Adds linear gradient support to 2D meshes in the canvas widget.

14 files changed, 308 insertions, 111 deletions

diff --git a/graphics/Cargo.toml b/graphics/Cargo.toml
index 49d4d9c6..ff6fcd4a 100644
--- a/graphics/Cargo.toml
+++ b/graphics/Cargo.toml
@@ -19,7 +19,7 @@ font-icons = []
 opengl = []
 
 [dependencies]
-glam = "0.10"
+glam = "0.21.3"
 raw-window-handle = "0.4"
 thiserror = "1.0"
 
diff --git a/graphics/src/gradient.rs b/graphics/src/gradient.rs
new file mode 100644
index 00000000..4d1eff62
--- /dev/null
+++ b/graphics/src/gradient.rs
@@ -0,0 +1,23 @@
+//! For creating a Gradient.
+
+use iced_native::Color;
+use crate::widget::canvas::gradient::Linear;
+
+#[derive(Debug, Clone, PartialEq)]
+/// A fill which transitions colors progressively along a direction, either linearly, radially,
+/// or conically.
+pub enum Gradient {
+    /// A linear gradient interpolates colors along a direction from its [`start`] to its [`end`]
+    /// point.
+    Linear(Linear),
+}
+
+
+#[derive(Debug, Clone, Copy, PartialEq)]
+/// A point along the gradient vector where the specified [`color`] is unmixed.
+pub struct ColorStop {
+    /// Offset along the gradient vector.
+    pub offset: f32,
+    /// The color of the gradient at the specified [`offset`].
+    pub color: Color,
+}
\ No newline at end of file
diff --git a/graphics/src/layer.rs b/graphics/src/layer.rs
index af545713..b7731922 100644
--- a/graphics/src/layer.rs
+++ b/graphics/src/layer.rs
@@ -7,9 +7,10 @@ use crate::{
 
 use iced_native::image;
 use iced_native::svg;
+use crate::shader::Shader;
 
 /// A group of primitives that should be clipped together.
-#[derive(Debug, Clone)]
+#[derive(Debug)]
 pub struct Layer<'a> {
     /// The clipping bounds of the [`Layer`].
     pub bounds: Rectangle,
@@ -18,7 +19,7 @@ pub struct Layer<'a> {
     pub quads: Vec<Quad>,
 
     /// The triangle meshes of the [`Layer`].
-    pub meshes: Vec<Mesh<'a>>,
+    pub meshes: Meshes<'a>,
 
     /// The text of the [`Layer`].
     pub text: Vec<Text<'a>>,
@@ -33,7 +34,7 @@ impl<'a> Layer<'a> {
         Self {
             bounds,
             quads: Vec::new(),
-            meshes: Vec::new(),
+            meshes: Meshes(Vec::new()),
             text: Vec::new(),
             images: Vec::new(),
         }
@@ -159,7 +160,11 @@ impl<'a> Layer<'a> {
                     border_color: border_color.into_linear(),
                 });
             }
-            Primitive::Mesh2D { buffers, size } => {
+            Primitive::Mesh2D {
+                buffers,
+                size,
+                shader,
+            } => {
                 let layer = &mut layers[current_layer];
 
                 let bounds = Rectangle::new(
@@ -169,11 +174,14 @@ impl<'a> Layer<'a> {
 
                 // Only draw visible content
                 if let Some(clip_bounds) = layer.bounds.intersection(&bounds) {
-                    layer.meshes.push(Mesh {
-                        origin: Point::new(translation.x, translation.y),
-                        buffers,
-                        clip_bounds,
-                    });
+                    layer.meshes.0.push(
+                        Mesh {
+                            origin: Point::new(translation.x, translation.y),
+                            buffers,
+                            clip_bounds,
+                            shader,
+                        }
+                    );
                 }
             }
             Primitive::Clip { bounds, content } => {
@@ -270,6 +278,9 @@ pub struct Mesh<'a> {
 
     /// The clipping bounds of the [`Mesh`].
     pub clip_bounds: Rectangle<f32>,
+
+    /// The shader of the [`Mesh`].
+    pub shader: &'a Shader,
 }
 
 /// A paragraph of text.
@@ -323,3 +334,21 @@ unsafe impl bytemuck::Zeroable for Quad {}
 
