Implement pure version of game_of_life example 🎉

Cargo.toml

@@ -88,6 +88,7 @@ members = [
     "examples/url_handler",
     "examples/pure/component",
     "examples/pure/counter",
+    "examples/pure/game_of_life",
     "examples/pure/pick_list",
     "examples/pure/todos",
     "examples/pure/tour",

examples/pure/game_of_life/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "pure_game_of_life"
+version = "0.1.0"
+authors = ["Héctor Ramón Jiménez <hector0193@gmail.com>"]
+edition = "2021"
+publish = false
+
+[dependencies]
+iced = { path = "../../..", features = ["pure", "canvas", "tokio", "debug"] }
+tokio = { version = "1.0", features = ["sync"] }
+itertools = "0.9"
+rustc-hash = "1.1"
+env_logger = "0.9"

examples/pure/game_of_life/README.md

@@ -0,0 +1,22 @@
+## Game of Life
+
+An interactive version of the [Game of Life], invented by [John Horton Conway].
+
+It runs a simulation in a background thread while allowing interaction with a `Canvas` that displays an infinite grid with zooming, panning, and drawing support.
+
+The __[`main`]__ file contains the relevant code of the example.
+
+<div align="center">
+  <a href="https://gfycat.com/WhichPaltryChick">
+    <img src="https://thumbs.gfycat.com/WhichPaltryChick-size_restricted.gif">
+  </a>
+</div>
+
+You can run it with `cargo run`:
+```
+cargo run --package game_of_life
+```
+
+[`main`]: src/main.rs
+[Game of Life]: https://en.wikipedia.org/wiki/Conway%27s_Game_of_Life
+[John Horton Conway]: https://en.wikipedia.org/wiki/John_Horton_Conway

