Show canvas doc example in multiple places

widget/src/helpers.rs

@@ -1000,6 +1000,57 @@ where
 /// Creates a new [`Canvas`].
 ///
 /// [`Canvas`]: crate::Canvas
+///
+/// ## Drawing a simple circle
+/// Here's how we can use a [`Canvas`] to draw a simple circle:
+///
+/// ```no_run
+/// # mod iced { pub mod widget { pub use iced_widget::*; } pub use iced_widget::Renderer; pub use iced_widget::core::*; }
+/// # pub type State = ();
+/// # pub type Element<'a, Message> = iced_widget::core::Element<'a, Message, iced_widget::Theme, iced_widget::Renderer>;
+/// #
+/// use iced::mouse;
+/// use iced::widget::canvas;
+/// use iced::{Color, Rectangle, Renderer, Theme};
+///
+/// // First, we define the data we need for drawing
+/// #[derive(Debug)]
+/// struct Circle {
+///     radius: f32,
+/// }
+///
+/// // Then, we implement the `Program` trait
+/// impl<Message> canvas::Program<Message> for Circle {
+///     // No internal state
+///     type State = ();
+///
+///     fn draw(
+///         &self,
+///         _state: &(),
+///         renderer: &Renderer,
+///         _theme: &Theme,
+///         bounds: Rectangle,
+///         _cursor: mouse::Cursor
+///     ) -> Vec<canvas::Geometry> {
+///         // We prepare a new `Frame`
+///         let mut frame = canvas::Frame::new(renderer, bounds.size());
+///
+///         // We create a `Path` representing a simple circle
+///         let circle = canvas::Path::circle(frame.center(), self.radius);
+///
+///         // And fill it with some color
+///         frame.fill(&circle, Color::BLACK);
+///
+///         // Then, we produce the geometry
+///         vec![frame.into_geometry()]
+///     }
+/// }
+///
+/// // Finally, we simply use our `Circle` to create the `Canvas`!
+/// fn view<'a, Message: 'a>(_state: &'a State) -> Element<'a, Message> {
+///     canvas(Circle { radius: 50.0 }).into()
+/// }
+/// ```
 #[cfg(feature = "canvas")]
 pub fn canvas<P, Message, Theme, Renderer>(
     program: P,