Implement `Canvas` support for `iced_tiny_skia`

6 files changed, 332 insertions, 50 deletions

diff --git a/renderer/src/backend.rs b/renderer/src/backend.rs
index b0a409dc..6c0b4e5c 100644
--- a/renderer/src/backend.rs
+++ b/renderer/src/backend.rs
@@ -1,4 +1,4 @@
-use crate::{Font, Point, Size};
+use crate::{Font, Geometry, Point, Size};
 
 use iced_graphics::backend;
 use iced_graphics::text;
@@ -12,6 +12,8 @@ pub enum Backend {
 }
 
 impl iced_graphics::Backend for Backend {
+    type Geometry = Geometry;
+
     fn trim_measurements(&mut self) {
         match self {
             Self::Wgpu(backend) => backend.trim_measurements(),
diff --git a/renderer/src/lib.rs b/renderer/src/lib.rs
index f9bfc373..d9c85e82 100644
--- a/renderer/src/lib.rs
+++ b/renderer/src/lib.rs
@@ -4,11 +4,14 @@ pub mod window;
 mod backend;
 mod settings;
 
+pub use iced_graphics::primitive;
+
 pub use backend::Backend;
+pub use primitive::Primitive;
 pub use settings::Settings;
 
 pub use iced_graphics::{
-    Antialiasing, Color, Error, Font, Point, Size, Viewport,
+    Antialiasing, Color, Error, Font, Point, Rectangle, Size, Vector, Viewport,
 };
 
 /// The default graphics renderer for [`iced`].
@@ -16,3 +19,12 @@ pub use iced_graphics::{
 /// [`iced`]: https://github.com/iced-rs/iced
 pub type Renderer<Theme = iced_native::Theme> =
     iced_graphics::Renderer<Backend, Theme>;
+
+#[derive(Debug, Clone)]
+pub struct Geometry(pub(crate) Primitive);
+
+impl From<Geometry> for Primitive {
+    fn from(geometry: Geometry) -> Self {
+        geometry.0
+    }
+}
diff --git a/renderer/src/widget.rs b/renderer/src/widget.rs
index 417cc06f..6c0c2a83 100644
--- a/renderer/src/widget.rs
+++ b/renderer/src/widget.rs
@@ -1,5 +1,11 @@
-#[cfg(feature = "qr_code")]
-pub use iced_graphics::widget::qr_code;
+#[cfg(feature = "canvas")]
+pub mod canvas;
 
