Early UI work.

Cargo.toml

@@ -1,3 +1,3 @@
 [workspace]
 resolver = "3"
-members = ["lib/*"]
+members = ["lib/*", "examples/*"]

examples/wayland_wgpu_demo/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "ruin_ui_wayland_demo"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+ruin_ui = { path = "../../lib/ui" }
+ruin_ui_platform_wayland = { path = "../../lib/ui_platform_wayland" }
+ruin_ui_renderer_wgpu = { path = "../../lib/ui_renderer_wgpu" }

examples/wayland_wgpu_demo/src/main.rs

@@ -0,0 +1,62 @@
+use std::error::Error;
+
+use ruin_ui::{Color, Rect, SceneSnapshot, UiSize, WindowSpec};
+use ruin_ui_platform_wayland::WaylandWindow;
+use ruin_ui_renderer_wgpu::{RenderError, WgpuSceneRenderer};
+
+fn build_demo_scene() -> SceneSnapshot {
+    let mut scene = SceneSnapshot::new(1, UiSize::new(800.0, 500.0));
+    scene.push_quad(
+        Rect::new(0.0, 0.0, 800.0, 500.0),
+        Color::rgb(0x10, 0x14, 0x24),
+    );
+    scene.push_quad(
+        Rect::new(32.0, 32.0, 736.0, 72.0),
+        Color::rgb(0x2D, 0x3E, 0x68),
+    );
+    scene.push_quad(
+        Rect::new(32.0, 136.0, 352.0, 300.0),
+        Color::rgb(0x6A, 0x3D, 0x3D),
+    );
+    scene.push_quad(
+        Rect::new(416.0, 136.0, 352.0, 300.0),
+        Color::rgb(0x3A, 0x5E, 0x49),
+    );
+    scene
+}
+
+fn main() -> Result<(), Box<dyn Error>> {
+    let scene = build_demo_scene();
+    let mut window = WaylandWindow::open(
+        WindowSpec::new("RUIN Wayland / wgpu demo")
+            .app_id("dev.ruin.prototype")
+            .requested_inner_size(scene.logical_size),
+    )?;
+    let mut renderer = WgpuSceneRenderer::new(
+        window.surface_target(),
+        scene.logical_size.width as u32,
+        scene.logical_size.height as u32,
+    )?;
+
+    println!("Opening RUIN Wayland / wgpu demo window...");
+    while window.is_running() {
+        window.dispatch()?;
+        if let Some(frame) = window.prepare_frame() {
+            if frame.resized {
+                renderer.resize(frame.width, frame.height);
+            }
+            match renderer.render(&scene) {
+                Ok(()) => {}
+                Err(RenderError::Lost | RenderError::Outdated) => {
+                    renderer.resize(frame.width, frame.height);
+                    window.request_redraw();
+                }
+                Err(RenderError::Timeout | RenderError::Occluded | RenderError::Validation) => {
+                    window.request_redraw();
+                }
+            }
+        }
+    }
+
+    Ok(())
+}

lib/ui/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "ruin_ui"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+ruin_reactivity = { path = "../reactivity" }
+ruin_runtime = { package = "ruin-runtime", path = "../runtime" }
+tracing = { version = "0.1", default-features = false, features = ["std"] }
+
+[dev-dependencies]
+tracing-subscriber = { version = "0.3", default-features = false, features = ["env-filter", "fmt", "std"] }

lib/ui/examples/explicit_ui_prototype.rs

@@ -0,0 +1,247 @@
+use ruin_reactivity::{Cell, cell};
+use ruin_ui::{
+    Color, PlatformEvent, Point, PreparedText, Rect, SceneSnapshot, UiRuntime, UiSize,
+    WindowController, WindowSpec, WindowUpdate,
+};
+use tracing_subscriber::layer::SubscriberExt;
+use tracing_subscriber::util::SubscriberInitExt;
+use tracing_subscriber::{EnvFilter, fmt};
+
+fn install_tracing() {
+    let filter = EnvFilter::try_from_default_env().unwrap_or_else(|_| {
+        EnvFilter::new(
+            "info,ruin_runtime::runtime=debug,ruin_ui::platform=debug,ruin_reactivity::effect=debug",
+        )
+    });
+
+    let fmt_layer = fmt::layer()
+        .with_target(true)
+        .with_thread_ids(true)
+        .with_thread_names(true)
+        .compact();
+
+    let _ = tracing_subscriber::registry()
+        .with(filter)
+        .with(fmt_layer)
+        .try_init();
+}
+
+fn log_platform_event(event: &PlatformEvent) {
+    match event {
+        PlatformEvent::Opened { window_id } => {
+            tracing::info!(event = "window_opened", window_id = window_id.raw());
+        }
+        PlatformEvent::Configured {
+            window_id,
+            configuration,
+        } => {
+            tracing::info!(
+                event = "window_configured",
+                window_id = window_id.raw(),
+                width = configuration.actual_inner_size.width,
+                height = configuration.actual_inner_size.height,
+                visible = configuration.visible,
+                "window configured"
+            );
+        }
+        PlatformEvent::VisibilityChanged { window_id, visible } => {
+            tracing::info!(
+                event = "visibility_changed",
+                window_id = window_id.raw(),
+                visible,
+                "window visibility changed"
+            );
+        }
+        PlatformEvent::FramePresented {
+            window_id,
+            scene_version,
+            item_count,
+        } => {
+            tracing::info!(
+                event = "frame_presented",
+                window_id = window_id.raw(),
+                scene_version,
+                item_count,
+                "headless backend presented scene"
+            );
+        }
+        PlatformEvent::Closed { window_id } => {
+            tracing::info!(event = "window_closed", window_id = window_id.raw());
+        }
+        PlatformEvent::CloseRequested { window_id } => {
+            tracing::info!(
+                event = "close_requested",
+                window_id = window_id.raw(),
+                "compositor-like close request received"
+            );
+        }
+    }
+}
+
+fn attach_window_scene(window: &WindowController) -> (Cell<usize>, ruin_reactivity::EffectHandle) {
+    let counter = cell(0usize);
+    let scene_window = window.clone();
+    let scene_effect = scene_window.attach_scene_effect({
+        let counter = counter.clone();
+        move || {
+            let version = counter.get() as u64 + 1;
+            let value = counter.get();
+            let mut scene = SceneSnapshot::new(version, UiSize::new(640.0, 360.0));
+            scene
+                .push_quad(
+                    Rect::new(0.0, 0.0, 640.0, 360.0),
+                    Color::rgb(0x12, 0x19, 0x28),
+                )
+                .push_quad(
+                    Rect::new(24.0, 24.0, 592.0, 64.0),
+                    Color::rgb(0x2B, 0x3A, 0x67),
+                )
+                .push_text(PreparedText::monospace(
+                    format!("RUIN explicit prototype | counter = {value}"),
+                    Point::new(40.0, 64.0),
+                    18.0,
+                    9.0,
+                    Color::rgb(0xFF, 0xFF, 0xFF),
+                ));
+            scene
+        }
+    });
+
+    (counter, scene_effect)
+}
+
+#[ruin_runtime::async_main]
+async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    install_tracing();
+
+    tracing::info!(
+        event = "prototype_start",
+        "starting explicit-construction UI prototype with a headless backend"
+    );
+
+    let mut ui = UiRuntime::headless();
+    let window = ui.create_window(
+        WindowSpec::new("RUIN Explicit Prototype")
+            .app_id("dev.ruin.prototype")
+            .requested_inner_size(UiSize::new(640.0, 360.0)),
+    )?;
+    let (counter, _scene_effect) = attach_window_scene(&window);
+    let _ = counter.set(1);
+    let _ = counter.set(2);
+    let _ = counter.set(3);
+
+    let event = ui
+        .wait_for_event_matching(|event| {
+            matches!(
+                event,
+                PlatformEvent::Configured { window_id, .. } if *window_id == window.id()
+            )
+        })
+        .await?;
+    log_platform_event(&event);
+
+    let event = ui
+        .wait_for_event_matching(
+            |event| matches!(event, PlatformEvent::Opened { window_id } if *window_id == window.id()),
+        )
+        .await?;
+    log_platform_event(&event);
+
+    let event = ui
+        .wait_for_event_matching(|event| {
+            matches!(
+                event,
+                PlatformEvent::FramePresented {
+                    window_id,
+                    scene_version: 4,
+                    ..
+                } if *window_id == window.id()
+            )
+        })
+        .await?;
+    log_platform_event(&event);
+
+    window.update(WindowUpdate::new().visible(false))?;
+    let event = ui
+        .wait_for_event_matching(|event| {
+            matches!(
+                event,
+                PlatformEvent::VisibilityChanged {
+                    window_id,
+                    visible: false,
+                } if *window_id == window.id()
+            )
+        })
+        .await?;
+    log_platform_event(&event);
+
+    window.update(WindowUpdate::new().visible(true))?;
+    let event = ui
+        .wait_for_event_matching(|event| {
+            matches!(
+                event,
+                PlatformEvent::VisibilityChanged {
+                    window_id,
+                    visible: true,
+                } if *window_id == window.id()
+            )
+        })
+        .await?;
+    log_platform_event(&event);
+
+    let _ = counter.set(4);
+    let event = ui
+        .wait_for_event_matching(|event| {
+            matches!(
+                event,
+                PlatformEvent::FramePresented {
+                    window_id,
+                    scene_version: 4,
+                    ..
+                } if *window_id == window.id()
+            )
+        })
+        .await?;
+    log_platform_event(&event);
+
+    let event = ui
+        .wait_for_event_matching(|event| {
+            matches!(
+                event,
+                PlatformEvent::FramePresented {
+                    window_id,
+                    scene_version: 5,
+                    ..
+                } if *window_id == window.id()
+            )
+        })
+        .await?;
+    log_platform_event(&event);
+
+    window.emit_close_requested()?;
+    let event = ui
+        .wait_for_event_matching(|event| {
+            matches!(
+                event,
+                PlatformEvent::CloseRequested { window_id } if *window_id == window.id()
+            )
+        })
+        .await?;
+    log_platform_event(&event);
+
+    window.update(WindowUpdate::new().open(false))?;
+    let event = ui
+        .wait_for_event_matching(
+            |event| matches!(event, PlatformEvent::Closed { window_id } if *window_id == window.id()),
+        )
+        .await?;
+    log_platform_event(&event);
+
+    ui.shutdown()?;
+
+    tracing::info!(
+        event = "prototype_done",
+        "explicit-construction UI prototype finished"
+    );
+    Ok(())
+}

