Implement reactive-rendering for canvas

widget/src/action.rs

@@ -0,0 +1,89 @@
+use crate::core::event;
+use crate::core::time::Instant;
+use crate::core::window;
+
+/// A runtime action that can be performed by some widgets.
+#[derive(Debug, Clone)]
+pub struct Action<Message> {
+    message_to_publish: Option<Message>,
+    redraw_request: Option<window::RedrawRequest>,
+    event_status: event::Status,
+}
+
+impl<Message> Action<Message> {
+    fn new() -> Self {
+        Self {
+            message_to_publish: None,
+            redraw_request: None,
+            event_status: event::Status::Ignored,
+        }
+    }
+
+    /// Creates a new "capturing" [`Action`]. A capturing [`Action`]
+    /// will make other widgets consider it final and prevent further
+    /// processing.
+    ///
+    /// Prevents "event bubbling".
+    pub fn capture() -> Self {
+        Self {
+            event_status: event::Status::Captured,
+            ..Self::new()
+        }
+    }
+
+    /// Creates a new [`Action`] that publishes the given `Message` for
+    /// the application to handle.
+    ///
+    /// Publishing a `Message` always produces a redraw.
+    pub fn publish(message: Message) -> Self {
+        Self {
+            message_to_publish: Some(message),
+            ..Self::new()
+        }
+    }
+
+    /// Creates a new [`Action`] that requests a redraw to happen as
+    /// soon as possible; without publishing any `Message`.
+    pub fn request_redraw() -> Self {
+        Self {
+            redraw_request: Some(window::RedrawRequest::NextFrame),
+            ..Self::new()
+        }
+    }
+
+    /// Creates a new [`Action`] that requests a redraw to happen at
+    /// the given [`Instant`]; without publishing any `Message`.
+    ///
+    /// This can be useful to efficiently animate content, like a
+    /// blinking caret on a text input.
+    pub fn request_redraw_at(at: Instant) -> Self {
+        Self {
+            redraw_request: Some(window::RedrawRequest::At(at)),
+            ..Self::new()
+        }
+    }
+
+    /// Marks the [`Action`] as "capturing". See [`Self::capture`].
+    pub fn and_capture(mut self) -> Self {
+        self.event_status = event::Status::Captured;
+        self
+    }
+
+    /// Converts the [`Action`] into its internal parts.
+    ///
+    /// This method is meant to be used by runtimes, libraries, or internal
+    /// widget implementations.
+    pub fn into_inner(
+        self,
+    ) -> (
+        Option<Message>,
+        Option<window::RedrawRequest>,
+        event::Status,
+    ) {
+        (
+            self.message_to_publish,
+            self.redraw_request,
+            self.event_status,
+        )
+    }
+}

widget/src/canvas.rs

@@ -48,24 +48,24 @@
 //!     canvas(Circle { radius: 50.0 }).into()
 //! }
 //! ```
-pub mod event;
-
 mod program;
 
-pub use event::Event;
 pub use program::Program;
 
+pub use crate::core::event::Event;
 pub use crate::graphics::cache::Group;
 pub use crate::graphics::geometry::{
     fill, gradient, path, stroke, Fill, Gradient, Image, LineCap, LineDash,
     LineJoin, Path, Stroke, Style, Text,
 };
+pub use crate::Action;
 
-use crate::core;
+use crate::core::event;
 use crate::core::layout::{self, Layout};
 use crate::core::mouse;
 use crate::core::renderer;
 use crate::core::widget::tree::{self, Tree};
+use crate::core::window;
 use crate::core::{
     Clipboard, Element, Length, Rectangle, Shell, Size, Vector, Widget,
 };
@@ -148,6 +148,7 @@ where
     message_: PhantomData<Message>,
     theme_: PhantomData<Theme>,
     renderer_: PhantomData<Renderer>,
+    last_mouse_interaction: Option<mouse::Interaction>,
 }
 
 impl<P, Message, Theme, Renderer> Canvas<P, Message, Theme, Renderer>
@@ -166,6 +167,7 @@ where
             message_: PhantomData,
             theme_: PhantomData,
             renderer_: PhantomData,
+            last_mouse_interaction: None,
         }
     }
 
@@ -216,39 +218,60 @@ where
     fn update(
         &mut self,
         tree: &mut Tree,
-        event: core::Event,
+        event: Event,
         layout: Layout<'_>,
         cursor: mouse::Cursor,
-        _renderer: &Renderer,
+        renderer: &Renderer,
         _clipboard: &mut dyn Clipboard,
         shell: &mut Shell<'_, Message>,
-        _viewport: &Rectangle,
+        viewport: &Rectangle,
     ) {
         let bounds = layout.bounds();
 
