init v.1.0.0

Co-authored-by: Copilot <copilot@github.com>

crates/adapters/assets/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "assets"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+authors.workspace = true
+
+[dependencies]
+application = { workspace = true }
+
+[dev-dependencies]
+application = { workspace = true }

crates/adapters/assets/src/lib.rs

@@ -0,0 +1,113 @@
+use std::{
+    env, fmt, fs, io,
+    path::{Path, PathBuf},
+};
+
+use application::{ApplicationError, LogoSourcePort};
+
+const LOGO_ENV: &str = "DVD_LOGO";
+const CONFIG_DIR: &str = "dvd-thing";
+const LOGO_FILE: &str = "logo.png";
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Platform {
+    Xdg,
+    MacOs,
+    Windows,
+}
+
+impl Platform {
+    pub const CURRENT: Platform = if cfg!(windows) {
+        Platform::Windows
+    } else if cfg!(target_os = "macos") {
+        Platform::MacOs
+    } else {
+        Platform::Xdg
+    };
+}
+
+pub fn config_path(platform: Platform, env: impl Fn(&str) -> Option<PathBuf>) -> Option<PathBuf> {
+    let lookup = |key: &str| set(env(key));
+
+    let base = match platform {
+        Platform::Xdg => absolute(lookup("XDG_CONFIG_HOME"))
+            .or_else(|| lookup("HOME").map(|home| home.join(".config")))?,
+        Platform::MacOs => absolute(lookup("XDG_CONFIG_HOME")).or_else(|| {
+            lookup("HOME").map(|home| home.join("Library").join("Application Support"))
+        })?,
+        Platform::Windows => lookup("APPDATA")
+            .or_else(|| lookup("USERPROFILE").map(|home| home.join("AppData").join("Roaming")))?,
+    };
+
+    Some(base.join(CONFIG_DIR).join(LOGO_FILE))
+}
+
+fn set(path: Option<PathBuf>) -> Option<PathBuf> {
+    path.filter(|path| !path.as_os_str().is_empty())
+}
+
+fn absolute(path: Option<PathBuf>) -> Option<PathBuf> {
+    path.filter(|path| path.is_absolute())
+}
+
+pub struct FileLogoSource {
+    bytes: Option<Vec<u8>>,
+}
+
+impl FileLogoSource {
+    pub fn from_env() -> Result<Self, ApplicationError> {
+        FileLogoSource::from_environment(Platform::CURRENT, &|key| {
+            env::var_os(key).map(PathBuf::from)
+        })
+    }
+
+    pub fn from_environment(
+        platform: Platform,
+        env: &impl Fn(&str) -> Option<PathBuf>,
+    ) -> Result<Self, ApplicationError> {
+        FileLogoSource::new(set(env(LOGO_ENV)), config_path(platform, env))
+    }
+
+    pub fn new(
+        explicit: Option<PathBuf>,
+        configured: Option<PathBuf>,
+    ) -> Result<Self, ApplicationError> {
+        let bytes = match (&explicit, &configured) {
+            (Some(path), _) => Some(
+                read(path)
+                    .map_err(|e| failed(path, &format!("{e} (from ${LOGO_ENV})")))?
+                    .ok_or_else(|| failed(path, &format!("no such file (from ${LOGO_ENV})")))?,
+            ),
+            (None, Some(path)) => read(path).map_err(|e| failed(path, &e.to_string()))?,
+            (None, None) => None,
+        };
+
+        Ok(FileLogoSource { bytes })
+    }
+}
+
+impl fmt::Debug for FileLogoSource {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("FileLogoSource")
+            .field("bytes", &self.bytes.as_ref().map(Vec::len))
+            .finish()
+    }
+}
+
+impl LogoSourcePort for FileLogoSource {
+    fn load(&self) -> Result<Option<&[u8]>, ApplicationError> {
+        Ok(self.bytes.as_deref())
+    }
+}
+
+fn read(path: &Path) -> io::Result<Option<Vec<u8>>> {
+    match fs::read(path) {
+        Ok(bytes) => Ok(Some(bytes)),
+        Err(e) if e.kind() == io::ErrorKind::NotFound => Ok(None),
+        Err(e) => Err(e),
+    }
+}
+
+fn failed(path: &Path, reason: &str) -> ApplicationError {
+    ApplicationError::logo_source(format_args!("{}: {reason}", path.display()))
+}

crates/adapters/assets/tests/common/mod.rs

@@ -0,0 +1,41 @@
+#![allow(dead_code)]
+
+use std::{
+    fs,
+    path::{Path, PathBuf},
+};
+
+pub const LOGO_BYTES: &[u8] = b"pretend png";
+
+pub fn path(value: &str) -> Option<PathBuf> {
+    Some(PathBuf::from(value))
+}
+
+pub fn env_of(pairs: &[(&str, &str)]) -> impl Fn(&str) -> Option<PathBuf> + use<> {
+    let pairs: Vec<(String, PathBuf)> = pairs
+        .iter()
+        .map(|(key, value)| ((*key).to_owned(), PathBuf::from(value)))
+        .collect();
+
+    move |key| {
+        pairs
+            .iter()
+            .find(|(name, _)| name == key)
+            .map(|(_, value)| value.clone())
+    }
+}
+
+pub fn scratch(name: &str) -> PathBuf {
+    let directory = std::env::temp_dir().join(format!("dvd-thing-test-{name}"));
+
+    let _ = fs::remove_dir_all(&directory);
+    fs::create_dir_all(&directory).expect("temp directory must be creatable");
+
+    directory
+}
+
+pub fn write_logo(directory: &Path) -> PathBuf {
+    let file = directory.join("logo.png");
+    fs::write(&file, LOGO_BYTES).expect("temp file must be writable");
+    file
+}

crates/adapters/assets/tests/config_path.rs

@@ -0,0 +1,117 @@
+mod common;
+
+use assets::{Platform, config_path};
+use common::{env_of, path};
+
+#[test]
+fn xdg_prefers_config_home() {
+    let env = env_of(&[("XDG_CONFIG_HOME", "/xdg"), ("HOME", "/home/user")]);
+
+    assert_eq!(
+        config_path(Platform::Xdg, env),
+        path("/xdg/dvd-thing/logo.png")
+    );
+}
+
+#[test]
+fn xdg_falls_back_to_home_dot_config() {
+    let env = env_of(&[("HOME", "/home/user")]);
+
+    assert_eq!(
+        config_path(Platform::Xdg, env),
+        path("/home/user/.config/dvd-thing/logo.png")
+    );
+}
+
+#[test]
+fn xdg_ignores_a_relative_config_home() {
+    let env = env_of(&[("XDG_CONFIG_HOME", "relative/dir"), ("HOME", "/home/user")]);
+
+    assert_eq!(
+        config_path(Platform::Xdg, env),
+        path("/home/user/.config/dvd-thing/logo.png")
+    );
+}
+
+#[test]
+fn macos_uses_application_support() {
+    let env = env_of(&[("HOME", "/Users/gabriel")]);
+
+    assert_eq!(
+        config_path(Platform::MacOs, env),
+        path("/Users/gabriel/Library/Application Support/dvd-thing/logo.png")
+    );
+}
+
+#[test]
+fn macos_still_honours_an_explicit_xdg_config_home() {
+    let env = env_of(&[("XDG_CONFIG_HOME", "/Users/gabriel/.config")]);
+
+    assert_eq!(
+        config_path(Platform::MacOs, env),
+        path("/Users/gabriel/.config/dvd-thing/logo.png")
+    );
+}
+
+#[test]
+fn windows_prefers_appdata() {
+    let env = env_of(&[
+        ("APPDATA", r"C:\Users\gabriel\AppData\Roaming"),
+        ("USERPROFILE", r"C:\Users\gabriel"),
+    ]);
+
+    assert_eq!(
+        config_path(Platform::Windows, env),
+        path(r"C:\Users\gabriel\AppData\Roaming/dvd-thing/logo.png")
+    );
+}
+
+#[test]
+fn windows_falls_back_to_user_profile() {
+    let env = env_of(&[("USERPROFILE", r"C:\Users\gabriel")]);
+
+    assert_eq!(
+        config_path(Platform::Windows, env),
+        path(r"C:\Users\gabriel/AppData/Roaming/dvd-thing/logo.png")
+    );
+}
+
+#[test]
+fn windows_ignores_unix_variables() {
+    let env = env_of(&[("HOME", "/home/user"), ("XDG_CONFIG_HOME", "/xdg")]);
+
+    assert_eq!(config_path(Platform::Windows, env), None);
+}
+
+#[test]
+fn an_empty_environment_yields_no_path() {
+    for platform in [Platform::Xdg, Platform::MacOs, Platform::Windows] {
+        assert_eq!(config_path(platform, env_of(&[])), None);
+    }
+}
+
+#[test]
+fn an_empty_variable_counts_as_unset() {
+    let env = env_of(&[("XDG_CONFIG_HOME", ""), ("HOME", "/home/user")]);
+
+    assert_eq!(
+        config_path(Platform::Xdg, env),
+        path("/home/user/.config/dvd-thing/logo.png")
+    );
+}
+
+#[test]
+fn an_empty_home_does_not_produce_a_relative_path() {
+    assert_eq!(config_path(Platform::Xdg, env_of(&[("HOME", "")])), None);
+    assert_eq!(config_path(Platform::MacOs, env_of(&[("HOME", "")])), None);
+}
+
+#[test]
+fn an_empty_appdata_falls_back_to_user_profile() {
+    let env = env_of(&[("APPDATA", ""), ("USERPROFILE", r"C:\Users\gabriel")]);
+
+    assert_eq!(
+        config_path(Platform::Windows, env),
+        path(r"C:\Users\gabriel/AppData/Roaming/dvd-thing/logo.png")
+    );
+}

