Fix path and polygon strokes

1 files changed, 37 insertions, 21 deletions

diff --git a/library/src/visualize/polygon.rs b/library/src/visualize/polygon.rs
index 4b4adf7b..559ebec3 100644
--- a/library/src/visualize/polygon.rs
+++ b/library/src/visualize/polygon.rs
@@ -7,12 +7,12 @@ use crate::prelude::*;
 /// ## Example
 /// ```example
 /// #polygon(
-///   fill: red,
-///   stroke: 2pt + black,
-///   (0pt, 0pt),
-///   (50%, 0pt),
-///   (50%, 4cm),
-///   (20%, 4cm),
+///   fill: blue.lighten(80%),
+///   stroke: blue,
+///   (20%, 0pt),
+///   (60%, 0pt),
+///   (80%, 2cm),
+///   (0%,  2cm),
 /// )
 /// ```
 ///
@@ -27,11 +27,20 @@ pub struct PolygonElem {
     /// [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.
+    /// How to stroke the polygon. This can be:
+    ///
+    /// - `{none}` to disable the stroke.
+    /// - `{auto}` for a stroke of `{1pt}` black if and if only if no fill is
+    ///   given.
+    /// - A length specifying the stroke's thickness. The color is inherited,
+    ///   defaulting to black.
+    /// - A color to use for the stroke. The thickness is inherited, defaulting
+    ///   to `{1pt}`.
+    /// - A stroke combined from color and thickness using the `+` operator as
+    ///   in `{2pt + red}`.
     #[resolve]
     #[fold]
-    pub stroke: Option<PartialStroke>,
+    pub stroke: Smart<Option<PartialStroke>>,
 
     /// The vertices of the polygon. Each point is specified as an array of two
     /// [relative lengths]($type/relative-length).
@@ -61,21 +70,28 @@ impl Layout for PolygonElem {
         let mut frame = Frame::new(size);
 
         // Only create a path if there are more than zero points.
-        if !points.is_empty() {
-            let fill = self.fill(styles);
-            let stroke = self.stroke(styles).map(PartialStroke::unwrap_or_default);
+        if points.is_empty() {
+            return Ok(Fragment::frame(frame));
+        }
 
-            // Construct a closed path given all points.
-            let mut path = Path::new();
-            path.move_to(points[0]);
-            for &point in &points[1..] {
-                path.line_to(point);
-            }
-            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(Stroke::default()),
+            Smart::Auto => None,
+            Smart::Custom(stroke) => stroke.map(PartialStroke::unwrap_or_default),
+        };
 
-            let shape = Shape { geometry: Geometry::Path(path), stroke, fill };
-            frame.push(Point::zero(), FrameItem::Shape(shape, self.span()));
+        // Construct a closed path given all points.
+        let mut path = Path::new();
+        path.move_to(points[0]);
+        for &point in &points[1..] {
+            path.line_to(point);
         }
+        path.close_path();
+
+        let shape = Shape { geometry: Geometry::Path(path), stroke, fill };
+        frame.push(Point::zero(), FrameItem::Shape(shape, self.span()));
 
         Ok(Fragment::frame(frame))
     }