 #[allow(unsafe_code)]
 unsafe impl bytemuck::Pod for Quad {}
+
+#[derive(Debug)]
+/// A collection of meshes.
+pub struct Meshes<'a>(pub Vec<Mesh<'a>>);
+
+impl<'a> Meshes<'a> {
+    /// Returns the number of total vertices & total indices of all [`Mesh`]es.
+    pub fn attribute_count(&self) -> (usize, usize) {
+        self.0
+            .iter()
+            .map(|Mesh { buffers, .. }| {
+                (buffers.vertices.len(), buffers.indices.len())
+            })
+            .fold((0, 0), |(total_v, total_i), (v, i)| {
+                (total_v + v, total_i + i)
+            })
+    }
+}
\ No newline at end of file
diff --git a/graphics/src/lib.rs b/graphics/src/lib.rs
index 11082472..ce9b1b07 100644
--- a/graphics/src/lib.rs
+++ b/graphics/src/lib.rs
@@ -35,6 +35,8 @@ pub mod renderer;
 pub mod triangle;
 pub mod widget;
 pub mod window;
+pub mod shader;
+pub mod gradient;
 
 pub use antialiasing::Antialiasing;
 pub use backend::Backend;
diff --git a/graphics/src/primitive.rs b/graphics/src/primitive.rs
index 5f7a344d..4f79a74c 100644
--- a/graphics/src/primitive.rs
+++ b/graphics/src/primitive.rs
@@ -2,7 +2,7 @@ use iced_native::image;
 use iced_native::svg;
 use iced_native::{Background, Color, Font, Rectangle, Size, Vector};
 
-use crate::alignment;
+use crate::{alignment, shader};
 use crate::triangle;
 
 use std::sync::Arc;
@@ -88,6 +88,9 @@ pub enum Primitive {
         ///
         /// Any geometry that falls out of this region will be clipped.
         size: Size,
+
+        /// The shader of the mesh
+        shader: shader::Shader,
     },
     /// A cached primitive.
     ///
diff --git a/graphics/src/shader.rs b/graphics/src/shader.rs
new file mode 100644
index 00000000..b9071c74
--- /dev/null
+++ b/graphics/src/shader.rs
@@ -0,0 +1,42 @@
+//! Supported shaders;
+
+use crate::{Color, widget};
+use crate::gradient::Gradient;
+use crate::widget::canvas::{FillStyle, StrokeStyle};
+
+#[derive(Debug, Clone)]
+/// Supported shaders for primitives.
+pub enum Shader {
+    /// Fill a primitive with a solid color.
+    Solid(Color),
+    /// Fill a primitive with an interpolated color.
+    Gradient(Gradient)
+}
+
+impl <'a> Into<Shader> for StrokeStyle<'a> {
+    fn into(self) -> Shader {
+        match self {
+            StrokeStyle::Solid(color) => Shader::Solid(color),
+            StrokeStyle::Gradient(gradient) => gradient.clone().into()
+        }
+    }
+}
+
+impl <'a> Into<Shader> for FillStyle<'a> {
+    fn into(self) -> Shader {
+        match self {
+            FillStyle::Solid(color) => Shader::Solid(color),
+            FillStyle::Gradient(gradient) => gradient.clone().into()
+        }
+    }
+}
+
+impl <'a> Into<Shader> for widget::canvas::Gradient {
+    fn into(self) -> Shader {
+        match self {
+            widget::canvas::Gradient::Linear(linear) => {
+                Shader::Gradient(Gradient::Linear(linear))
+            }
+        }
+    }
+}
\ No newline at end of file
diff --git a/graphics/src/transformation.rs b/graphics/src/transformation.rs
index 2a19caed..03f453db 100644
--- a/graphics/src/transformation.rs
+++ b/graphics/src/transformation.rs
@@ -8,7 +8,7 @@ pub struct Transformation(Mat4);
 impl Transformation {
     /// Get the identity transformation.
     pub fn identity() -> Transformation {
-        Transformation(Mat4::identity())
+        Transformation(Mat4::IDENTITY)
     }
 