examples/pure/game_of_life/src/main.rs

@@ -0,0 +1,899 @@
+//! This example showcases an interactive version of the Game of Life, invented
+//! by John Conway. It leverages a `Canvas` together with other widgets.
+mod preset;
+mod style;
+
+use grid::Grid;
+use iced::executor;
+use iced::pure::widget::{
+    button, checkbox, column, container, pick_list, row, slider, text,
+};
+use iced::pure::{Application, Element};
+use iced::time;
+use iced::window;
+use iced::{Alignment, Color, Command, Length, Settings, Subscription};
+use preset::Preset;
+use std::time::{Duration, Instant};
+
+pub fn main() -> iced::Result {
+    env_logger::builder().format_timestamp(None).init();
+
+    GameOfLife::run(Settings {
+        antialiasing: true,
+        window: window::Settings {
+            position: window::Position::Centered,
+            ..window::Settings::default()
+        },
+        ..Settings::default()
+    })
+}
+
+#[derive(Default)]
+struct GameOfLife {
+    grid: Grid,
+    is_playing: bool,
+    queued_ticks: usize,
+    speed: usize,
+    next_speed: Option<usize>,
+    version: usize,
+}
+
+#[derive(Debug, Clone)]
+enum Message {
+    Grid(grid::Message, usize),
+    Tick(Instant),
+    TogglePlayback,
+    ToggleGrid(bool),
+    Next,
+    Clear,
+    SpeedChanged(f32),
+    PresetPicked(Preset),
+}
+
+impl Application for GameOfLife {
+    type Message = Message;
+    type Executor = executor::Default;
+    type Flags = ();
+
+    fn new(_flags: ()) -> (Self, Command<Message>) {
+        (
+            Self {
+                speed: 5,
+                ..Self::default()
+            },
+            Command::none(),
+        )
+    }
+
+    fn title(&self) -> String {
+        String::from("Game of Life - Iced")
+    }
+
+    fn background_color(&self) -> Color {
+        style::BACKGROUND
+    }
+
+    fn update(&mut self, message: Message) -> Command<Message> {
+        match message {
+            Message::Grid(message, version) => {
+                if version == self.version {
+                    self.grid.update(message);
+                }
+            }
+            Message::Tick(_) | Message::Next => {
+                self.queued_ticks = (self.queued_ticks + 1).min(self.speed);
+
+                if let Some(task) = self.grid.tick(self.queued_ticks) {
+                    if let Some(speed) = self.next_speed.take() {
+                        self.speed = speed;
+                    }
+
+                    self.queued_ticks = 0;
+
+                    let version = self.version;
+
+                    return Command::perform(task, move |message| {
+                        Message::Grid(message, version)
+                    });
+                }
+            }
+            Message::TogglePlayback => {
+                self.is_playing = !self.is_playing;
+            }
+            Message::ToggleGrid(show_grid_lines) => {
+                self.grid.toggle_lines(show_grid_lines);
+            }
+            Message::Clear => {
+                self.grid.clear();
+                self.version += 1;
+            }
+            Message::SpeedChanged(speed) => {
+                if self.is_playing {
+                    self.next_speed = Some(speed.round() as usize);
+                } else {
+                    self.speed = speed.round() as usize;
+                }
+            }
+            Message::PresetPicked(new_preset) => {
+                self.grid = Grid::from_preset(new_preset);
+                self.version += 1;
+            }
+        }
+
+        Command::none()
+    }
+
+    fn subscription(&self) -> Subscription<Message> {
+        if self.is_playing {
+            time::every(Duration::from_millis(1000 / self.speed as u64))
+                .map(Message::Tick)
+        } else {
+            Subscription::none()
+        }
+    }
+
+    fn view(&self) -> Element<Message> {
+        let version = self.version;
+        let selected_speed = self.next_speed.unwrap_or(self.speed);
+        let controls = view_controls(
+            self.is_playing,
+            self.grid.are_lines_visible(),
+            selected_speed,
+            self.grid.preset(),
+        );
+
+        let content = column()
+            .push(
+                self.grid
+                    .view()
+                    .map(move |message| Message::Grid(message, version)),
+            )
+            .push(controls);
+
+        container(content)
+            .width(Length::Fill)
+            .height(Length::Fill)
+            .style(style::Container)
+            .into()
+    }
+}
+
+fn view_controls<'a>(
+    is_playing: bool,
+    is_grid_enabled: bool,
+    speed: usize,
+    preset: Preset,
+) -> Element<'a, Message> {
+    let playback_controls = row()
+        .spacing(10)
+        .push(
+            button(if is_playing { "Pause" } else { "Play" })
+                .on_press(Message::TogglePlayback)
+                .style(style::Button),
+        )
+        .push(button("Next").on_press(Message::Next).style(style::Button));
+
+    let speed_controls = row()
+        .width(Length::Fill)
+        .align_items(Alignment::Center)
+        .spacing(10)
+        .push(
+            slider(1.0..=1000.0, speed as f32, Message::SpeedChanged)
+                .style(style::Slider),
+        )
+        .push(text(format!("x{}", speed)).size(16));
+
+    row()
+        .padding(10)
+        .spacing(20)
+        .align_items(Alignment::Center)
+        .push(playback_controls)
+        .push(speed_controls)
+        .push(
+            checkbox("Grid", is_grid_enabled, Message::ToggleGrid)
+                .size(16)
+                .spacing(5)
+                .text_size(16),
+        )
+        .push(
+            pick_list(preset::ALL, Some(preset), Message::PresetPicked)
+                .padding(8)