crates/adapters/assets/tests/loading.rs

@@ -0,0 +1,86 @@
+mod common;
+
+use application::LogoSourcePort;
+use assets::{FileLogoSource, Platform};
+use common::{LOGO_BYTES, env_of, scratch, write_logo};
+
+#[test]
+fn reads_an_explicit_path() {
+    let logo = write_logo(&scratch("explicit"));
+
+    let source = FileLogoSource::new(Some(logo), None).unwrap();
+
+    assert_eq!(source.load().unwrap(), Some(LOGO_BYTES));
+}
+
+#[test]
+fn a_missing_explicit_path_is_an_error() {
+    let missing = scratch("explicit-missing").join("absent.png");
+
+    let error = FileLogoSource::new(Some(missing), None).unwrap_err();
+
+    assert!(error.to_string().contains("DVD_LOGO"));
+}
+
+#[test]
+fn an_explicit_path_wins_over_the_configured_one() {
+    let directory = scratch("explicit-wins");
+    let explicit = directory.join("chosen.png");
+    std::fs::write(&explicit, b"chosen").unwrap();
+
+    let source = FileLogoSource::new(Some(explicit), Some(write_logo(&directory))).unwrap();
+
+    assert_eq!(source.load().unwrap(), Some(b"chosen".as_slice()));
+}
+
+#[test]
+fn reads_the_configured_path() {
+    let logo = write_logo(&scratch("configured"));
+
+    let source = FileLogoSource::new(None, Some(logo)).unwrap();
+
+    assert_eq!(source.load().unwrap(), Some(LOGO_BYTES));
+}
+
+#[test]
+fn a_missing_configured_path_is_not_an_error() {
+    let missing = scratch("configured-missing").join("absent.png");
+
+    let source = FileLogoSource::new(None, Some(missing)).unwrap();
+
+    assert_eq!(source.load().unwrap(), None);
+}
+
+#[test]
+fn no_paths_at_all_yields_nothing() {
+    let source = FileLogoSource::new(None, None).unwrap();
+
+    assert_eq!(source.load().unwrap(), None);
+}
+
+#[test]
+fn an_unreadable_configured_path_is_an_error() {
+    let directory = scratch("configured-unreadable");
+    std::fs::create_dir_all(directory.join("logo.png")).unwrap();
+
+    assert!(FileLogoSource::new(None, Some(directory.join("logo.png"))).is_err());
+}
+
+#[test]
+fn an_empty_dvd_logo_variable_is_treated_as_unset() {
+    let env = env_of(&[("DVD_LOGO", ""), ("HOME", "")]);
+
+    let source = FileLogoSource::from_environment(Platform::Xdg, &env).unwrap();
+
+    assert_eq!(source.load().unwrap(), None);
+}
+
+#[test]
+fn a_set_dvd_logo_variable_still_wins() {
+    let logo = write_logo(&scratch("env-explicit"));
+    let env = env_of(&[("DVD_LOGO", logo.to_str().unwrap()), ("HOME", "")]);
+
+    let source = FileLogoSource::from_environment(Platform::Xdg, &env).unwrap();
+
+    assert_eq!(source.load().unwrap(), Some(LOGO_BYTES));
+}

crates/adapters/wayland/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "wayland"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+authors.workspace = true
+
+[dependencies]
+domain = { workspace = true }
+application = { workspace = true }
+
+wayland-client = "0.31"
+smithay-client-toolkit = { version = "0.21", default-features = false }
+tiny-skia = "0.12"
+rustix = { version = "1.1", features = ["event"] }
+signal-hook = { version = "0.4", default-features = false }

