Implement reactive-rendering for canvas

examples/bezier_tool/src/main.rs

@@ -57,8 +57,9 @@ impl Example {
 
 mod bezier {
     use iced::mouse;
-    use iced::widget::canvas::event::{self, Event};
-    use iced::widget::canvas::{self, Canvas, Frame, Geometry, Path, Stroke};
+    use iced::widget::canvas::{
+        self, Canvas, Event, Frame, Geometry, Path, Stroke,
+    };
     use iced::{Element, Fill, Point, Rectangle, Renderer, Theme};
 
     #[derive(Default)]
@@ -96,48 +97,47 @@ mod bezier {
             event: Event,
             bounds: Rectangle,
             cursor: mouse::Cursor,
-        ) -> (event::Status, Option<Curve>) {
-            let Some(cursor_position) = cursor.position_in(bounds) else {
-                return (event::Status::Ignored, None);
-            };
+        ) -> Option<canvas::Action<Curve>> {
+            let cursor_position = cursor.position_in(bounds)?;
 
             match event {
-                Event::Mouse(mouse_event) => {
-                    let message = match mouse_event {
-                        mouse::Event::ButtonPressed(mouse::Button::Left) => {
-                            match *state {
-                                None => {
-                                    *state = Some(Pending::One {
-                                        from: cursor_position,
-                                    });
-
-                                    None
-                                }
-                                Some(Pending::One { from }) => {
-                                    *state = Some(Pending::Two {
-                                        from,
-                                        to: cursor_position,
-                                    });
-
-                                    None
-                                }
-                                Some(Pending::Two { from, to }) => {
-                                    *state = None;
-
-                                    Some(Curve {
-                                        from,
-                                        to,
-                                        control: cursor_position,
-                                    })
-                                }
-                            }
+                Event::Mouse(mouse::Event::ButtonPressed(
+                    mouse::Button::Left,
+                )) => Some(
+                    match *state {
+                        None => {
+                            *state = Some(Pending::One {
+                                from: cursor_position,
+                            });
+
+                            canvas::Action::request_redraw()
                         }
-                        _ => None,
-                    };
+                        Some(Pending::One { from }) => {
+                            *state = Some(Pending::Two {
+                                from,
+                                to: cursor_position,
+                            });
 
-                    (event::Status::Captured, message)
+                            canvas::Action::request_redraw()
+                        }
+                        Some(Pending::Two { from, to }) => {
+                            *state = None;
+
+                            canvas::Action::publish(Curve {
+                                from,
+                                to,
+                                control: cursor_position,
+                            })
+                        }
+                    }
+                    .and_capture(),
+                ),
+                Event::Mouse(mouse::Event::CursorMoved { .. })
+                    if state.is_some() =>
+                {
+                    Some(canvas::Action::request_redraw())
                 }
-                _ => (event::Status::Ignored, None),
+                _ => None,
             }
         }
 

examples/game_of_life/src/main.rs

@@ -193,8 +193,9 @@ mod grid {
     use iced::mouse;
     use iced::touch;
     use iced::widget::canvas;
-    use iced::widget::canvas::event::{self, Event};
-    use iced::widget::canvas::{Cache, Canvas, Frame, Geometry, Path, Text};
+    use iced::widget::canvas::{
+        Cache, Canvas, Event, Frame, Geometry, Path, Text,
+    };
     use iced::{
         Color, Element, Fill, Point, Rectangle, Renderer, Size, Theme, Vector,
     };
@@ -383,14 +384,12 @@ mod grid {
             event: Event,
             bounds: Rectangle,
             cursor: mouse::Cursor,
-        ) -> (event::Status, Option<Message>) {
+        ) -> Option<canvas::Action<Message>> {
             if let Event::Mouse(mouse::Event::ButtonReleased(_)) = event {
                 *interaction = Interaction::None;
             }
 
-            let Some(cursor_position) = cursor.position_in(bounds) else {
-                return (event::Status::Ignored, None);
-            };
+            let cursor_position = cursor.position_in(bounds)?;
 
             let cell = Cell::at(self.project(cursor_position, bounds.size()));
             let is_populated = self.state.contains(&cell);
@@ -413,7 +412,12 @@ mod grid {
                         populate.or(unpopulate)
                     };
 
-                    (event::Status::Captured, message)
+                    Some(
+                        message
+                            .map(canvas::Action::publish)
+                            .unwrap_or(canvas::Action::request_redraw())
+                            .and_capture(),
+                    )
                 }
                 Event::Mouse(mouse_event) => match mouse_event {
                     mouse::Event::ButtonPressed(button) => {
@@ -438,7 +442,12 @@ mod grid {
                             _ => None,
                         };
 
-                        (event::Status::Captured, message)
+                        Some(
+                            message
+                                .map(canvas::Action::publish)
+                                .unwrap_or(canvas::Action::request_redraw())
+                                .and_capture(),
+                        )
                     }
                     mouse::Event::CursorMoved { .. } => {
                         let message = match *interaction {
@@ -454,12 +463,14 @@ mod grid {
                             Interaction::None => None,
                         };
 
