Create `iced_widget` subcrate and re-organize the whole codebase

1 files changed, 608 insertions, 0 deletions

diff --git a/core/src/element.rs b/core/src/element.rs
new file mode 100644
index 00000000..98c53737
--- /dev/null
+++ b/core/src/element.rs
@@ -0,0 +1,608 @@
+use crate::event::{self, Event};
+use crate::layout;
+use crate::mouse;
+use crate::overlay;
+use crate::renderer;
+use crate::widget;
+use crate::widget::tree::{self, Tree};
+use crate::{
+    Clipboard, Color, Layout, Length, Point, Rectangle, Shell, Widget,
+};
+
+use std::any::Any;
+use std::borrow::Borrow;
+
+/// A generic [`Widget`].
+///
+/// It is useful to build composable user interfaces that do not leak
+/// implementation details in their __view logic__.
+///
+/// If you have a [built-in widget], you should be able to use `Into<Element>`
+/// to turn it into an [`Element`].
+///
+/// [built-in widget]: crate::widget
+#[allow(missing_debug_implementations)]
+pub struct Element<'a, Message, Renderer> {
+    widget: Box<dyn Widget<Message, Renderer> + 'a>,
+}
+
+impl<'a, Message, Renderer> Element<'a, Message, Renderer> {
+    /// Creates a new [`Element`] containing the given [`Widget`].
+    pub fn new(widget: impl Widget<Message, Renderer> + 'a) -> Self
+    where
+        Renderer: crate::Renderer,
+    {
+        Self {
+            widget: Box::new(widget),
+        }
+    }
+
+    /// Returns a reference to the [`Widget`] of the [`Element`],
+    pub fn as_widget(&self) -> &dyn Widget<Message, Renderer> {
+        self.widget.as_ref()
+    }
+
+    /// Returns a mutable reference to the [`Widget`] of the [`Element`],
+    pub fn as_widget_mut(&mut self) -> &mut dyn Widget<Message, Renderer> {
+        self.widget.as_mut()
+    }
+
+    /// Applies a transformation to the produced message of the [`Element`].
+    ///
+    /// This method is useful when you want to decouple different parts of your
+    /// UI and make them __composable__.
+    ///
+    /// # Example
+    /// Imagine we want to use [our counter](index.html#usage). But instead of
+    /// showing a single counter, we want to display many of them. We can reuse
+    /// the `Counter` type as it is!
+    ///
+    /// We use composition to model the __state__ of our new application:
+    ///
+    /// ```
+    /// # mod counter {
+    /// #     pub struct Counter;
+    /// # }
+    /// use counter::Counter;
+    ///
+    /// struct ManyCounters {
+    ///     counters: Vec<Counter>,
+    /// }
+    /// ```
+    ///
+    /// We can store the state of multiple counters now. However, the
+    /// __messages__ we implemented before describe the user interactions
+    /// of a __single__ counter. Right now, we need to also identify which
+    /// counter is receiving user interactions. Can we use composition again?
+    /// Yes.
+    ///
+    /// ```
+    /// # mod counter {
+    /// #     #[derive(Debug, Clone, Copy)]
+    /// #     pub enum Message {}
+    /// # }
+    /// #[derive(Debug, Clone, Copy)]
+    /// pub enum Message {
+    ///     Counter(usize, counter::Message)
+    /// }
+    /// ```
+    ///
+    /// We compose the previous __messages__ with the index of the counter
+    /// producing them. Let's implement our __view logic__ now:
+    ///
+    /// ```no_run
+    /// # mod counter {
+    /// #     #[derive(Debug, Clone, Copy)]
+    /// #     pub enum Message {}
+    /// #     pub struct Counter;
+    /// #
+    /// #     impl Counter {
+    /// #         pub fn view(
+    /// #             &self,
+    /// #         ) -> iced_core::Element<Message, iced_core::renderer::Null> {
+    /// #             unimplemented!()
+    /// #         }
+    /// #     }
+    /// # }
+    /// #
+    /// # mod iced {
+    /// #     pub use iced_core::renderer::Null as Renderer;