crates/adapters/wayland/src/display.rs

@@ -0,0 +1,219 @@
+use std::io::{ErrorKind, Read};
+
+use application::{ApplicationError, DisplayOverlayPort};
+use domain::Dimensions;
+use rustix::event::{PollFd, PollFlags, poll};
+use smithay_client_toolkit::{
+    compositor::{CompositorState, Region},
+    output::OutputState,
+    registry::RegistryState,
+    shell::{
+        WaylandSurface,
+        wlr_layer::{Anchor, KeyboardInteractivity, Layer, LayerShell, LayerSurface},
+    },
+    shm::Shm,
+};
+use wayland_client::{
+    Connection, EventQueue, QueueHandle, globals::registry_queue_init,
+    protocol::wl_surface::WlSurface,
+};
+
+use crate::state::WaylandState;
+
+const DEFAULT_SURFACE_SIZE: Dimensions = match Dimensions::new(800, 600) {
+    Some(size) => size,
+    None => panic!("default surface size must be non-zero"),
+};
+
+const SHUTDOWN_SIGNALS: [i32; 2] = [signal_hook::consts::SIGINT, signal_hook::consts::SIGTERM];
+
+pub struct WaylandDisplay {
+    connection: Connection,
+    event_queue: EventQueue<WaylandState>,
+    qh: QueueHandle<WaylandState>,
+    state: WaylandState,
+    layer_surface: LayerSurface,
+    signal_pipe: std::io::PipeReader,
+}
+
+impl WaylandDisplay {
+    pub fn new() -> Result<Self, ApplicationError> {
+        let connection = Connection::connect_to_env().map_err(init_err)?;
+        let (globals, mut event_queue) = registry_queue_init(&connection).map_err(init_err)?;
+        let qh = event_queue.handle();
+
+        let compositor_state = CompositorState::bind(&globals, &qh).map_err(init_err)?;
+        let layer_shell = LayerShell::bind(&globals, &qh).map_err(init_err)?;
+        let shm = Shm::bind(&globals, &qh).map_err(init_err)?;
+
+        let mut state = WaylandState {
+            registry_state: RegistryState::new(&globals),
+            output_state: OutputState::new(&globals, &qh),
+            compositor_state,
+            layer_shell,
+            shm,
+            surface_dimensions: DEFAULT_SURFACE_SIZE,
+            configured: false,
+            redraw_requested: false,
+            exit: false,
+        };
+
+        let surface = state.compositor_state.create_surface(&qh);
+
+        let empty_region = Region::new(&state.compositor_state).map_err(init_err)?;
+        surface.set_input_region(Some(empty_region.wl_region()));
+        drop(empty_region);
+
+        let layer_surface = state.layer_shell.create_layer_surface(
+            &qh,
+            surface,
+            Layer::Overlay,
+            Some("dvd-screensaver"),
+            None,
+        );
+
+        layer_surface.set_anchor(Anchor::TOP | Anchor::BOTTOM | Anchor::LEFT | Anchor::RIGHT);
+        layer_surface.set_keyboard_interactivity(KeyboardInteractivity::None);
+        layer_surface.commit();
+
+        let signal_pipe = install_signal_handlers()?;
+
+        while !state.configured && !state.exit {
+            event_queue
+                .blocking_dispatch(&mut state)
+                .map_err(init_err)?;
+        }
+
+        Ok(WaylandDisplay {
+            connection,
+            event_queue,
+            qh,
+            state,
+            layer_surface,
+            signal_pipe,
+        })
+    }
+
+    pub fn wl_surface(&self) -> WlSurface {
+        self.layer_surface.wl_surface().clone()
+    }
+
+    pub fn qh(&self) -> &QueueHandle<WaylandState> {
+        &self.qh
+    }
+
+    pub fn shm(&self) -> &Shm {
+        &self.state.shm
+    }
+
+    fn dispatch_blocking(&mut self) -> Result<(), ApplicationError> {
+        if self
+            .event_queue
+            .dispatch_pending(&mut self.state)
+            .map_err(loop_err)?
+            > 0
+        {
+            return Ok(());
+        }
+
+        let Some(read_guard) = self.event_queue.prepare_read() else {
+            self.event_queue
+                .dispatch_pending(&mut self.state)
+                .map_err(loop_err)?;
+            return Ok(());
+        };
+
+        self.connection.flush().map_err(loop_err)?;
+
+        let wayland_fd = read_guard.connection_fd();
+        let mut fds = [
+            PollFd::new(&wayland_fd, PollFlags::IN),
+            PollFd::new(&self.signal_pipe, PollFlags::IN),
+        ];
+
+        match poll(&mut fds, None) {
+            Ok(_) => {}
+            Err(rustix::io::Errno::INTR) => return Ok(()),
+            Err(e) => return Err(loop_err(e)),
+        }
+
+        let signalled = fds[1].revents().intersects(PollFlags::IN);
+        let readable = fds[0].revents().intersects(PollFlags::IN);
+
+        if signalled {
+            self.drain_signal_pipe();
+            self.state.exit = true;
+            return Ok(());
+        }
+
+        if readable {
+            match read_guard.read() {
+                Ok(_) => {}
+                Err(e) if is_would_block(&e) => {}
+                Err(e) => return Err(loop_err(e)),
+            }
+            self.event_queue
+                .dispatch_pending(&mut self.state)
+                .map_err(loop_err)?;
+        }
+
+        Ok(())
+    }
+
+    fn drain_signal_pipe(&mut self) {
+        let mut scratch = [0u8; 16];
+        let _ = self.signal_pipe.read(&mut scratch);
+    }
+}
+
+impl DisplayOverlayPort for WaylandDisplay {
+    fn screen_dimensions(&self) -> Dimensions {
+        self.state.surface_dimensions
+    }
+
+    fn wait_for_frame(&mut self) -> Result<bool, ApplicationError> {
+        loop {
+            if self.state.exit {
+                return Ok(false);
+            }
+
+            if self.state.redraw_requested {
+                self.state.redraw_requested = false;
+                return Ok(true);
+            }
+
+            self.dispatch_blocking()?;
+        }
+    }
+}
+
+impl Drop for WaylandDisplay {
+    fn drop(&mut self) {
+        self.layer_surface.wl_surface().attach(None, 0, 0);
+        self.layer_surface.commit();
+        let _ = self.connection.flush();
+    }
+}
+
+fn install_signal_handlers() -> Result<std::io::PipeReader, ApplicationError> {
+    let (reader, writer) = std::io::pipe().map_err(init_err)?;
+
+    for signal in SHUTDOWN_SIGNALS {
+        signal_hook::low_level::pipe::register(signal, writer.try_clone().map_err(init_err)?)
+            .map_err(init_err)?;
+    }
+
+    Ok(reader)
+}
+
+fn is_would_block(err: &wayland_client::backend::WaylandError) -> bool {
+    matches!(err, wayland_client::backend::WaylandError::Io(e) if e.kind() == ErrorKind::WouldBlock)
+}
+
+fn init_err(e: impl std::fmt::Display) -> ApplicationError {
+    ApplicationError::display_initialization(e)
+}
+
+fn loop_err(e: impl std::fmt::Display) -> ApplicationError {
+    ApplicationError::event_loop(e)
+}

crates/adapters/wayland/src/image.rs

@@ -0,0 +1,123 @@
+use application::{ApplicationError, LogoSourcePort};
+use domain::{Color, Dimensions};
+use tiny_skia::{FilterQuality, Pixmap, PixmapMut, PixmapPaint, PremultipliedColorU8, Transform};
+
+pub struct LogoImage {
+    source: Pixmap,
+    scaled: Option<(Dimensions, Pixmap)>,
+    tinted: Vec<(Dimensions, Color, Pixmap)>,
+}
+
+impl LogoImage {
+    pub fn load(source: &impl LogoSourcePort) -> Result<Option<Self>, ApplicationError> {
+        let Some(encoded) = source.load()? else {
+            return Ok(None);
+        };
+
+        let source = Pixmap::decode_png(encoded)
+            .map_err(|e| ApplicationError::logo_source(format_args!("not a usable PNG: {e}")))?;
+
+        Ok(Some(LogoImage {
+            source,
+            scaled: None,
+            tinted: Vec::new(),
+        }))
+    }
+
+    pub fn tinted(&mut self, size: Dimensions, color: Color) -> Option<&Pixmap> {
+        if let Some(index) = self
+            .tinted
+            .iter()
+            .position(|(cached, tint, _)| *cached == size && *tint == color)
+        {
+            return Some(&self.tinted[index].2);
+        }
+
+        let mut pixmap = self.scale_to(size)?.clone();
+        tint(&mut pixmap, color);
+
+        self.tinted.retain(|(cached, _, _)| *cached == size);
+        self.tinted.push((size, color, pixmap));
+
+        self.tinted.last().map(|(_, _, pixmap)| pixmap)
+    }
+
+    fn scale_to(&mut self, size: Dimensions) -> Option<&Pixmap> {
+        if !self
+            .scaled
+            .as_ref()
+            .is_some_and(|(cached, _)| *cached == size)
+        {
+            let mut target = Pixmap::new(size.width(), size.height())?;
+
+            target.draw_pixmap(
+                0,
+                0,
+                self.source.as_ref(),
+                &PixmapPaint {
+                    quality: FilterQuality::Bicubic,
+                    ..Default::default()
+                },
+                Transform::from_scale(
+                    size.width() as f32 / self.source.width() as f32,
+                    size.height() as f32 / self.source.height() as f32,
+                ),
+                None,
+            );
+
+            self.scaled = Some((size, target));
+        }
+
+        self.scaled.as_ref().map(|(_, pixmap)| pixmap)
+    }
+}
+
+fn tint(pixmap: &mut Pixmap, color: Color) {
+    let (r, g, b) = surface_channels(color);
+
+    for pixel in pixmap.pixels_mut() {
+        let alpha = pixel.alpha();
+
+        *pixel = PremultipliedColorU8::from_rgba(
+            premultiply(r, alpha),
+            premultiply(g, alpha),
+            premultiply(b, alpha),
+            alpha,
+        )
+        .unwrap_or(PremultipliedColorU8::TRANSPARENT);
+    }
+}
+
+fn premultiply(channel: u8, alpha: u8) -> u8 {
+    ((channel as u16 * alpha as u16) / 255) as u8
+}
+
+pub fn blit(destination: &mut PixmapMut, x: i32, y: i32, source: &Pixmap) {
+    let width = destination.width() as i32;
+    let height = destination.height() as i32;
+
+    let left = x.max(0);
+    let top = y.max(0);
+    let right = (x + source.width() as i32).min(width);
+    let bottom = (y + source.height() as i32).min(height);
+
+    if left >= right || top >= bottom {
+        return;
+    }
+
+    let span = ((right - left) * 4) as usize;
+    let source_width = source.width() as usize;
+    let source_data = source.data();
+    let destination_data = destination.data_mut();
+
+    for row in top..bottom {
+        let from = (((row - y) as usize) * source_width + (left - x) as usize) * 4;
+        let to = ((row as usize) * width as usize + left as usize) * 4;
+
+        destination_data[to..to + span].copy_from_slice(&source_data[from..from + span]);
+    }
+}
+
+pub fn surface_channels(color: Color) -> (u8, u8, u8) {
+    (color.b, color.g, color.r)
+}