     /// Creates an orthographic projection.
@@ -51,3 +51,9 @@ impl From<Transformation> for [f32; 16] {
         *t.as_ref()
     }
 }
+
+impl Into<Mat4> for Transformation {
+    fn into(self) -> Mat4 {
+        self.0
+    }
+}
\ No newline at end of file
diff --git a/graphics/src/triangle.rs b/graphics/src/triangle.rs
index 05028f51..92709fe2 100644
--- a/graphics/src/triangle.rs
+++ b/graphics/src/triangle.rs
@@ -6,20 +6,22 @@ use bytemuck::{Pod, Zeroable};
 pub struct Mesh2D {
     /// The vertices of the mesh
     pub vertices: Vec<Vertex2D>,
-
     /// The list of vertex indices that defines the triangles of the mesh.
-    ///
-    /// Therefore, this list should always have a length that is a multiple of
-    /// 3.
     pub indices: Vec<u32>,
 }
 
-/// A two-dimensional vertex with some color in __linear__ RGBA.
+/// A two-dimensional vertex.
 #[derive(Copy, Clone, Debug, Zeroable, Pod)]
 #[repr(C)]
 pub struct Vertex2D {
-    /// The vertex position
+    /// The vertex position in 2D space.
     pub position: [f32; 2],
-    /// The vertex color in __linear__ RGBA.
-    pub color: [f32; 4],
+}
+
+/// Convert from lyon's position data to Iced's Vertex2D type.
+impl Vertex2D {
+    /// Converts from [`lyon::math::Point`] to [`Vertex2D`]. Used for generating primitives.
+    pub fn from(points: Vec<lyon::math::Point>) -> Vec<Vertex2D> {
+        points.iter().map(|p| Vertex2D { position: [p.x, p.y]}).collect()
+    }
 }
diff --git a/graphics/src/widget/canvas.rs b/graphics/src/widget/canvas.rs
index 88403fd7..09aad98d 100644
--- a/graphics/src/widget/canvas.rs
+++ b/graphics/src/widget/canvas.rs
@@ -5,6 +5,7 @@
 //! and more!
 
 pub mod event;
+pub mod gradient;
 pub mod path;
 
 mod cache;
@@ -19,12 +20,13 @@ mod text;
 pub use cache::Cache;
 pub use cursor::Cursor;
 pub use event::Event;
-pub use fill::{Fill, FillRule};
+pub use fill::{Fill, FillRule, FillStyle};
 pub use frame::Frame;
 pub use geometry::Geometry;
+pub use gradient::Gradient;
 pub use path::Path;
 pub use program::Program;
-pub use stroke::{LineCap, LineDash, LineJoin, Stroke};
+pub use stroke::{LineCap, LineDash, LineJoin, Stroke, StrokeStyle};
 pub use text::Text;
 
 use crate::{Backend, Primitive, Renderer};
diff --git a/graphics/src/widget/canvas/fill.rs b/graphics/src/widget/canvas/fill.rs
index 56495435..02d2311f 100644
--- a/graphics/src/widget/canvas/fill.rs
+++ b/graphics/src/widget/canvas/fill.rs
@@ -1,12 +1,14 @@
 use iced_native::Color;
 
+use crate::widget::canvas::Gradient;
+
 /// The style used to fill geometry.
-#[derive(Debug, Clone, Copy)]
-pub struct Fill {
-    /// The color used to fill geometry.
+#[derive(Debug, Clone)]
+pub struct Fill<'a> {
+    /// The color or gradient of the fill.
     ///
-    /// By default, it is set to `BLACK`.
-    pub color: Color,
+    /// By default, it is set to [`FillStyle::Solid`] `BLACK`.
+    pub style: FillStyle<'a>,
 
     /// The fill rule defines how to determine what is inside and what is
     /// outside of a shape.
@@ -19,24 +21,33 @@ pub struct Fill {
     pub rule: FillRule,
 }
 
-impl Default for Fill {
-    fn default() -> Fill {
+impl <'a> Default for Fill<'a> {
+    fn default() -> Fill<'a> {
         Fill {
-            color: Color::BLACK,
+            style: FillStyle::Solid(Color::BLACK),
             rule: FillRule::NonZero,
         }
     }
 }
 
-impl From<Color> for Fill {
-    fn from(color: Color) -> Fill {
+impl<'a> From<Color> for Fill<'a> {
+    fn from(color: Color) -> Fill<'a> {
         Fill {
-            color,
+            style: FillStyle::Solid(color),
             ..Fill::default()
         }
     }
 }
 