-        let canvas_event = match event {
-            core::Event::Mouse(mouse_event) => Some(Event::Mouse(mouse_event)),
-            core::Event::Touch(touch_event) => Some(Event::Touch(touch_event)),
-            core::Event::Keyboard(keyboard_event) => {
-                Some(Event::Keyboard(keyboard_event))
-            }
-            core::Event::Window(_) => None,
-        };
+        let state = tree.state.downcast_mut::<P::State>();
+        let is_redraw_request = matches!(
+            event,
+            Event::Window(window::Event::RedrawRequested(_now)),
+        );
 
-        if let Some(canvas_event) = canvas_event {
-            let state = tree.state.downcast_mut::<P::State>();
-
-            let (event_status, message) =
-                self.program.update(state, canvas_event, bounds, cursor);
+        if let Some(action) = self.program.update(state, event, bounds, cursor)
+        {
+            let (message, redraw_request, event_status) = action.into_inner();
 
             if let Some(message) = message {
                 shell.publish(message);
             }
 
+            if let Some(redraw_request) = redraw_request {
+                match redraw_request {
+                    window::RedrawRequest::NextFrame => {
+                        shell.request_redraw();
+                    }
+                    window::RedrawRequest::At(at) => {
+                        shell.request_redraw_at(at);
+                    }
+                }
+            }
+
             if event_status == event::Status::Captured {
                 shell.capture_event();
             }
         }
+
+        if shell.redraw_request() != Some(window::RedrawRequest::NextFrame) {
+            let mouse_interaction = self
+                .mouse_interaction(tree, layout, cursor, viewport, renderer);
+
+            if is_redraw_request {
+                self.last_mouse_interaction = Some(mouse_interaction);
+            } else if self.last_mouse_interaction.is_some_and(
+                |last_mouse_interaction| {
+                    last_mouse_interaction != mouse_interaction
+                },
+            ) {
+                shell.request_redraw();
+            }
+        }
     }
 
     fn mouse_interaction(

widget/src/canvas/event.rs

@@ -1,21 +0,0 @@
-//! Handle events of a canvas.
-use crate::core::keyboard;
-use crate::core::mouse;
-use crate::core::touch;
-
-pub use crate::core::event::Status;
-
-/// A [`Canvas`] event.
-///
-/// [`Canvas`]: crate::Canvas
-#[derive(Debug, Clone, PartialEq)]
-pub enum Event {
-    /// A mouse event.
-    Mouse(mouse::Event),
-
-    /// A touch event.
-    Touch(touch::Event),
-
-    /// A keyboard event.
-    Keyboard(keyboard::Event),
-}

widget/src/canvas/program.rs

@@ -1,8 +1,8 @@
-use crate::canvas::event::{self, Event};
 use crate::canvas::mouse;
-use crate::canvas::Geometry;
+use crate::canvas::{Event, Geometry};
 use crate::core::Rectangle;
 use crate::graphics::geometry;
+use crate::Action;
 
 /// The state and logic of a [`Canvas`].
 ///
@@ -22,8 +22,9 @@ where
     /// When a [`Program`] is used in a [`Canvas`], the runtime will call this
     /// method for each [`Event`].
     ///
-    /// This method can optionally return a `Message` to notify an application
-    /// of any meaningful interactions.
+    /// This method can optionally return an [`Action`] to either notify an
+    /// application of any meaningful interactions, capture the event, or
+    /// request a redraw.
     ///
     /// By default, this method does and returns nothing.
     ///
@@ -34,8 +35,8 @@ where
         _event: Event,
         _bounds: Rectangle,
         _cursor: mouse::Cursor,
-    ) -> (event::Status, Option<Message>) {
-        (event::Status::Ignored, None)
+    ) -> Option<Action<Message>> {
+        None
     }
 
     /// Draws the state of the [`Program`], producing a bunch of [`Geometry`].
@@ -84,7 +85,7 @@ where
         event: Event,
         bounds: Rectangle,
         cursor: mouse::Cursor,
-    ) -> (event::Status, Option<Message>) {
+    ) -> Option<Action<Message>> {
         T::update(self, state, event, bounds, cursor)
     }
 

widget/src/lib.rs

@@ -8,6 +8,7 @@ pub use iced_renderer::graphics;
 pub use iced_runtime as runtime;
 pub use iced_runtime::core;
 
+mod action;
 mod column;
 mod mouse_area;
 mod row;
@@ -131,4 +132,5 @@ pub use qr_code::QRCode;
 pub mod markdown;
 
 pub use crate::core::theme::{self, Theme};
+pub use action::Action;
 pub use renderer::Renderer;