+    /// #     pub use iced_core::Element;
+    /// #
+    /// #     pub mod widget {
+    /// #         pub struct Row<Message> {
+    /// #             _t: std::marker::PhantomData<Message>,
+    /// #         }
+    /// #
+    /// #         impl<Message> Row<Message> {
+    /// #             pub fn new() -> Self {
+    /// #                 unimplemented!()
+    /// #             }
+    /// #
+    /// #             pub fn spacing(mut self, _: u32) -> Self {
+    /// #                 unimplemented!()
+    /// #             }
+    /// #
+    /// #             pub fn push(
+    /// #                 mut self,
+    /// #                 _: iced_core::Element<Message, iced_core::renderer::Null>,
+    /// #             ) -> Self {
+    /// #                 unimplemented!()
+    /// #             }
+    /// #         }
+    /// #     }
+    /// # }
+    /// #
+    /// use counter::Counter;
+    ///
+    /// use iced::widget::Row;
+    /// use iced::{Element, Renderer};
+    ///
+    /// struct ManyCounters {
+    ///     counters: Vec<Counter>,
+    /// }
+    ///
+    /// #[derive(Debug, Clone, Copy)]
+    /// pub enum Message {
+    ///     Counter(usize, counter::Message),
+    /// }
+    ///
+    /// impl ManyCounters {
+    ///     pub fn view(&mut self) -> Row<Message> {
+    ///         // We can quickly populate a `Row` by folding over our counters
+    ///         self.counters.iter_mut().enumerate().fold(
+    ///             Row::new().spacing(20),
+    ///             |row, (index, counter)| {
+    ///                 // We display the counter
+    ///                 let element: Element<counter::Message, Renderer> =
+    ///                     counter.view().into();
+    ///
+    ///                 row.push(
+    ///                     // Here we turn our `Element<counter::Message>` into
+    ///                     // an `Element<Message>` by combining the `index` and the
+    ///                     // message of the `element`.
+    ///                     element
+    ///                         .map(move |message| Message::Counter(index, message)),
+    ///                 )
+    ///             },
+    ///         )
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// Finally, our __update logic__ is pretty straightforward: simple
+    /// delegation.
+    ///
+    /// ```
+    /// # mod counter {
+    /// #     #[derive(Debug, Clone, Copy)]
+    /// #     pub enum Message {}
+    /// #     pub struct Counter;
+    /// #
+    /// #     impl Counter {
+    /// #         pub fn update(&mut self, _message: Message) {}
+    /// #     }
+    /// # }
+    /// #
+    /// # use counter::Counter;
+    /// #
+    /// # struct ManyCounters {
+    /// #     counters: Vec<Counter>,
+    /// # }
+    /// #
+    /// # #[derive(Debug, Clone, Copy)]
+    /// # pub enum Message {
+    /// #    Counter(usize, counter::Message)
+    /// # }
+    /// impl ManyCounters {
+    ///     pub fn update(&mut self, message: Message) {
+    ///         match message {
+    ///             Message::Counter(index, counter_msg) => {
+    ///                 if let Some(counter) = self.counters.get_mut(index) {
+    ///                     counter.update(counter_msg);
+    ///                 }
+    ///             }
+    ///         }
+    ///     }
+    /// }
+    /// ```
+    pub fn map<B>(
+        self,
+        f: impl Fn(Message) -> B + 'a,
+    ) -> Element<'a, B, Renderer>
+    where
+        Message: 'a,
+        Renderer: crate::Renderer + 'a,
+        B: 'a,
+    {
+        Element::new(Map::new(self.widget, f))
+    }
+
+    /// Marks the [`Element`] as _to-be-explained_.
+    ///
+    /// The [`Renderer`] will explain the layout of the [`Element`] graphically.
+    /// This can be very useful for debugging your layout!