-                        let event_status = match interaction {
-                            Interaction::None => event::Status::Ignored,
-                            _ => event::Status::Captured,
-                        };
+                        let action = message
+                            .map(canvas::Action::publish)
+                            .unwrap_or(canvas::Action::request_redraw());
 
-                        (event_status, message)
+                        Some(match interaction {
+                            Interaction::None => action,
+                            _ => action.and_capture(),
+                        })
                     }
                     mouse::Event::WheelScrolled { delta } => match delta {
                         mouse::ScrollDelta::Lines { y, .. }
@@ -496,18 +507,21 @@ mod grid {
                                         None
                                     };
 
-                                (
-                                    event::Status::Captured,
-                                    Some(Message::Scaled(scaling, translation)),
+                                Some(
+                                    canvas::Action::publish(Message::Scaled(
+                                        scaling,
+                                        translation,
+                                    ))
+                                    .and_capture(),
                                 )
                             } else {
-                                (event::Status::Captured, None)
+                                Some(canvas::Action::capture())
                             }
                         }
                     },
-                    _ => (event::Status::Ignored, None),
+                    _ => None,
                 },
-                _ => (event::Status::Ignored, None),
+                _ => None,
             }
         }
 

examples/multitouch/src/main.rs

@@ -3,9 +3,8 @@
 //! computers like Microsoft Surface.
 use iced::mouse;
 use iced::touch;
-use iced::widget::canvas::event;
 use iced::widget::canvas::stroke::{self, Stroke};
-use iced::widget::canvas::{self, Canvas, Geometry};
+use iced::widget::canvas::{self, Canvas, Event, Geometry};
 use iced::{Color, Element, Fill, Point, Rectangle, Renderer, Theme};
 
 use std::collections::HashMap;
@@ -56,25 +55,25 @@ impl canvas::Program<Message> for Multitouch {
     fn update(
         &self,
         _state: &mut Self::State,
-        event: event::Event,
+        event: Event,
         _bounds: Rectangle,
         _cursor: mouse::Cursor,
-    ) -> (event::Status, Option<Message>) {
-        match event {
-            event::Event::Touch(touch_event) => match touch_event {
+    ) -> Option<canvas::Action<Message>> {
+        let message = match event {
+            Event::Touch(
                 touch::Event::FingerPressed { id, position }
-                | touch::Event::FingerMoved { id, position } => (
-                    event::Status::Captured,
-                    Some(Message::FingerPressed { id, position }),
-                ),
+                | touch::Event::FingerMoved { id, position },
+            ) => Some(Message::FingerPressed { id, position }),
+            Event::Touch(
                 touch::Event::FingerLifted { id, .. }
-                | touch::Event::FingerLost { id, .. } => (
-                    event::Status::Captured,
-                    Some(Message::FingerLifted { id }),
-                ),
-            },
-            _ => (event::Status::Ignored, None),
-        }
+                | touch::Event::FingerLost { id, .. },
+            ) => Some(Message::FingerLifted { id }),
+            _ => None,
+        };
+
+        message
+            .map(canvas::Action::publish)
+            .map(canvas::Action::and_capture)
     }
 
     fn draw(

examples/sierpinski_triangle/src/main.rs

@@ -1,6 +1,5 @@
 use iced::mouse;
-use iced::widget::canvas::event::{self, Event};
-use iced::widget::canvas::{self, Canvas, Geometry};
+use iced::widget::canvas::{self, Canvas, Event, Geometry};
 use iced::widget::{column, row, slider, text};
 use iced::{Center, Color, Fill, Point, Rectangle, Renderer, Size, Theme};
 
@@ -80,26 +79,22 @@ impl canvas::Program<Message> for SierpinskiGraph {
         event: Event,
         bounds: Rectangle,
         cursor: mouse::Cursor,
-    ) -> (event::Status, Option<Message>) {
-        let Some(cursor_position) = cursor.position_in(bounds) else {
-            return (event::Status::Ignored, None);
-        };
+    ) -> Option<canvas::Action<Message>> {
+        let cursor_position = cursor.position_in(bounds)?;
 
         match event {
-            Event::Mouse(mouse_event) => {
-                let message = match mouse_event {
-                    iced::mouse::Event::ButtonPressed(
-                        iced::mouse::Button::Left,
-                    ) => Some(Message::PointAdded(cursor_position)),
-                    iced::mouse::Event::ButtonPressed(
-                        iced::mouse::Button::Right,
-                    ) => Some(Message::PointRemoved),
-                    _ => None,
-                };
-                (event::Status::Captured, message)
-            }
-            _ => (event::Status::Ignored, None),
+            Event::Mouse(mouse::Event::ButtonPressed(button)) => match button {
+                mouse::Button::Left => Some(canvas::Action::publish(
+                    Message::PointAdded(cursor_position),
+                )),
+                mouse::Button::Right => {
+                    Some(canvas::Action::publish(Message::PointRemoved))
+                }
+                _ => None,
+            },
+            _ => None,
         }
+        .map(canvas::Action::and_capture)
     }
 
     fn draw(

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,
+        )
+    }
+}