crates/adapters/wayland/src/lib.rs

@@ -0,0 +1,8 @@
+mod display;
+mod image;
+mod renderer;
+mod state;
+
+pub use display::WaylandDisplay;
+pub use renderer::SoftwareRenderer;
+pub use state::WaylandState;

crates/adapters/wayland/src/renderer.rs

@@ -0,0 +1,304 @@
+use application::{ApplicationError, DisplayOverlayPort, LogoSourcePort, RendererPort};
+use domain::{Dimensions, ScreensaverScene, Sprite, SpriteKind};
+use smithay_client_toolkit::{
+    compositor::FrameCallbackData,
+    shm::slot::{Buffer, SlotPool},
+};
+use tiny_skia::{BlendMode, Color, IntRect, Paint, PixmapMut, Rect, Transform};
+use wayland_client::{QueueHandle, protocol::wl_shm, protocol::wl_surface::WlSurface};
+
+use crate::{
+    display::WaylandDisplay,
+    image::{LogoImage, blit, surface_channels},
+    state::WaylandState,
+};
+
+#[cfg(target_endian = "big")]
+compile_error!("Argb8888 byte order and tiny-skia premultiplication assume a little-endian target");
+
+const BYTES_PER_PIXEL: u32 = 4;
+const FORMAT: wl_shm::Format = wl_shm::Format::Argb8888;
+
+const BUFFER_COUNT: usize = 2;
+
+#[derive(Clone, Copy)]
+struct BufferSpec {
+    size: Dimensions,
+    stride: i32,
+}
+
+impl BufferSpec {
+    fn new(size: Dimensions) -> Self {
+        BufferSpec {
+            size,
+            stride: (size.width() * BYTES_PER_PIXEL) as i32,
+        }
+    }
+
+    fn width(&self) -> i32 {
+        self.size.width() as i32
+    }
+
+    fn height(&self) -> i32 {
+        self.size.height() as i32
+    }
+
+    fn byte_len(&self) -> usize {
+        self.size.height() as usize * self.stride as usize
+    }
+
+    fn matches(&self, buffer: &Buffer) -> bool {
+        buffer.stride() == self.stride && buffer.height() == self.height()
+    }
+}
+
+enum Clear {
+    Everything,
+    Region(IntRect),
+    Nothing,
+}
+
+struct Frame {
+    buffer: Buffer,
+    painted: Option<IntRect>,
+}
+
+impl Frame {
+    fn new(pool: &mut SlotPool, spec: BufferSpec) -> Result<Self, ApplicationError> {
+        let (buffer, _) = pool
+            .create_buffer(spec.width(), spec.height(), spec.stride, FORMAT)
+            .map_err(render_err)?;
+
+        Ok(Frame {
+            buffer,
+            painted: None,
+        })
+    }
+}
+
+pub struct SoftwareRenderer {
+    surface: WlSurface,
+    qh: QueueHandle<WaylandState>,
+    pool: SlotPool,
+    logo: Option<LogoImage>,
+    frames: [Frame; BUFFER_COUNT],
+    next: usize,
+    presented: Option<IntRect>,
+    committed: bool,
+}
+
+impl SoftwareRenderer {
+    pub fn new(
+        display: &WaylandDisplay,
+        logo: &impl LogoSourcePort,
+    ) -> Result<Self, ApplicationError> {
+        let spec = BufferSpec::new(display.screen_dimensions());
+
+        let mut pool =
+            SlotPool::new(BUFFER_COUNT * spec.byte_len(), display.shm()).map_err(render_err)?;
+
+        let frames: [Frame; BUFFER_COUNT] = (0..BUFFER_COUNT)
+            .map(|_| Frame::new(&mut pool, spec))
+            .collect::<Result<Vec<_>, _>>()?
+            .try_into()
+            .map_err(|_| render_err("buffer count mismatch"))?;
+
+        Ok(SoftwareRenderer {
+            surface: display.wl_surface(),
+            qh: display.qh().clone(),
+            pool,
+            logo: LogoImage::load(logo)?,
+            frames,
+            next: 0,
+            presented: None,
+            committed: false,
+        })
+    }
+
+    fn advance(&mut self) -> usize {
+        let index = self.next;
+        self.next = (self.next + 1) % self.frames.len();
+        index
+    }
+
+    fn prepare_buffer(
+        &mut self,
+        index: usize,
+        spec: BufferSpec,
+    ) -> Result<Clear, ApplicationError> {
+        let pool = &mut self.pool;
+        let frame = &mut self.frames[index];
+
+        if spec.matches(&frame.buffer) && pool.canvas(&frame.buffer).is_some() {
+            return Ok(match frame.painted.take() {
+                Some(region) => Clear::Region(region),
+                None => Clear::Nothing,
+            });
+        }
+
+        *frame = Frame::new(pool, spec)?;
+        Ok(Clear::Everything)
+    }
+
+    fn paint(
+        &mut self,
+        index: usize,
+        spec: BufferSpec,
+        scene: &ScreensaverScene,
+        clear: Clear,
+    ) -> Result<Option<IntRect>, ApplicationError> {
+        let pool = &mut self.pool;
+        let logo = &mut self.logo;
+        let frame = &self.frames[index];
+
+        let canvas = pool
+            .canvas(&frame.buffer)
+            .ok_or_else(|| render_err("buffer still held by compositor"))?;
+
+        let mut pixmap = PixmapMut::from_bytes(canvas, spec.size.width(), spec.size.height())
+            .ok_or_else(|| render_err("canvas does not match surface size"))?;
+
+        let mut paint = Paint {
+            anti_alias: false,
+            ..Default::default()
+        };
+
+        match clear {
+            Clear::Everything => pixmap.fill(Color::TRANSPARENT),
+            Clear::Region(region) => {
+                paint.blend_mode = BlendMode::Clear;
+                pixmap.fill_rect(int_to_rect(region), &paint, Transform::identity(), None);
+            }
+            Clear::Nothing => {}
+        }
+
+        let mut painted: Option<Rect> = None;
+
+        paint.blend_mode = BlendMode::SourceOver;
+        for sprite in scene.sprites() {
+            let Some(rect) = sprite_rect(&sprite) else {
+                continue;
+            };
+
+            match sprite.kind() {
+                SpriteKind::Logo => {
+                    let tinted = logo
+                        .as_mut()
+                        .and_then(|image| image.tinted(sprite.dimensions(), sprite.color()));
+
+                    match tinted {
+                        Some(tinted) => blit(&mut pixmap, rect.x() as i32, rect.y() as i32, tinted),
+                        None => {
+                            paint.set_color(paint_color(sprite.color()));
+                            pixmap.fill_rect(rect, &paint, Transform::identity(), None);
+                        }
+                    }
+                }
+                SpriteKind::Sparkle => {
+                    paint.set_color(paint_color(sprite.color()));
+                    pixmap.fill_rect(rect, &paint, Transform::identity(), None);
+                }
+            }
+
+            painted = Some(match painted {
+                Some(acc) => acc.join(&rect).unwrap_or(acc),
+                None => rect,
+            });
+        }
+
+        Ok(painted
+            .and_then(|rect| rect.round_out())
+            .and_then(|rect| clamp_to_surface(rect, spec)))
+    }
+
+    fn damage_moved_logo(&self, previous: Option<IntRect>, drawn: Option<IntRect>) {
+        for rect in [previous, drawn].into_iter().flatten() {
+            self.surface.damage_buffer(
+                rect.x(),
+                rect.y(),
+                rect.width() as i32,
+                rect.height() as i32,
+            );
+        }
+    }
+
+    fn present(&self, index: usize) -> Result<(), ApplicationError> {
+        self.surface
+            .frame(&self.qh, FrameCallbackData(self.surface.clone()));
+
+        self.frames[index]
+            .buffer
+            .attach_to(&self.surface)
+            .map_err(render_err)?;
+        self.surface.commit();
+
+        Ok(())
+    }
+}
+
+impl RendererPort for SoftwareRenderer {
+    fn render_frame(
+        &mut self,
+        scene: &ScreensaverScene,
+        screen_size: Dimensions,
+    ) -> Result<(), ApplicationError> {
+        let spec = BufferSpec::new(screen_size);
+
+        let index = self.advance();
+        let clear = self.prepare_buffer(index, spec)?;
+        let reallocated = matches!(clear, Clear::Everything);
+
+        let drawn = self.paint(index, spec, scene, clear)?;
+        self.frames[index].painted = drawn;
+
+        let previous = std::mem::replace(&mut self.presented, drawn);
+
+        if reallocated || !self.committed {
+            self.surface
+                .damage_buffer(0, 0, spec.width(), spec.height());
+        } else {
+            self.damage_moved_logo(previous, drawn);
+        }
+
+        self.present(index)?;
+        self.committed = true;
+
+        Ok(())
+    }
+}
+
+fn sprite_rect(sprite: &Sprite) -> Option<Rect> {
+    let position = sprite.position();
+    let dimensions = sprite.dimensions();
+
+    Rect::from_xywh(
+        position.x(),
+        position.y(),
+        dimensions.width() as f32,
+        dimensions.height() as f32,
+    )
+}
+
+fn clamp_to_surface(rect: IntRect, spec: BufferSpec) -> Option<IntRect> {
+    IntRect::from_ltrb(0, 0, spec.width(), spec.height())
+        .and_then(|surface| rect.intersect(&surface))
+}
+
+fn paint_color(color: domain::Color) -> Color {
+    let (r, g, b) = surface_channels(color);
+    Color::from_rgba8(r, g, b, color.a)
+}
+
+fn int_to_rect(rect: IntRect) -> Rect {
+    Rect::from_ltrb(
+        rect.left() as f32,
+        rect.top() as f32,
+        rect.right() as f32,
+        rect.bottom() as f32,
+    )
+    .expect("IntRect always has positive extents")
+}
+
+fn render_err(e: impl std::fmt::Display) -> ApplicationError {
+    ApplicationError::rendering_failed(e)
+}