lib/ui/src/lib.rs

@@ -0,0 +1,26 @@
+//! Shared explicit-construction UI substrate for RUIN.
+//!
+//! This crate intentionally starts with explicit Rust data construction rather than a proc-macro
+//! authoring layer. The goal is to validate the threading, windowing, and scene handoff model
+//! before committing to ergonomic surface syntax. Concrete platform and renderer backends live in
+//! sibling crates.
+
+pub(crate) mod trace_targets {
+    pub const PLATFORM: &str = "ruin_ui::platform";
+    pub const SCENE: &str = "ruin_ui::scene";
+}
+
+mod platform;
+mod runtime;
+mod scene;
+mod window;
+
+pub use platform::{PlatformClosed, PlatformEvent, PlatformProxy, PlatformRuntime, start_headless};
+pub use runtime::{EventStreamClosed, UiRuntime, WindowController};
+pub use scene::{
+    Color, DisplayItem, GlyphInstance, Point, PreparedText, Quad, Rect, SceneSnapshot, Translation,
+    UiSize,
+};
+pub use window::{
+    DecorationMode, WindowConfigured, WindowId, WindowLifecycle, WindowSpec, WindowUpdate,
+};

lib/ui/src/platform.rs

@@ -0,0 +1,647 @@
+//! Headless platform/render worker for the explicit-construction prototype.
+
+use std::cell::RefCell;
+use std::collections::BTreeMap;
+use std::fmt;
+use std::rc::Rc;
+use std::sync::Arc;
+use std::sync::atomic::{AtomicU64, Ordering};
+
+use ruin_runtime::channel::mpsc;
+use ruin_runtime::{WorkerHandle, queue_future, queue_microtask, spawn_worker};
+use tracing::{debug, info};
+
+use crate::scene::{SceneSnapshot, UiSize};
+use crate::trace_targets;
+use crate::window::{WindowConfigured, WindowId, WindowLifecycle, WindowSpec, WindowUpdate};
+
+#[derive(Clone)]
+pub struct PlatformProxy {
+    command_tx: mpsc::UnboundedSender<PlatformCommand>,
+    next_window_id: Arc<AtomicU64>,
+}
+
+/// Low-level platform/runtime host for the explicit prototype.
+///
+/// The headless backend currently co-locates logical platform and rendering work on one runtime
+/// worker thread, but the event/snapshot API is intentionally shaped so future backends can split
+/// them if needed.
+pub struct PlatformRuntime {
+    proxy: PlatformProxy,
+    events: mpsc::Receiver<PlatformEvent>,
+    _worker: WorkerHandle,
+}
+
+#[derive(Clone, Debug, PartialEq)]
+pub enum PlatformEvent {
+    Opened {
+        window_id: WindowId,
+    },
+    Closed {
+        window_id: WindowId,
+    },
+    VisibilityChanged {
+        window_id: WindowId,
+        visible: bool,
+    },
+    Configured {
+        window_id: WindowId,
+        configuration: WindowConfigured,
+    },
+    FramePresented {
+        window_id: WindowId,
+        scene_version: u64,
+        item_count: usize,
+    },
+    CloseRequested {
+        window_id: WindowId,
+    },
+}
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub struct PlatformClosed;
+
+impl fmt::Display for PlatformClosed {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str("platform worker is closed")
+    }
+}
+
+impl std::error::Error for PlatformClosed {}
+
+#[derive(Clone, Debug)]
+enum PlatformCommand {
+    CreateWindow {
+        window_id: WindowId,
+        spec: WindowSpec,
+    },
+    UpdateWindow {
+        window_id: WindowId,
+        update: WindowUpdate,
+    },
+    ReplaceScene {
+        window_id: WindowId,
+        scene: SceneSnapshot,
+    },
+    EmitCloseRequested {
+        window_id: WindowId,
+    },
+    Shutdown,
+}
+
+#[derive(Clone)]
+struct HeadlessState {
+    events: mpsc::UnboundedSender<PlatformEvent>,
+    windows: BTreeMap<WindowId, HeadlessWindow>,
+}
+
+#[derive(Clone)]
+struct HeadlessWindow {
+    spec: WindowSpec,
+    lifecycle: WindowLifecycle,
+    configuration: WindowConfigured,
+    pending_scene: Option<SceneSnapshot>,
+    render_scheduled: bool,
+}
+
+impl HeadlessWindow {
+    fn new(spec: WindowSpec) -> Self {
+        let actual_inner_size = spec
+            .requested_inner_size
+            .unwrap_or_else(|| UiSize::new(800.0, 600.0));
+        Self {
+            spec,
+            lifecycle: WindowLifecycle::LogicalClosed,
+            configuration: WindowConfigured {
+                actual_inner_size,
+                scale_factor: 1.0,
+                visible: false,
+                maximized: false,
+                fullscreen: false,
+            },
+            pending_scene: None,
+            render_scheduled: false,
+        }
+    }
+}
+
+impl PlatformRuntime {
+    pub fn headless() -> Self {
+        start_headless()
+    }
+
+    pub fn proxy(&self) -> PlatformProxy {
+        self.proxy.clone()
+    }
+
+    pub async fn next_event(&mut self) -> Option<PlatformEvent> {
+        self.events.recv().await
+    }
+}
+
+impl PlatformProxy {
+    pub fn create_window(&self, spec: WindowSpec) -> Result<WindowId, PlatformClosed> {
+        let window_id = WindowId::from_raw(self.next_window_id.fetch_add(1, Ordering::Relaxed));
+        self.send(PlatformCommand::CreateWindow { window_id, spec })?;
+        Ok(window_id)
+    }
+
+    pub fn update_window(
+        &self,
+        window_id: WindowId,
+        update: WindowUpdate,
+    ) -> Result<(), PlatformClosed> {
+        self.send(PlatformCommand::UpdateWindow { window_id, update })
+    }
+
+    pub fn replace_scene(
+        &self,
+        window_id: WindowId,
+        scene: SceneSnapshot,
+    ) -> Result<(), PlatformClosed> {
+        self.send(PlatformCommand::ReplaceScene { window_id, scene })
+    }
+
+    pub fn emit_close_requested(&self, window_id: WindowId) -> Result<(), PlatformClosed> {
+        self.send(PlatformCommand::EmitCloseRequested { window_id })
+    }
+
+    pub fn shutdown(&self) -> Result<(), PlatformClosed> {
+        self.send(PlatformCommand::Shutdown)
+    }
+
+    fn send(&self, command: PlatformCommand) -> Result<(), PlatformClosed> {
+        self.command_tx.send(command).map_err(|_| PlatformClosed)
+    }
+}
+
+/// Starts the headless prototype backend.
+///
+/// Policy note: when a window becomes visible again, the backend may re-present the latest retained
+/// scene for that window even if the scene version itself did not change. Visibility restoration is
+/// treated as a presentation-affecting state change.
+pub fn start_headless() -> PlatformRuntime {
+    let (command_tx, mut command_rx) = mpsc::unbounded_channel::<PlatformCommand>();
+    let (event_tx, event_rx) = mpsc::unbounded_channel::<PlatformEvent>();
+
+    let worker = spawn_worker(
+        move || {
+            let state = Rc::new(RefCell::new(HeadlessState {
+                events: event_tx.clone(),
+                windows: BTreeMap::new(),
+            }));
+
+            queue_future(async move {
+                debug!(
+                    target: trace_targets::PLATFORM,
+                    event = "worker_started",
+                    backend = "headless",
+                    "starting headless platform worker"
+                );
+
+                while let Some(command) = command_rx.recv().await {
+                    match command {
+                        PlatformCommand::CreateWindow { window_id, spec } => {
+                            handle_create_window(&state, window_id, spec);
+                        }
+                        PlatformCommand::UpdateWindow { window_id, update } => {
+                            handle_update_window(&state, window_id, update);
+                        }
+                        PlatformCommand::ReplaceScene { window_id, scene } => {
+                            handle_replace_scene(&state, window_id, scene);
+                        }
+                        PlatformCommand::EmitCloseRequested { window_id } => {
+                            let sender = state.borrow().events.clone();
+                            let _ = sender.send(PlatformEvent::CloseRequested { window_id });
+                        }
+                        PlatformCommand::Shutdown => {
+                            debug!(
+                                target: trace_targets::PLATFORM,
+                                event = "worker_shutdown_requested",
+                                "shutting down headless platform worker"
+                            );
+                            break;
+                        }
+                    }
+                }
+            });
+        },
+        || {
+            debug!(
+                target: trace_targets::PLATFORM,
+                event = "worker_exited",
+                backend = "headless",
+                "headless platform worker exited"
+            );
+        },
+    );
+
+    PlatformRuntime {
+        proxy: PlatformProxy {
+            command_tx,
+            next_window_id: Arc::new(AtomicU64::new(1)),
+        },
+        events: event_rx,
+        _worker: worker,
+    }
+}
+
+fn handle_create_window(state: &Rc<RefCell<HeadlessState>>, window_id: WindowId, spec: WindowSpec) {
+    debug!(
+        target: trace_targets::PLATFORM,
+        event = "create_window",
+        window_id = window_id.raw(),
+        title = spec.title.as_str(),
+        open = spec.open,
+        visible = spec.visible,
+        "creating logical window"
+    );
+
+    state
+        .borrow_mut()
+        .windows
+        .insert(window_id, HeadlessWindow::new(spec.clone()));
+
+    if spec.open {
+        begin_open_transition(Rc::clone(state), window_id);
+    }
+}
+
+fn handle_update_window(
+    state: &Rc<RefCell<HeadlessState>>,
+    window_id: WindowId,
+    update: WindowUpdate,
+) {
+    let mut action = UpdateAction::None;
+    {
+        let mut state_ref = state.borrow_mut();
+        let Some(window) = state_ref.windows.get_mut(&window_id) else {
+            return;
+        };
+        let was_open = window.spec.open;
+        let was_visible = window.spec.visible;
+        update.apply_to(&mut window.spec);
+
+        if let Some(requested_inner_size) = window.spec.requested_inner_size {
+            window.configuration.actual_inner_size = requested_inner_size;
+        }
+        window.configuration.maximized = window.spec.maximized;
+        window.configuration.fullscreen = window.spec.fullscreen;
+
+        match (was_open, window.spec.open) {
+            (false, true) => action = UpdateAction::Open,
+            (true, false) => action = UpdateAction::Close,
+            _ => {}
+        }
+
+        if was_open == window.spec.open && was_visible != window.spec.visible {
+            action = UpdateAction::Visibility(window.spec.visible);
+        }
+    }
+
+    match action {
+        UpdateAction::None => {
+            maybe_schedule_render(Rc::clone(state), window_id);
+        }
+        UpdateAction::Open => begin_open_transition(Rc::clone(state), window_id),
+        UpdateAction::Close => close_window(state, window_id),
+        UpdateAction::Visibility(visible) => set_visibility(state, window_id, visible),
+    }
+}
+
+fn handle_replace_scene(
+    state: &Rc<RefCell<HeadlessState>>,
+    window_id: WindowId,
+    scene: SceneSnapshot,
+) {
+    #[cfg(debug_assertions)]
+    tracing::trace!(
+        target: trace_targets::PLATFORM,
+        event = "replace_scene",
+        window_id = window_id.raw(),
+        version = scene.version,
+        items = scene.item_count(),
+        "received scene snapshot"
+    );
+
+    if let Some(window) = state.borrow_mut().windows.get_mut(&window_id) {
