typst/library/src/visualize/path.rs

use self::PathVertex::{AllControlPoints, MirroredControlPoint, Vertex};
use crate::prelude::*;
use kurbo::{CubicBez, ParamCurveExtrema};

/// A path going through a list of points, connected through Bezier curves.
///
/// ## Example
/// ```example
/// #set page(height: 100pt)
/// #path((10%, 10%), ((20%, 20%), (5%, 5%)))
/// #path((10%, 10%), (10%, 15%))
/// ```
///
/// Display: Path
/// Category: visualize
#[element(Layout)]
pub struct PathElem {
    /// Whether to close this path with one last bezier curve. This last curve
    /// still takes into account the control points.
    /// If you want to close with a straight line, simply add one last point
    /// that's the same as the start point.
    #[default(false)]
    pub closed: bool,

    /// How to fill the polygon. See the
    /// [rectangle's documentation]($func/rect.fill) for more details.
    ///
    /// Currently all paths are filled according to the
    /// [non-zero winding rule](https://en.wikipedia.org/wiki/Nonzero-rule).
    pub fill: Option<Paint>,

    /// How to stroke the polygon. See the [lines's
    /// documentation]($func/line.stroke) for more details.
    #[resolve]
    #[fold]
    #[default(Some(PartialStroke::default()))]
    pub stroke: Option<PartialStroke>,

    /// The vertices of the path.
    ///
    /// Each vertex can be defined in 3 ways:
    ///
    /// - A regular point, like [line]($func/line)
    /// - An array of two points, the first being the vertex and the second
    ///   being the control point.
    ///   The control point is expressed relative to the vertex and is mirrored
    ///    to get the second control point.
    ///   The control point itself refers to the control point that affects the curve coming _into_ this vertex, including for the first point.
    /// - An array of three points, the first being the vertex and the next being the control points (control point for curves coming in and out respectively)
    #[variadic]
    pub vertices: Vec<PathVertex>,
}

impl Layout for PathElem {
    fn layout(
        &self,
        _: &mut Vt,
        styles: StyleChain,
        regions: Regions,
    ) -> SourceResult<Fragment> {
        let resolve = |axes: Axes<Rel<Length>>| {
            axes.resolve(styles)
                .zip(regions.base())
                .map(|(l, b)| l.relative_to(b))
                .to_point()
        };

        let vertices: Vec<PathVertex> = self.vertices();
        let points: Vec<Point> = vertices.iter().map(|c| resolve(c.vertex())).collect();

        let mut size = Size::zero();

        // Only create a path if there are more than zero points.
        let path = if points.len() > 0 {
            // Construct a closed path given all points.
            let mut path = Path::new();
            path.move_to(points[0]);

            let mut add_cubic = |from_point: Point,
                                 to_point: Point,
                                 from: PathVertex,
                                 to: PathVertex| {
                let from_control_point = resolve(from.control_point_from()) + from_point;
                let to_control_point = resolve(to.control_point_to()) + to_point;

                path.cubic_to(from_control_point, to_control_point, to_point);

                let p0 = kurbo::Point::new(from_point.x.to_raw(), from_point.y.to_raw());
                let p1 = kurbo::Point::new(
                    from_control_point.x.to_raw(),
                    from_control_point.y.to_raw(),
                );
                let p2 = kurbo::Point::new(
                    to_control_point.x.to_raw(),
                    to_control_point.y.to_raw(),
                );
                let p3 = kurbo::Point::new(to_point.x.to_raw(), to_point.y.to_raw());
                let extrema = CubicBez::new(p0, p1, p2, p3).bounding_box();
                size.x.set_max(Abs::raw(extrema.x1));
                size.y.set_max(Abs::raw(extrema.y1));
            };

            for (vertex_window, point_window) in
                vertices.windows(2).zip(points.windows(2))
            {
                let from = vertex_window[0];
                let to = vertex_window[1];
                let from_point = point_window[0];
                let to_point = point_window[1];

                add_cubic(from_point, to_point, from, to);
            }

            if self.closed(styles) {
                let from = *vertices.last().unwrap(); // We checked that we have at least one element.
                let to = vertices[0];
                let from_point = *points.last().unwrap();
                let to_point = points[0];

                add_cubic(from_point, to_point, from, to);
            }

            Some(path)
        } else {
            None
        };

        let mut frame = Frame::new(size);
        if let Some(path) = path {
            let fill = self.fill(styles);
            let stroke = self.stroke(styles).map(PartialStroke::unwrap_or_default);
            let shape = Shape { geometry: Geometry::Path(path), stroke, fill };
            frame.push(Point::zero(), FrameItem::Shape(shape, self.span()));
        }

        Ok(Fragment::frame(frame))
    }
}

#[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
pub enum PathVertex {
    Vertex(Axes<Rel<Length>>),
    MirroredControlPoint(Axes<Rel<Length>>, Axes<Rel<Length>>),
    AllControlPoints(Axes<Rel<Length>>, Axes<Rel<Length>>, Axes<Rel<Length>>),
}

impl PathVertex {
    pub fn vertex(&self) -> Axes<Rel<Length>> {
        match self {
            Vertex(x) => *x,
            MirroredControlPoint(x, _) => *x,
            AllControlPoints(x, _, _) => *x,
        }
    }

    pub fn control_point_from(&self) -> Axes<Rel<Length>> {
        match self {
            Vertex(_) => Axes::new(Rel::zero(), Rel::zero()),
            MirroredControlPoint(_, a) => a.map(|x| -x),
            AllControlPoints(_, _, b) => *b,
        }
    }

    pub fn control_point_to(&self) -> Axes<Rel<Length>> {
        match self {
            Vertex(_) => Axes::new(Rel::zero(), Rel::zero()),
            MirroredControlPoint(_, a) => *a,
            AllControlPoints(_, a, _) => *a,
        }
    }
}

cast_from_value! {
    PathVertex,
    array: Array => {
        let mut iter = array.into_iter();
        match (iter.next(), iter.next(), iter.next(), iter.next()) {
            (Some(a), None, None, None) => {
                Vertex(a.cast()?)
            },
            (Some(a), Some(b), None, None) => {
                if Axes::<Rel<Length>>::is(&a) {
                    MirroredControlPoint(a.cast()?, b.cast()?)
                } else {
                    Vertex(Axes::new(a.cast()?, b.cast()?))
                }
            },
            (Some(a), Some(b), Some(c), None) => {
                AllControlPoints(a.cast()?, b.cast()?, c.cast()?)
            },
            _ => Err("path vertex must have 1, 2, or 3 points")?,
        }
    },
}

cast_to_value! {
    v: PathVertex => {
        match v {
            PathVertex::Vertex(x) => {
                Value::from(x)
            },
            PathVertex::MirroredControlPoint(x, c) => {
                Value::Array(array![x, c])
            },
            PathVertex::AllControlPoints(x, c1, c2) => {
                Value::Array(array![x, c1, c2])
            },
        }
    }
}