+/// The color or gradient of a [`Fill`].
+#[derive(Debug, Clone)]
+pub enum FillStyle<'a> {
+    /// A solid color
+    Solid(Color),
+    /// A color gradient
+    Gradient(&'a Gradient),
+}
+
 /// The fill rule defines how to determine what is inside and what is outside of
 /// a shape.
 ///
diff --git a/graphics/src/widget/canvas/frame.rs b/graphics/src/widget/canvas/frame.rs
index 516539ca..8845bc6a 100644
--- a/graphics/src/widget/canvas/frame.rs
+++ b/graphics/src/widget/canvas/frame.rs
@@ -3,11 +3,13 @@ use std::borrow::Cow;
 use iced_native::{Point, Rectangle, Size, Vector};
 
 use crate::triangle;
-use crate::widget::canvas::path;
-use crate::widget::canvas::{Fill, Geometry, Path, Stroke, Text};
+use crate::widget::canvas::{path, Fill, Geometry, Path, Stroke, Text};
 use crate::Primitive;
 
+use crate::shader::Shader;
+use crate::triangle::Vertex2D;
 use lyon::tessellation;
+use lyon::tessellation::geometry_builder::Positions;
 
 /// The frame of a [`Canvas`].
 ///
@@ -15,7 +17,7 @@ use lyon::tessellation;
 #[allow(missing_debug_implementations)]
 pub struct Frame {
     size: Size,
-    buffers: lyon::tessellation::VertexBuffers<triangle::Vertex2D, u32>,
+    buffers: Vec<(tessellation::VertexBuffers<lyon::math::Point, u32>, Shader)>,
     primitives: Vec<Primitive>,
     transforms: Transforms,
     fill_tessellator: tessellation::FillTessellator,
@@ -42,7 +44,7 @@ impl Frame {
     pub fn new(size: Size) -> Frame {
         Frame {
             size,
-            buffers: lyon::tessellation::VertexBuffers::new(),
+            buffers: Vec::new(),
             primitives: Vec::new(),
             transforms: Transforms {
                 previous: Vec::new(),
@@ -82,18 +84,18 @@ impl Frame {
 
     /// Draws the given [`Path`] on the [`Frame`] by filling it with the
     /// provided style.
-    pub fn fill(&mut self, path: &Path, fill: impl Into<Fill>) {
-        let Fill { color, rule } = fill.into();
+    pub fn fill<'a>(&mut self, path: &Path, fill: impl Into<Fill<'a>>) {
+        let Fill { style, rule } = fill.into();
 
-        let mut buffers = tessellation::BuffersBuilder::new(
-            &mut self.buffers,
-            FillVertex(color.into_linear()),
-        );
+        let mut buf = tessellation::VertexBuffers::new();
+
+        let mut buffers =
+            tessellation::BuffersBuilder::new(&mut buf, Positions);
 
         let options =
             tessellation::FillOptions::default().with_fill_rule(rule.into());
 
-        let result = if self.transforms.current.is_identity {
+        if self.transforms.current.is_identity {
             self.fill_tessellator.tessellate_path(
                 path.raw(),
                 &options,
@@ -107,25 +109,24 @@ impl Frame {
                 &options,
                 &mut buffers,
             )
-        };
+        }.expect("Tessellate path.");
 
-        result.expect("Tessellate path");
+        self.buffers.push((buf, style.into()))
     }
 
     /// Draws an axis-aligned rectangle given its top-left corner coordinate and
     /// its `Size` on the [`Frame`] by filling it with the provided style.
-    pub fn fill_rectangle(
+    pub fn fill_rectangle<'a>(
         &mut self,
         top_left: Point,
         size: Size,
-        fill: impl Into<Fill>,
+        fill: impl Into<Fill<'a>>,
     ) {
-        let Fill { color, rule } = fill.into();
+        let Fill { style, rule } = fill.into();
+
+        let mut buf = tessellation::VertexBuffers::new();
 
-        let mut buffers = tessellation::BuffersBuilder::new(
-            &mut self.buffers,
-            FillVertex(color.into_linear()),
-        );
+        let mut buffers = tessellation::BuffersBuilder::new(&mut buf, Positions);
 
         let top_left =
             self.transforms.current.raw.transform_point(
@@ -147,6 +148,8 @@ impl Frame {
                 &mut buffers,
             )
             .expect("Fill rectangle");
+
+        self.buffers.push((buf, style.into()))
     }
 
     /// Draws the stroke of the given [`Path`] on the [`Frame`] with the
@@ -154,10 +157,9 @@ impl Frame {
     pub fn stroke<'a>(&mut self, path: &Path, stroke: impl Into<Stroke<'a>>) {
         let stroke = stroke.into();
 
