Draft `Responsive` widget

3 files changed, 192 insertions, 1 deletions

diff --git a/native/src/lib.rs b/native/src/lib.rs
index 4753bba2..4211995f 100644
--- a/native/src/lib.rs
+++ b/native/src/lib.rs
@@ -31,7 +31,7 @@
 #![doc(
     html_logo_url = "https://raw.githubusercontent.com/iced-rs/iced/9ab6923e943f784985e9ef9ca28b10278297225d/docs/logo.svg"
 )]
-#![deny(missing_docs)]
+//#![deny(missing_docs)]
 #![deny(missing_debug_implementations)]
 #![deny(unused_results)]
 #![forbid(unsafe_code)]
diff --git a/native/src/widget.rs b/native/src/widget.rs
index caa3f0bc..d1619bf3 100644
--- a/native/src/widget.rs
+++ b/native/src/widget.rs
@@ -20,6 +20,7 @@ pub mod pane_grid;
 pub mod pick_list;
 pub mod progress_bar;
 pub mod radio;
+pub mod responsive;
 pub mod row;
 pub mod rule;
 pub mod scrollable;
@@ -50,6 +51,8 @@ pub use progress_bar::ProgressBar;
 #[doc(no_inline)]
 pub use radio::Radio;
 #[doc(no_inline)]
+pub use responsive::Responsive;
+#[doc(no_inline)]
 pub use row::Row;
 #[doc(no_inline)]
 pub use rule::Rule;
diff --git a/native/src/widget/responsive.rs b/native/src/widget/responsive.rs
new file mode 100644
index 00000000..0cb85d45
--- /dev/null
+++ b/native/src/widget/responsive.rs
@@ -0,0 +1,188 @@
+use crate::event::{self, Event};
+use crate::layout::{self, Layout};
+use crate::renderer;
+use crate::{
+    Clipboard, Element, Hasher, Length, Point, Rectangle, Shell, Size, Widget,
+};
+
+use std::cell::RefCell;
+use std::hash::Hasher as _;
+
+#[derive(Debug, Clone, Default)]
+pub struct State {
+    last_size: Option<Size>,
+    last_layout: layout::Node,
+    last_layout_hash: u64,
+}
+
+impl State {
+    pub fn new() -> State {
+        State::default()
+    }
+}
+
+#[allow(missing_debug_implementations)]
+pub struct Responsive<'a, Message, Renderer>(
+    RefCell<Internal<'a, Message, Renderer>>,
+);
+
+impl<'a, Message, Renderer> Responsive<'a, Message, Renderer> {
+    pub fn new(
+        state: &'a mut State,
+        view: impl FnOnce(Size) -> Element<'a, Message, Renderer> + 'a,
+    ) -> Self {
+        Self(RefCell::new(Internal {
+            state,
+            content: Content::Pending(Some(Box::new(view))),
+        }))
+    }
+}
+
+impl<'a, Message, Renderer> Widget<Message, Renderer>
+    for Responsive<'a, Message, Renderer>
+where
+    Renderer: crate::Renderer,
+{
+    fn width(&self) -> Length {
+        Length::Fill
+    }
+
+    fn height(&self) -> Length {
+        Length::Fill
+    }
+
+    fn hash_layout(&self, _hasher: &mut Hasher) {}
+
+    fn layout(
+        &self,
+        _renderer: &Renderer,
+        limits: &layout::Limits,
+    ) -> layout::Node {
+        let size = limits.max();
+
+        self.0.borrow_mut().state.last_size = Some(size);
+
+        layout::Node::new(size)
+    }
+
+    fn on_event(
+        &mut self,
+        event: Event,
+        layout: Layout<'_>,
+        cursor_position: Point,
+        renderer: &Renderer,
+        clipboard: &mut dyn Clipboard,
+        shell: &mut Shell<'_, Message>,
+    ) -> event::Status {
+        use std::ops::DerefMut;
+
+        let mut internal = self.0.borrow_mut();
+
+        let Internal { content, state } = internal.deref_mut();
+
+        let content = content.resolve(state, renderer);
+
+        let content_layout = Layout::with_offset(
+            layout.position() - Point::ORIGIN,
+            &state.last_layout,
+        );
+
+        content.on_event(
+            event,
+            content_layout,
+            cursor_position,
+            renderer,
+            clipboard,
+            shell,
+        )
+    }
+
+    fn draw(
+        &self,
+        renderer: &mut Renderer,
+        style: &renderer::Style,
+        layout: Layout<'_>,
+        cursor_position: Point,
+        viewport: &Rectangle,
+    ) {
+        use std::ops::DerefMut;
+
+        let mut internal = self.0.borrow_mut();
+
+        let Internal { content, state } = internal.deref_mut();
+
+        let content = content.resolve(state, renderer);
+
+        let content_layout = Layout::with_offset(
+            layout.position() - Point::ORIGIN,
+            &state.last_layout,
+        );
+
+        content.draw(renderer, style, content_layout, cursor_position, viewport)
+    }
+}
+
+struct Internal<'a, Message, Renderer> {
+    state: &'a mut State,
+    content: Content<'a, Message, Renderer>,
+}
+
+enum Content<'a, Message, Renderer> {
+    Pending(
+        Option<Box<dyn FnOnce(Size) -> Element<'a, Message, Renderer> + 'a>>,
+    ),
+    Ready(Element<'a, Message, Renderer>),
+}
+
+impl<'a, Message, Renderer> Content<'a, Message, Renderer>
+where
+    Renderer: crate::Renderer,
+{
+    fn resolve(
+        &mut self,
+        state: &mut State,
+        renderer: &Renderer,
+    ) -> &mut Element<'a, Message, Renderer> {
+        match self {
+            Content::Ready(element) => element,
+            Content::Pending(view) => {
+                let element =
+                    view.take().unwrap()(state.last_size.unwrap_or(Size::ZERO));
+
+                let new_layout_hash = {
+                    let mut hasher = Hasher::default();
+                    element.hash_layout(&mut hasher);
+
+                    hasher.finish()
+                };
+
+                if new_layout_hash != state.last_layout_hash {
+                    state.last_layout = element.layout(
+                        renderer,
+                        &layout::Limits::new(
+                            Size::ZERO,
+                            state.last_size.unwrap_or(Size::ZERO),
+                        ),
+                    );
+
+                    state.last_layout_hash = new_layout_hash;
+                }
+
+                *self = Content::Ready(element);
+
+                self.resolve(state, renderer)
+            }
+        }
+    }
+}
+
+impl<'a, Message, Renderer> From<Responsive<'a, Message, Renderer>>
+    for Element<'a, Message, Renderer>
+where
+    Renderer: crate::Renderer + 'a,
+    Message: 'a,
+{
+    fn from(responsive: Responsive<'a, Message, Renderer>) -> Self {
+        Self::new(responsive)
+    }
+}