crates/adapters/wayland/src/state.rs

@@ -0,0 +1,155 @@
+use domain::Dimensions;
+use smithay_client_toolkit::{
+    compositor::{CompositorHandler, CompositorState},
+    delegate_dispatch2, delegate_registry,
+    output::{OutputHandler, OutputState},
+    registry::{ProvidesRegistryState, RegistryState},
+    registry_handlers,
+    shell::wlr_layer::{LayerShell, LayerShellHandler, LayerSurface, LayerSurfaceConfigure},
+    shm::{Shm, ShmHandler},
+};
+use wayland_client::{
+    Connection, QueueHandle,
+    protocol::{wl_output, wl_surface},
+};
+
+pub struct WaylandState {
+    pub registry_state: RegistryState,
+    pub output_state: OutputState,
+    pub compositor_state: CompositorState,
+    pub layer_shell: LayerShell,
+    pub shm: Shm,
+
+    pub surface_dimensions: Dimensions,
+    pub configured: bool,
+
+    pub redraw_requested: bool,
+    pub exit: bool,
+}
+
+impl CompositorHandler for WaylandState {
+    fn scale_factor_changed(
+        &mut self,
+        _conn: &Connection,
+        _qh: &QueueHandle<Self>,
+        _surface: &wl_surface::WlSurface,
+        _new_factor: i32,
+    ) {
+    }
+
+    fn transform_changed(
+        &mut self,
+        _conn: &Connection,
+        _qh: &QueueHandle<Self>,
+        _surface: &wl_surface::WlSurface,
+        _new_transform: wl_output::Transform,
+    ) {
+    }
+
+    fn frame(
+        &mut self,
+        _conn: &Connection,
+        _qh: &QueueHandle<Self>,
+        _surface: &wl_surface::WlSurface,
+        _time: u32,
+    ) {
+        self.redraw_requested = true;
+    }
+
+    fn surface_enter(
+        &mut self,
+        _conn: &Connection,
+        _qh: &QueueHandle<Self>,
+        _surface: &wl_surface::WlSurface,
+        _output: &wl_output::WlOutput,
+    ) {
+    }
+
+    fn surface_leave(
+        &mut self,
+        _conn: &Connection,
+        _qh: &QueueHandle<Self>,
+        _surface: &wl_surface::WlSurface,
+        _output: &wl_output::WlOutput,
+    ) {
+    }
+}
+
+impl OutputHandler for WaylandState {
+    fn output_state(&mut self) -> &mut OutputState {
+        &mut self.output_state
+    }
+
+    fn new_output(
+        &mut self,
+        _conn: &Connection,
+        _qh: &QueueHandle<Self>,
+        _output: wl_output::WlOutput,
+    ) {
+    }
+
+    fn update_output(
+        &mut self,
+        _conn: &Connection,
+        _qh: &QueueHandle<Self>,
+        _output: wl_output::WlOutput,
+    ) {
+    }
+
+    fn output_destroyed(
+        &mut self,
+        _conn: &Connection,
+        _qh: &QueueHandle<Self>,
+        _output: wl_output::WlOutput,
+    ) {
+    }
+}
+
+impl LayerShellHandler for WaylandState {
+    fn closed(&mut self, _conn: &Connection, _qh: &QueueHandle<Self>, _layer: &LayerSurface) {
+        self.exit = true;
+    }
+
+    fn configure(
+        &mut self,
+        _conn: &Connection,
+        _qh: &QueueHandle<Self>,
+        _layer: &LayerSurface,
+        configure: LayerSurfaceConfigure,
+        _serial: u32,
+    ) {
+        let (width, height) = configure.new_size;
+        let current = self.surface_dimensions;
+
+        let width = if width == 0 { current.width() } else { width };
+        let height = if height == 0 {
+            current.height()
+        } else {
+            height
+        };
+
+        if let Some(size) = Dimensions::new(width, height) {
+            self.surface_dimensions = size;
+        }
+
+        self.configured = true;
+        self.redraw_requested = true;
+    }
+}
+
+impl ShmHandler for WaylandState {
+    fn shm_state(&mut self) -> &mut Shm {
+        &mut self.shm
+    }
+}
+
+impl ProvidesRegistryState for WaylandState {
+    fn registry(&mut self) -> &mut RegistryState {
+        &mut self.registry_state
+    }
+
+    registry_handlers![OutputState];
+}
+
+delegate_registry!(WaylandState);
+delegate_dispatch2!(WaylandState);

crates/application/Cargo.toml

@@ -0,0 +1,11 @@
+[package]
+name = "application"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+authors.workspace = true
+
+[dependencies]
+domain = { workspace = true }
+heapless = { version = "0.9.3", default-features = false }
+thiserror = { workspace = true }