 #[cfg(feature = "canvas")]
-pub use iced_graphics::widget::canvas;
+pub use canvas::Canvas;
+
+#[cfg(feature = "qr_code")]
+pub mod qr_code;
+
+#[cfg(feature = "qr_code")]
+pub use qr_code::QRCode;
diff --git a/renderer/src/widget/canvas.rs b/renderer/src/widget/canvas.rs
new file mode 100644
index 00000000..f40a1097
--- /dev/null
+++ b/renderer/src/widget/canvas.rs
@@ -0,0 +1,177 @@
+mod cache;
+
+pub use cache::Cache;
+
+pub use iced_native::widget::canvas::event::{self, Event};
+pub use iced_native::widget::canvas::fill::{self, Fill};
+pub use iced_native::widget::canvas::gradient::{self, Gradient};
+pub use iced_native::widget::canvas::path::{self, Path};
+pub use iced_native::widget::canvas::stroke::{self, Stroke};
+pub use iced_native::widget::canvas::{
+    Canvas, Cursor, LineCap, LineDash, LineJoin, Program, Renderer, Style, Text,
+};
+
+use crate::{Backend, Point, Rectangle, Size, Vector};
+
+pub use crate::Geometry;
+
+pub enum Frame {
+    Wgpu(iced_wgpu::widget::canvas::Frame),
+    TinySkia(iced_tiny_skia::canvas::Frame),
+}
+
+macro_rules! delegate {
+    ($frame:expr, $name:ident => $body:expr) => {
+        match $frame {
+            Self::Wgpu($name) => $body,
+            Self::TinySkia($name) => $body,
+        }
+    };
+}
+
+impl Frame {
+    pub fn new<Theme>(renderer: &crate::Renderer<Theme>, size: Size) -> Self {
+        match renderer.backend() {
+            Backend::Wgpu(_) => {
+                Frame::Wgpu(iced_wgpu::widget::canvas::Frame::new(size))
+            }
+            Backend::TinySkia(_) => {
+                Frame::TinySkia(iced_tiny_skia::canvas::Frame::new(size))
+            }
+        }
+    }
+
+    /// Returns the width of the [`Frame`].
+    #[inline]
+    pub fn width(&self) -> f32 {
+        delegate!(self, frame => frame.width())
+    }
+
+    /// Returns the height of the [`Frame`].
+    #[inline]
+    pub fn height(&self) -> f32 {
+        delegate!(self, frame => frame.height())
+    }
+
+    /// Returns the dimensions of the [`Frame`].
+    #[inline]
+    pub fn size(&self) -> Size {
+        delegate!(self, frame => frame.size())
+    }
+
+    /// Returns the coordinate of the center of the [`Frame`].
+    #[inline]
+    pub fn center(&self) -> Point {
+        delegate!(self, frame => frame.center())
+    }
+
+    /// 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>) {
+        delegate!(self, frame => frame.fill(path, fill));
+    }
+
+    /// 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(
+        &mut self,
+        top_left: Point,
+        size: Size,
+        fill: impl Into<Fill>,
+    ) {
+        delegate!(self, frame => frame.fill_rectangle(top_left, size, fill));
+    }
+
+    /// Draws the stroke of the given [`Path`] on the [`Frame`] with the
+    /// provided style.
+    pub fn stroke<'a>(&mut self, path: &Path, stroke: impl Into<Stroke<'a>>) {
+        delegate!(self, frame => frame.stroke(path, stroke));
+    }
+
+    /// Draws the characters of the given [`Text`] on the [`Frame`], filling
+    /// them with the given color.
+    ///
+    /// __Warning:__ Text currently does not work well with rotations and scale
+    /// transforms! The position will be correctly transformed, but the
+    /// resulting glyphs will not be rotated or scaled properly.
+    ///
+    /// Additionally, all text will be rendered on top of all the layers of
+    /// a [`Canvas`]. Therefore, it is currently only meant to be used for
+    /// overlays, which is the most common use case.
+    ///
+    /// Support for vectorial text is planned, and should address all these
+    /// limitations.
+    ///
+    /// [`Canvas`]: crate::widget::Canvas
+    pub fn fill_text(&mut self, text: impl Into<Text>) {
+        delegate!(self, frame => frame.fill_text(text));
+    }
+
+    /// Stores the current transform of the [`Frame`] and executes the given
+    /// drawing operations, restoring the transform afterwards.
+    ///
+    /// This method is useful to compose transforms and perform drawing
+    /// operations in different coordinate systems.
+    #[inline]
+    pub fn with_save(&mut self, f: impl FnOnce(&mut Frame)) {
+        delegate!(self, frame => frame.push_transform());
+
+        f(self);
+
+        delegate!(self, frame => frame.pop_transform());
+    }
+
+    /// Executes the given drawing operations within a [`Rectangle`] region,
+    /// clipping any geometry that overflows its bounds. Any transformations
+    /// performed are local to the provided closure.
+    ///
+    /// This method is useful to perform drawing operations that need to be