+                .text_size(16)
+                .style(style::PickList),
+        )
+        .push(button("Clear").on_press(Message::Clear).style(style::Clear))
+        .into()
+}
+
+mod grid {
+    use crate::Preset;
+    use iced::pure::canvas::event::{self, Event};
+    use iced::pure::canvas::{
+        self, Cache, Canvas, Cursor, Frame, Geometry, Path, Text,
+    };
+    use iced::pure::Element;
+    use iced::{
+        alignment, mouse, Color, Length, Point, Rectangle, Size, Vector,
+    };
+    use rustc_hash::{FxHashMap, FxHashSet};
+    use std::future::Future;
+    use std::ops::RangeInclusive;
+    use std::time::{Duration, Instant};
+
+    pub struct Grid {
+        state: State,
+        preset: Preset,
+        life_cache: Cache,
+        grid_cache: Cache,
+        translation: Vector,
+        scaling: f32,
+        show_lines: bool,
+        last_tick_duration: Duration,
+        last_queued_ticks: usize,
+    }
+
+    #[derive(Debug, Clone)]
+    pub enum Message {
+        Populate(Cell),
+        Unpopulate(Cell),
+        Translated(Vector),
+        Scaled(f32, Option<Vector>),
+        Ticked {
+            result: Result<Life, TickError>,
+            tick_duration: Duration,
+        },
+    }
+
+    #[derive(Debug, Clone)]
+    pub enum TickError {
+        JoinFailed,
+    }
+
+    impl Default for Grid {
+        fn default() -> Self {
+            Self::from_preset(Preset::default())
+        }
+    }
+
+    impl Grid {
+        const MIN_SCALING: f32 = 0.1;
+        const MAX_SCALING: f32 = 2.0;
+
+        pub fn from_preset(preset: Preset) -> Self {
+            Self {
+                state: State::with_life(
+                    preset
+                        .life()
+                        .into_iter()
+                        .map(|(i, j)| Cell { i, j })
+                        .collect(),
+                ),
+                preset,
+                life_cache: Cache::default(),
+                grid_cache: Cache::default(),
+                translation: Vector::default(),
+                scaling: 1.0,
+                show_lines: true,
+                last_tick_duration: Duration::default(),
+                last_queued_ticks: 0,
+            }
+        }
+
+        pub fn tick(
+            &mut self,
+            amount: usize,
+        ) -> Option<impl Future<Output = Message>> {
+            let tick = self.state.tick(amount)?;
+
+            self.last_queued_ticks = amount;
+
+            Some(async move {
+                let start = Instant::now();
+                let result = tick.await;
+                let tick_duration = start.elapsed() / amount as u32;
+
+                Message::Ticked {
+                    result,
+                    tick_duration,
+                }
+            })
+        }
+
+        pub fn update(&mut self, message: Message) {
+            match message {
+                Message::Populate(cell) => {
+                    self.state.populate(cell);
+                    self.life_cache.clear();
+
+                    self.preset = Preset::Custom;
+                }
+                Message::Unpopulate(cell) => {
+                    self.state.unpopulate(&cell);
+                    self.life_cache.clear();
+
+                    self.preset = Preset::Custom;
+                }
+                Message::Translated(translation) => {
+                    self.translation = translation;
+
+                    self.life_cache.clear();
+                    self.grid_cache.clear();
+                }
+                Message::Scaled(scaling, translation) => {
+                    self.scaling = scaling;
+
+                    if let Some(translation) = translation {
+                        self.translation = translation;
+                    }
+
+                    self.life_cache.clear();
+                    self.grid_cache.clear();
+                }
+                Message::Ticked {
+                    result: Ok(life),
+                    tick_duration,
+                } => {
+                    self.state.update(life);
+                    self.life_cache.clear();
+
+                    self.last_tick_duration = tick_duration;
+                }
+                Message::Ticked {
+                    result: Err(error), ..
+                } => {
+                    dbg!(error);
+                }
+            }
+        }
+
+        pub fn view<'a>(&'a self) -> Element<'a, Message> {
+            Canvas::new(self)
+                .width(Length::Fill)
+                .height(Length::Fill)
+                .into()
+        }
+
+        pub fn clear(&mut self) {
+            self.state = State::default();
+            self.preset = Preset::Custom;
+
+            self.life_cache.clear();
+        }
+
+        pub fn preset(&self) -> Preset {
+            self.preset
+        }
+
+        pub fn toggle_lines(&mut self, enabled: bool) {
+            self.show_lines = enabled;
+        }
+
+        pub fn are_lines_visible(&self) -> bool {
+            self.show_lines
+        }
+
+        fn visible_region(&self, size: Size) -> Region {
+            let width = size.width / self.scaling;
+            let height = size.height / self.scaling;
+
+            Region {
+                x: -self.translation.x - width / 2.0,
+                y: -self.translation.y - height / 2.0,
+                width,
+                height,
+            }
+        }
+
+        fn project(&self, position: Point, size: Size) -> Point {
+            let region = self.visible_region(size);
+
+            Point::new(
+                position.x / self.scaling + region.x,
+                position.y / self.scaling + region.y,
+            )
+        }
+    }
+
+    impl canvas::Program for Grid {
+        type Message = Message;
+        type State = Interaction;