crates/application/src/errors.rs

@@ -0,0 +1,55 @@
+use core::fmt::{self, Display, Write};
+
+pub type Message = heapless::String<104, u8>;
+
+#[derive(Debug, thiserror::Error)]
+pub enum ApplicationError {
+    #[error("Failed to initialize display: {0}")]
+    DisplayInitialization(Message),
+    #[error("Display event loop failure: {0}")]
+    EventLoop(Message),
+    #[error("Render pipeline failure: {0}")]
+    RenderingFailed(Message),
+    #[error("Failed to load logo: {0}")]
+    LogoSource(Message),
+    #[error("Domain configuration error: {0}")]
+    DomainError(#[from] domain::DomainError),
+}
+
+impl ApplicationError {
+    pub fn display_initialization(reason: impl Display) -> Self {
+        Self::DisplayInitialization(message(reason))
+    }
+
+    pub fn event_loop(reason: impl Display) -> Self {
+        Self::EventLoop(message(reason))
+    }
+
+    pub fn rendering_failed(reason: impl Display) -> Self {
+        Self::RenderingFailed(message(reason))
+    }
+
+    pub fn logo_source(reason: impl Display) -> Self {
+        Self::LogoSource(message(reason))
+    }
+}
+
+fn message(reason: impl Display) -> Message {
+    let mut buffer = Message::new();
+    let _ = write!(Truncating(&mut buffer), "{reason}");
+    buffer
+}
+
+struct Truncating<'a>(&'a mut Message);
+
+impl Write for Truncating<'_> {
+    fn write_str(&mut self, text: &str) -> fmt::Result {
+        for character in text.chars() {
+            if self.0.push(character).is_err() {
+                break;
+            }
+        }
+
+        Ok(())
+    }
+}

crates/application/src/lib.rs

@@ -0,0 +1,9 @@
+#![no_std]
+
+mod errors;
+mod ports;
+mod use_cases;
+
+pub use errors::{ApplicationError, Message};
+pub use ports::{DisplayOverlayPort, LogoSourcePort, RendererPort};
+pub use use_cases::{run, step};

crates/application/src/ports.rs

@@ -0,0 +1,20 @@
+use domain::{Dimensions, ScreensaverScene};
+
+use crate::ApplicationError;
+
+pub trait DisplayOverlayPort {
+    fn screen_dimensions(&self) -> Dimensions;
+    fn wait_for_frame(&mut self) -> Result<bool, ApplicationError>;
+}
+
+pub trait RendererPort {
+    fn render_frame(
+        &mut self,
+        scene: &ScreensaverScene,
+        screen_size: Dimensions,
+    ) -> Result<(), ApplicationError>;
+}
+
+pub trait LogoSourcePort {
+    fn load(&self) -> Result<Option<&[u8]>, ApplicationError>;
+}

crates/application/src/use_cases.rs

@@ -0,0 +1,37 @@
+use domain::ScreensaverScene;
+
+use crate::{
+    errors::ApplicationError,
+    ports::{DisplayOverlayPort, RendererPort},
+};
+
+pub fn step<D, R>(
+    display: &mut D,
+    renderer: &mut R,
+    scene: &mut ScreensaverScene,
+) -> Result<(), ApplicationError>
+where
+    D: DisplayOverlayPort,
+    R: RendererPort,
+{
+    let bounds = display.screen_dimensions();
+
+    scene.tick(bounds);
+    renderer.render_frame(scene, bounds)
+}
+
+pub fn run<D, R>(
+    display: &mut D,
+    renderer: &mut R,
+    scene: &mut ScreensaverScene,
+) -> Result<(), ApplicationError>
+where
+    D: DisplayOverlayPort,
+    R: RendererPort,
+{
+    while display.wait_for_frame()? {
+        step(display, renderer, scene)?;
+    }
+
+    Ok(())
+}

crates/bin/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "bin"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+authors.workspace = true
+
+[[bin]]
+name = "dvd-thing"
+path = "src/main.rs"
+
+[dependencies]
+domain = { workspace = true }
+application = { workspace = true }
+wayland = { workspace = true }
+assets = { workspace = true }

crates/bin/src/main.rs

@@ -0,0 +1,39 @@
+use std::process::ExitCode;
+
+use application::DisplayOverlayPort;
+use assets::FileLogoSource;
+use domain::{Color, Dimensions, ScreensaverScene, Vector2D};
+use wayland::{SoftwareRenderer, WaylandDisplay};
+
+const LOGO: Dimensions = match Dimensions::new(320, 198) {
+    Some(size) => size,
+    None => panic!("logo dimensions must be non-zero"),
+};
+const SPEED: Vector2D = match Vector2D::new(3.0, 2.0) {
+    Some(speed) => speed,
+    None => panic!("logo speed must be finite"),
+};
+const START_COLOR: Color = Color {
+    r: 255,
+    g: 0,
+    b: 0,
+    a: 255,
+};
+
+fn main() -> ExitCode {
+    match run() {
+        Ok(()) => ExitCode::SUCCESS,
+        Err(e) => {
+            eprintln!("dvd-thing: {e}");
+            ExitCode::FAILURE
+        }
+    }
+}
+
+fn run() -> Result<(), application::ApplicationError> {
+    let mut display = WaylandDisplay::new()?;
+    let mut renderer = SoftwareRenderer::new(&display, &FileLogoSource::from_env()?)?;
+    let mut scene = ScreensaverScene::new(LOGO, SPEED, START_COLOR, display.screen_dimensions())?;
+
+    application::run(&mut display, &mut renderer, &mut scene)
+}

crates/domain/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "domain"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+authors.workspace = true
+
+[dependencies]
+thiserror = { workspace = true }
+libm = { version = "0.2", default-features = false }

crates/domain/src/errors.rs

@@ -0,0 +1,14 @@
+use thiserror::Error;
+
+#[derive(Error, Debug, PartialEq)]
+pub enum DomainError {
+    #[error(
+        "Logo dimension ({width}x{height}) exceeds boundary screen size ({bounds_w}x{bounds_h})"
+    )]
+    InvalidDimensions {
+        width: u32,
+        height: u32,
+        bounds_w: u32,
+        bounds_h: u32,
+    },
+}

crates/domain/src/lib.rs

@@ -0,0 +1,13 @@
+#![no_std]
+
+mod errors;
+mod logo;
+mod scene;
+mod sparkle;
+mod sprite;
+mod value_objects;
+
+pub use errors::DomainError;
+pub use scene::ScreensaverScene;
+pub use sprite::{Sprite, SpriteKind};
+pub use value_objects::{Color, Dimensions, Point2D, Vector2D};

