload artefact: DarkRoom-*-setup.exe        # on tags only, like the APK

Same gotchas as the Android leg, which its comments already record: the host has no Node, so the checkout is plain git; workflow inputs arrive as strings; the image build needs the host Docker daemon and runs outside a container. None of that is new.

Cost. A cold build of the whole graph for a second target is roughly the desktop leg again — tract, Slint's compiler, wgpu — so with the cargo cache warm it is minutes and cold it is the better part of half an hour. Worth noting because the runner is one machine and the legs run in parallel on it; if it starts starving the desktop leg, needs: desktop serialises them.

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8. Requirements

Three, added to requirements.md §3.8 under a #### Windows heading beside the Linux ones. Phrased to be testable, and each one is something §3 or §5 would otherwise leave as a convention.

FR-PLAT-WIN-1 — Known folders. Configuration under %APPDATA%\darkroom; data, cache and state under %LOCALAPPDATA%\darkroom. No file under the user's profile root and nothing relative to the working directory. The directory layout beneath those roots is the same as under XDG, so a library directory moves between platforms unchanged.

FR-PLAT-WIN-2 — Installer. A per-user installer that needs no elevation, registers an uninstaller, and whose uninstaller removes what the installer wrote and nothing the application wrote. Models are installed beside the executable and found there last, after the user's own directories.

FR-PLAT-WIN-3 — Built from Linux. The Windows binary and its installer are produced by the Linux CI from the same commit as every other channel, with no Windows machine in the build. Verification on Windows is a release step, recorded per release, not a build step.

NFR-COMPAT-2's channel table in distribution.md §1 gains a row. NFR-PORT-3 gets its first real test, and the commit that closes §3.2 records the answer.

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9. Order

1. --version in main.rs, and the .cargo/config.toml target block. Trivial, and the smoke test in §6 needs both before anything else can be measured.
2. rustup target add x86_64-pc-windows-gnu, pacman -S mingw-w64-gcc, and a first cargo build --target … on the developer machine — before the container exists, because the list in §3.2 is a reading of the source and the compiler's list will be longer. Fix the cfg fallout as it appears. This is the afternoon that decides whether §1's optimism holds.
3. §3.2 items 1–4, each its own commit, each stating which NFR-PORT interface it implemented.
4. §3.2 item 6 — the resource block — and the NSIS script; makensis by hand; wine64 setup.exe /S by hand. Now there is an artefact.
5. The container, the image workflow, the CI leg. Only after 4 works locally, for the same reason the Android image was reproduced from the tree after it had lived on one laptop.
6. A build on a real Windows machine, and a note in the release saying what was checked.

Steps 1–2 are cheap and either confirm this document or replace §3.2 with the true list. Nothing past step 2 should be started on the strength of this document alone.