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//! This example illustrates the various features of Bevy UI.
use bevy::{
a11y::{
accesskit::{NodeBuilder, Role},
AccessibilityNode,
},
input::mouse::{MouseScrollUnit, MouseWheel},
prelude::*,
winit::WinitSettings,
};
fn main() {
App::new()
.add_plugins(DefaultPlugins)
// Only run the app when there is user input. This will significantly reduce CPU/GPU use.
.insert_resource(WinitSettings::desktop_app())
.add_systems(Startup, setup)
.add_systems(Update, mouse_scroll)
.run();
}
fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
// Camera
commands.spawn(Camera2dBundle::default());
// root node
commands
.spawn(NodeBundle {
style: Style {
width: Val::Percent(100.0),
height: Val::Percent(100.0),
justify_content: JustifyContent::SpaceBetween,
..default()
},
..default()
})
.with_children(|parent| {
// left vertical fill (border)
parent
.spawn(NodeBundle {
style: Style {
width: Val::Px(200.),
border: UiRect::all(Val::Px(2.)),
..default()
},
background_color: Color::rgb(0.65, 0.65, 0.65).into(),
..default()
})
.with_children(|parent| {
// left vertical fill (content)
parent
.spawn(NodeBundle {
style: Style {
width: Val::Percent(100.),
..default()
},
background_color: Color::rgb(0.15, 0.15, 0.15).into(),
..default()
})
.with_children(|parent| {
// text
parent.spawn((
TextBundle::from_section(
"Text Example",
TextStyle {
font: asset_server.load("fonts/FiraSans-Bold.ttf"),
font_size: 30.0,
..default()
},
)
.with_style(Style {
margin: UiRect::all(Val::Px(5.)),
..default()
}),
// Because this is a distinct label widget and
// not button/list item text, this is necessary
// for accessibility to treat the text accordingly.
Label,
));
});
});
// right vertical fill
parent
.spawn(NodeBundle {
style: Style {
flex_direction: FlexDirection::Column,
justify_content: JustifyContent::Center,
align_items: AlignItems::Center,
width: Val::Px(200.),
..default()
},
background_color: Color::rgb(0.15, 0.15, 0.15).into(),
..default()
})
.with_children(|parent| {
// Title
parent.spawn((
TextBundle::from_section(
"Scrolling list",
TextStyle {
font: asset_server.load("fonts/FiraSans-Bold.ttf"),
font_size: 25.,
..default()
},
),
Label,
));
// List with hidden overflow
parent
.spawn(NodeBundle {
style: Style {
flex_direction: FlexDirection::Column,
align_self: AlignSelf::Stretch,
height: Val::Percent(50.),
overflow: Overflow::clip_y(),
..default()
},
background_color: Color::rgb(0.10, 0.10, 0.10).into(),
..default()
})
.with_children(|parent| {
// Moving panel
parent
.spawn((
NodeBundle {
style: Style {
flex_direction: FlexDirection::Column,
align_items: AlignItems::Center,
..default()
},
..default()
},
ScrollingList::default(),
AccessibilityNode(NodeBuilder::new(Role::List)),
))
.with_children(|parent| {
// List items
for i in 0..30 {
parent.spawn((
TextBundle::from_section(
format!("Item {i}"),
TextStyle {
font: asset_server
.load("fonts/FiraSans-Bold.ttf"),
font_size: 20.,
..default()
},
),
Label,
AccessibilityNode(NodeBuilder::new(Role::ListItem)),
));
}
});
});
});
parent
.spawn(NodeBundle {
style: Style {
width: Val::Px(200.0),
height: Val::Px(200.0),
position_type: PositionType::Absolute,
left: Val::Px(210.),
bottom: Val::Px(10.),
border: UiRect::all(Val::Px(20.)),
..default()
},
border_color: Color::GREEN.into(),
background_color: Color::rgb(0.4, 0.4, 1.).into(),
..default()
})
.with_children(|parent| {
parent.spawn(NodeBundle {
style: Style {
width: Val::Percent(100.0),
height: Val::Percent(100.0),
..default()
},
background_color: Color::rgb(0.8, 0.8, 1.).into(),
..default()
});
});
// render order test: reddest in the back, whitest in the front (flex center)
parent
.spawn(NodeBundle {
style: Style {
width: Val::Percent(100.0),
height: Val::Percent(100.0),
position_type: PositionType::Absolute,
align_items: AlignItems::Center,
justify_content: JustifyContent::Center,
..default()
},
..default()
})
.with_children(|parent| {
parent
.spawn(NodeBundle {
style: Style {
width: Val::Px(100.0),
height: Val::Px(100.0),
..default()
},
background_color: Color::rgb(1.0, 0.0, 0.).into(),
..default()
})
.with_children(|parent| {
parent.spawn(NodeBundle {
style: Style {
// Take the size of the parent node.