+
+        fn update(
+            &self,
+            interaction: &mut Interaction,
+            event: Event,
+            bounds: Rectangle,
+            cursor: Cursor,
+        ) -> (event::Status, Option<Message>) {
+            if let Event::Mouse(mouse::Event::ButtonReleased(_)) = event {
+                *interaction = Interaction::None;
+            }
+
+            let cursor_position =
+                if let Some(position) = cursor.position_in(&bounds) {
+                    position
+                } else {
+                    return (event::Status::Ignored, None);
+                };
+
+            let cell = Cell::at(self.project(cursor_position, bounds.size()));
+            let is_populated = self.state.contains(&cell);
+
+            let (populate, unpopulate) = if is_populated {
+                (None, Some(Message::Unpopulate(cell)))
+            } else {
+                (Some(Message::Populate(cell)), None)
+            };
+
+            match event {
+                Event::Mouse(mouse_event) => match mouse_event {
+                    mouse::Event::ButtonPressed(button) => {
+                        let message = match button {
+                            mouse::Button::Left => {
+                                *interaction = if is_populated {
+                                    Interaction::Erasing
+                                } else {
+                                    Interaction::Drawing
+                                };
+
+                                populate.or(unpopulate)
+                            }
+                            mouse::Button::Right => {
+                                *interaction = Interaction::Panning {
+                                    translation: self.translation,
+                                    start: cursor_position,
+                                };
+
+                                None
+                            }
+                            _ => None,
+                        };
+
+                        (event::Status::Captured, message)
+                    }
+                    mouse::Event::CursorMoved { .. } => {
+                        let message = match *interaction {
+                            Interaction::Drawing => populate,
+                            Interaction::Erasing => unpopulate,
+                            Interaction::Panning { translation, start } => {
+                                Some(Message::Translated(
+                                    translation
+                                        + (cursor_position - start)
+                                            * (1.0 / self.scaling),
+                                ))
+                            }
+                            _ => None,
+                        };
+
+                        let event_status = match interaction {
+                            Interaction::None => event::Status::Ignored,
+                            _ => event::Status::Captured,
+                        };
+
+                        (event_status, message)
+                    }
+                    mouse::Event::WheelScrolled { delta } => match delta {
+                        mouse::ScrollDelta::Lines { y, .. }
+                        | mouse::ScrollDelta::Pixels { y, .. } => {
+                            if y < 0.0 && self.scaling > Self::MIN_SCALING
+                                || y > 0.0 && self.scaling < Self::MAX_SCALING
+                            {
+                                let old_scaling = self.scaling;
+
+                                let scaling = (self.scaling * (1.0 + y / 30.0))
+                                    .max(Self::MIN_SCALING)
+                                    .min(Self::MAX_SCALING);
+
+                                let translation =
+                                    if let Some(cursor_to_center) =
+                                        cursor.position_from(bounds.center())
+                                    {
+                                        let factor = scaling - old_scaling;
+
+                                        Some(
+                                            self.translation
+                                                - Vector::new(
+                                                    cursor_to_center.x * factor
+                                                        / (old_scaling
+                                                            * old_scaling),
+                                                    cursor_to_center.y * factor
+                                                        / (old_scaling
+                                                            * old_scaling),
+                                                ),
+                                        )
+                                    } else {
+                                        None
+                                    };
+
+                                (
+                                    event::Status::Captured,
+                                    Some(Message::Scaled(scaling, translation)),
+                                )
+                            } else {
+                                (event::Status::Captured, None)
+                            }
+                        }
+                    },
+                    _ => (event::Status::Ignored, None),
+                },
+                _ => (event::Status::Ignored, None),
+            }
+        }
+
+        fn draw(
+            &self,
+            _interaction: &Interaction,
+            bounds: Rectangle,
+            cursor: Cursor,
+        ) -> Vec<Geometry> {
+            let center = Vector::new(bounds.width / 2.0, bounds.height / 2.0);
+
+            let life = self.life_cache.draw(bounds.size(), |frame| {