+    /// clipped.
+    #[inline]
+    pub fn with_clip(&mut self, region: Rectangle, f: impl FnOnce(&mut Frame)) {
+        let mut frame = match self {
+            Self::Wgpu(_) => {
+                Self::Wgpu(iced_wgpu::widget::canvas::Frame::new(region.size()))
+            }
+            Self::TinySkia(_) => Self::TinySkia(
+                iced_tiny_skia::canvas::Frame::new(region.size()),
+            ),
+        };
+
+        f(&mut frame);
+
+        let translation = Vector::new(region.x, region.y);
+
+        match (self, frame) {
+            (Self::Wgpu(target), Self::Wgpu(frame)) => {
+                target.clip(frame, translation);
+            }
+            (Self::TinySkia(target), Self::TinySkia(frame)) => {
+                target.clip(frame, translation);
+            }
+            _ => unreachable!(),
+        };
+    }
+
+    /// Applies a translation to the current transform of the [`Frame`].
+    #[inline]
+    pub fn translate(&mut self, translation: Vector) {
+        delegate!(self, frame => frame.translate(translation));
+    }
+
+    /// Applies a rotation in radians to the current transform of the [`Frame`].
+    #[inline]
+    pub fn rotate(&mut self, angle: f32) {
+        delegate!(self, frame => frame.rotate(angle));
+    }
+
+    /// Applies a scaling to the current transform of the [`Frame`].
+    #[inline]
+    pub fn scale(&mut self, scale: f32) {
+        delegate!(self, frame => frame.scale(scale));
+    }
+
+    pub fn into_geometry(self) -> Geometry {
+        Geometry(delegate!(self, frame => frame.into_primitive()))
+    }
+}
diff --git a/renderer/src/widget/canvas/cache.rs b/renderer/src/widget/canvas/cache.rs
new file mode 100644
index 00000000..7d6b4811
--- /dev/null
+++ b/renderer/src/widget/canvas/cache.rs
@@ -0,0 +1,85 @@
+use crate::widget::canvas::{Frame, Geometry};
+use crate::{Primitive, Renderer, Size};
+
+use std::cell::RefCell;
+use std::sync::Arc;
+
+/// A simple cache that stores generated [`Geometry`] to avoid recomputation.
+///
+/// A [`Cache`] will not redraw its geometry unless the dimensions of its layer
+/// change or it is explicitly cleared.
+#[derive(Debug, Default)]
+pub struct Cache {
+    state: RefCell<State>,
+}
+
+#[derive(Debug, Default)]
+enum State {
+    #[default]
+    Empty,
+    Filled {
+        bounds: Size,
+        primitive: Arc<Primitive>,
+    },
+}
+
+impl Cache {
+    /// Creates a new empty [`Cache`].
+    pub fn new() -> Self {
+        Cache {
+            state: Default::default(),
+        }
+    }
+
+    /// Clears the [`Cache`], forcing a redraw the next time it is used.
+    pub fn clear(&self) {
+        *self.state.borrow_mut() = State::Empty;
+    }
+
+    /// Draws [`Geometry`] using the provided closure and stores it in the
+    /// [`Cache`].
+    ///
+    /// The closure will only be called when
+    /// - the bounds have changed since the previous draw call.
+    /// - the [`Cache`] is empty or has been explicitly cleared.
+    ///
+    /// Otherwise, the previously stored [`Geometry`] will be returned. The
+    /// [`Cache`] is not cleared in this case. In other words, it will keep
+    /// returning the stored [`Geometry`] if needed.
+    pub fn draw<Theme>(
+        &self,
+        renderer: &Renderer<Theme>,
+        bounds: Size,
+        draw_fn: impl FnOnce(&mut Frame),
+    ) -> Geometry {
+        use std::ops::Deref;
+
+        if let State::Filled {
+            bounds: cached_bounds,
+            primitive,
+        } = self.state.borrow().deref()
+        {
+            if *cached_bounds == bounds {
+                return Geometry(Primitive::Cache {
+                    content: primitive.clone(),
+                });
+            }
+        }
+
+        let mut frame = Frame::new(renderer, bounds);
+        draw_fn(&mut frame);
+
+        let primitive = {
+            let geometry = frame.into_geometry();
+
+            Arc::new(geometry.0)
+        };
+
+        *self.state.borrow_mut() = State::Filled {
+            bounds,
+            primitive: primitive.clone(),
+        };
+
+        Geometry(Primitive::Cache { content: primitive })
+    }
+}
diff --git a/graphics/src/widget/qr_code.rs b/renderer/src/widget/qr_code.rs
index 12ce5b1f..aae4ec88 100644
--- a/graphics/src/widget/qr_code.rs
+++ b/renderer/src/widget/qr_code.rs
@@ -1,7 +1,8 @@
 //! Encode and display information in a QR code.
-use crate::renderer::{self, Renderer};
 use crate::widget::canvas;
-use crate::Backend;
+use crate::Renderer;
+
+use iced_graphics::renderer;
 
