Path support (#536)

4 files changed, 214 insertions, 2 deletions

diff --git a/library/src/lib.rs b/library/src/lib.rs
index cabafd8c..c11b818e 100644
--- a/library/src/lib.rs
+++ b/library/src/lib.rs
@@ -84,6 +84,7 @@ fn global(math: Module, calc: Module) -> Module {
     global.define("ellipse", visualize::EllipseElem::func());
     global.define("circle", visualize::CircleElem::func());
     global.define("polygon", visualize::PolygonElem::func());
+    global.define("path", visualize::PathElem::func());
 
     // Meta.
     global.define("document", meta::DocumentElem::func());
diff --git a/library/src/visualize/mod.rs b/library/src/visualize/mod.rs
index 06eec23d..4cf5d04f 100644
--- a/library/src/visualize/mod.rs
+++ b/library/src/visualize/mod.rs
@@ -2,10 +2,12 @@
 
 mod image;
 mod line;
+mod path;
 mod polygon;
 mod shape;
 
 pub use self::image::*;
 pub use self::line::*;
+pub use self::path::*;
 pub use self::polygon::*;
 pub use self::shape::*;
diff --git a/library/src/visualize/path.rs b/library/src/visualize/path.rs
new file mode 100644
index 00000000..44f506e8
--- /dev/null
+++ b/library/src/visualize/path.rs
@@ -0,0 +1,210 @@
+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])
+            },
+        }
+    }
+}
diff --git a/library/src/visualize/polygon.rs b/library/src/visualize/polygon.rs
index 642349fa..4b4adf7b 100644
--- a/library/src/visualize/polygon.rs
+++ b/library/src/visualize/polygon.rs
@@ -58,8 +58,7 @@ impl Layout for PolygonElem {
             .collect();
 
         let size = points.iter().fold(Point::zero(), |max, c| c.max(max)).to_size();
-        let target = regions.expand.select(regions.size, size);
-        let mut frame = Frame::new(target);
+        let mut frame = Frame::new(size);
 
         // Only create a path if there are more than zero points.
         if !points.is_empty() {