+                let background = Path::rectangle(Point::ORIGIN, frame.size());
+                frame.fill(&background, Color::from_rgb8(0x40, 0x44, 0x4B));
+
+                frame.with_save(|frame| {
+                    frame.translate(center);
+                    frame.scale(self.scaling);
+                    frame.translate(self.translation);
+                    frame.scale(Cell::SIZE as f32);
+
+                    let region = self.visible_region(frame.size());
+
+                    for cell in region.cull(self.state.cells()) {
+                        frame.fill_rectangle(
+                            Point::new(cell.j as f32, cell.i as f32),
+                            Size::UNIT,
+                            Color::WHITE,
+                        );
+                    }
+                });
+            });
+
+            let overlay = {
+                let mut frame = Frame::new(bounds.size());
+
+                let hovered_cell =
+                    cursor.position_in(&bounds).map(|position| {
+                        Cell::at(self.project(position, frame.size()))
+                    });
+
+                if let Some(cell) = hovered_cell {
+                    frame.with_save(|frame| {
+                        frame.translate(center);
+                        frame.scale(self.scaling);
+                        frame.translate(self.translation);
+                        frame.scale(Cell::SIZE as f32);
+
+                        frame.fill_rectangle(
+                            Point::new(cell.j as f32, cell.i as f32),
+                            Size::UNIT,
+                            Color {
+                                a: 0.5,
+                                ..Color::BLACK
+                            },
+                        );
+                    });
+                }
+
+                let text = Text {
+                    color: Color::WHITE,
+                    size: 14.0,
+                    position: Point::new(frame.width(), frame.height()),
+                    horizontal_alignment: alignment::Horizontal::Right,
+                    vertical_alignment: alignment::Vertical::Bottom,
+                    ..Text::default()
+                };
+
+                if let Some(cell) = hovered_cell {
+                    frame.fill_text(Text {
+                        content: format!("({}, {})", cell.j, cell.i),
+                        position: text.position - Vector::new(0.0, 16.0),
+                        ..text
+                    });
+                }
+
+                let cell_count = self.state.cell_count();
+
+                frame.fill_text(Text {
+                    content: format!(
+                        "{} cell{} @ {:?} ({})",
+                        cell_count,
+                        if cell_count == 1 { "" } else { "s" },
+                        self.last_tick_duration,
+                        self.last_queued_ticks
+                    ),
+                    ..text
+                });
+
+                frame.into_geometry()
+            };
+
+            if self.scaling < 0.2 || !self.show_lines {
+                vec![life, overlay]
+            } else {
+                let grid = self.grid_cache.draw(bounds.size(), |frame| {
+                    frame.translate(center);
+                    frame.scale(self.scaling);
+                    frame.translate(self.translation);
+                    frame.scale(Cell::SIZE as f32);
+
+                    let region = self.visible_region(frame.size());
+                    let rows = region.rows();
+                    let columns = region.columns();
+                    let (total_rows, total_columns) =
+                        (rows.clone().count(), columns.clone().count());
+                    let width = 2.0 / Cell::SIZE as f32;
+                    let color = Color::from_rgb8(70, 74, 83);
+
+                    frame.translate(Vector::new(-width / 2.0, -width / 2.0));
+
+                    for row in region.rows() {
+                        frame.fill_rectangle(
+                            Point::new(*columns.start() as f32, row as f32),
+                            Size::new(total_columns as f32, width),
+                            color,
+                        );
+                    }
+
+                    for column in region.columns() {
+                        frame.fill_rectangle(
+                            Point::new(column as f32, *rows.start() as f32),
+                            Size::new(width, total_rows as f32),
+                            color,
+                        );
+                    }
+                });
+
+                vec![life, grid, overlay]
+            }
+        }
+
+        fn mouse_interaction(
+            &self,
+            interaction: &Interaction,
+            bounds: Rectangle,
+            cursor: Cursor,
+        ) -> mouse::Interaction {
+            match interaction {
+                Interaction::Drawing => mouse::Interaction::Crosshair,
+                Interaction::Erasing => mouse::Interaction::Crosshair,
+                Interaction::Panning { .. } => mouse::Interaction::Grabbing,
+                Interaction::None if cursor.is_over(&bounds) => {
+                    mouse::Interaction::Crosshair
+                }
+                _ => mouse::Interaction::default(),
+            }
+        }
+    }
+
+    #[derive(Default)]
+    struct State {
+        life: Life,
+        births: FxHashSet<Cell>,
+        is_ticking: bool,
+    }
+
+    impl State {
+        pub fn with_life(life: Life) -> Self {
+            Self {
+                life,
+                ..Self::default()
+            }
+        }
+
+        fn cell_count(&self) -> usize {
+            self.life.len() + self.births.len()
