A desktop UI stack written entirely in C — layout engine, platform bindings, Fluent Design controls, and a declarative Elm-architecture view layer — with zero C++ and zero runtime dependencies beyond the OS.
int main(void) {
Model model = { .count = 0 };
return flux_run(
&(FluxAppConfig){ .title = L"Hello", .width = 640, .height = 480 },
&model, update, view);
}block-beta
columns 3
block:desc:3
columns 3
xentkit["xent-kit — Elm MVU declarative layer"]:3
fluxent["FluXent\n(Windows)"] nexent["NeXent\n(macOS)"] luxent["LuXent\n(BSD · Linux)"]
d2d["D2D / DComp\nDirectWrite\nWinRT"] metal["Metal\nCoreText\nCoreAnimation"] arcan["Arcan / 9P\nHarfBuzz + FreeType\nEGL"]
cwinrt["cwinrt\nWinRT C projection"] objc["ObjC runtime\nbridge"] shmif["SHMIF\n9P mount"]
xent["xent-core — layout · tree · text · semantics · SIMD"]:3
end
style xentkit fill:#3b82f6,color:#fff,stroke:none
style xent fill:#3b82f6,color:#fff,stroke:none
style fluxent fill:#22c55e,color:#fff,stroke:none
style nexent fill:#a1a1aa,color:#fff,stroke:none
style luxent fill:#a1a1aa,color:#fff,stroke:none
style d2d fill:#22c55e,color:#fff,stroke:none
style metal fill:#a1a1aa,color:#fff,stroke:none
style arcan fill:#a1a1aa,color:#fff,stroke:none
style cwinrt fill:#22c55e,color:#fff,stroke:none
style objc fill:#a1a1aa,color:#fff,stroke:none
style shmif fill:#a1a1aa,color:#fff,stroke:none
Note
Green = shipped Grey = planned
xent-core and xent-kit are platform-agnostic and shared across every
target. Each platform provides its own rendering backend and system bindings;
xent-kit's reconciler diffs against whichever backend is underneath.
Platform-agnostic layout engine and node tree.
| Layout protocols | Flex (CSS Flexbox), Grid (WinUI Star/Auto/Pixel), SwiftStack (SwiftUI VStack/HStack semantics), Absolute |
| Data layout | Structure-of-Arrays — one contiguous float array per property, SIMD-friendly |
| SIMD | Optional ISPC backend (SSE4 + AVX2 multi-target dispatch) for hot layout paths |
| Text | Pluggable backend with measurement cache; built-in monospace fallback for headless use |
| Correctness | Yoga-ported conformance suite (13k lines), 19 unit-test targets, regression-gated benchmarks |
| Accessibility | Semantic roles, labels, checked/enabled/expanded states, focus + tab-index in the core tree |
Public API surface
XentContext *xent_create_context(XentConfig const *config);
XentNodeId xent_create_node(XentContext *ctx);
bool xent_set_protocol(XentContext *ctx, XentNodeId node, XentProtocol protocol);
bool xent_set_flex_direction(XentContext *ctx, XentNodeId node, XentFlexDirection dir);
bool xent_set_stack_axis(XentContext *ctx, XentNodeId node, XentAxis axis);
bool xent_layout(XentContext *ctx, XentNodeId root, float w, float h);
// … size, margin, padding, gap, min/max, percent, aspect-ratio, grid tracks,
// direction (LTR/RTL), wrap-content, z-index, dirty flags, profiling …
Platform-agnostic declarative UI toolkit — Elm Architecture in C.
Each frame the app's view builds a throwaway element tree from arena memory;
the reconciler diffs it against the previous frame and patches retained controls.
Controls never call back directly — they post XtkMsg values consumed by update.