+        window.pending_scene = Some(scene);
+    } else {
+        return;
+    }
+
+    maybe_schedule_render(Rc::clone(state), window_id);
+}
+
+fn maybe_schedule_render(state: Rc<RefCell<HeadlessState>>, window_id: WindowId) {
+    let should_schedule = {
+        let mut state_ref = state.borrow_mut();
+        let Some(window) = state_ref.windows.get_mut(&window_id) else {
+            return;
+        };
+        if window.render_scheduled {
+            false
+        } else {
+            window.render_scheduled = true;
+            true
+        }
+    };
+
+    if should_schedule {
+        queue_microtask(move || present_latest_scene(&state, window_id));
+    }
+}
+
+fn begin_open_transition(state: Rc<RefCell<HeadlessState>>, window_id: WindowId) {
+    {
+        let mut state_ref = state.borrow_mut();
+        let Some(window) = state_ref.windows.get_mut(&window_id) else {
+            return;
+        };
+        window.lifecycle = WindowLifecycle::Opening;
+    }
+
+    queue_microtask(move || {
+        {
+            let mut state_ref = state.borrow_mut();
+            let Some(window) = state_ref.windows.get_mut(&window_id) else {
+                return;
+            };
+            window.lifecycle = WindowLifecycle::AwaitingInitialConfigure;
+            window.configuration.visible = window.spec.visible;
+            window.configuration.maximized = window.spec.maximized;
+            window.configuration.fullscreen = window.spec.fullscreen;
+            window.lifecycle = if window.spec.visible {
+                WindowLifecycle::OpenVisible
+            } else {
+                WindowLifecycle::OpenHidden
+            };
+        }
+
+        emit_event(
+            &state,
+            PlatformEvent::Configured {
+                window_id,
+                configuration: state
+                    .borrow()
+                    .windows
+                    .get(&window_id)
+                    .expect("window should exist during configure")
+                    .configuration,
+            },
+        );
+        emit_event(&state, PlatformEvent::Opened { window_id });
+        maybe_schedule_render(state, window_id);
+    });
+}
+
+fn close_window(state: &Rc<RefCell<HeadlessState>>, window_id: WindowId) {
+    let should_emit = {
+        let mut state_ref = state.borrow_mut();
+        let Some(window) = state_ref.windows.get_mut(&window_id) else {
+            return;
+        };
+        if window.lifecycle == WindowLifecycle::LogicalClosed {
+            false
+        } else {
+            window.lifecycle = WindowLifecycle::Closing;
+            window.render_scheduled = false;
+            window.configuration.visible = false;
+            window.lifecycle = WindowLifecycle::LogicalClosed;
+            true
+        }
+    };
+
+    if should_emit {
+        emit_event(state, PlatformEvent::Closed { window_id });
+    }
+}
+
+fn set_visibility(state: &Rc<RefCell<HeadlessState>>, window_id: WindowId, visible: bool) {
+    let should_emit = {
+        let mut state_ref = state.borrow_mut();
+        let Some(window) = state_ref.windows.get_mut(&window_id) else {
+            return;
+        };
+        if !window.spec.open {
+            false
+        } else {
+            window.configuration.visible = visible;
+            window.lifecycle = if visible {
+                WindowLifecycle::OpenVisible
+            } else {
+                WindowLifecycle::OpenHidden
+            };
+            true
+        }
+    };
+
+    if should_emit {
+        emit_event(
+            state,
+            PlatformEvent::VisibilityChanged { window_id, visible },
+        );
+        maybe_schedule_render(Rc::clone(state), window_id);
+    }
+}
+
+fn present_latest_scene(state: &Rc<RefCell<HeadlessState>>, window_id: WindowId) {
+    let presentation = {
+        let mut state_ref = state.borrow_mut();
+        let Some(window) = state_ref.windows.get_mut(&window_id) else {
+            return;
+        };
+        window.render_scheduled = false;
+        if window.lifecycle != WindowLifecycle::OpenVisible {
+            return;
+        }
+        let Some(scene) = window.pending_scene.clone() else {
+            return;
+        };
+        Some((scene.version, scene.item_count(), window.spec.title.clone()))
+    };
+
+    let Some((scene_version, item_count, title)) = presentation else {
+        return;
+    };
+
+    info!(
+        target: trace_targets::PLATFORM,
+        event = "present_scene",
+        backend = "headless",
+        window_id = window_id.raw(),
+        title = title.as_str(),
+        scene_version,
+        item_count,
+        "presenting latest scene snapshot"
+    );
+    emit_event(
+        state,
+        PlatformEvent::FramePresented {
+            window_id,
+            scene_version,
+            item_count,
+        },
+    );
+}
+
+fn emit_event(state: &Rc<RefCell<HeadlessState>>, event: PlatformEvent) {
+    let sender = state.borrow().events.clone();
+    let _ = sender.send(event);
+}
+
+enum UpdateAction {
+    None,
+    Open,
+    Close,
+    Visibility(bool),
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{PlatformEvent, start_headless};
+    use crate::scene::{Color, Point, PreparedText, Rect, SceneSnapshot, UiSize};
+    use crate::window::{WindowSpec, WindowUpdate};
+    use ruin_runtime::{current_thread_handle, queue_future, run};
+    use std::sync::{Arc, Mutex};
+
+    #[test]
+    fn headless_platform_coalesces_latest_scene_per_window() {
+        let observed = Arc::new(Mutex::new(Vec::<PlatformEvent>::new()));
+        let done = Arc::new(Mutex::new(false));
+        let main = current_thread_handle();
+
+        queue_future({
+            let observed = Arc::clone(&observed);
+            let done = Arc::clone(&done);
+            async move {
+                let mut platform = start_headless();
+                let proxy = platform.proxy();
+                let window_id = proxy
+                    .create_window(
+                        WindowSpec::new("coalesce").requested_inner_size(UiSize::new(320.0, 180.0)),
+                    )
+                    .expect("window should be created");
+
+                let mut one = SceneSnapshot::new(1, UiSize::new(320.0, 180.0));
+                one.push_quad(
+                    Rect::new(0.0, 0.0, 320.0, 180.0),
+                    Color::rgb(0x22, 0x22, 0x33),
+                );
+                let mut two = SceneSnapshot::new(2, UiSize::new(320.0, 180.0));
+                two.push_quad(
+                    Rect::new(0.0, 0.0, 320.0, 180.0),
+                    Color::rgb(0x33, 0x22, 0x22),
+                );
+                let mut three = SceneSnapshot::new(3, UiSize::new(320.0, 180.0));
+                three
+                    .push_quad(
+                        Rect::new(0.0, 0.0, 320.0, 180.0),
+                        Color::rgb(0x22, 0x33, 0x22),
+                    )
+                    .push_text(PreparedText::monospace(
+                        "v3",
+                        Point::new(16.0, 28.0),
+                        16.0,
+                        8.0,
+                        Color::rgb(0xFF, 0xFF, 0xFF),
+                    ));
+
+                proxy
+                    .replace_scene(window_id, one)
+                    .expect("scene v1 should queue");
+                proxy
+                    .replace_scene(window_id, two)
+                    .expect("scene v2 should queue");
+                proxy
+                    .replace_scene(window_id, three)
+                    .expect("scene v3 should queue");
+
+                while let Some(event) = platform.next_event().await {
+                    observed.lock().unwrap().push(event.clone());
+                    if let PlatformEvent::FramePresented {
+                        window_id: presented,
+                        scene_version,
+                        ..
+                    } = event
+                    {
+                        assert_eq!(presented, window_id);
+                        assert_eq!(scene_version, 3);
+                        proxy.shutdown().expect("shutdown should queue");
+                        break;
+                    }
+                }
+
+                while platform.next_event().await.is_some() {}
+                *done.lock().unwrap() = true;
+                let _ = main.queue_task(|| {});
+            }
+        });
+
+        run();
+        assert!(*done.lock().unwrap());
+    }
+
+    #[test]
+    fn open_false_closes_and_reopen_reconfigures() {
+        let counts = Arc::new(Mutex::new((0usize, 0usize, 0usize)));
+        let done = Arc::new(Mutex::new(false));
+        let main = current_thread_handle();
+
+        queue_future({
+            let counts = Arc::clone(&counts);
+            let done = Arc::clone(&done);
+            async move {
+                let mut platform = start_headless();
+                let proxy = platform.proxy();
+                let window_id = proxy
+                    .create_window(
+                        WindowSpec::new("reopen").requested_inner_size(UiSize::new(640.0, 360.0)),
+                    )
+                    .expect("window should be created");
+
+                let mut saw_initial_open = false;
+                while let Some(event) = platform.next_event().await {
+                    match event {
+                        PlatformEvent::Configured { window_id: id, .. } if id == window_id => {
+                            counts.lock().unwrap().0 += 1;
+                        }
+                        PlatformEvent::Opened { window_id: id } if id == window_id => {
+                            counts.lock().unwrap().1 += 1;
+                            if !saw_initial_open {
+                                saw_initial_open = true;
+                                proxy
+                                    .update_window(window_id, WindowUpdate::new().open(false))
+                                    .expect("close should queue");
+                                proxy
+                                    .update_window(window_id, WindowUpdate::new().open(true))
+                                    .expect("reopen should queue");
+                            }
+                        }
+                        PlatformEvent::Closed { window_id: id } if id == window_id => {
+                            counts.lock().unwrap().2 += 1;
+                        }
+                        _ => {}
+                    }
+
+                    let (configured, opened, closed) = *counts.lock().unwrap();
+                    if configured >= 2 && opened >= 2 && closed >= 1 {
+                        proxy.shutdown().expect("shutdown should queue");
+                        break;
+                    }
+                }
+
+                while platform.next_event().await.is_some() {}
+                *done.lock().unwrap() = true;
+                let _ = main.queue_task(|| {});
+            }
+        });
+
+        run();
+        let (configured, opened, closed) = *counts.lock().unwrap();
+        assert_eq!(configured, 2);
+        assert_eq!(opened, 2);
+        assert_eq!(closed, 1);
+        assert!(*done.lock().unwrap());
+    }
+}