+        }
+
+        fn contains(&self, cell: &Cell) -> bool {
+            self.life.contains(cell) || self.births.contains(cell)
+        }
+
+        fn cells(&self) -> impl Iterator<Item = &Cell> {
+            self.life.iter().chain(self.births.iter())
+        }
+
+        fn populate(&mut self, cell: Cell) {
+            if self.is_ticking {
+                self.births.insert(cell);
+            } else {
+                self.life.populate(cell);
+            }
+        }
+
+        fn unpopulate(&mut self, cell: &Cell) {
+            if self.is_ticking {
+                let _ = self.births.remove(cell);
+            } else {
+                self.life.unpopulate(cell);
+            }
+        }
+
+        fn update(&mut self, mut life: Life) {
+            self.births.drain().for_each(|cell| life.populate(cell));
+
+            self.life = life;
+            self.is_ticking = false;
+        }
+
+        fn tick(
+            &mut self,
+            amount: usize,
+        ) -> Option<impl Future<Output = Result<Life, TickError>>> {
+            if self.is_ticking {
+                return None;
+            }
+
+            self.is_ticking = true;
+
+            let mut life = self.life.clone();
+
+            Some(async move {
+                tokio::task::spawn_blocking(move || {
+                    for _ in 0..amount {
+                        life.tick();
+                    }
+
+                    life
+                })
+                .await
+                .map_err(|_| TickError::JoinFailed)
+            })
+        }
+    }
+
+    #[derive(Clone, Default)]
+    pub struct Life {
+        cells: FxHashSet<Cell>,
+    }
+
+    impl Life {
+        fn len(&self) -> usize {
+            self.cells.len()
+        }
+
+        fn contains(&self, cell: &Cell) -> bool {
+            self.cells.contains(cell)
+        }
+
+        fn populate(&mut self, cell: Cell) {
+            self.cells.insert(cell);
+        }
+
+        fn unpopulate(&mut self, cell: &Cell) {
+            let _ = self.cells.remove(cell);
+        }
+
+        fn tick(&mut self) {
+            let mut adjacent_life = FxHashMap::default();
+
+            for cell in &self.cells {
+                let _ = adjacent_life.entry(*cell).or_insert(0);
+
+                for neighbor in Cell::neighbors(*cell) {
+                    let amount = adjacent_life.entry(neighbor).or_insert(0);
+
+                    *amount += 1;
+                }
+            }
+
+            for (cell, amount) in adjacent_life.iter() {
+                match amount {
+                    2 => {}
+                    3 => {
+                        let _ = self.cells.insert(*cell);
+                    }
+                    _ => {
+                        let _ = self.cells.remove(cell);
+                    }
+                }
+            }
+        }
+
+        pub fn iter(&self) -> impl Iterator<Item = &Cell> {
+            self.cells.iter()
+        }
+    }
+
+    impl std::iter::FromIterator<Cell> for Life {
+        fn from_iter<I: IntoIterator<Item = Cell>>(iter: I) -> Self {
+            Life {
+                cells: iter.into_iter().collect(),
+            }
+        }
+    }
+
+    impl std::fmt::Debug for Life {
+        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+            f.debug_struct("Life")
+                .field("cells", &self.cells.len())
+                .finish()
+        }
+    }
+
+    #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+    pub struct Cell {
+        i: isize,
+        j: isize,
+    }
+
+    impl Cell {
+        const SIZE: usize = 20;
+
+        fn at(position: Point) -> Cell {
+            let i = (position.y / Cell::SIZE as f32).ceil() as isize;
+            let j = (position.x / Cell::SIZE as f32).ceil() as isize;
+
+            Cell {
+                i: i.saturating_sub(1),
+                j: j.saturating_sub(1),
+            }
+        }
+
+        fn cluster(cell: Cell) -> impl Iterator<Item = Cell> {
+            use itertools::Itertools;
+
+            let rows = cell.i.saturating_sub(1)..=cell.i.saturating_add(1);
+            let columns = cell.j.saturating_sub(1)..=cell.j.saturating_add(1);
+
+            rows.cartesian_product(columns).map(|(i, j)| Cell { i, j })
+        }
+
+        fn neighbors(cell: Cell) -> impl Iterator<Item = Cell> {
+            Cell::cluster(cell).filter(move |candidate| *candidate != cell)
+        }
+    }
+
+    pub struct Region {
+        x: f32,
+        y: f32,
+        width: f32,
+        height: f32,
+    }
+
+    impl Region {
+        fn rows(&self) -> RangeInclusive<isize> {
+            let first_row = (self.y / Cell::SIZE as f32).floor() as isize;
+
+            let visible_rows =
+                (self.height / Cell::SIZE as f32).ceil() as isize;
+
+            first_row..=first_row + visible_rows
+        }
+
+        fn columns(&self) -> RangeInclusive<isize> {
+            let first_column = (self.x / Cell::SIZE as f32).floor() as isize;
+
+            let visible_columns =
+                (self.width / Cell::SIZE as f32).ceil() as isize;
+
+            first_column..=first_column + visible_columns
+        }
+
+        fn cull<'a>(
+            &self,
+            cells: impl Iterator<Item = &'a Cell>,
+        ) -> impl Iterator<Item = &'a Cell> {
+            let rows = self.rows();
+            let columns = self.columns();
+
+            cells.filter(move |cell| {
+                rows.contains(&cell.i) && columns.contains(&cell.j)
+            })
+        }
+    }
+
+    pub enum Interaction {
+        None,
+        Drawing,
+        Erasing,
+        Panning { translation: Vector, start: Point },
+    }
+
+    impl Default for Interaction {
+        fn default() -> Self {
+            Self::None
+        }
+    }
+}

