iced/examples/bezier_tool/src/main.rs

//! This example showcases an interactive `Canvas` for drawing Bézier curves.
use iced::widget::{button, column, text};
use iced::{Alignment, Element, Length, Sandbox, Settings};

pub fn main() -> iced::Result {
    Example::run(Settings {
        antialiasing: true,
        ..Settings::default()
    })
}

#[derive(Default)]
struct Example {
    bezier: bezier::State,
    curves: Vec<bezier::Curve>,
}

#[derive(Debug, Clone, Copy)]
enum Message {
    AddCurve(bezier::Curve),
    Clear,
}

impl Sandbox for Example {
    type Message = Message;

    fn new() -> Self {
        Example::default()
    }

    fn title(&self) -> String {
        String::from("Bezier tool - Iced")
    }

    fn update(&mut self, message: Message) {
        match message {
            Message::AddCurve(curve) => {
                self.curves.push(curve);
                self.bezier.request_redraw();
            }
            Message::Clear => {
                self.bezier = bezier::State::default();
                self.curves.clear();
            }
        }
    }

    fn view(&self) -> Element<Message> {
        column![
            text("Bezier tool example").width(Length::Shrink).size(50),
            self.bezier.view(&self.curves).map(Message::AddCurve),
            button("Clear").padding(8).on_press(Message::Clear),
        ]
        .padding(20)
        .spacing(20)
        .align_items(Alignment::Center)
        .into()
    }
}

mod bezier {
    use iced::mouse;
    use iced::widget::canvas::event::{self, Event};
    use iced::widget::canvas::{self, Canvas, Frame, Geometry, Path, Stroke};
    use iced::{Element, Length, Point, Rectangle, Renderer, Theme};

    #[derive(Default)]
    pub struct State {
        cache: canvas::Cache,
    }

    impl State {
        pub fn view<'a>(&'a self, curves: &'a [Curve]) -> Element<'a, Curve> {
            Canvas::new(Bezier {
                state: self,
                curves,
            })
            .width(Length::Fill)
            .height(Length::Fill)
            .into()
        }

        pub fn request_redraw(&mut self) {
            self.cache.clear();
        }
    }

    struct Bezier<'a> {
        state: &'a State,
        curves: &'a [Curve],
    }

    impl<'a> canvas::Program<Curve> for Bezier<'a> {
        type State = Option<Pending>;

        fn update(
            &self,
            state: &mut Self::State,
            event: Event,
            bounds: Rectangle,
            cursor: mouse::Cursor,
        ) -> (event::Status, Option<Curve>) {
            let Some(cursor_position) = cursor.position_in(bounds) else {
                return (event::Status::Ignored, None);
            };

            match event {
                Event::Mouse(mouse_event) => {
                    let message = match mouse_event {
                        mouse::Event::ButtonPressed(mouse::Button::Left) => {
                            match *state {
                                None => {
                                    *state = Some(Pending::One {
                                        from: cursor_position,
                                    });

                                    None
                                }
                                Some(Pending::One { from }) => {
                                    *state = Some(Pending::Two {
                                        from,
                                        to: cursor_position,
                                    });

                                    None
                                }
                                Some(Pending::Two { from, to }) => {
                                    *state = None;

                                    Some(Curve {
                                        from,
                                        to,
                                        control: cursor_position,
                                    })
                                }
                            }
                        }
                        _ => None,
                    };

                    (event::Status::Captured, message)
                }
                _ => (event::Status::Ignored, None),
            }
        }

        fn draw(
            &self,
            state: &Self::State,
            renderer: &Renderer,
            _theme: &Theme,
            bounds: Rectangle,
            cursor: mouse::Cursor,
        ) -> Vec<Geometry> {
            let content = self.state.cache.draw(
                renderer,
                bounds.size(),
                |frame: &mut Frame| {
                    Curve::draw_all(self.curves, frame);

                    frame.stroke(
                        &Path::rectangle(Point::ORIGIN, frame.size()),
                        Stroke::default().with_width(2.0),
                    );
                },
            );

            if let Some(pending) = state {
                let pending_curve = pending.draw(renderer, bounds, cursor);

                vec![content, pending_curve]
            } else {
                vec![content]
            }
        }

        fn mouse_interaction(
            &self,
            _state: &Self::State,
            bounds: Rectangle,
            cursor: mouse::Cursor,
        ) -> mouse::Interaction {
            if cursor.is_over(bounds) {
                mouse::Interaction::Crosshair
            } else {
                mouse::Interaction::default()
            }
        }
    }

    #[derive(Debug, Clone, Copy)]
    pub struct Curve {
        from: Point,
        to: Point,
        control: Point,
    }

    impl Curve {
        fn draw_all(curves: &[Curve], frame: &mut Frame) {
            let curves = Path::new(|p| {
                for curve in curves {
                    p.move_to(curve.from);
                    p.quadratic_curve_to(curve.control, curve.to);
                }
            });

            frame.stroke(&curves, Stroke::default().with_width(2.0));
        }
    }

    #[derive(Debug, Clone, Copy)]
    enum Pending {
        One { from: Point },
        Two { from: Point, to: Point },
    }

    impl Pending {
        fn draw(
            &self,
            renderer: &Renderer,
            bounds: Rectangle,
            cursor: mouse::Cursor,
        ) -> Geometry {
            let mut frame = Frame::new(renderer, bounds.size());

            if let Some(cursor_position) = cursor.position_in(bounds) {
                match *self {
                    Pending::One { from } => {
                        let line = Path::line(from, cursor_position);
                        frame.stroke(&line, Stroke::default().with_width(2.0));
                    }
                    Pending::Two { from, to } => {
                        let curve = Curve {
                            from,
                            to,
                            control: cursor_position,
                        };

                        Curve::draw_all(&[curve], &mut frame);
                    }
                };
            }

            frame.into_geometry()
        }
    }
}