# facet_gtk facet's GTK 4 backend — the Linux/BSD counterpart of [`facet_appkit`](/docs/packages/facet_appkit) and [`facet_uikit`](/docs/packages/facet_uikit). facet owns the description tree and **all** layout (the shared `flex_layout` engine). This package answers the contract's verbs with GTK and records in [MANIFEST.md](https://github.com/netdur/cplus/blob/v0.0.28/vendor/facet_gtk/MANIFEST.md) what it has not answered yet. ``` facet_gtk the registration surface: install(), and nothing else views the Renderer's five verbs + intrinsic size controls one GTK body per node kind, and the CSS each one composes input the READ half — gestures, keys, control actions, sender readers paint the shared band — background / radius / opacity / enabled / tooltip geometry computed frames -> GtkFixed placements, and a scroll's extent scheduler schedule + the Scheduler service, over the GLib main loop window the GtkWindow host, the run loop, and the menus chrome the toolbar, the window buttons, and the drag region swipe swipe-to-reveal, assembled — GTK has no such row anim the two things that move on their own: a progress tween, a GIF recycler list, collection and tree over GtkListView — rows built as they scroll in dialogs alert / choose / prompt as facet trees, and the file chooser drawing the canvas replay, against cairo and Pango web a WebKitGTK view, opened at runtime rather than linked ``` ## Status is a measurement ``` $ python3 tools/parity.py appkit 338 / 360 93% uikit 335 / 360 93% gtk 353 / 360 98% <-- this package appkit 68 / 68 100% uikit 67 / 68 98% gtk 68 / 68 100% <-- this package ``` **Two numbers, because props are WRITES and handlers are READS** — a backend at 100% on props can still be a control that is clicked and calls nothing. Both are measured now, and both are gated: `--check` carries a floor per axis, because the two fail differently. A missing prop is a control that ignores you; a missing handler is a control that never answers. The second number reaching 68/68 does not mean every handler is EXACT — two are narrowed by facet's own contract rather than by GTK, and `MANIFEST.md` §3 names both. What it means is that no declared handler is silently dead. Read [MANIFEST.md](https://github.com/netdur/cplus/blob/v0.0.28/vendor/facet_gtk/MANIFEST.md) before trusting any adjective — including that one. `tools/parity.py --check` fails if the number drops, so a refactor that quietly loses a verb is caught by the gate rather than by someone noticing a control stopped working. ## Two ways to check it ```bash cd vendor/facet_gtk && ../../target/release/cpc test # 212 tests, no display needed cd examples/facet_gtk_probe && ../../target/release/cpc run cd examples/facet_gallery && ../../target/release/cpc run # ...and the gallery can walk ITSELF — every demo, one a tick: FACET_GALLERY_WALK=1 ./target/debug/facet_gallery # 35 screens, warnings visible FACET_GTK_SCROLL=1 ./target/debug/facet_gallery # every scroll move, and who made it FACET_GTK_SELECT=1 ./target/debug/facet_gallery # a nav select, bracketed: at click, after # the handler, and again 500ms later FACET_GTK_FRAMES=1 ./target/debug/facet_gallery # the computed frame tree FACET_GTK_SYNC=1 ./target/debug/facet_gallery # what a frame costs, in its four parts — # mount, solve, place, menu. A debt row is a # guess until it is a number; MANIFEST §2's # `relayout_all` row was retired by this one ``` The suite pins everything the backend DECIDES — the mappings, the CSS it composes, the bits it claims, the encoders — and makes no widget, because a suite that needs a login session is a suite that stops running. The probe is the other half: whether the switch reported its change, whether the slider fired while it was being dragged, whether the field kept its caret. An agent has no hands, so that half is an app you run. The gallery is the third: it is the same application macOS runs, unchanged, and it reaches this backend through `facet_runtime/runtime_linux.cplus`. If it builds and comes up, the whole stack — contract, backend, facade, app — is wired end to end. ## Seeing what was computed ```bash FACET_GTK_FRAMES=1 ./target/debug/facet_gallery 2>&1 | head -40 ``` One line per node: its key, its kind, the frame flex computed, and whether it has a widget. This is the package's one diagnostic and it exists because a backend under an external layout engine fails in a way a screenshot cannot explain — every control in the right place and none of them visible. `w=0` on a kind that has a body is that bug; `view=-` on a backed kind is the other one. Both have already happened here, and both were found in a second by this. ## It runs That is new. The previous generation of this package could only ever be type-checked — it targeted a superseded 34-entry per-kind `Renderer`, imported `facet::Renderer` from a module that no longer exports it, and the GTK stack did not link on Linux at all. All three are fixed; this one is built and run. ```cplus import "facet_gtk/facet_gtk" as backend; fn main() -> i32 { backend::install(); var root: facet::Node = ui(); let _ok: bool = backend::open_window(#addr_of(root), "facet · GTK 4", 520.0f64, 340.0f64); var lp: glib::MainLoop = glib::MainLoop::new(glib::main_context_default(), false); lp.run(); return 0; } ``` The tree `ui()` builds is portable: it is the same description `facet_appkit` would mount on a Mac. ## The two rules worth knowing before editing **One code path for create and apply.** `create` configures a new widget with `paint::all_bits()`, which is the same call `apply` makes with the node's real dirty word. A prop honoured on update is therefore honoured on create, and the two cannot drift. Every write is gated on its bit. **Ownership.** A fresh GtkWidget carries a *floating* reference. `create` sinks it (facet holds the widget in the node) and `view_release` drops it. Without the sink an unparented widget leaks; without the release, a removed one does.