examples/pure/game_of_life/src/preset.rs

@@ -0,0 +1,142 @@
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Preset {
+    Custom,
+    XKCD,
+    Glider,
+    SmallExploder,
+    Exploder,
+    TenCellRow,
+    LightweightSpaceship,
+    Tumbler,
+    GliderGun,
+    Acorn,
+}
+
+pub static ALL: &[Preset] = &[
+    Preset::Custom,
+    Preset::XKCD,
+    Preset::Glider,
+    Preset::SmallExploder,
+    Preset::Exploder,
+    Preset::TenCellRow,
+    Preset::LightweightSpaceship,
+    Preset::Tumbler,
+    Preset::GliderGun,
+    Preset::Acorn,
+];
+
+impl Preset {
+    pub fn life(self) -> Vec<(isize, isize)> {
+        #[rustfmt::skip]
+        let cells = match self {
+            Preset::Custom => vec![],
+            Preset::XKCD => vec![
+                "  xxx  ",
+                "  x x  ",
+                "  x x  ",
+                "   x   ",
+                "x xxx  ",
+                " x x x ",
+                "   x  x",
+                "  x x  ",
+                "  x x  ",
+            ],
+            Preset::Glider => vec![
+                " x ",
+                "  x",
+                "xxx"
+            ],
+            Preset::SmallExploder => vec![
+                " x ",
+                "xxx",
+                "x x",
+                " x ",
+            ],
+            Preset::Exploder => vec![
+                "x x x",
+                "x   x",
+                "x   x",
+                "x   x",
+                "x x x",
+            ],
+            Preset::TenCellRow => vec![
+                "xxxxxxxxxx",
+            ],
+            Preset::LightweightSpaceship => vec![
+                " xxxxx",
+                "x    x",
+                "     x",
+                "x   x ",
+            ],
+            Preset::Tumbler => vec![
+                " xx xx ",
+                " xx xx ",
+                "  x x  ",
+                "x x x x",
+                "x x x x",
+                "xx   xx",
+            ],
+            Preset::GliderGun => vec![
+                "                        x           ",
+                "                      x x           ",
+                "            xx      xx            xx",
+                "           x   x    xx            xx",
+                "xx        x     x   xx              ",
+                "xx        x   x xx    x x           ",
+                "          x     x       x           ",
+                "           x   x                    ",
+                "            xx                      ",
+            ],
+            Preset::Acorn => vec![
+                " x     ",
+                "   x   ",
+                "xx  xxx",
+            ],
+        };
+
+        let start_row = -(cells.len() as isize / 2);
+
+        cells
+            .into_iter()
+            .enumerate()
+            .flat_map(|(i, cells)| {
+                let start_column = -(cells.len() as isize / 2);
+
+                cells
+                    .chars()
+                    .enumerate()
+                    .filter(|(_, c)| !c.is_whitespace())
+                    .map(move |(j, _)| {
+                        (start_row + i as isize, start_column + j as isize)
+                    })
+            })
+            .collect()
+    }
+}
+
+impl Default for Preset {
+    fn default() -> Preset {
+        Preset::XKCD
+    }
+}
+
+impl std::fmt::Display for Preset {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(
+            f,
+            "{}",
+            match self {
+                Preset::Custom => "Custom",
+                Preset::XKCD => "xkcd #2293",
+                Preset::Glider => "Glider",
+                Preset::SmallExploder => "Small Exploder",
+                Preset::Exploder => "Exploder",
+                Preset::TenCellRow => "10 Cell Row",
+                Preset::LightweightSpaceship => "Lightweight spaceship",
+                Preset::Tumbler => "Tumbler",
+                Preset::GliderGun => "Gosper Glider Gun",
+                Preset::Acorn => "Acorn",
+            }
+        )
+    }
+}

