typst/crates/typst-library/src/visualize/path.rs

use kurbo::{CubicBez, ParamCurveExtrema};
use typst::eval::Reflect;

use crate::prelude::*;

use PathVertex::{AllControlPoints, MirroredControlPoint, Vertex};

/// A path through a list of points, connected by Bezier curves.
///
/// # Example
/// ```example
/// #path(
///   fill: blue.lighten(80%),
///   stroke: blue,
///   closed: true,
///   (0pt, 50pt),
///   (100%, 50pt),
///   ((50%, 0pt), (40pt, 0pt)),
/// )
/// ```
#[elem(Layout)]
pub struct PathElem {
    /// How to fill the path.
    ///
    /// When setting a fill, the default stroke disappears. To create a
    /// rectangle with both fill and stroke, you have to configure both.
    ///
    /// 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]($stroke) the path. This can be:
    ///
    /// Can be set to  `{none}` to disable the stroke or to `{auto}` for a
    /// stroke of `{1pt}` black if and if only if no fill is given.
    #[resolve]
    #[fold]
    pub stroke: Smart<Option<Stroke>>,

    /// Whether to close this path with one last bezier curve. This curve will
    /// takes into account the adjacent 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,

    /// The vertices of the path.
    ///
    /// Each vertex can be defined in 3 ways:
    ///
    /// - A regular point, as given to the [`line`]($line) or
    ///   [`polygon`]($polygon) function.
    /// - 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 given
    ///   control point is the one that affects the curve coming _into_ this
    ///   vertex (even for the first point). The mirrored control point affects
    ///   the curve going out of this vertex.
    /// - 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 {
    #[tracing::instrument(name = "PathElem::layout", skip_all)]
    fn layout(
        &self,
        _: &mut Vt,
        styles: StyleChain,
        regions: Regions,
    ) -> SourceResult<Fragment> {
        let resolve = |axes: Axes<Rel<Length>>| {
            axes.resolve(styles)
                .zip_map(regions.base(), Rel::relative_to)
                .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();
        if points.is_empty() {
            return Ok(Fragment::frame(Frame::soft(size)));
        }

        // Only create a path if there are more than zero points.
        // 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);
            path.close_path();
        }

        // Prepare fill and stroke.
        let fill = self.fill(styles);
        let stroke = match self.stroke(styles) {
            Smart::Auto if fill.is_none() => Some(FixedStroke::default()),
            Smart::Auto => None,
            Smart::Custom(stroke) => stroke.map(Stroke::unwrap_or_default),
        };

        let mut frame = Frame::soft(size);
        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! {
    PathVertex,
    self => match self {
        Vertex(x) => x.into_value(),
        MirroredControlPoint(x, c) => array![x, c].into_value(),
        AllControlPoints(x, c1, c2) => array![x, c1, c2].into_value(),
    },
    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>>::castable(&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()?)
            },
            _ => bail!("path vertex must have 1, 2, or 3 points"),
        }
    },
}