Implement `Canvas` support for `iced_tiny_skia`

2 files changed, 262 insertions, 0 deletions

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 })
+    }
+}