lib/ui/src/runtime.rs

@@ -0,0 +1,238 @@
+//! Explicit-construction UI runtime helpers.
+
+use ruin_reactivity::{EffectHandle, effect};
+
+use crate::platform::{PlatformClosed, PlatformEvent, PlatformProxy, PlatformRuntime};
+use crate::scene::SceneSnapshot;
+use crate::window::{WindowId, WindowSpec, WindowUpdate};
+
+/// High-level UI-side owner of platform event consumption.
+///
+/// The headless backend currently co-locates platform and rendering on one worker thread, but this
+/// runtime type deliberately treats them as logical subsystems behind an event/snapshot boundary so
+/// future backends can split them without rewriting the app-facing control flow.
+pub struct UiRuntime {
+    platform: PlatformRuntime,
+}
+
+/// Explicit handle for one declarative window instance.
+///
+/// The controller owns no native resources directly. Instead, it issues commands to the platform
+/// runtime and can host a reactive scene effect that pushes immutable scene snapshots whenever UI
+/// state changes.
+#[derive(Clone)]
+pub struct WindowController {
+    id: WindowId,
+    proxy: PlatformProxy,
+}
+
+/// Returned when the platform event stream closes before a matching event is observed.
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub struct EventStreamClosed;
+
+impl std::fmt::Display for EventStreamClosed {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str("platform event stream closed")
+    }
+}
+
+impl std::error::Error for EventStreamClosed {}
+
+impl UiRuntime {
+    /// Creates a UI runtime backed by the headless prototype backend.
+    pub fn headless() -> Self {
+        Self {
+            platform: PlatformRuntime::headless(),
+        }
+    }
+
+    /// Returns a cloneable proxy for low-level platform commands.
+    pub fn proxy(&self) -> PlatformProxy {
+        self.platform.proxy()
+    }
+
+    /// Creates a new declarative window and returns a controller for it.
+    pub fn create_window(&self, spec: WindowSpec) -> Result<WindowController, PlatformClosed> {
+        let id = self.proxy().create_window(spec)?;
+        Ok(WindowController {
+            id,
+            proxy: self.proxy(),
+        })
+    }
+
+    /// Waits for the next platform event.
+    pub async fn next_event(&mut self) -> Option<PlatformEvent> {
+        self.platform.next_event().await
+    }
+
+    /// Waits until an event matches `predicate`.
+    pub async fn wait_for_event_matching(
+        &mut self,
+        mut predicate: impl FnMut(&PlatformEvent) -> bool,
+    ) -> Result<PlatformEvent, EventStreamClosed> {
+        while let Some(event) = self.next_event().await {
+            if predicate(&event) {
+                return Ok(event);
+            }
+        }
+        Err(EventStreamClosed)
+    }
+
+    /// Requests shutdown of the platform runtime.
+    pub fn shutdown(&self) -> Result<(), PlatformClosed> {
+        self.proxy().shutdown()
+    }
+}
+
+impl WindowController {
+    /// Returns the logical window identifier.
+    pub const fn id(&self) -> WindowId {
+        self.id
+    }
+
+    /// Applies a window update.
+    pub fn update(&self, update: WindowUpdate) -> Result<(), PlatformClosed> {
+        self.proxy.update_window(self.id, update)
+    }
+
+    /// Replaces the latest retained scene for this window.
+    pub fn replace_scene(&self, scene: SceneSnapshot) -> Result<(), PlatformClosed> {
+        self.proxy.replace_scene(self.id, scene)
+    }
+
+    /// Emits a close-request event for this window.
+    pub fn emit_close_requested(&self) -> Result<(), PlatformClosed> {
+        self.proxy.emit_close_requested(self.id)
+    }
+
+    /// Attaches a reactive effect that rebuilds and replaces the window scene whenever dependent UI
+    /// state changes.
+    pub fn attach_scene_effect(
+        &self,
+        build_scene: impl Fn() -> SceneSnapshot + 'static,
+    ) -> EffectHandle {
+        let controller = self.clone();
+        effect(move || {
+            let scene = build_scene();
+            controller
+                .replace_scene(scene)
+                .expect("window controller should remain alive while scene effect is attached");
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::UiRuntime;
+    use crate::platform::PlatformEvent;
+    use crate::scene::{Color, Point, PreparedText, Rect, SceneSnapshot, UiSize};
+    use crate::window::{WindowSpec, WindowUpdate};
+    use ruin_runtime::{current_thread_handle, queue_future, run};
+    use std::future::Future;
+
+    fn run_async_test(future: impl Future<Output = ()> + 'static) {
+        let main = current_thread_handle();
+        queue_future(async move {
+            future.await;
+            let _ = main.queue_task(|| {});
+        });
+        run();
+    }
+
+    #[test]
+    fn visibility_restore_re_presents_latest_retained_scene() {
+        run_async_test(async move {
+            let mut ui = UiRuntime::headless();
+            let window = ui
+                .create_window(WindowSpec::new("visibility-policy").visible(true))
+                .expect("window should be created");
+
+            let mut scene = SceneSnapshot::new(1, UiSize::new(320.0, 180.0));
+            scene
+                .push_quad(
+                    Rect::new(0.0, 0.0, 320.0, 180.0),
+                    Color::rgb(0x20, 0x22, 0x35),
+                )
+                .push_text(PreparedText::monospace(
+                    "retained scene",
+                    Point::new(16.0, 28.0),
+                    16.0,
+                    8.0,
+                    Color::rgb(0xFF, 0xFF, 0xFF),
+                ));
+            window
+                .replace_scene(scene)
+                .expect("scene replacement should queue");
+
+            let _ = ui
+                .wait_for_event_matching(|event| {
+                    matches!(
+                        event,
+                        PlatformEvent::FramePresented {
+                            window_id,
+                            scene_version: 1,
+                            ..
+                        } if *window_id == window.id()
+                    )
+                })
+                .await
+                .expect("initial present should occur");
+
+            window
+                .update(WindowUpdate::new().visible(false))
+                .expect("hide should queue");
+            let _ = ui
+                .wait_for_event_matching(|event| {
+                    matches!(
+                        event,
+                        PlatformEvent::VisibilityChanged {
+                            window_id,
+                            visible: false,
+                        } if *window_id == window.id()
+                    )
+                })
+                .await
+                .expect("hide event should occur");
+
+            window
+                .update(WindowUpdate::new().visible(true))
+                .expect("show should queue");
+            let _ = ui
+                .wait_for_event_matching(|event| {
+                    matches!(
+                        event,
+                        PlatformEvent::VisibilityChanged {
+                            window_id,
+                            visible: true,
+                        } if *window_id == window.id()
+                    )
+                })
+                .await
+                .expect("show event should occur");
+
+            let event = ui
+                .wait_for_event_matching(|event| {
+                    matches!(
+                        event,
+                        PlatformEvent::FramePresented {
+                            window_id,
+                            scene_version: 1,
+                            ..
+                        } if *window_id == window.id()
+                    )
+                })
+                .await
+                .expect("visibility restore should re-present latest retained scene");
+
+            assert!(matches!(
+                event,
+                PlatformEvent::FramePresented {
+                    scene_version: 1,
+                    ..
+                }
+            ));
+
+            ui.shutdown().expect("shutdown should queue");
+        });
+    }
+}