XtkEl *view(XtkUi *ui, void *model) {
Model *m = model;
return xtk_column(ui, (XtkStackDesc){.gap = 12, .padding = {32,32,32,32}}, (XtkEl*[]){
xtk_text(ui, "Counter", (XtkTextDesc){.size = 24}),
xtk_text(ui, xtk_fmt(ui, "Count: %d", m->count), (XtkTextDesc){0}),
xtk_button(ui, "Increment", (XtkButtonDesc){.on_click = xtk_msg(MSG_INC)}),
m->count > 0
? xtk_button(ui, "Reset", (XtkButtonDesc){.on_click = xtk_msg(MSG_RESET)})
: NULL,
XTK_END});
}Compound literals + designated initializers make every property optional with a zero default.
NULLentries are conditional rendering. The gallery demo — NavigationView, 21 control pages — is ≈ 1200 lines of view code.
| Architecture | Elm MVU — Model struct + pure update(model, msg) + pure view(ui, model) |
| Element tree | Double-buffered arena allocation; previous frame's tree stays alive for diffing, then the old arena resets |
| Reconciler | Keyed + positional child matching with reorder detection; NULL = conditional skip |
| Backend | 9-function XtkBackend vtable — create, update, destroy, reorder, set_root, request_frame, show_popup, close_popup, set_cursor |
| Messages | Tagged-union XtkMsg with tag + value (int or float); ring-buffer queue (256 entries) |
| Controls | Button · Checkbox · RadioButton · ToggleSwitch · Slider · ComboBox · DropDownButton · SplitButton · TextBox · PasswordBox · NumberBox · ProgressBar · ProgressRing · ScrollViewer · Card · InfoBadge · InfoBar · Divider · Expander · Hyperlink · RepeatButton · Image · NavigationView · TabView · ContentDialog · MenuFlyout · MenuBar · Tooltip |
Public API surface
/* elements — each returns an arena-allocated XtkEl* */
XtkEl *xtk_button(XtkUi *ui, char const *label, XtkButtonDesc desc);
XtkEl *xtk_text(XtkUi *ui, char const *content, XtkTextDesc desc);
XtkEl *xtk_column(XtkUi *ui, XtkStackDesc desc, XtkEl *children[]);
XtkEl *xtk_row(XtkUi *ui, XtkStackDesc desc, XtkEl *children[]);
XtkEl *xtk_slider(XtkUi *ui, XtkSliderDesc desc);
XtkEl *xtk_nav_view(XtkUi *ui, XtkNavViewDesc desc, XtkEl *children[]);
XtkEl *xtk_tab_view(XtkUi *ui, XtkTabViewDesc desc, XtkEl *children[]);
XtkEl *xtk_content_dialog(XtkUi *ui, XtkContentDialogDesc desc, XtkEl *children[]);
// … checkbox, radio, toggle_switch, combo_box, card, expander, info_bar,
// menu_bar, dropdown_button, split_button, image, hyperlink, tooltip …
/* modifiers — return the same element pointer for chaining */
XtkEl *xtk_keyed(XtkUi *ui, char const *key, XtkEl *el);
XtkEl *xtk_sized(XtkEl *el, float w, float h);
XtkEl *xtk_grow(XtkEl *el, float grow);
/* messages */
XtkMsg xtk_msg(int tag);
XtkMsg xtk_msg_i(int tag, int value);
XtkMsg xtk_msg_f(int tag, float value);
/* utilities */
char const *xtk_fmt(XtkUi *ui, char const *fmt, ...);
XtkEl **xtk_children_alloc(XtkUi *ui, int capacity);
Pure C projection for the entire Windows Runtime.