width: Val::Percent(100.0),
height: Val::Percent(100.0),
position_type: PositionType::Absolute,
left: Val::Px(20.),
bottom: Val::Px(20.),
..default()
},
background_color: Color::rgb(1.0, 0.3, 0.3).into(),
..default()
});
parent.spawn(NodeBundle {
style: Style {
width: Val::Percent(100.0),
height: Val::Percent(100.0),
position_type: PositionType::Absolute,
left: Val::Px(40.),
bottom: Val::Px(40.),
..default()
},
background_color: Color::rgb(1.0, 0.5, 0.5).into(),
..default()
});
parent.spawn(NodeBundle {
style: Style {
width: Val::Percent(100.0),
height: Val::Percent(100.0),
position_type: PositionType::Absolute,
left: Val::Px(60.),
bottom: Val::Px(60.),
..default()
},
background_color: Color::rgb(1.0, 0.7, 0.7).into(),
..default()
});
// alpha test
parent.spawn(NodeBundle {
style: Style {
width: Val::Percent(100.0),
height: Val::Percent(100.0),
position_type: PositionType::Absolute,
left: Val::Px(80.),
bottom: Val::Px(80.),
..default()
},
background_color: Color::rgba(1.0, 0.9, 0.9, 0.4).into(),
..default()
});
});
});
// bevy logo (flex center)
parent
.spawn(NodeBundle {
style: Style {
width: Val::Percent(100.0),
position_type: PositionType::Absolute,
justify_content: JustifyContent::Center,
align_items: AlignItems::FlexStart,
..default()
},
..default()
})
.with_children(|parent| {
// bevy logo (image)
// A `NodeBundle` is used to display the logo the image as an `ImageBundle` can't automatically
// size itself with a child node present.
parent
.spawn((
NodeBundle {
style: Style {
width: Val::Px(500.0),
height: Val::Px(125.0),
margin: UiRect::top(Val::VMin(5.)),
..default()
},
// a `NodeBundle` is transparent by default, so to see the image we have to its color to `WHITE`
background_color: Color::WHITE.into(),
..default()
},
UiImage::new(asset_server.load("branding/bevy_logo_dark_big.png")),
))
.with_children(|parent| {
// alt text
// This UI node takes up no space in the layout and the `Text` component is used by the accessibility module
// and is not rendered.
parent.spawn((
NodeBundle {
style: Style {
display: Display::None,
..Default::default()
},
..Default::default()
},
Text::from_section("Bevy logo", TextStyle::default()),
));
});
});
});
}
#[derive(Component, Default)]
struct ScrollingList {
position: f32,
}
fn mouse_scroll(
mut mouse_wheel_events: EventReader<MouseWheel>,
mut query_list: Query<(&mut ScrollingList, &mut Style, &Parent, &Node)>,
query_node: Query<&Node>,
) {
for mouse_wheel_event in mouse_wheel_events.read() {
for (mut scrolling_list, mut style, parent, list_node) in &mut query_list {
let items_height = list_node.size().y;
let container_height = query_node.get(parent.get()).unwrap().size().y;
let max_scroll = (items_height - container_height).max(0.);
let dy = match mouse_wheel_event.unit {
MouseScrollUnit::Line => mouse_wheel_event.y * 20.,
MouseScrollUnit::Pixel => mouse_wheel_event.y,
};
scrolling_list.position += dy;
scrolling_list.position = scrolling_list.position.clamp(-max_scroll, 0.);
style.top = Val::Px(scrolling_list.position);
}
}
}