lib/ui/src/scene.rs

@@ -0,0 +1,210 @@
+//! Renderer-oriented scene snapshot types.
+
+use tracing::debug;
+
+use crate::trace_targets;
+
+pub type SceneVersion = u64;
+
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct Point {
+    pub x: f32,
+    pub y: f32,
+}
+
+impl Point {
+    pub const fn new(x: f32, y: f32) -> Self {
+        Self { x, y }
+    }
+}
+
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct UiSize {
+    pub width: f32,
+    pub height: f32,
+}
+
+impl UiSize {
+    pub const fn new(width: f32, height: f32) -> Self {
+        Self { width, height }
+    }
+}
+
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct Rect {
+    pub origin: Point,
+    pub size: UiSize,
+}
+
+impl Rect {
+    pub const fn new(x: f32, y: f32, width: f32, height: f32) -> Self {
+        Self {
+            origin: Point::new(x, y),
+            size: UiSize::new(width, height),
+        }
+    }
+}
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub struct Color {
+    pub r: u8,
+    pub g: u8,
+    pub b: u8,
+    pub a: u8,
+}
+
+impl Color {
+    pub const fn rgba(r: u8, g: u8, b: u8, a: u8) -> Self {
+        Self { r, g, b, a }
+    }
+
+    pub const fn rgb(r: u8, g: u8, b: u8) -> Self {
+        Self::rgba(r, g, b, 255)
+    }
+}
+
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct Translation {
+    pub x: f32,
+    pub y: f32,
+}
+
+impl Translation {
+    pub const fn new(x: f32, y: f32) -> Self {
+        Self { x, y }
+    }
+}
+
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct Quad {
+    pub rect: Rect,
+    pub color: Color,
+}
+
+impl Quad {
+    pub const fn new(rect: Rect, color: Color) -> Self {
+        Self { rect, color }
+    }
+}
+
+#[derive(Clone, Debug, PartialEq)]
+pub struct GlyphInstance {
+    pub glyph: String,
+    pub position: Point,
+    pub advance: f32,
+}
+
+#[derive(Clone, Debug, PartialEq)]
+pub struct PreparedText {
+    pub text: String,
+    pub font_size: f32,
+    pub color: Color,
+    pub glyphs: Vec<GlyphInstance>,
+}
+
+impl PreparedText {
+    pub fn monospace(
+        text: impl Into<String>,
+        origin: Point,
+        font_size: f32,
+        advance: f32,
+        color: Color,
+    ) -> Self {
+        let text = text.into();
+        let mut x = origin.x;
+        let mut glyphs = Vec::with_capacity(text.chars().count());
+        for ch in text.chars() {
+            glyphs.push(GlyphInstance {
+                glyph: ch.to_string(),
+                position: Point::new(x, origin.y),
+                advance,
+            });
+            x += advance;
+        }
+
+        Self {
+            text,
+            font_size,
+            color,
+            glyphs,
+        }
+    }
+}
+
+#[derive(Clone, Debug, PartialEq)]
+pub enum DisplayItem {
+    Quad(Quad),
+    Text(PreparedText),
+    PushClip(Rect),
+    PopClip,
+    PushTransform(Translation),
+    PopTransform,
+    LayerBegin { opacity: f32 },
+    LayerEnd,
+}
+
+#[derive(Clone, Debug, PartialEq)]
+pub struct SceneSnapshot {
+    pub version: SceneVersion,
+    pub logical_size: UiSize,
+    pub items: Vec<DisplayItem>,
+}
+
+impl SceneSnapshot {
+    pub fn new(version: SceneVersion, logical_size: UiSize) -> Self {
+        debug!(
+            target: trace_targets::SCENE,
+            event = "create_scene",
+            version,
+            width = logical_size.width,
+            height = logical_size.height,
+            "creating scene snapshot"
+        );
+        Self {
+            version,
+            logical_size,
+            items: Vec::new(),
+        }
+    }
+
+    pub fn item_count(&self) -> usize {
+        self.items.len()
+    }
+
+    pub fn push_item(&mut self, item: DisplayItem) -> &mut Self {
+        self.items.push(item);
+        self
+    }
+
+    pub fn push_quad(&mut self, rect: Rect, color: Color) -> &mut Self {
+        self.push_item(DisplayItem::Quad(Quad::new(rect, color)))
+    }
+
+    pub fn push_text(&mut self, text: PreparedText) -> &mut Self {
+        self.push_item(DisplayItem::Text(text))
+    }
+
+    pub fn push_clip(&mut self, rect: Rect) -> &mut Self {
+        self.push_item(DisplayItem::PushClip(rect))
+    }
+
+    pub fn pop_clip(&mut self) -> &mut Self {
+        self.push_item(DisplayItem::PopClip)
+    }
+
+    pub fn push_transform(&mut self, translation: Translation) -> &mut Self {
+        self.push_item(DisplayItem::PushTransform(translation))
+    }
+
+    pub fn pop_transform(&mut self) -> &mut Self {
+        self.push_item(DisplayItem::PopTransform)
+    }
+
+    pub fn begin_layer(&mut self, opacity: f32) -> &mut Self {
+        self.push_item(DisplayItem::LayerBegin { opacity })
+    }
+
+    pub fn end_layer(&mut self) -> &mut Self {
+        self.push_item(DisplayItem::LayerEnd)
+    }
+}