| Generator | Reads .winmd as PE + ECMA-335 #~ metadata — no cor.h, no COM SDK headers |
| Coverage | 342 Windows.* namespaces; one header + one impl per namespace |
| Runtime | init · hstring (UTF-8/16) · factory (cached) · async (event + poll) · delegate · event — 951 lines total |
| Naming | Frozen mangling spec; overloads keyed by type signature, not ordinal — SDK additions never rename existing symbols |
| CI gates | Determinism (byte-stable) · Golden (ABI SHA-256) · PIID vs cppwinrt · Slot vs ABI · All-header compile · All-impl link · clang -Werror · MinGW full link × 4 arch · E2E on hardware |
| Toolchains | MSVC · clang-cl · clang · llvm-mingw |
C++/WinRT migration cheat sheet
| C++/WinRT | cwinrt |
|---|---|
winrt::init_apartment() |
cwinrt_init(RO_INIT_MULTITHREADED) |
Calendar c; |
WGL_Calendar *c; wgl_calendar_new(&c); |
c.Year() |
int32_t y; wgl_calendar_get__year(c, &y); |
obj.as<T>() |
cwinrt_query(obj, &CWINRT_IID_T, &out) |
co_await op; |
cwinrt_async_wait((IUnknown *)op, INFINITE); |
event += h; |
on_event(self, fn, ctx) → cwinrt_token |
| RAII release | ((IUnknown *)p)->lpVtbl->Release((IUnknown *)p) |
WinUI 3-class Fluent Design backend for xent-kit, driven by xent-core layout and cwinrt platform integration.
| Render | Direct2D / DirectWrite with snapshot diff + per-node cache; or Windows.UI.Composition retained tree with identity-stable visual reconciler, compositor-thread animations, and InteractionTracker scrolling |
| Theming | Live system accent + light/dark palettes using WinUI 3 design tokens; pixel-matched color values |
| Input | Hit testing · keyboard focus · DirectManipulation inertial scroll · InteractionTracker |
| Accessibility | Win32 UI Automation provider — control types, patterns, focus/invoke events |
| Bridge | Implements xent-kit's 9-function XtkBackend vtable; maps declarative element diffs to retained Fluent controls |
| Dual API | Declarative Elm path via xent-kit (flux_run), or imperative retained-mode path via flux_create_* for full node-level control |
| Gallery | Bundled WinUI Gallery-class demo app — NavigationView shell, 21 control pages, ≈ 1200 lines of pure view code |
| Tests | Headless reconciler lifecycle, keyed add/remove sequences, cross-axis geometry, CSS §9.4 grow+wrap regression, subtree destruction + leak detection — all GPU-free |
Gallery pages
Home · Button · Checkbox · RadioButton · ToggleSwitch · Slider · ComboBox · DropDownButton · SplitButton · RepeatButton · Hyperlink · TextBox · PasswordBox · NumberBox · Typography · ProgressBar · ProgressRing · InfoBadge · InfoBar · Image · Expander · Divider · Card · ScrollViewer · MenuBar · TabView · NavigationView · ContentDialog · Tooltip · Settings
| Target | Backend | Binding layer | Status |
|---|---|---|---|
| Windows 10+ | D2D · DirectWrite · DComp | cwinrt (WinRT C projection) | ✅ |
| macOS | Metal · CoreAnimation · CoreText | ObjC runtime bridge | 🔲 |
| OpenBSD | Arcan | SHMIF · 9P | 🔲 |
| FreeBSD | Arcan | SHMIF · 9P | 🔲 |
| musl Linux | Arcan | SHMIF · 9P | 🔲 |
The BSD and Linux stack targets Arcan — a
single-protocol (SHMIF) display server with security-oriented composition —
and exposes UI resources over 9P for Plan 9-style
composability and network transparency.
OpenBSD is the primary development platform for LuXent; its pledge/unveil
model and strict libc complement Arcan's design. Downstream porting follows
least-friction order: FreeBSD first, then musl-based Linux
(Chimera Linux,
Void Linux).
All repositories use xmake.
# xent-core
xmake && xmake test
# xent-kit
xmake && xmake test
# cwinrt (Windows, requires Windows SDK)
xmake build cwinrt-gen cwinrt-rt test_smoke
xmake run test_smoke
# fluxent gallery (Windows 10 1903+)
xmake run gallery
# fluxent hello demo (Windows 10 1903+)
xmake run hello_fluxentEvery repository under Project Xent is released under the 0BSD license.