-        let mut buffers = tessellation::BuffersBuilder::new(
-            &mut self.buffers,
-            StrokeVertex(stroke.color.into_linear()),
-        );
+        let mut buf = tessellation::VertexBuffers::new();
+
+        let mut buffers = tessellation::BuffersBuilder::new(&mut buf, Positions);
 
         let mut options = tessellation::StrokeOptions::default();
         options.line_width = stroke.width;
@@ -171,7 +173,7 @@ impl Frame {
             Cow::Owned(path::dashed(path, stroke.line_dash))
         };
 
-        let result = if self.transforms.current.is_identity {
+        if self.transforms.current.is_identity {
             self.stroke_tessellator.tessellate_path(
                 path.raw(),
                 &options,
@@ -185,9 +187,9 @@ impl Frame {
                 &options,
                 &mut buffers,
             )
-        };
+        }.expect("Stroke path");
 
-        result.expect("Stroke path");
+        self.buffers.push((buf, stroke.style.into()))
     }
 
     /// Draws the characters of the given [`Text`] on the [`Frame`], filling
@@ -206,8 +208,6 @@ impl Frame {
     ///
     /// [`Canvas`]: crate::widget::Canvas
     pub fn fill_text(&mut self, text: impl Into<Text>) {
-        use std::f32;
-
         let text = text.into();
 
         let position = if self.transforms.current.is_identity {
@@ -331,52 +331,19 @@ impl Frame {
     }
 
     fn into_primitives(mut self) -> Vec<Primitive> {
-        if !self.buffers.indices.is_empty() {
-            self.primitives.push(Primitive::Mesh2D {
-                buffers: triangle::Mesh2D {
-                    vertices: self.buffers.vertices,
-                    indices: self.buffers.indices,
-                },
-                size: self.size,
-            });
+        for (buffer, shader) in self.buffers {
+            if !buffer.indices.is_empty() {
+                self.primitives.push(Primitive::Mesh2D {
+                    buffers: triangle::Mesh2D {
+                        vertices: Vertex2D::from(buffer.vertices),
+                        indices: buffer.indices,
+                    },
+                    size: self.size,
+                    shader,
+                })
+            }
         }
 