crates/domain/src/logo.rs

@@ -0,0 +1,125 @@
+use crate::{Color, Dimensions, Point2D, Sprite, SpriteKind, Vector2D};
+
+struct Axis {
+    position: f32,
+    impact: Option<f32>,
+    bounced: bool,
+}
+
+fn advance(position: f32, velocity: f32, extent: u32, bound: u32) -> Axis {
+    if extent > bound {
+        return Axis {
+            position: 0.0,
+            impact: None,
+            bounced: false,
+        };
+    }
+
+    let next = position + velocity;
+
+    let impact = if next < 0.0 {
+        Some(0.0)
+    } else if next + extent as f32 >= bound as f32 {
+        Some(bound as f32)
+    } else {
+        None
+    };
+
+    match impact {
+        Some(_) => Axis {
+            position: position - velocity,
+            impact,
+            bounced: true,
+        },
+        None => Axis {
+            position: next,
+            impact: None,
+            bounced: false,
+        },
+    }
+}
+
+pub(crate) struct BouncingLogo {
+    position: Point2D,
+    velocity: Vector2D,
+    dimensions: Dimensions,
+    color: Color,
+}
+
+impl BouncingLogo {
+    pub(crate) const fn new(
+        position: Point2D,
+        velocity: Vector2D,
+        dimensions: Dimensions,
+        color: Color,
+    ) -> Self {
+        Self {
+            position,
+            velocity,
+            dimensions,
+            color,
+        }
+    }
+
+    pub(crate) fn tick(&mut self, bounds: Dimensions) -> Option<Point2D> {
+        let x = advance(
+            self.position.x(),
+            self.velocity.dx(),
+            self.dimensions.width(),
+            bounds.width(),
+        );
+        let y = advance(
+            self.position.y(),
+            self.velocity.dy(),
+            self.dimensions.height(),
+            bounds.height(),
+        );
+
+        if x.bounced {
+            self.velocity = self.velocity.reflected_x();
+        }
+        if y.bounced {
+            self.velocity = self.velocity.reflected_y();
+        }
+
+        if let Some(position) = Point2D::new(x.position, y.position) {
+            self.position = position;
+        }
+
+        if x.bounced || y.bounced {
+            self.mutate_color();
+        }
+
+        match (x.impact, y.impact) {
+            (Some(corner_x), Some(corner_y)) => Point2D::new(corner_x, corner_y),
+            _ => None,
+        }
+    }
+
+    fn mutate_color(&mut self) {
+        self.color = match (self.color.r, self.color.g, self.color.b) {
+            (255, 0, 0) => Color {
+                r: 0,
+                g: 255,
+                b: 0,
+                a: 255,
+            },
+            (0, 255, 0) => Color {
+                r: 0,
+                g: 0,
+                b: 255,
+                a: 255,
+            },
+            _ => Color {
+                r: 255,
+                g: 0,
+                b: 0,
+                a: 255,
+            },
+        };
+    }
+
+    pub(crate) const fn sprite(&self) -> Sprite {
+        Sprite::new(SpriteKind::Logo, self.position, self.dimensions, self.color)
+    }
+}

crates/domain/src/scene.rs

@@ -0,0 +1,73 @@
+use crate::{
+    Color, Dimensions, DomainError, Point2D, Sprite, Vector2D,
+    logo::BouncingLogo,
+    sparkle::{self, Sparkle},
+};
+
+const MAX_SPARKLES: usize = sparkle::BURST as usize * (sparkle::LIFETIME_FRAMES as usize + 1);
+
+pub struct ScreensaverScene {
+    logo: BouncingLogo,
+    sparkles: [Option<Sparkle>; MAX_SPARKLES],
+}
+
+impl ScreensaverScene {
+    pub fn new(
+        logo: Dimensions,
+        speed: Vector2D,
+        color: Color,
+        bounds: Dimensions,
+    ) -> Result<Self, DomainError> {
+        if logo.width() > bounds.width() || logo.height() > bounds.height() {
+            return Err(DomainError::InvalidDimensions {
+                width: logo.width(),
+                height: logo.height(),
+                bounds_w: bounds.width(),
+                bounds_h: bounds.height(),
+            });
+        }
+
+        let position = Point2D::new(
+            (bounds.width() - logo.width()) as f32 / 2.0,
+            (bounds.height() - logo.height()) as f32 / 2.0,
+        )
+        .unwrap_or_default();
+
+        Ok(Self {
+            logo: BouncingLogo::new(position, speed, logo, color),
+            sparkles: [const { None }; MAX_SPARKLES],
+        })
+    }
+
+    pub fn tick(&mut self, bounds: Dimensions) {
+        for slot in &mut self.sparkles {
+            if let Some(sparkle) = slot {
+                sparkle.tick();
+
+                if !sparkle.is_alive() {
+                    *slot = None;
+                }
+            }
+        }
+
+        if let Some(corner) = self.logo.tick(bounds) {
+            self.spawn(Sparkle::burst(corner));
+        }
+    }
+
+    pub fn sprites(&self) -> impl Iterator<Item = Sprite> + '_ {
+        core::iter::once(self.logo.sprite())
+            .chain(self.sparkles.iter().flatten().map(Sparkle::sprite))
+    }
+
+    fn spawn(&mut self, burst: impl Iterator<Item = Sparkle>) {
+        let mut free = self.sparkles.iter_mut().filter(|slot| slot.is_none());
+
+        for sparkle in burst {
+            match free.next() {
+                Some(slot) => *slot = Some(sparkle),
+                None => break,
+            }
+        }
+    }
+}

crates/domain/src/sparkle.rs

@@ -0,0 +1,60 @@
+use crate::{Color, Dimensions, Point2D, Sprite, SpriteKind, Vector2D};
+
+pub(crate) const BURST: u32 = 12;
+const SPEED: f32 = 3.0;
+pub(crate) const LIFETIME_FRAMES: u8 = 8;
+const FADE_PER_FRAME: u8 = u8::MAX / LIFETIME_FRAMES;
+const SIZE: Dimensions = match Dimensions::new(8, 8) {
+    Some(size) => size,
+    None => panic!("sparkle size must be non-zero"),
+};
+const COLOR: Color = Color {
+    r: 255,
+    g: 215,
+    b: 0,
+    a: 255,
+};
+
+pub(crate) struct Sparkle {
+    position: Point2D,
+    velocity: Vector2D,
+    dimensions: Dimensions,
+    color: Color,
+}
+
+impl Sparkle {
+    pub(crate) fn burst(origin: Point2D) -> impl Iterator<Item = Sparkle> {
+        (0..BURST).filter_map(move |step| {
+            let angle = step as f32 * (core::f32::consts::TAU / BURST as f32);
+            let velocity = Vector2D::new(libm::cosf(angle) * SPEED, libm::sinf(angle) * SPEED)?;
+
+            Some(Sparkle {
+                position: origin,
+                velocity,
+                dimensions: SIZE,
+                color: COLOR,
+            })
+        })
+    }
+
+    pub(crate) fn tick(&mut self) {
+        if let Some(position) = self.position.translated(self.velocity) {
+            self.position = position;
+        }
+
+        self.color.a = self.color.a.saturating_sub(FADE_PER_FRAME);
+    }
+
+    pub(crate) fn is_alive(&self) -> bool {
+        self.color.a > 0
+    }
+
+    pub(crate) const fn sprite(&self) -> Sprite {
+        Sprite::new(
+            SpriteKind::Sparkle,
+            self.position,
+            self.dimensions,
+            self.color,
+        )
+    }
+}

crates/domain/src/sprite.rs

@@ -0,0 +1,47 @@
+use crate::{Color, Dimensions, Point2D};
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum SpriteKind {
+    Logo,
+    Sparkle,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub struct Sprite {
+    kind: SpriteKind,
+    position: Point2D,
+    dimensions: Dimensions,
+    color: Color,
+}
+
+impl Sprite {
+    pub(crate) const fn new(
+        kind: SpriteKind,
+        position: Point2D,
+        dimensions: Dimensions,
+        color: Color,
+    ) -> Self {
+        Self {
+            kind,
+            position,
+            dimensions,
+            color,
+        }
+    }
+
+    pub const fn kind(&self) -> SpriteKind {
+        self.kind
+    }
+
+    pub const fn position(&self) -> Point2D {
+        self.position
+    }
+
+    pub const fn dimensions(&self) -> Dimensions {
+        self.dimensions
+    }
+
+    pub const fn color(&self) -> Color {
+        self.color
+    }
+}