lib/ui/src/window.rs

@@ -0,0 +1,235 @@
+//! Common window model types.
+
+use crate::scene::UiSize;
+
+#[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
+pub struct WindowId(u64);
+
+impl WindowId {
+    pub const fn from_raw(raw: u64) -> Self {
+        Self(raw)
+    }
+
+    pub const fn raw(self) -> u64 {
+        self.0
+    }
+}
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum DecorationMode {
+    Auto,
+    Server,
+    Client,
+}
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum WindowLifecycle {
+    LogicalClosed,
+    Opening,
+    AwaitingInitialConfigure,
+    OpenHidden,
+    OpenVisible,
+    Closing,
+}
+
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct WindowConfigured {
+    pub actual_inner_size: UiSize,
+    pub scale_factor: f32,
+    pub visible: bool,
+    pub maximized: bool,
+    pub fullscreen: bool,
+}
+
+#[derive(Clone, Debug, PartialEq)]
+pub struct WindowSpec {
+    pub key: Option<String>,
+    pub title: String,
+    pub app_id: Option<String>,
+    pub open: bool,
+    pub visible: bool,
+    pub requested_inner_size: Option<UiSize>,
+    pub min_inner_size: Option<UiSize>,
+    pub max_inner_size: Option<UiSize>,
+    pub decorations: DecorationMode,
+    pub maximized: bool,
+    pub fullscreen: bool,
+    pub resizable: bool,
+}
+
+impl WindowSpec {
+    pub fn new(title: impl Into<String>) -> Self {
+        Self {
+            key: None,
+            title: title.into(),
+            app_id: None,
+            open: true,
+            visible: true,
+            requested_inner_size: None,
+            min_inner_size: None,
+            max_inner_size: None,
+            decorations: DecorationMode::Auto,
+            maximized: false,
+            fullscreen: false,
+            resizable: true,
+        }
+    }
+
+    pub fn key(mut self, key: impl Into<String>) -> Self {
+        self.key = Some(key.into());
+        self
+    }
+
+    pub fn app_id(mut self, app_id: impl Into<String>) -> Self {
+        self.app_id = Some(app_id.into());
+        self
+    }
+
+    pub fn open(mut self, open: bool) -> Self {
+        self.open = open;
+        self
+    }
+
+    pub fn visible(mut self, visible: bool) -> Self {
+        self.visible = visible;
+        self
+    }
+
+    pub fn requested_inner_size(mut self, size: UiSize) -> Self {
+        self.requested_inner_size = Some(size);
+        self
+    }
+
+    pub fn min_inner_size(mut self, size: UiSize) -> Self {
+        self.min_inner_size = Some(size);
+        self
+    }
+
+    pub fn max_inner_size(mut self, size: UiSize) -> Self {
+        self.max_inner_size = Some(size);
+        self
+    }
+
+    pub fn decorations(mut self, decorations: DecorationMode) -> Self {
+        self.decorations = decorations;
+        self
+    }
+
+    pub fn maximized(mut self, maximized: bool) -> Self {
+        self.maximized = maximized;
+        self
+    }
+
+    pub fn fullscreen(mut self, fullscreen: bool) -> Self {
+        self.fullscreen = fullscreen;
+        self
+    }
+
+    pub fn resizable(mut self, resizable: bool) -> Self {
+        self.resizable = resizable;
+        self
+    }
+}
+
+#[derive(Clone, Debug, Default, PartialEq)]
+pub struct WindowUpdate {
+    pub title: Option<String>,
+    pub open: Option<bool>,
+    pub visible: Option<bool>,
+    pub requested_inner_size: Option<Option<UiSize>>,
+    pub min_inner_size: Option<Option<UiSize>>,
+    pub max_inner_size: Option<Option<UiSize>>,
+    pub decorations: Option<DecorationMode>,
+    pub maximized: Option<bool>,
+    pub fullscreen: Option<bool>,
+    pub resizable: Option<bool>,
+}
+
+impl WindowUpdate {
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    pub fn title(mut self, title: impl Into<String>) -> Self {
+        self.title = Some(title.into());
+        self
+    }
+
+    pub fn open(mut self, open: bool) -> Self {
+        self.open = Some(open);
+        self
+    }
+
+    pub fn visible(mut self, visible: bool) -> Self {
+        self.visible = Some(visible);
+        self
+    }
+
+    pub fn requested_inner_size(mut self, size: Option<UiSize>) -> Self {
+        self.requested_inner_size = Some(size);
+        self
+    }
+
+    pub fn min_inner_size(mut self, size: Option<UiSize>) -> Self {
+        self.min_inner_size = Some(size);
+        self
+    }
+
+    pub fn max_inner_size(mut self, size: Option<UiSize>) -> Self {
+        self.max_inner_size = Some(size);
+        self
+    }
+
+    pub fn decorations(mut self, decorations: DecorationMode) -> Self {
+        self.decorations = Some(decorations);
+        self
+    }
+
+    pub fn maximized(mut self, maximized: bool) -> Self {
+        self.maximized = Some(maximized);
+        self
+    }
+
+    pub fn fullscreen(mut self, fullscreen: bool) -> Self {
+        self.fullscreen = Some(fullscreen);
+        self
+    }
+
+    pub fn resizable(mut self, resizable: bool) -> Self {
+        self.resizable = Some(resizable);
+        self
+    }
+
+    pub(crate) fn apply_to(&self, spec: &mut WindowSpec) {
+        if let Some(title) = &self.title {
+            spec.title = title.clone();
+        }
+        if let Some(open) = self.open {
+            spec.open = open;
+        }
+        if let Some(visible) = self.visible {
+            spec.visible = visible;
+        }
+        if let Some(requested_inner_size) = self.requested_inner_size {
+            spec.requested_inner_size = requested_inner_size;
+        }
+        if let Some(min_inner_size) = self.min_inner_size {
+            spec.min_inner_size = min_inner_size;
+        }
+        if let Some(max_inner_size) = self.max_inner_size {
+            spec.max_inner_size = max_inner_size;
+        }
+        if let Some(decorations) = self.decorations {
+            spec.decorations = decorations;
+        }
+        if let Some(maximized) = self.maximized {
+            spec.maximized = maximized;
+        }
+        if let Some(fullscreen) = self.fullscreen {
+            spec.fullscreen = fullscreen;
+        }
+        if let Some(resizable) = self.resizable {
+            spec.resizable = resizable;
+        }
+    }
+}

lib/ui_platform_wayland/Cargo.toml

@@ -0,0 +1,11 @@
+[package]
+name = "ruin_ui_platform_wayland"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+raw-window-handle = "0.6"
+ruin_ui = { path = "../ui" }
+wayland-backend = { version = "0.3", features = ["client_system"] }
+wayland-client = "0.31"
+wayland-protocols = { version = "0.32", features = ["client"] }

