Add line dash API

examples/solar_system/src/main.rs

@@ -163,6 +163,10 @@ impl<Message> canvas::Program<Message> for State {
                 Stroke {
                     width: 1.0,
                     color: Color::from_rgba8(0, 153, 255, 0.1),
+                    line_dash: canvas::LineDash {
+                        offset: 0,
+                        segments: &[3.0, 6.0],
+                    },
                     ..Stroke::default()
                 },
             );

graphics/src/widget/canvas.rs

@@ -35,7 +35,7 @@ pub use frame::Frame;
 pub use geometry::Geometry;
 pub use path::Path;
 pub use program::Program;
-pub use stroke::{LineCap, LineJoin, Stroke};
+pub use stroke::{LineCap, LineDash, LineJoin, Stroke};
 pub use text::Text;
 
 /// A widget capable of drawing 2D graphics.

graphics/src/widget/canvas/frame.rs

@@ -1,6 +1,9 @@
+use std::borrow::Cow;
+
 use iced_native::{Point, Rectangle, Size, Vector};
 
 use crate::{
+    canvas::path,
     canvas::{Fill, Geometry, Path, Stroke, Text},
     triangle, Primitive,
 };
@@ -150,7 +153,7 @@ impl Frame {
 
     /// Draws the stroke of the given [`Path`] on the [`Frame`] with the
     /// provided style.
-    pub fn stroke(&mut self, path: &Path, stroke: impl Into<Stroke>) {
+    pub fn stroke<'a>(&mut self, path: &Path, stroke: impl Into<Stroke<'a>>) {
         let stroke = stroke.into();
 
         let mut buffers = tessellation::BuffersBuilder::new(
@@ -164,6 +167,12 @@ impl Frame {
         options.end_cap = stroke.line_cap.into();
         options.line_join = stroke.line_join.into();
 
+        let path = if stroke.line_dash.segments.is_empty() {
+            Cow::Borrowed(path)
+        } else {
+            Cow::Owned(path::dashed(path, stroke.line_dash))
+        };
+
         let result = if self.transforms.current.is_identity {
             self.stroke_tessellator.tessellate_path(
                 path.raw(),

graphics/src/widget/canvas/path.rs

@@ -7,7 +7,11 @@ mod builder;
 pub use arc::Arc;
 pub use builder::Builder;
 
+use crate::canvas::LineDash;
+
 use iced_native::{Point, Size};
+use lyon::algorithms::walk::{walk_along_path, RepeatedPattern};
+use lyon::path::iterator::PathIterator;
 
 /// An immutable set of points that may or may not be connected.
 ///
@@ -66,3 +70,43 @@ impl Path {
         }
     }
 }
+
+pub(super) fn dashed(path: &Path, line_dash: LineDash<'_>) -> Path {
+    Path::new(|builder| {
+        let segments_odd = (line_dash.segments.len() % 2 == 1).then(|| {
+            [&line_dash.segments[..], &line_dash.segments[..]].concat()
+        });
+
+        let mut draw_line = false;
+
+        walk_along_path(
+            path.raw().iter().flattened(0.01),
+            0.0,
+            &mut RepeatedPattern {
+                callback: |position: lyon::algorithms::math::Point,
+                           _tangent,
+                           _distance| {
+                    let point = Point {
+                        x: position.x,
+                        y: position.y,
+                    };
+
+                    if draw_line {
+                        builder.line_to(point);
+                    } else {
+                        builder.move_to(point);
+                    }
+
+                    draw_line = !draw_line;
+
+                    true
+                },
+                index: line_dash.offset,
+                intervals: segments_odd
+                    .as_ref()
+                    .map(Vec::as_slice)
+                    .unwrap_or(line_dash.segments),
+            },
+        );
+    })
+}

graphics/src/widget/canvas/stroke.rs

@@ -2,7 +2,7 @@ use iced_native::Color;
 
 /// The style of a stroke.
 #[derive(Debug, Clone, Copy)]
-pub struct Stroke {
+pub struct Stroke<'a> {
     /// The color of the stroke.
     pub color: Color,
     /// The distance between the two edges of the stroke.
@@ -12,37 +12,40 @@ pub struct Stroke {
     /// The shape to be used at the corners of paths or basic shapes when they
     /// are stroked.
     pub line_join: LineJoin,
+    /// The dash pattern used when stroking the line.
+    pub line_dash: LineDash<'a>,
 }
 
-impl Stroke {
+impl<'a> Stroke<'a> {
     /// Sets the color of the [`Stroke`].
-    pub fn with_color(self, color: Color) -> Stroke {
+    pub fn with_color(self, color: Color) -> Self {
         Stroke { color, ..self }
     }
 
     /// Sets the width of the [`Stroke`].
-    pub fn with_width(self, width: f32) -> Stroke {
+    pub fn with_width(self, width: f32) -> Self {
         Stroke { width, ..self }
     }
 
     /// Sets the [`LineCap`] of the [`Stroke`].
-    pub fn with_line_cap(self, line_cap: LineCap) -> Stroke {
+    pub fn with_line_cap(self, line_cap: LineCap) -> Self {
         Stroke { line_cap, ..self }
     }
 
     /// Sets the [`LineJoin`] of the [`Stroke`].
-    pub fn with_line_join(self, line_join: LineJoin) -> Stroke {
+    pub fn with_line_join(self, line_join: LineJoin) -> Self {
         Stroke { line_join, ..self }
     }
 }
 
-impl Default for Stroke {
-    fn default() -> Stroke {
+impl<'a> Default for Stroke<'a> {
+    fn default() -> Self {
         Stroke {
             color: Color::BLACK,
             width: 1.0,
             line_cap: LineCap::default(),
             line_join: LineJoin::default(),
+            line_dash: LineDash::default(),
         }
     }
 }
@@ -103,3 +106,13 @@ impl From<LineJoin> for lyon::tessellation::LineJoin {
         }
     }
 }
+
+/// The dash pattern used when stroking the line.
+#[derive(Debug, Clone, Copy, Default)]
+pub struct LineDash<'a> {
+    /// The alternating lengths of lines and gaps which describe the pattern.
+    pub segments: &'a [f32],
+
+    /// The offset of [`LineDash::segments`] to start the pattern.
+    pub offset: usize,
+}