 use iced_native::layout;
 use iced_native::widget::Tree;
@@ -48,10 +49,7 @@ impl<'a> QRCode<'a> {
     }
 }
 
-impl<'a, Message, B, T> Widget<Message, Renderer<B, T>> for QRCode<'a>
-where
-    B: Backend,
-{
+impl<'a, Message, Theme> Widget<Message, Renderer<Theme>> for QRCode<'a> {
     fn width(&self) -> Length {
         Length::Shrink
     }
@@ -62,7 +60,7 @@ where
 
     fn layout(
         &self,
-        _renderer: &Renderer<B, T>,
+        _renderer: &Renderer<Theme>,
         _limits: &layout::Limits,
     ) -> layout::Node {
         let side_length = (self.state.width + 2 * QUIET_ZONE) as f32
@@ -74,8 +72,8 @@ where
     fn draw(
         &self,
         _state: &Tree,
-        renderer: &mut Renderer<B, T>,
-        _theme: &T,
+        renderer: &mut Renderer<Theme>,
+        _theme: &Theme,
         _style: &renderer::Style,
         layout: Layout<'_>,
         _cursor_position: Point,
@@ -87,50 +85,52 @@ where
         let side_length = self.state.width + 2 * QUIET_ZONE;
 
         // Reuse cache if possible
-        let geometry = self.state.cache.draw(bounds.size(), |frame| {
-            // Scale units to cell size
-            frame.scale(f32::from(self.cell_size));
-
-            // Draw background
-            frame.fill_rectangle(
-                Point::ORIGIN,
-                Size::new(side_length as f32, side_length as f32),
-                self.light,
-            );
-
-            // Avoid drawing on the quiet zone
-            frame.translate(Vector::new(QUIET_ZONE as f32, QUIET_ZONE as f32));
-
-            // Draw contents
-            self.state
-                .contents
-                .iter()
-                .enumerate()
-                .filter(|(_, value)| **value == qrcode::Color::Dark)
-                .for_each(|(index, _)| {
-                    let row = index / self.state.width;
-                    let column = index % self.state.width;
-
-                    frame.fill_rectangle(
-                        Point::new(column as f32, row as f32),
-                        Size::UNIT,
-                        self.dark,
-                    );
-                });
-        });
+        let geometry =
+            self.state.cache.draw(renderer, bounds.size(), |frame| {
+                // Scale units to cell size
+                frame.scale(f32::from(self.cell_size));
+
+                // Draw background
+                frame.fill_rectangle(
+                    Point::ORIGIN,
+                    Size::new(side_length as f32, side_length as f32),
+                    self.light,
+                );
+
+                // Avoid drawing on the quiet zone
+                frame.translate(Vector::new(
+                    QUIET_ZONE as f32,
+                    QUIET_ZONE as f32,
+                ));
+
+                // Draw contents
+                self.state
+                    .contents
+                    .iter()
+                    .enumerate()
+                    .filter(|(_, value)| **value == qrcode::Color::Dark)
+                    .for_each(|(index, _)| {
+                        let row = index / self.state.width;
+                        let column = index % self.state.width;
+
+                        frame.fill_rectangle(
+                            Point::new(column as f32, row as f32),
+                            Size::UNIT,
+                            self.dark,
+                        );
+                    });
+            });
 
         let translation = Vector::new(bounds.x, bounds.y);
 
         renderer.with_translation(translation, |renderer| {
-            renderer.draw_primitive(geometry.into_primitive());
+            renderer.draw_primitive(geometry.0);
         });
     }
 }
 
-impl<'a, Message, B, T> From<QRCode<'a>>
-    for Element<'a, Message, Renderer<B, T>>
-where
-    B: Backend,
+impl<'a, Message, Theme> From<QRCode<'a>>
+    for Element<'a, Message, Renderer<Theme>>
 {
     fn from(qr_code: QRCode<'a>) -> Self {
         Self::new(qr_code)