lib/ui_platform_wayland/src/lib.rs

@@ -0,0 +1,271 @@
+use std::error::Error;
+use std::ffi::c_void;
+use std::num::NonZeroU32;
+use std::ptr::NonNull;
+
+use raw_window_handle::{
+    DisplayHandle, HandleError, HasDisplayHandle, HasWindowHandle, RawDisplayHandle,
+    RawWindowHandle, WaylandDisplayHandle, WaylandWindowHandle, WindowHandle,
+};
+use ruin_ui::{UiSize, WindowSpec};
+use wayland_client::globals::{GlobalListContents, registry_queue_init};
+use wayland_client::protocol::{wl_compositor, wl_registry, wl_surface};
+use wayland_client::{Connection, Dispatch, Proxy, QueueHandle, delegate_noop};
+use wayland_protocols::xdg::shell::client::{xdg_surface, xdg_toplevel, xdg_wm_base};
+
+#[derive(Clone)]
+pub struct WaylandSurfaceTarget {
+    connection: Connection,
+    surface: wl_surface::WlSurface,
+}
+
+impl HasDisplayHandle for WaylandSurfaceTarget {
+    fn display_handle(&self) -> Result<DisplayHandle<'_>, HandleError> {
+        let ptr = NonNull::new(self.connection.backend().display_ptr().cast::<c_void>())
+            .ok_or(HandleError::Unavailable)?;
+        let raw = RawDisplayHandle::Wayland(WaylandDisplayHandle::new(ptr));
+        Ok(unsafe { DisplayHandle::borrow_raw(raw) })
+    }
+}
+
+impl HasWindowHandle for WaylandSurfaceTarget {
+    fn window_handle(&self) -> Result<WindowHandle<'_>, HandleError> {
+        let ptr = NonNull::new(self.surface.id().as_ptr().cast::<c_void>())
+            .ok_or(HandleError::Unavailable)?;
+        let raw = RawWindowHandle::Wayland(WaylandWindowHandle::new(ptr));
+        Ok(unsafe { WindowHandle::borrow_raw(raw) })
+    }
+}
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub struct FrameRequest {
+    pub width: u32,
+    pub height: u32,
+    pub resized: bool,
+}
+
+pub struct WaylandWindow {
+    event_queue: wayland_client::EventQueue<State>,
+    surface_target: WaylandSurfaceTarget,
+    state: State,
+}
+
+struct State {
+    running: bool,
+    _connection: Connection,
+    _compositor: wl_compositor::WlCompositor,
+    _surface: wl_surface::WlSurface,
+    _xdg_surface: xdg_surface::XdgSurface,
+    _toplevel: xdg_toplevel::XdgToplevel,
+    _wm_base: xdg_wm_base::XdgWmBase,
+    current_size: (u32, u32),
+    configured: bool,
+    pending_size: Option<(u32, u32)>,
+    needs_redraw: bool,
+}
+
+impl State {
+    fn request_redraw(&mut self) {
+        self.needs_redraw = true;
+    }
+}
+
+impl WaylandWindow {
+    pub fn open(spec: WindowSpec) -> Result<Self, Box<dyn Error>> {
+        let connection = Connection::connect_to_env()?;
+        let (globals, event_queue) = registry_queue_init::<State>(&connection)?;
+        let qh = event_queue.handle();
+
+        let compositor: wl_compositor::WlCompositor = globals.bind(&qh, 4..=6, ())?;
+        let wm_base: xdg_wm_base::XdgWmBase = globals.bind(&qh, 1..=6, ())?;
+        let surface = compositor.create_surface(&qh, ());
+        let xdg_surface = wm_base.get_xdg_surface(&surface, &qh, ());
+        let toplevel = xdg_surface.get_toplevel(&qh, ());
+        toplevel.set_title(spec.title.clone());
+        if let Some(app_id) = spec.app_id.as_ref() {
+            toplevel.set_app_id(app_id.clone());
+        }
+
+        apply_size_constraints(&toplevel, &spec);
+        if spec.maximized {
+            toplevel.set_maximized();
+        }
+        if spec.fullscreen {
+            toplevel.set_fullscreen(None);
+        }
+
+        surface.commit();
+        connection.flush()?;
+
+        let initial_size = spec
+            .requested_inner_size
+            .unwrap_or_else(|| UiSize::new(800.0, 500.0));
+        let initial_width = initial_size.width.max(1.0).round() as u32;
+        let initial_height = initial_size.height.max(1.0).round() as u32;
+        let surface_target = WaylandSurfaceTarget {
+            connection: connection.clone(),
+            surface: surface.clone(),
+        };
+
+        Ok(Self {
+            event_queue,
+            surface_target,
+            state: State {
+                running: true,
+                _connection: connection,
+                _compositor: compositor,
+                _surface: surface,
+                _xdg_surface: xdg_surface,
+                _toplevel: toplevel,
+                _wm_base: wm_base,
+                current_size: (initial_width, initial_height),
+                configured: false,
+                pending_size: None,
+                needs_redraw: false,
+            },
+        })
+    }
+
+    pub fn surface_target(&self) -> WaylandSurfaceTarget {
+        self.surface_target.clone()
+    }
+
+    pub fn is_running(&self) -> bool {
+        self.state.running
+    }
+
+    pub fn dispatch(&mut self) -> Result<(), Box<dyn Error>> {
+        self.event_queue.blocking_dispatch(&mut self.state)?;
+        Ok(())
+    }
+
+    pub fn request_redraw(&mut self) {
+        self.state.request_redraw();
+    }
+
+    pub fn prepare_frame(&mut self) -> Option<FrameRequest> {
+        if !self.state.configured {
+            return None;
+        }
+
+        if let Some((width, height)) = self.state.pending_size.take() {
+            self.state.current_size = (width, height);
+            self.state.needs_redraw = false;
+            return Some(FrameRequest {
+                width,
+                height,
+                resized: true,
+            });
+        }
+
+        if self.state.needs_redraw {
+            self.state.needs_redraw = false;
+            return Some(FrameRequest {
+                width: self.state.current_size.0,
+                height: self.state.current_size.1,
+                resized: false,
+            });
+        }
+
+        None
+    }
+}
+
+impl Dispatch<wl_registry::WlRegistry, GlobalListContents> for State {
+    fn event(
+        _state: &mut Self,
+        _proxy: &wl_registry::WlRegistry,
+        _event: wl_registry::Event,
+        _data: &GlobalListContents,
+        _conn: &Connection,
+        _qh: &QueueHandle<Self>,
+    ) {
+    }
+}
+
+delegate_noop!(State: ignore wl_compositor::WlCompositor);
+delegate_noop!(State: ignore wl_surface::WlSurface);
+
+impl Dispatch<xdg_wm_base::XdgWmBase, ()> for State {
+    fn event(
+        _state: &mut Self,
+        wm_base: &xdg_wm_base::XdgWmBase,
+        event: xdg_wm_base::Event,
+        _data: &(),
+        _conn: &Connection,
+        _qh: &QueueHandle<Self>,
+    ) {
+        if let xdg_wm_base::Event::Ping { serial } = event {
+            wm_base.pong(serial);
+        }
+    }
+}
+
+impl Dispatch<xdg_surface::XdgSurface, ()> for State {
+    fn event(
+        state: &mut Self,
+        xdg_surface: &xdg_surface::XdgSurface,
+        event: xdg_surface::Event,
+        _data: &(),
+        _conn: &Connection,
+        _qh: &QueueHandle<Self>,
+    ) {
+        if let xdg_surface::Event::Configure { serial } = event {
+            xdg_surface.ack_configure(serial);
+            state.configured = true;
+            state.request_redraw();
+        }
+    }
+}
+
+impl Dispatch<xdg_toplevel::XdgToplevel, ()> for State {
+    fn event(
+        state: &mut Self,
+        _proxy: &xdg_toplevel::XdgToplevel,
+        event: xdg_toplevel::Event,
+        _data: &(),
+        _conn: &Connection,
+        _qh: &QueueHandle<Self>,
+    ) {
+        match event {
+            xdg_toplevel::Event::Close => {
+                state.running = false;
+            }
+            xdg_toplevel::Event::Configure {
+                width,
+                height,
+                states: _,
+            } => {
+                let width = NonZeroU32::new(width as u32)
+                    .map(NonZeroU32::get)
+                    .unwrap_or(state.current_size.0);
+                let height = NonZeroU32::new(height as u32)
+                    .map(NonZeroU32::get)
+                    .unwrap_or(state.current_size.1);
+                state.pending_size = Some((width, height));
+                state.request_redraw();
+            }
+            _ => {}
+        }
+    }
+}
+
+fn apply_size_constraints(toplevel: &xdg_toplevel::XdgToplevel, spec: &WindowSpec) {
+    if spec.resizable {
+        let min = spec.min_inner_size.unwrap_or_else(|| UiSize::new(0.0, 0.0));
+        let max = spec.max_inner_size.unwrap_or_else(|| UiSize::new(0.0, 0.0));
+        toplevel.set_min_size(min.width.round() as i32, min.height.round() as i32);
+        toplevel.set_max_size(max.width.round() as i32, max.height.round() as i32);
+        return;
+    }
+
+    let fixed = spec
+        .requested_inner_size
+        .or(spec.min_inner_size)
+        .or(spec.max_inner_size)
+        .unwrap_or_else(|| UiSize::new(800.0, 500.0));
+    let width = fixed.width.max(1.0).round() as i32;
+    let height = fixed.height.max(1.0).round() as i32;
+    toplevel.set_min_size(width, height);
+    toplevel.set_max_size(width, height);
+}

lib/ui_renderer_wgpu/Cargo.toml

@@ -0,0 +1,11 @@
+[package]
+name = "ruin_ui_renderer_wgpu"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+bytemuck = { version = "1", features = ["derive"] }
+pollster = "0.4"
+raw-window-handle = "0.6"
+ruin_ui = { path = "../ui" }
+wgpu = "29"