crates/domain/src/value_objects.rs

@@ -0,0 +1,97 @@
+#[derive(Debug, Clone, Copy, PartialEq, Default)]
+pub struct Point2D {
+    x: f32,
+    y: f32,
+}
+
+impl Point2D {
+    pub const fn new(x: f32, y: f32) -> Option<Self> {
+        if x.is_finite() && y.is_finite() {
+            Some(Self { x, y })
+        } else {
+            None
+        }
+    }
+
+    pub const fn x(&self) -> f32 {
+        self.x
+    }
+
+    pub const fn y(&self) -> f32 {
+        self.y
+    }
+
+    pub(crate) fn translated(self, by: Vector2D) -> Option<Self> {
+        Self::new(self.x + by.dx, self.y + by.dy)
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub struct Vector2D {
+    dx: f32,
+    dy: f32,
+}
+
+impl Vector2D {
+    pub const fn new(dx: f32, dy: f32) -> Option<Self> {
+        if dx.is_finite() && dy.is_finite() {
+            Some(Self { dx, dy })
+        } else {
+            None
+        }
+    }
+
+    pub const fn dx(&self) -> f32 {
+        self.dx
+    }
+
+    pub const fn dy(&self) -> f32 {
+        self.dy
+    }
+
+    pub(crate) const fn reflected_x(self) -> Self {
+        Self {
+            dx: -self.dx,
+            dy: self.dy,
+        }
+    }
+
+    pub(crate) const fn reflected_y(self) -> Self {
+        Self {
+            dx: self.dx,
+            dy: -self.dy,
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub struct Dimensions {
+    width: u32,
+    height: u32,
+}
+
+impl Dimensions {
+    pub const fn new(width: u32, height: u32) -> Option<Self> {
+        if width == 0 || height == 0 {
+            None
+        } else {
+            Some(Self { width, height })
+        }
+    }
+
+    pub const fn width(&self) -> u32 {
+        self.width
+    }
+
+    pub const fn height(&self) -> u32 {
+        self.height
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub struct Color {
+    pub r: u8,
+    pub g: u8,
+    pub b: u8,
+    pub a: u8,
+}

crates/domain/tests/common/mod.rs

@@ -0,0 +1,62 @@
+#![allow(dead_code)]
+
+use domain::{Color, Dimensions, DomainError, Point2D, ScreensaverScene, Sprite, Vector2D};
+
+pub const LOGO: Dimensions = size(200, 100);
+pub const ROOMY: Dimensions = size(800, 600);
+pub const TINY: Dimensions = size(50, 50);
+
+pub const SNUG: Dimensions = size(LOGO.width() + 2, LOGO.height() + 2);
+pub const EDGE_ONLY: Dimensions = size(LOGO.width() + 2, ROOMY.height());
+
+pub const SPEED: Vector2D = velocity(3.0, 2.0);
+pub const RED: Color = Color {
+    r: 255,
+    g: 0,
+    b: 0,
+    a: 255,
+};
+
+pub const fn size(width: u32, height: u32) -> Dimensions {
+    match Dimensions::new(width, height) {
+        Some(size) => size,
+        None => panic!("test dimensions must be non-zero"),
+    }
+}
+
+const fn velocity(dx: f32, dy: f32) -> Vector2D {
+    match Vector2D::new(dx, dy) {
+        Some(velocity) => velocity,
+        None => panic!("test velocity must be finite"),
+    }
+}
+
+pub fn point(x: f32, y: f32) -> Point2D {
+    Point2D::new(x, y).expect("test point must be finite")
+}
+
+pub fn try_scene(logo: Dimensions, bounds: Dimensions) -> Result<ScreensaverScene, DomainError> {
+    ScreensaverScene::new(logo, SPEED, RED, bounds)
+}
+
+pub fn scene_in(bounds: Dimensions) -> ScreensaverScene {
+    try_scene(LOGO, bounds).expect("LOGO must fit the test bounds")
+}
+
+pub fn advance(scene: &mut ScreensaverScene, bounds: Dimensions, frames: u32) {
+    for _ in 0..frames {
+        scene.tick(bounds);
+    }
+}
+
+pub fn sprite_count(scene: &ScreensaverScene) -> usize {
+    scene.sprites().count()
+}
+
+pub fn logo_sprite(scene: &ScreensaverScene) -> Sprite {
+    scene.sprites().next().expect("the logo is always present")
+}
+
+pub fn bottom_right(bounds: Dimensions) -> Point2D {
+    point(bounds.width() as f32, bounds.height() as f32)
+}

crates/domain/tests/construction.rs

@@ -0,0 +1,37 @@
+mod common;
+
+use common::{LOGO, ROOMY, scene_in, size, sprite_count, try_scene};
+use domain::{Dimensions, Point2D, Vector2D};
+
+#[test]
+fn dimensions_reject_zero_extents() {
+    assert!(Dimensions::new(0, 10).is_none());
+    assert!(Dimensions::new(10, 0).is_none());
+    assert!(Dimensions::new(10, 10).is_some());
+}
+
+#[test]
+fn points_reject_non_finite_coordinates() {
+    assert!(Point2D::new(f32::NAN, 0.0).is_none());
+    assert!(Point2D::new(0.0, f32::INFINITY).is_none());
+    assert!(Point2D::new(-1.0, 1.0).is_some());
+}
+
+#[test]
+fn vectors_reject_non_finite_components() {
+    assert!(Vector2D::new(f32::NAN, 1.0).is_none());
+    assert!(Vector2D::new(1.0, f32::NEG_INFINITY).is_none());
+    assert!(Vector2D::new(0.0, 0.0).is_some());
+}
+
+#[test]
+fn the_logo_must_fit_inside_the_bounds() {
+    assert!(try_scene(LOGO, LOGO).is_ok());
+    assert!(try_scene(size(LOGO.width() + 1, LOGO.height()), LOGO).is_err());
+    assert!(try_scene(size(LOGO.width(), LOGO.height() + 1), LOGO).is_err());
+}
+
+#[test]
+fn a_new_scene_holds_only_the_logo() {
+    assert_eq!(sprite_count(&scene_in(ROOMY)), 1);
+}

crates/domain/tests/motion.rs

@@ -0,0 +1,75 @@
+mod common;
+
+use common::{
+    EDGE_ONLY, ROOMY, SNUG, TINY, advance, bottom_right, logo_sprite, scene_in, sprite_count,
+};
+
+#[test]
+fn hitting_a_corner_bursts_sparkles_at_that_corner() {
+    let mut scene = scene_in(SNUG);
+
+    advance(&mut scene, SNUG, 1);
+
+    let corner = bottom_right(SNUG);
+
+    assert!(scene.sprites().any(|sprite| sprite.position() == corner));
+    assert!(sprite_count(&scene) > 1);
+}
+
+#[test]
+fn hitting_a_single_edge_recolours_but_does_not_burst() {
+    let mut scene = scene_in(EDGE_ONLY);
+    let before = logo_sprite(&scene).color();
+
+    advance(&mut scene, EDGE_ONLY, 1);
+
+    assert_ne!(logo_sprite(&scene).color(), before);
+    assert_eq!(sprite_count(&scene), 1);
+}
+
+#[test]
+fn sparkles_expire_so_the_scene_reaches_a_steady_size() {
+    let mut scene = scene_in(SNUG);
+
+    advance(&mut scene, SNUG, 64);
+    let steady = sprite_count(&scene);
+    advance(&mut scene, SNUG, 512);
+
+    assert_eq!(sprite_count(&scene), steady);
+}
+
+#[test]
+fn the_sparkle_buffer_holds_the_worst_case_without_dropping_any() {
+    let mut scene = scene_in(SNUG);
+
+    advance(&mut scene, SNUG, 256);
+
+    assert_eq!(sprite_count(&scene), 12 * 9 + 1);
+}
+
+#[test]
+fn bounds_shrinking_below_the_logo_neither_recolours_nor_bursts() {
+    let mut scene = scene_in(ROOMY);
+    let before = logo_sprite(&scene).color();
+
+    advance(&mut scene, TINY, 64);
+
+    assert_eq!(logo_sprite(&scene).color(), before);
+    assert_eq!(sprite_count(&scene), 1);
+}
+
+#[test]
+fn the_logo_never_leaves_the_bounds() {
+    let mut scene = scene_in(ROOMY);
+
+    for _ in 0..2048 {
+        advance(&mut scene, ROOMY, 1);
+
+        let logo = logo_sprite(&scene);
+        let (position, size) = (logo.position(), logo.dimensions());
+
+        assert!(position.x() >= 0.0 && position.y() >= 0.0);
+        assert!(position.x() + size.width() as f32 <= ROOMY.width() as f32);
+        assert!(position.y() + size.height() as f32 <= ROOMY.height() as f32);
+    }
+}