+    ///
+    /// [`Renderer`]: crate::Renderer
+    pub fn explain<C: Into<Color>>(
+        self,
+        color: C,
+    ) -> Element<'a, Message, Renderer>
+    where
+        Message: 'static,
+        Renderer: crate::Renderer + 'a,
+    {
+        Element {
+            widget: Box::new(Explain::new(self, color.into())),
+        }
+    }
+}
+
+impl<'a, Message, Renderer> Borrow<dyn Widget<Message, Renderer> + 'a>
+    for Element<'a, Message, Renderer>
+{
+    fn borrow(&self) -> &(dyn Widget<Message, Renderer> + 'a) {
+        self.widget.borrow()
+    }
+}
+
+impl<'a, Message, Renderer> Borrow<dyn Widget<Message, Renderer> + 'a>
+    for &Element<'a, Message, Renderer>
+{
+    fn borrow(&self) -> &(dyn Widget<Message, Renderer> + 'a) {
+        self.widget.borrow()
+    }
+}
+
+struct Map<'a, A, B, Renderer> {
+    widget: Box<dyn Widget<A, Renderer> + 'a>,
+    mapper: Box<dyn Fn(A) -> B + 'a>,
+}
+
+impl<'a, A, B, Renderer> Map<'a, A, B, Renderer> {
+    pub fn new<F>(
+        widget: Box<dyn Widget<A, Renderer> + 'a>,
+        mapper: F,
+    ) -> Map<'a, A, B, Renderer>
+    where
+        F: 'a + Fn(A) -> B,
+    {
+        Map {
+            widget,
+            mapper: Box::new(mapper),
+        }
+    }
+}
+
+impl<'a, A, B, Renderer> Widget<B, Renderer> for Map<'a, A, B, Renderer>
+where
+    Renderer: crate::Renderer + 'a,
+    A: 'a,
+    B: 'a,
+{
+    fn tag(&self) -> tree::Tag {
+        self.widget.tag()
+    }
+
+    fn state(&self) -> tree::State {
+        self.widget.state()
+    }
+
+    fn children(&self) -> Vec<Tree> {
+        self.widget.children()
+    }
+
+    fn diff(&self, tree: &mut Tree) {
+        self.widget.diff(tree)
+    }
+
+    fn width(&self) -> Length {
+        self.widget.width()
+    }
+
+    fn height(&self) -> Length {
+        self.widget.height()
+    }
+
+    fn layout(
+        &self,
+        renderer: &Renderer,
+        limits: &layout::Limits,
+    ) -> layout::Node {
+        self.widget.layout(renderer, limits)
+    }
+
+    fn operate(
+        &self,
+        tree: &mut Tree,
+        layout: Layout<'_>,
+        renderer: &Renderer,
+        operation: &mut dyn widget::Operation<B>,
+    ) {
+        struct MapOperation<'a, B> {
+            operation: &'a mut dyn widget::Operation<B>,
+        }
+
+        impl<'a, T, B> widget::Operation<T> for MapOperation<'a, B> {
+            fn container(
+                &mut self,
+                id: Option<&widget::Id>,
+                operate_on_children: &mut dyn FnMut(
+                    &mut dyn widget::Operation<T>,
+                ),
+            ) {
+                self.operation.container(id, &mut |operation| {
+                    operate_on_children(&mut MapOperation { operation });
+                });
+            }
+
+            fn focusable(
+                &mut self,
+                state: &mut dyn widget::operation::Focusable,
+                id: Option<&widget::Id>,
+            ) {
+                self.operation.focusable(state, id);
+            }
+
+            fn scrollable(
+                &mut self,
+                state: &mut dyn widget::operation::Scrollable,
+                id: Option<&widget::Id>,
+            ) {
+                self.operation.scrollable(state, id);
+            }
+
+            fn text_input(
+                &mut self,
+                state: &mut dyn widget::operation::TextInput,
+                id: Option<&widget::Id>,
+            ) {
+                self.operation.text_input(state, id);
+            }
+
+            fn custom(&mut self, state: &mut dyn Any, id: Option<&widget::Id>) {
+                self.operation.custom(state, id);
+            }
+        }
+
+        self.widget.operate(
+            tree,
+            layout,
+            renderer,
+            &mut MapOperation { operation },
+        );
+    }
+
+    fn on_event(
+        &mut self,
+        tree: &mut Tree,
+        event: Event,
+        layout: Layout<'_>,
+        cursor_position: Point,
+        renderer: &Renderer,
+        clipboard: &mut dyn Clipboard,
+        shell: &mut Shell<'_, B>,
+    ) -> event::Status {
+        let mut local_messages = Vec::new();
+        let mut local_shell = Shell::new(&mut local_messages);
+
+        let status = self.widget.on_event(
+            tree,
+            event,
+            layout,
+            cursor_position,
+            renderer,
+            clipboard,
+            &mut local_shell,
+        );
+
+        shell.merge(local_shell, &self.mapper);
+
+        status
+    }
+
+    fn draw(
+        &self,
+        tree: &Tree,
+        renderer: &mut Renderer,
+        theme: &Renderer::Theme,
+        style: &renderer::Style,
+        layout: Layout<'_>,
+        cursor_position: Point,