lib/ui_renderer_wgpu/src/lib.rs

@@ -0,0 +1,317 @@
+use std::error::Error;
+
+use bytemuck::{Pod, Zeroable};
+use raw_window_handle::{HasDisplayHandle, HasWindowHandle};
+use ruin_ui::{Color, DisplayItem, Rect, SceneSnapshot};
+use wgpu::util::DeviceExt;
+
+#[repr(C)]
+#[derive(Clone, Copy, Pod, Zeroable)]
+struct Vertex {
+    position: [f32; 2],
+    color: [f32; 4],
+}
+
+const VERTEX_ATTRIBUTES: [wgpu::VertexAttribute; 2] =
+    wgpu::vertex_attr_array![0 => Float32x2, 1 => Float32x4];
+
+impl Vertex {
+    const LAYOUT: wgpu::VertexBufferLayout<'static> = wgpu::VertexBufferLayout {
+        array_stride: std::mem::size_of::<Vertex>() as u64,
+        step_mode: wgpu::VertexStepMode::Vertex,
+        attributes: &VERTEX_ATTRIBUTES,
+    };
+
+    fn layout() -> wgpu::VertexBufferLayout<'static> {
+        Self::LAYOUT
+    }
+}
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum RenderError {
+    Lost,
+    Outdated,
+    Timeout,
+    Occluded,
+    Validation,
+}
+
+pub struct WgpuSceneRenderer {
+    surface: wgpu::Surface<'static>,
+    device: wgpu::Device,
+    queue: wgpu::Queue,
+    config: wgpu::SurfaceConfiguration,
+    pipeline: wgpu::RenderPipeline,
+}
+
+impl WgpuSceneRenderer {
+    pub fn new(
+        target: impl HasDisplayHandle + HasWindowHandle + Send + Sync + 'static,
+        width: u32,
+        height: u32,
+    ) -> Result<Self, Box<dyn Error>> {
+        let instance = wgpu::Instance::new(wgpu::InstanceDescriptor::new_without_display_handle());
+        let surface = instance.create_surface(target)?;
+        let adapter = pollster::block_on(instance.request_adapter(&wgpu::RequestAdapterOptions {
+            power_preference: wgpu::PowerPreference::HighPerformance,
+            force_fallback_adapter: false,
+            compatible_surface: Some(&surface),
+        }))?;
+        let (device, queue) =
+            pollster::block_on(adapter.request_device(&wgpu::DeviceDescriptor::default()))?;
+
+        let caps = surface.get_capabilities(&adapter);
+        let format = caps
+            .formats
+            .iter()
+            .copied()
+            .find(wgpu::TextureFormat::is_srgb)
+            .unwrap_or(caps.formats[0]);
+        let config = wgpu::SurfaceConfiguration {
+            usage: wgpu::TextureUsages::RENDER_ATTACHMENT,
+            format,
+            width: width.max(1),
+            height: height.max(1),
+            present_mode: wgpu::PresentMode::AutoVsync,
+            desired_maximum_frame_latency: 2,
+            alpha_mode: caps.alpha_modes[0],
+            view_formats: vec![],
+        };
+        surface.configure(&device, &config);
+
+        let shader = device.create_shader_module(wgpu::ShaderModuleDescriptor {
+            label: Some("ruin-ui-renderer-wgpu-shader"),
+            source: wgpu::ShaderSource::Wgsl(
+                r#"
+struct VertexIn {
+    @location(0) position: vec2<f32>,
+    @location(1) color: vec4<f32>,
+};
+
+struct VertexOut {
+    @builtin(position) position: vec4<f32>,
+    @location(0) color: vec4<f32>,
+};
+
+@vertex
+fn vs_main(input: VertexIn) -> VertexOut {
+    var out: VertexOut;
+    out.position = vec4(input.position, 0.0, 1.0);
+    out.color = input.color;
+    return out;
+}
+
+@fragment
+fn fs_main(input: VertexOut) -> @location(0) vec4<f32> {
+    return input.color;
+}
+"#
+                .into(),
+            ),
+        });
+
+        let pipeline_layout = device.create_pipeline_layout(&wgpu::PipelineLayoutDescriptor {
+            label: Some("ruin-ui-renderer-wgpu-pipeline-layout"),
+            bind_group_layouts: &[],
+            immediate_size: 0,
+        });
+        let pipeline = device.create_render_pipeline(&wgpu::RenderPipelineDescriptor {
+            label: Some("ruin-ui-renderer-wgpu-pipeline"),
+            layout: Some(&pipeline_layout),
+            vertex: wgpu::VertexState {
+                module: &shader,
+                entry_point: Some("vs_main"),
+                buffers: &[Vertex::layout()],
+                compilation_options: wgpu::PipelineCompilationOptions::default(),
+            },
+            fragment: Some(wgpu::FragmentState {
+                module: &shader,
+                entry_point: Some("fs_main"),
+                targets: &[Some(wgpu::ColorTargetState {
+                    format,
+                    blend: Some(wgpu::BlendState::ALPHA_BLENDING),
+                    write_mask: wgpu::ColorWrites::ALL,
+                })],
+                compilation_options: wgpu::PipelineCompilationOptions::default(),
+            }),
+            primitive: wgpu::PrimitiveState::default(),
+            depth_stencil: None,
+            multisample: wgpu::MultisampleState::default(),
+            multiview_mask: None,
+            cache: None,
+        });
+
+        Ok(Self {
+            surface,
+            device,
+            queue,
+            config,
+            pipeline,
+        })
+    }
+
+    pub fn size(&self) -> (u32, u32) {
+        (self.config.width, self.config.height)
+    }
+
+    pub fn resize(&mut self, width: u32, height: u32) {
+        self.config.width = width.max(1);
+        self.config.height = height.max(1);
+        self.surface.configure(&self.device, &self.config);
+    }
+
+    pub fn render(&mut self, scene: &SceneSnapshot) -> Result<(), RenderError> {
+        let vertices = build_vertices(scene);
+        let frame = match self.surface.get_current_texture() {
+            wgpu::CurrentSurfaceTexture::Success(frame)
+            | wgpu::CurrentSurfaceTexture::Suboptimal(frame) => frame,
+            wgpu::CurrentSurfaceTexture::Lost => return Err(RenderError::Lost),
+            wgpu::CurrentSurfaceTexture::Outdated => return Err(RenderError::Outdated),
+            wgpu::CurrentSurfaceTexture::Timeout => return Err(RenderError::Timeout),
+            wgpu::CurrentSurfaceTexture::Occluded => return Err(RenderError::Occluded),
+            wgpu::CurrentSurfaceTexture::Validation => return Err(RenderError::Validation),
+        };
+        let view = frame
+            .texture
+            .create_view(&wgpu::TextureViewDescriptor::default());
+        let vertex_buffer = self
+            .device
+            .create_buffer_init(&wgpu::util::BufferInitDescriptor {
+                label: Some("ruin-ui-renderer-wgpu-vertices"),
+                contents: bytemuck::cast_slice(&vertices),
+                usage: wgpu::BufferUsages::VERTEX,
+            });
+        let mut encoder = self
+            .device
+            .create_command_encoder(&wgpu::CommandEncoderDescriptor {
+                label: Some("ruin-ui-renderer-wgpu-encoder"),
+            });
+        {
+            let mut pass = encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
+                label: Some("ruin-ui-renderer-wgpu-pass"),
+                color_attachments: &[Some(wgpu::RenderPassColorAttachment {
+                    view: &view,
+                    depth_slice: None,
+                    resolve_target: None,
+                    ops: wgpu::Operations {
+                        load: wgpu::LoadOp::Clear(wgpu::Color {
+                            r: 0.03,
+                            g: 0.04,
+                            b: 0.08,
+                            a: 1.0,
+                        }),
+                        store: wgpu::StoreOp::Store,
+                    },
+                })],
+                depth_stencil_attachment: None,
+                timestamp_writes: None,
+                occlusion_query_set: None,
+                multiview_mask: None,
+            });
+            if !vertices.is_empty() {
+                pass.set_pipeline(&self.pipeline);
+                pass.set_vertex_buffer(0, vertex_buffer.slice(..));
+                pass.draw(0..vertices.len() as u32, 0..1);
+            }
+        }
+        self.queue.submit([encoder.finish()]);
+        frame.present();
+        Ok(())
+    }
+}
+
+fn build_vertices(scene: &SceneSnapshot) -> Vec<Vertex> {
+    let width = scene.logical_size.width.max(1.0);
+    let height = scene.logical_size.height.max(1.0);
+    let mut vertices = Vec::new();
+
+    for item in &scene.items {
+        if let DisplayItem::Quad(quad) = item {
+            push_quad_vertices(&mut vertices, quad.rect, quad.color, width, height);
+        }
+    }
+
+    vertices
+}
+
+fn push_quad_vertices(
+    vertices: &mut Vec<Vertex>,
+    rect: Rect,
+    color: Color,
+    width: f32,
+    height: f32,
+) {
+    let left = to_ndc_x(rect.origin.x, width);
+    let right = to_ndc_x(rect.origin.x + rect.size.width, width);
+    let top = to_ndc_y(rect.origin.y, height);
+    let bottom = to_ndc_y(rect.origin.y + rect.size.height, height);
+    let color = [
+        color.r as f32 / 255.0,
+        color.g as f32 / 255.0,
+        color.b as f32 / 255.0,
+        color.a as f32 / 255.0,
+    ];
+
+    vertices.extend_from_slice(&[
+        Vertex {
+            position: [left, top],
+            color,
+        },
+        Vertex {
+            position: [right, top],
+            color,
+        },
+        Vertex {
+            position: [right, bottom],
+            color,
+        },
+        Vertex {
+            position: [left, top],
+            color,
+        },
+        Vertex {
+            position: [right, bottom],
+            color,
+        },
+        Vertex {
+            position: [left, bottom],
+            color,
+        },
+    ]);
+}
+
+fn to_ndc_x(x: f32, width: f32) -> f32 {
+    (x / width) * 2.0 - 1.0
+}
+
+fn to_ndc_y(y: f32, height: f32) -> f32 {
+    1.0 - (y / height) * 2.0
+}
+
+#[cfg(test)]
+mod tests {
+    use super::build_vertices;
+    use ruin_ui::{Color, PreparedText, Rect, SceneSnapshot, UiSize};
+
+    #[test]
+    fn quad_scenes_expand_to_six_vertices_per_quad() {
+        let mut scene = SceneSnapshot::new(1, UiSize::new(100.0, 50.0));
+        scene.push_quad(
+            Rect::new(0.0, 0.0, 100.0, 50.0),
+            Color::rgb(0x11, 0x22, 0x33),
+        );
+        scene.push_quad(
+            Rect::new(10.0, 10.0, 20.0, 20.0),
+            Color::rgb(0x44, 0x55, 0x66),
+        );
+        scene.push_text(PreparedText {
+            text: "ignored".into(),
+            font_size: 16.0,
+            color: Color::rgb(0xFF, 0xFF, 0xFF),
+            glyphs: Vec::new(),
+        });
+
+        let vertices = build_vertices(&scene);
+        assert_eq!(vertices.len(), 12);
+    }
+}