example: Add a HelloWorld example. (#1133)

Ref #1132 to make a minimized app

crates/story/examples/hello_world.rs

@@ -0,0 +1,78 @@
+use gpui::*;
+use gpui_component::{
+    button::{Button, ButtonVariants},
+    Root, StyledExt,
+};
+
+pub struct HelloWorld;
+
+impl Render for HelloWorld {
+    fn render(&mut self, _: &mut Window, _: &mut Context<Self>) -> impl IntoElement {
+        div()
+            .v_flex()
+            .gap_2()
+            .size_full()
+            .items_center()
+            .justify_center()
+            .text_center()
+            .child("Hello, World!")
+            .child(
+                Button::new("ok")
+                    .primary()
+                    .label("Let's Go!")
+                    .on_click(|_, _, _| println!("Clicked!")),
+            )
+    }
+}
+
+fn main() {
+    let app = Application::new();
+
+    app.run(move |cx| {
+        gpui_component::init(cx);
+
+        cx.activate(true);
+
+        let mut window_size = size(px(640.), px(480.));
+        if let Some(display) = cx.primary_display() {
+            let display_size = display.bounds().size;
+            window_size.width = window_size.width.min(display_size.width * 0.85);
+            window_size.height = window_size.height.min(display_size.height * 0.85);
+        }
+        let window_bounds = Bounds::centered(None, window_size, cx);
+
+        cx.spawn(async move |cx| {
+            let options = WindowOptions {
+                window_bounds: Some(WindowBounds::Windowed(window_bounds)),
+                titlebar: None,
+                window_min_size: Some(gpui::Size {
+                    width: px(640.),
+                    height: px(480.),
+                }),
+                kind: WindowKind::Normal,
+                #[cfg(target_os = "linux")]
+                window_background: gpui::WindowBackgroundAppearance::Transparent,
+                #[cfg(target_os = "linux")]
+                window_decorations: Some(gpui::WindowDecorations::Client),
+                ..Default::default()
+            };
+
+            let window = cx
+                .open_window(options, |window, cx| {
+                    let view = cx.new(|_| HelloWorld);
+                    cx.new(|cx| Root::new(view.into(), window, cx))
+                })
+                .expect("failed to open window");
+
+            window
+                .update(cx, |_, window, _| {
+                    window.activate_window();
+                    window.set_window_title("Example");
+                })
+                .expect("failed to update window");
+
+            Ok::<_, anyhow::Error>(())
+        })
+        .detach();
+    });
+}