Implement sierpinski-triangle example

examples/sierpinski_triangle/Cargo.toml

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+[package]
+name = "sierpinski_triangle"
+version = "0.1.0"
+authors = ["xkenmon <xkenmon@gmail.com>"]
+edition = "2018"
+publish = false
+
+[dependencies]
+iced = { path = "../..", features = ["canvas", "debug"] }
+rand = "0.8.4"

examples/sierpinski_triangle/README.md

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+## Sierpinski Triangle Emulator
+
+A simple [Sierpiński triangle](https://en.wikipedia.org/wiki/Sierpi%C5%84ski_triangle) Emulator, use canvas and slider.
+
+Left-click add fixed point, right-click remove fixed point.
+
+<div align="center">
+  <a href="https://gfycat.com/flippantrectangularechidna">
+    <img src="https://thumbs.gfycat.com/FlippantRectangularEchidna-size_restricted.gif">
+  </a>
+</div>
+
+You can run with cargo:
+```
+cargo run --package sierpinski_triangle
+```

examples/sierpinski_triangle/src/main.rs

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+use std::fmt::Debug;
+
+use iced::executor;
+use iced::widget::canvas::event::{self, Event};
+use iced::widget::canvas::{self, Canvas};
+use iced::widget::{column, row, slider, text};
+use iced::{
+    Application, Color, Command, Length, Point, Rectangle, Settings, Size,
+    Theme,
+};
+
+use rand::Rng;
+
+fn main() -> iced::Result {
+    SierpinskiEmulator::run(Settings {
+        antialiasing: true,
+        ..Settings::default()
+    })
+}
+
+#[derive(Debug)]
+struct SierpinskiEmulator {
+    graph: SierpinskiGraph,
+}
+
+#[derive(Debug, Clone)]
+pub enum Message {
+    IterationSet(i32),
+    PointAdded(Point),
+    PointRemoved,
+}
+
+impl Application for SierpinskiEmulator {
+    type Executor = executor::Default;
+    type Message = Message;
+    type Theme = Theme;
+    type Flags = ();
+
+    fn new(_flags: Self::Flags) -> (Self, iced::Command<Self::Message>) {
+        let emulator = SierpinskiEmulator {
+            graph: SierpinskiGraph::new(),
+        };
+        (emulator, Command::none())
+    }
+
+    fn title(&self) -> String {
+        "Sierpinski Triangle Emulator".to_string()
+    }
+
+    fn update(
+        &mut self,
+        message: Self::Message,
+    ) -> iced::Command<Self::Message> {
+        match message {
+            Message::IterationSet(cur_iter) => {
+                self.graph.iteration = cur_iter;
+            }
+            Message::PointAdded(point) => {
+                self.graph.fix_points.push(point);
+                self.graph.random_points.clear();
+            }
+            Message::PointRemoved => {
+                self.graph.fix_points.pop();
+                self.graph.random_points.clear();
+            }
+        }
+
+        self.graph.redraw();
+
+        Command::none()
+    }
+
+    fn view(&self) -> iced::Element<'_, Self::Message> {
+        column![
+            Canvas::new(&self.graph)
+                .width(Length::Fill)
+                .height(Length::Fill),
+            row![
+                text(format!("Iteration: {:?}", self.graph.iteration)),
+                slider(0..=10000, self.graph.iteration, Message::IterationSet)
+                    .width(Length::Fill)
+            ]
+            .padding(10)
+            .spacing(20),
+        ]
+        .width(Length::Fill)
+        .align_items(iced::Alignment::Center)
+        .into()
+    }
+}
+
+#[derive(Default, Debug)]
+struct SierpinskiGraph {
+    iteration: i32,
+    fix_points: Vec<Point>,
+    random_points: Vec<Point>,
+    cache: canvas::Cache,
+}
+
+impl canvas::Program<Message> for SierpinskiGraph {
+    type State = ();
+
+    fn update(
+        &self,
+        _state: &mut Self::State,
+        event: Event,
+        bounds: Rectangle,
+        cursor: canvas::Cursor,
+    ) -> (event::Status, Option<Message>) {
+        let cursor_position =
+            if let Some(position) = cursor.position_in(&bounds) {
+                position
+            } else {
+                return (event::Status::Ignored, None);
+            };
+
+        match event {
+            Event::Mouse(mouse_event) => {
+                let message = match mouse_event {
+                    iced::mouse::Event::ButtonPressed(
+                        iced::mouse::Button::Left,
+                    ) => Some(Message::PointAdded(cursor_position)),
+                    iced::mouse::Event::ButtonPressed(
+                        iced::mouse::Button::Right,
+                    ) => Some(Message::PointRemoved),
+                    _ => None,
+                };
+                (event::Status::Captured, message)
+            }
+            _ => (event::Status::Ignored, None),
+        }
+    }
+
+    fn draw(
+        &self,
+        _state: &Self::State,
+        _theme: &Theme,
+        bounds: Rectangle,
+        _cursor: canvas::Cursor,
+    ) -> Vec<canvas::Geometry> {
+        let geom = self.cache.draw(bounds.size(), |frame| {
+            frame.stroke(
+                &canvas::Path::rectangle(Point::ORIGIN, frame.size()),
+                canvas::Stroke::default(),
+            );
+
+            if self.fix_points.is_empty() {
+                return;
+            }
+
+            let mut last = None;
+
+            for _ in 0..self.iteration {
+                let p = self.gen_rand_point(last);
+                let path = canvas::Path::rectangle(p, Size::new(1_f32, 1_f32));
+
+                frame.stroke(&path, canvas::Stroke::default());
+
+                last = Some(p);
+            }
+
+            self.fix_points.iter().for_each(|p| {
+                let path = canvas::Path::circle(*p, 5.0);
+                frame.fill(&path, Color::from_rgb8(0x12, 0x93, 0xD8));
+            });
+        });
+
+        vec![geom]
+    }
+}
+
+impl SierpinskiGraph {
+    fn new() -> SierpinskiGraph {
+        SierpinskiGraph::default()
+    }
+
+    fn redraw(&mut self) {
+        self.cache.clear();
+    }
+
+    fn gen_rand_point(&self, last: Option<Point>) -> Point {
+        let dest_point_idx =
+            rand::thread_rng().gen_range(0..self.fix_points.len());
+
+        let dest_point = self.fix_points[dest_point_idx];
+        let cur_point = last.or_else(|| Some(self.fix_points[0])).unwrap();
+
+        Point::new(
+            (dest_point.x + cur_point.x) / 2_f32,
+            (dest_point.y + cur_point.y) / 2_f32,
+        )
+    }
+}