         self.primitives
     }
 }
-
-struct FillVertex([f32; 4]);
-
-impl lyon::tessellation::FillVertexConstructor<triangle::Vertex2D>
-    for FillVertex
-{
-    fn new_vertex(
-        &mut self,
-        vertex: lyon::tessellation::FillVertex<'_>,
-    ) -> triangle::Vertex2D {
-        let position = vertex.position();
-
-        triangle::Vertex2D {
-            position: [position.x, position.y],
-            color: self.0,
-        }
-    }
-}
-
-struct StrokeVertex([f32; 4]);
-
-impl lyon::tessellation::StrokeVertexConstructor<triangle::Vertex2D>
-    for StrokeVertex
-{
-    fn new_vertex(
-        &mut self,
-        vertex: lyon::tessellation::StrokeVertex<'_, '_>,
-    ) -> triangle::Vertex2D {
-        let position = vertex.position();
-
-        triangle::Vertex2D {
-            position: [position.x, position.y],
-            color: self.0,
-        }
-    }
-}
diff --git a/graphics/src/widget/canvas/gradient.rs b/graphics/src/widget/canvas/gradient.rs
new file mode 100644
index 00000000..7d2daabc
--- /dev/null
+++ b/graphics/src/widget/canvas/gradient.rs
@@ -0,0 +1,21 @@
+//! Define a color gradient.
+use iced_native::Point;
+
+pub mod linear;
+
+pub use linear::Linear;
+
+/// A gradient that can be used in the style of [`super::Fill`] or [`super::Stroke`].
+#[derive(Debug, Clone)]
+pub enum Gradient {
+    /// A linear gradient
+    Linear(Linear),
+    //TODO: radial, conical
+}
+
+impl Gradient {
+    /// Creates a new linear [`linear::Builder`].
+    pub fn linear(start: Point, end: Point) -> linear::Builder {
+        linear::Builder::new(start, end)
+    }
+}
\ No newline at end of file
diff --git a/graphics/src/widget/canvas/gradient/linear.rs b/graphics/src/widget/canvas/gradient/linear.rs
new file mode 100644
index 00000000..37533e19
--- /dev/null
+++ b/graphics/src/widget/canvas/gradient/linear.rs
@@ -0,0 +1,73 @@
+//! A linear color gradient.
+use iced_native::{Color, Point};
+
+use crate::gradient::ColorStop;
+
+use super::Gradient;
+
+/// A linear gradient that can be used in the style of [`super::Fill`] or [`super::Stroke`].
+#[derive(Debug, Clone, PartialEq)]
+pub struct Linear {
+    /// The point where the linear gradient begins.
+    pub start: Point,
+    /// The point where the linear gradient ends.
+    pub end: Point,
+    /// [`ColorStop`]s along the linear gradient path.
+    pub color_stops: Vec<ColorStop>,
+}
+
+/// A [`Linear`] builder.
+#[derive(Debug)]
+pub struct Builder {
+    start: Point,
+    end: Point,
+    stops: Vec<(f32, Color)>,
+    valid: bool,
+}
+
+impl Builder {
+    /// Creates a new [`Builder`].
+    pub fn new(start: Point, end: Point) -> Self {
+        Self {
+            start,
+            end,
+            stops: vec![],
+            valid: true,
+        }
+    }
+
+    /// Adds a new stop, defined by an offset and a color, to the gradient.
+    ///
+    /// `offset` must be between `0.0` and `1.0`.
+    pub fn add_stop(mut self, offset: f32, color: Color) -> Self {
+        if !(0.0..=1.0).contains(&offset) {
+            self.valid = false;
+        }
+
+        self.stops.push((offset, color));
+        self
+    }
+
+    /// Builds the linear [`Gradient`] of this [`Builder`].
+    ///
+    /// Returns `None` if no stops were added to the builder or
+    /// if stops not between 0.0 and 1.0 were added.
+    pub fn build(self) -> Option<Gradient> {
+        if self.stops.is_empty() || !self.valid {
+            return None;
+        }
+
+        Some(Gradient::Linear(Linear {
+            start: self.start,
+            end: self.end,
+            color_stops: self
+                .stops
+                .into_iter()
+                .map(|f| ColorStop {
+                    offset: f.0,
+                    color: f.1,
+                })
+                .collect(),
+        }))
+    }
+}
diff --git a/graphics/src/widget/canvas/stroke.rs b/graphics/src/widget/canvas/stroke.rs
index 6accc2fb..c319b398 100644
--- a/graphics/src/widget/canvas/stroke.rs
+++ b/graphics/src/widget/canvas/stroke.rs
@@ -1,10 +1,14 @@
 use iced_native::Color;
 
+use crate::widget::canvas::Gradient;
+
 /// The style of a stroke.
-#[derive(Debug, Clone, Copy)]
+#[derive(Debug, Clone)]
 pub struct Stroke<'a> {
-    /// The color of the stroke.
-    pub color: Color,
+    /// The color or gradient of the stroke.
+    ///
+    /// By default, it is set to [`StrokeStyle::Solid`] `BLACK`.
+    pub style: StrokeStyle<'a>,
     /// The distance between the two edges of the stroke.
     pub width: f32,
     /// The shape to be used at the end of open subpaths when they are stroked.
@@ -19,7 +23,10 @@ pub struct Stroke<'a> {
 impl<'a> Stroke<'a> {
     /// Sets the color of the [`Stroke`].
     pub fn with_color(self, color: Color) -> Self {
-        Stroke { color, ..self }
+        Stroke {
+            style: StrokeStyle::Solid(color),
+            ..self
+        }
     }
 
     /// Sets the width of the [`Stroke`].
@@ -41,7 +48,7 @@ impl<'a> Stroke<'a> {
 impl<'a> Default for Stroke<'a> {
     fn default() -> Self {
         Stroke {
-            color: Color::BLACK,
+            style: StrokeStyle::Solid(Color::BLACK),
             width: 1.0,
             line_cap: LineCap::default(),
             line_join: LineJoin::default(),
@@ -50,6 +57,15 @@ impl<'a> Default for Stroke<'a> {
     }
 }
 
+/// The color or gradient of a [`Stroke`].
+#[derive(Debug, Clone, Copy)]
+pub enum StrokeStyle<'a> {
+    /// A solid color
+    Solid(Color),
+    /// A color gradient
+    Gradient(&'a Gradient),
+}
+
 /// The shape used at the end of open subpaths when they are stroked.
 #[derive(Debug, Clone, Copy)]
 pub enum LineCap {