egui/egui_demo_lib/src/apps/demo/paint_bezier.rs

use egui::epaint::{CubicBezierShape, PathShape, QuadraticBezierShape};
use egui::*;

#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
#[cfg_attr(feature = "serde", serde(default))]
pub struct PaintBezier {
    /// Bézier curve degree, it can be 3, 4.
    degree: usize,
    /// The control points. The [`Self::degree`] first of them are used.
    control_points: [Pos2; 4],

    /// Stroke for Bézier curve.
    stroke: Stroke,

    /// Fill for Bézier curve.
    fill: Color32,

    /// Stroke for auxiliary lines.
    aux_stroke: Stroke,

    bounding_box_stroke: Stroke,
}

impl Default for PaintBezier {
    fn default() -> Self {
        Self {
            degree: 4,
            control_points: [
                pos2(50.0, 50.0),
                pos2(60.0, 250.0),
                pos2(200.0, 200.0),
                pos2(250.0, 50.0),
            ],
            stroke: Stroke::new(1.0, Color32::LIGHT_BLUE),
            fill: Color32::from_rgb(50, 100, 150).linear_multiply(0.25),
            aux_stroke: Stroke::new(1.0, Color32::RED.linear_multiply(0.25)),
            bounding_box_stroke: Stroke::new(0.0, Color32::LIGHT_GREEN.linear_multiply(0.25)),
        }
    }
}

impl PaintBezier {
    pub fn ui_control(&mut self, ui: &mut egui::Ui) {
        ui.collapsing("Colors", |ui| {
            ui.horizontal(|ui| {
                ui.label("Fill color:");
                ui.color_edit_button_srgba(&mut self.fill);
            });
            egui::stroke_ui(ui, &mut self.stroke, "Curve Stroke");
            egui::stroke_ui(ui, &mut self.aux_stroke, "Auxiliary Stroke");
            egui::stroke_ui(ui, &mut self.bounding_box_stroke, "Bounding Box Stroke");
        });

        ui.collapsing("Global tessellation options", |ui| {
            let mut tessellation_options = *(ui.ctx().tessellation_options());
            let tessellation_options = &mut tessellation_options;
            tessellation_options.ui(ui);
            let mut new_tessellation_options = ui.ctx().tessellation_options();
            *new_tessellation_options = *tessellation_options;
        });

        ui.radio_value(&mut self.degree, 3, "Quadratic Bézier");
        ui.radio_value(&mut self.degree, 4, "Cubic Bézier");
        ui.label("Move the points by dragging them.");
        ui.small("Only convex curves can be accurately filled.");
    }

    pub fn ui_content(&mut self, ui: &mut Ui) -> egui::Response {
        let (response, painter) =
            ui.allocate_painter(Vec2::new(ui.available_width(), 300.0), Sense::hover());

        let to_screen = emath::RectTransform::from_to(
            Rect::from_min_size(Pos2::ZERO, response.rect.size()),
            response.rect,
        );

        let control_point_radius = 8.0;

        let mut control_point_shapes = vec![];

        for (i, point) in self.control_points.iter_mut().enumerate().take(self.degree) {
            let size = Vec2::splat(2.0 * control_point_radius);

            let point_in_screen = to_screen.transform_pos(*point);
            let point_rect = Rect::from_center_size(point_in_screen, size);
            let point_id = response.id.with(i);
            let point_response = ui.interact(point_rect, point_id, Sense::drag());

            *point += point_response.drag_delta();
            *point = to_screen.from().clamp(*point);

            let point_in_screen = to_screen.transform_pos(*point);
            let stroke = ui.style().interact(&point_response).fg_stroke;

            control_point_shapes.push(Shape::circle_stroke(
                point_in_screen,
                control_point_radius,
                stroke,
            ));
        }

        let points_in_screen: Vec<Pos2> = self
            .control_points
            .iter()
            .take(self.degree)
            .map(|p| to_screen * *p)
            .collect();

        match self.degree {
            3 => {
                let points = points_in_screen.clone().try_into().unwrap();
                let shape =
                    QuadraticBezierShape::from_points_stroke(points, true, self.fill, self.stroke);
                painter.add(epaint::RectShape::stroke(
                    shape.visual_bounding_rect(),
                    0.0,
                    self.bounding_box_stroke,
                ));
                painter.add(shape);
            }
            4 => {
                let points = points_in_screen.clone().try_into().unwrap();
                let shape =
                    CubicBezierShape::from_points_stroke(points, true, self.fill, self.stroke);
                painter.add(epaint::RectShape::stroke(
                    shape.visual_bounding_rect(),
                    0.0,
                    self.bounding_box_stroke,
                ));
                painter.add(shape);
            }
            _ => {
                unreachable!();
            }
        };

        painter.add(PathShape::line(points_in_screen, self.aux_stroke));
        painter.extend(control_point_shapes);

        response
    }
}

impl super::Demo for PaintBezier {
    fn name(&self) -> &'static str {
        "） Bézier Curve"
    }

    fn show(&mut self, ctx: &Context, open: &mut bool) {
        use super::View as _;
        Window::new(self.name())
            .open(open)
            .vscroll(false)
            .resizable(false)
            .default_size([300.0, 350.0])
            .show(ctx, |ui| self.ui(ui));
    }
}

impl super::View for PaintBezier {
    fn ui(&mut self, ui: &mut Ui) {
        ui.vertical_centered(|ui| {
            ui.add(crate::__egui_github_link_file!());
        });
        self.ui_control(ui);

        Frame::dark_canvas(ui.style()).show(ui, |ui| {
            self.ui_content(ui);
        });
    }
}