+        viewport: &Rectangle,
+    ) {
+        self.widget.draw(
+            tree,
+            renderer,
+            theme,
+            style,
+            layout,
+            cursor_position,
+            viewport,
+        )
+    }
+
+    fn mouse_interaction(
+        &self,
+        tree: &Tree,
+        layout: Layout<'_>,
+        cursor_position: Point,
+        viewport: &Rectangle,
+        renderer: &Renderer,
+    ) -> mouse::Interaction {
+        self.widget.mouse_interaction(
+            tree,
+            layout,
+            cursor_position,
+            viewport,
+            renderer,
+        )
+    }
+
+    fn overlay<'b>(
+        &'b mut self,
+        tree: &'b mut Tree,
+        layout: Layout<'_>,
+        renderer: &Renderer,
+    ) -> Option<overlay::Element<'b, B, Renderer>> {
+        let mapper = &self.mapper;
+
+        self.widget
+            .overlay(tree, layout, renderer)
+            .map(move |overlay| overlay.map(mapper))
+    }
+}
+
+struct Explain<'a, Message, Renderer: crate::Renderer> {
+    element: Element<'a, Message, Renderer>,
+    color: Color,
+}
+
+impl<'a, Message, Renderer> Explain<'a, Message, Renderer>
+where
+    Renderer: crate::Renderer,
+{
+    fn new(element: Element<'a, Message, Renderer>, color: Color) -> Self {
+        Explain { element, color }
+    }
+}
+
+impl<'a, Message, Renderer> Widget<Message, Renderer>
+    for Explain<'a, Message, Renderer>
+where
+    Renderer: crate::Renderer,
+{
+    fn width(&self) -> Length {
+        self.element.widget.width()
+    }
+
+    fn height(&self) -> Length {
+        self.element.widget.height()
+    }
+
+    fn tag(&self) -> tree::Tag {
+        self.element.widget.tag()
+    }
+
+    fn state(&self) -> tree::State {
+        self.element.widget.state()
+    }
+
+    fn children(&self) -> Vec<Tree> {
+        self.element.widget.children()
+    }
+
+    fn diff(&self, tree: &mut Tree) {
+        self.element.widget.diff(tree);
+    }
+
+    fn layout(
+        &self,
+        renderer: &Renderer,
+        limits: &layout::Limits,
+    ) -> layout::Node {
+        self.element.widget.layout(renderer, limits)
+    }
+
+    fn operate(
+        &self,
+        state: &mut Tree,
+        layout: Layout<'_>,
+        renderer: &Renderer,
+        operation: &mut dyn widget::Operation<Message>,
+    ) {
+        self.element
+            .widget
+            .operate(state, layout, renderer, operation)
+    }
+
+    fn on_event(
+        &mut self,
+        state: &mut Tree,
+        event: Event,
+        layout: Layout<'_>,
+        cursor_position: Point,
+        renderer: &Renderer,
+        clipboard: &mut dyn Clipboard,
+        shell: &mut Shell<'_, Message>,
+    ) -> event::Status {
+        self.element.widget.on_event(
+            state,
+            event,
+            layout,
+            cursor_position,
+            renderer,
+            clipboard,
+            shell,
+        )
+    }
+
+    fn draw(
+        &self,
+        state: &Tree,
+        renderer: &mut Renderer,
+        theme: &Renderer::Theme,
+        style: &renderer::Style,
+        layout: Layout<'_>,
+        cursor_position: Point,
+        viewport: &Rectangle,
+    ) {
+        fn explain_layout<Renderer: crate::Renderer>(
+            renderer: &mut Renderer,
+            color: Color,
+            layout: Layout<'_>,
+        ) {
+            renderer.fill_quad(
+                renderer::Quad {
+                    bounds: layout.bounds(),
+                    border_color: color,
+                    border_width: 1.0,
+                    border_radius: 0.0.into(),
+                },
+                Color::TRANSPARENT,
+            );
+
+            for child in layout.children() {
+                explain_layout(renderer, color, child);
+            }
+        }
+
+        self.element.widget.draw(
+            state,
+            renderer,
+            theme,
+            style,
+            layout,
+            cursor_position,
+            viewport,
+        );
+
+        explain_layout(renderer, self.color, layout);
+    }
+
+    fn mouse_interaction(
+        &self,
+        state: &Tree,
+        layout: Layout<'_>,
+        cursor_position: Point,
+        viewport: &Rectangle,
+        renderer: &Renderer,
+    ) -> mouse::Interaction {
+        self.element.widget.mouse_interaction(
+            state,
+            layout,
+            cursor_position,
+            viewport,
+            renderer,
+        )
+    }
+
+    fn overlay<'b>(
+        &'b mut self,
+        state: &'b mut Tree,
+        layout: Layout<'_>,
+        renderer: &Renderer,
+    ) -> Option<overlay::Element<'b, Message, Renderer>> {
+        self.element.widget.overlay(state, layout, renderer)
+    }
+}