Draft virtual Button, Column, and Text

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

examples/virtual_counter/src/main.rs

@@ -0,0 +1,61 @@
+use iced::{Alignment, Element, Sandbox, Settings};
+use iced_virtual::{Button, Column, Text, Virtual};
+
+pub fn main() -> iced::Result {
+    Counter::run(Settings::default())
+}
+
+struct Counter {
+    value: i32,
+    state: iced_virtual::State<Message, iced::Renderer>,
+}
+
+#[derive(Debug, Clone, Copy)]
+enum Message {
+    IncrementPressed,
+    DecrementPressed,
+}
+
+impl Sandbox for Counter {
+    type Message = Message;
+
+    fn new() -> Self {
+        Self {
+            value: 0,
+            state: iced_virtual::State::new(),
+        }
+    }
+
+    fn title(&self) -> String {
+        String::from("Counter - Iced")
+    }
+
+    fn update(&mut self, message: Message) {
+        match message {
+            Message::IncrementPressed => {
+                self.value += 1;
+            }
+            Message::DecrementPressed => {
+                self.value -= 1;
+            }
+        }
+    }
+
+    fn view(&mut self) -> Element<Message> {
+        let content = Column::new()
+            .padding(20)
+            .align_items(Alignment::Center)
+            .push(
+                Button::new(Text::new("Increment"))
+                    .on_press(Message::IncrementPressed),
+            )
+            .push(Text::new(self.value.to_string()).size(50))
+            .push(
+                Button::new(Text::new("Decrement"))
+                    .on_press(Message::DecrementPressed),
+            );
+
+        Virtual::new(&mut self.state, iced_virtual::Element::new(content))
+            .into()
+    }
+}