Draft virtual Button, Column, and Text

... as well as a very naive diffing strategy!

virtual/src/lib.rs

@@ -1,33 +1,75 @@
-mod element;
 pub mod widget;
 
-pub use element::Element;
-pub use widget::Widget;
+pub(crate) mod flex;
 
+pub use widget::*;
+
+use iced_native::event::{self, Event};
 use iced_native::layout::{self, Layout};
+use iced_native::mouse;
 use iced_native::renderer;
-use iced_native::{Hasher, Length, Point, Rectangle};
+use iced_native::{Clipboard, Hasher, Length, Point, Rectangle, Shell};
 
 pub struct Virtual<'a, Message, Renderer> {
     state: &'a mut State<Message, Renderer>,
 }
 
+impl<'a, Message, Renderer> Virtual<'a, Message, Renderer>
+where
+    Message: 'static,
+    Renderer: iced_native::Renderer + 'static,
+{
+    pub fn new(
+        state: &'a mut State<Message, Renderer>,
+        content: Element<Message, Renderer>,
+    ) -> Self {
+        let _ = state.diff(content);
+
+        Self { state }
+    }
+}
+
 pub struct State<Message, Renderer> {
-    widget_tree: widget::Tree<Message, Renderer>,
+    state_tree: widget::Tree<Message, Renderer>,
     last_element: Element<Message, Renderer>,
 }
 
+impl<Message, Renderer> State<Message, Renderer>
+where
+    Message: 'static,
+    Renderer: iced_native::Renderer + 'static,
+{
+    pub fn new() -> Self {
+        let last_element = Element::new(widget::Column::new());
+
+        Self {
+            state_tree: widget::Tree::new(&last_element),
+            last_element,
+        }
+    }
+
+    fn diff(&mut self, new_element: Element<Message, Renderer>) {
+        self.state_tree.diff(&self.last_element, &new_element);
+
+        self.last_element = new_element;
+    }
+}
+
 impl<'a, Message, Renderer> iced_native::Widget<Message, Renderer>
     for Virtual<'a, Message, Renderer>
 where
     Renderer: iced_native::Renderer,
 {
     fn width(&self) -> Length {
-        self.state.widget_tree.width()
+        self.state.last_element.as_widget().width()
     }
 
     fn height(&self) -> Length {
-        self.state.widget_tree.height()
+        self.state.last_element.as_widget().height()
+    }
+
+    fn hash_layout(&self, state: &mut Hasher) {
+        self.state.last_element.as_widget().hash_layout(state)
     }
 
     fn layout(
@@ -35,11 +77,27 @@ where
         renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {
-        self.state.widget_tree.layout(renderer, limits)
+        self.state.last_element.as_widget().layout(renderer, limits)
     }
 
-    fn hash_layout(&self, state: &mut Hasher) {
-        self.state.widget_tree.hash_layout(state)
+    fn on_event(
+        &mut self,
+        event: Event,
+        layout: Layout<'_>,
+        cursor_position: Point,
+        renderer: &Renderer,
+        clipboard: &mut dyn Clipboard,
+        shell: &mut Shell<'_, Message>,
+    ) -> event::Status {
+        self.state.last_element.as_widget_mut().on_event(
+            &mut self.state.state_tree,
+            event,
+            layout,
+            cursor_position,
+            renderer,
+            clipboard,
+            shell,
+        )
     }
 
     fn draw(
@@ -50,7 +108,8 @@ where
         cursor_position: Point,
         viewport: &Rectangle,
     ) {
-        self.state.widget_tree.draw(
+        self.state.last_element.as_widget().draw(
+            &self.state.state_tree,
             renderer,
             style,
             layout,
@@ -58,4 +117,30 @@ where
             viewport,
         )
     }
+
+    fn mouse_interaction(
+        &self,
+        layout: Layout<'_>,
+        cursor_position: Point,
+        viewport: &Rectangle,
+        renderer: &Renderer,
+    ) -> mouse::Interaction {
+        self.state.last_element.as_widget().mouse_interaction(
+            &self.state.state_tree,
+            layout,
+            cursor_position,
+            viewport,
+            renderer,
+        )
+    }
+}
+
+impl<'a, Message, Renderer> Into<iced_native::Element<'a, Message, Renderer>>
+    for Virtual<'a, Message, Renderer>
+where
+    Renderer: iced_native::Renderer,
+{
+    fn into(self) -> iced_native::Element<'a, Message, Renderer> {
+        iced_native::Element::new(self)
+    }
 }