examples/pure/game_of_life/src/style.rs

@@ -0,0 +1,186 @@
+use iced::{button, container, pick_list, slider, Background, Color};
+
+const ACTIVE: Color = Color::from_rgb(
+    0x72 as f32 / 255.0,
+    0x89 as f32 / 255.0,
+    0xDA as f32 / 255.0,
+);
+
+const DESTRUCTIVE: Color = Color::from_rgb(
+    0xC0 as f32 / 255.0,
+    0x47 as f32 / 255.0,
+    0x47 as f32 / 255.0,
+);
+
+const HOVERED: Color = Color::from_rgb(
+    0x67 as f32 / 255.0,
+    0x7B as f32 / 255.0,
+    0xC4 as f32 / 255.0,
+);
+
+pub const BACKGROUND: Color = Color::from_rgb(
+    0x2F as f32 / 255.0,
+    0x31 as f32 / 255.0,
+    0x36 as f32 / 255.0,
+);
+
+pub struct Container;
+
+impl container::StyleSheet for Container {
+    fn style(&self) -> container::Style {
+        container::Style {
+            text_color: Some(Color::WHITE),
+            ..container::Style::default()
+        }
+    }
+}
+
+pub struct Button;
+
+impl button::StyleSheet for Button {
+    fn active(&self) -> button::Style {
+        button::Style {
+            background: Some(Background::Color(ACTIVE)),
+            border_radius: 3.0,
+            text_color: Color::WHITE,
+            ..button::Style::default()
+        }
+    }
+
+    fn hovered(&self) -> button::Style {
+        button::Style {
+            background: Some(Background::Color(HOVERED)),
+            text_color: Color::WHITE,
+            ..self.active()
+        }
+    }
+
+    fn pressed(&self) -> button::Style {
+        button::Style {
+            border_width: 1.0,
+            border_color: Color::WHITE,
+            ..self.hovered()
+        }
+    }
+}
+
+pub struct Clear;
+
+impl button::StyleSheet for Clear {
+    fn active(&self) -> button::Style {
+        button::Style {
+            background: Some(Background::Color(DESTRUCTIVE)),
+            border_radius: 3.0,
+            text_color: Color::WHITE,
+            ..button::Style::default()
+        }
+    }
+
+    fn hovered(&self) -> button::Style {
+        button::Style {
+            background: Some(Background::Color(Color {
+                a: 0.5,
+                ..DESTRUCTIVE
+            })),
+            text_color: Color::WHITE,
+            ..self.active()
+        }
+    }
+
+    fn pressed(&self) -> button::Style {
+        button::Style {
+            border_width: 1.0,
+            border_color: Color::WHITE,
+            ..self.hovered()
+        }
+    }
+}
+
+pub struct Slider;
+
+impl slider::StyleSheet for Slider {
+    fn active(&self) -> slider::Style {
+        slider::Style {
+            rail_colors: (ACTIVE, Color { a: 0.1, ..ACTIVE }),
+            handle: slider::Handle {
+                shape: slider::HandleShape::Circle { radius: 9.0 },
+                color: ACTIVE,
+                border_width: 0.0,
+                border_color: Color::TRANSPARENT,
+            },
+        }
+    }
+
+    fn hovered(&self) -> slider::Style {
+        let active = self.active();
+
+        slider::Style {
+            handle: slider::Handle {
+                color: HOVERED,
+                ..active.handle
+            },
+            ..active
+        }
+    }
+
+    fn dragging(&self) -> slider::Style {
+        let active = self.active();
+
+        slider::Style {
+            handle: slider::Handle {
+                color: Color::from_rgb(0.85, 0.85, 0.85),
+                ..active.handle
+            },
+            ..active
+        }
+    }
+}
+
+pub struct PickList;
+
+impl pick_list::StyleSheet for PickList {
+    fn menu(&self) -> pick_list::Menu {
+        pick_list::Menu {
+            text_color: Color::WHITE,
+            background: BACKGROUND.into(),
+            border_width: 1.0,
+            border_color: Color {
+                a: 0.7,
+                ..Color::BLACK
+            },
+            selected_background: Color {
+                a: 0.5,
+                ..Color::BLACK
+            }
+            .into(),
+            selected_text_color: Color::WHITE,
+        }
+    }
+
+    fn active(&self) -> pick_list::Style {
+        pick_list::Style {
+            text_color: Color::WHITE,
+            background: BACKGROUND.into(),
+            border_width: 1.0,
+            border_color: Color {
+                a: 0.6,
+                ..Color::BLACK
+            },
+            border_radius: 2.0,
+            icon_size: 0.5,
+            ..pick_list::Style::default()
+        }
+    }
+
+    fn hovered(&self) -> pick_list::Style {
+        let active = self.active();
+
+        pick_list::Style {
+            border_color: Color {
+                a: 0.9,
+                ..Color::BLACK
+            },
+            ..active
+        }
+    }
+}

src/pure.rs

@@ -48,11 +48,11 @@ pub type Image = iced_pure::Image<crate::widget::image::Handle>;
 mod application;
 mod sandbox;
 
+pub use application::Application;
+pub use sandbox::Sandbox;
+
 #[cfg(feature = "canvas")]
 pub use iced_graphics::widget::pure::canvas;
 
 #[cfg(feature = "canvas")]
 pub use canvas::Canvas;
-
-pub use application::Application;
-pub use sandbox::Sandbox;