Create visible_bounds example

examples/visible_bounds/Cargo.toml

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+[package]
+name = "visible_bounds"
+version = "0.1.0"
+authors = ["Héctor Ramón Jiménez <hector0193@gmail.com>"]
+edition = "2021"
+publish = false
+
+[dependencies]
+iced = { path = "../..", features = ["debug"] }
+once_cell = "1"

examples/visible_bounds/src/main.rs

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+use iced::executor;
+use iced::mouse;
+use iced::subscription::{self, Subscription};
+use iced::theme::{self, Theme};
+use iced::widget::{column, container, scrollable, text, vertical_space};
+use iced::{
+    Application, Command, Element, Event, Length, Point, Rectangle, Settings,
+};
+
+pub fn main() -> iced::Result {
+    Example::run(Settings::default())
+}
+
+struct Example {
+    mouse_position: Option<Point>,
+    outer_bounds: Option<Rectangle>,
+    inner_bounds: Option<Rectangle>,
+}
+
+#[derive(Debug, Clone, Copy)]
+enum Message {
+    MouseMoved(Point),
+    Scrolled(scrollable::Viewport),
+    OuterBoundsFetched(Option<Rectangle>),
+    InnerBoundsFetched(Option<Rectangle>),
+}
+
+impl Application for Example {
+    type Message = Message;
+    type Theme = Theme;
+    type Flags = ();
+    type Executor = executor::Default;
+
+    fn new(_flags: Self::Flags) -> (Self, Command<Message>) {
+        (
+            Self {
+                mouse_position: None,
+                outer_bounds: None,
+                inner_bounds: None,
+            },
+            Command::none(),
+        )
+    }
+
+    fn title(&self) -> String {
+        String::from("Visible bounds - Iced")
+    }
+
+    fn update(&mut self, message: Message) -> Command<Message> {
+        match message {
+            Message::MouseMoved(position) => {
+                self.mouse_position = Some(position);
+
+                Command::none()
+            }
+            Message::Scrolled(_) => Command::batch(vec![
+                container::visible_bounds(OUTER_CONTAINER.clone())
+                    .map(Message::OuterBoundsFetched),
+                container::visible_bounds(INNER_CONTAINER.clone())
+                    .map(Message::InnerBoundsFetched),
+            ]),
+            Message::OuterBoundsFetched(outer_bounds) => {
+                self.outer_bounds = outer_bounds;
+
+                Command::none()
+            }
+            Message::InnerBoundsFetched(inner_bounds) => {
+                self.inner_bounds = inner_bounds;
+
+                Command::none()
+            }
+        }
+    }
+
+    fn view(&self) -> Element<Message> {
+        let view_bounds = |label, bounds| {
+            text(format!(
+                "The {label} container is {}",
+                match bounds {
+                    Some(bounds) => format!("visible at {:?}", bounds),
+                    None => "not visible".to_string(),
+                }
+            ))
+        };
+
+        column![
+            text(format!(
+                "Mouse position is {}",
+                match self.mouse_position {
+                    Some(Point { x, y }) => format!("({x}, {y})"),
+                    None => "unknown".to_string(),
+                }
+            )),
+            view_bounds("outer", self.outer_bounds),
+            view_bounds("inner", self.inner_bounds),
+            scrollable(
+                column![
+                    text("Scroll me!"),
+                    vertical_space(400),
+                    container(text("I am the outer container!"))
+                        .id(OUTER_CONTAINER.clone())
+                        .padding(40)
+                        .style(theme::Container::Box),
+                    vertical_space(400),
+                    scrollable(
+                        column![
+                            text("Scroll me!"),
+                            vertical_space(400),
+                            container(text("I am the inner container!"))
+                                .id(INNER_CONTAINER.clone())
+                                .padding(40)
+                                .style(theme::Container::Box),
+                            vertical_space(400)
+                        ]
+                        .padding(20)
+                    )
+                    .on_scroll(Message::Scrolled)
+                    .width(Length::Fill)
+                    .height(300),
+                ]
+                .padding(20)
+            )
+            .on_scroll(Message::Scrolled)
+            .width(Length::Fill)
+            .height(300),
+        ]
+        .spacing(10)
+        .padding(20)
+        .into()
+    }
+
+    fn subscription(&self) -> Subscription<Message> {
+        subscription::events_with(|event, _| match event {
+            Event::Mouse(mouse::Event::CursorMoved { position }) => {
+                Some(Message::MouseMoved(position))
+            }
+            _ => None,
+        })
+    }
+
+    fn theme(&self) -> Theme {
+        Theme::Dark
+    }
+}
+
+use once_cell::sync::Lazy;
+
+static OUTER_CONTAINER: Lazy<container::Id> =
+    Lazy::new(|| container::Id::new("outer"));
+static INNER_CONTAINER: Lazy<container::Id> =
+    Lazy::new(|| container::Id::new("inner"));