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scroll.rs
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scroll.rs
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//! This example illustrates scrolling in Bevy UI.
use accesskit::{Node as Accessible, Role};
use bevy::{
a11y::AccessibilityNode,
input::mouse::{MouseScrollUnit, MouseWheel},
picking::focus::HoverMap,
prelude::*,
winit::WinitSettings,
};
fn main() {
let mut app = App::new();
app.add_plugins(DefaultPlugins)
.insert_resource(WinitSettings::desktop_app())
.add_systems(Startup, setup)
.add_systems(Update, update_scroll_position);
app.run();
}
const FONT_SIZE: f32 = 20.;
const LINE_HEIGHT: f32 = 21.;
fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
// Camera
commands.spawn((Camera2d, IsDefaultUiCamera));
// root node
commands
.spawn(Node {
width: Val::Percent(100.0),
height: Val::Percent(100.0),
justify_content: JustifyContent::SpaceBetween,
flex_direction: FlexDirection::Column,
..default()
})
.insert(PickingBehavior::IGNORE)
.with_children(|parent| {
// horizontal scroll example
parent
.spawn(Node {
width: Val::Percent(100.),
flex_direction: FlexDirection::Column,
..default()
})
.with_children(|parent| {
// header
parent.spawn((
Text::new("Horizontally Scrolling list (Ctrl + Mousewheel)"),
TextFont {
font: asset_server.load("fonts/FiraSans-Bold.ttf"),
font_size: FONT_SIZE,
..default()
},
Label,
));
// horizontal scroll container
parent
.spawn((
Node {
width: Val::Percent(80.),
margin: UiRect::all(Val::Px(10.)),
flex_direction: FlexDirection::Row,
overflow: Overflow::scroll_x(), // n.b.
..default()
},
BackgroundColor(Color::srgb(0.10, 0.10, 0.10)),
))
.with_children(|parent| {
for i in 0..100 {
parent.spawn((Text(format!("Item {i}")),
TextFont {
font: asset_server
.load("fonts/FiraSans-Bold.ttf"),
..default()
},
Label,
AccessibilityNode(Accessible::new(Role::ListItem)),
))
.insert(Node {
min_width: Val::Px(200.),
align_content: AlignContent::Center,
..default()
})
.insert(PickingBehavior {
should_block_lower: false,
..default()
})
.observe(|
trigger: Trigger<Pointer<Down>>,
mut commands: Commands
| {
if trigger.event().button == PointerButton::Primary {
commands.entity(trigger.entity()).despawn_recursive();
}
});
}
});
});
// container for all other examples
parent
.spawn(Node {
width: Val::Percent(100.),
height: Val::Percent(100.),
flex_direction: FlexDirection::Row,
justify_content: JustifyContent::SpaceBetween,
..default()
})
.with_children(|parent| {
// vertical scroll example
parent
.spawn(Node {
flex_direction: FlexDirection::Column,
justify_content: JustifyContent::Center,
align_items: AlignItems::Center,
width: Val::Px(200.),
..default()
})
.with_children(|parent| {
// Title
parent.spawn((
Text::new("Vertically Scrolling List"),
TextFont {
font: asset_server.load("fonts/FiraSans-Bold.ttf"),
font_size: FONT_SIZE,
..default()
},
Label,
));
// Scrolling list
parent
.spawn((
Node {
flex_direction: FlexDirection::Column,
align_self: AlignSelf::Stretch,
height: Val::Percent(50.),
overflow: Overflow::scroll_y(), // n.b.
..default()
},
BackgroundColor(Color::srgb(0.10, 0.10, 0.10)),
))
.with_children(|parent| {
// List items
for i in 0..25 {
parent
.spawn(Node {
min_height: Val::Px(LINE_HEIGHT),
max_height: Val::Px(LINE_HEIGHT),
..default()
})
.insert(PickingBehavior {
should_block_lower: false,
..default()
})
.with_children(|parent| {
parent
.spawn((
Text(format!("Item {i}")),
TextFont {
font: asset_server
.load("fonts/FiraSans-Bold.ttf"),
..default()
},
Label,
AccessibilityNode(Accessible::new(
Role::ListItem,
)),
))
.insert(PickingBehavior {
should_block_lower: false,
..default()
});
});
}
});
});
// Bidirectional scroll example
parent
.spawn(Node {
flex_direction: FlexDirection::Column,
justify_content: JustifyContent::Center,
align_items: AlignItems::Center,
width: Val::Px(200.),
..default()
})
.with_children(|parent| {
// Title
parent.spawn((
Text::new("Bidirectionally Scrolling List"),
TextFont {
font: asset_server.load("fonts/FiraSans-Bold.ttf"),
font_size: FONT_SIZE,
..default()
},
Label,
));
// Scrolling list
parent
.spawn((
Node {
flex_direction: FlexDirection::Column,
align_self: AlignSelf::Stretch,
height: Val::Percent(50.),
overflow: Overflow::scroll(), // n.b.
..default()
},
BackgroundColor(Color::srgb(0.10, 0.10, 0.10)),
))
.with_children(|parent| {
// Rows in each column
for oi in 0..10 {
parent
.spawn(Node {
flex_direction: FlexDirection::Row,
..default()
})
.insert(PickingBehavior::IGNORE)
.with_children(|parent| {
// Elements in each row
for i in 0..25 {
parent
.spawn((
Text(format!("Item {}", (oi * 25) + i)),
TextFont {
font: asset_server.load(
"fonts/FiraSans-Bold.ttf",
),
..default()
},
Label,
AccessibilityNode(Accessible::new(
Role::ListItem,
)),
))
.insert(PickingBehavior {
should_block_lower: false,
..default()
});
}
});
}
});
});
// Nested scrolls example
parent
.spawn(Node {
flex_direction: FlexDirection::Column,
justify_content: JustifyContent::Center,
align_items: AlignItems::Center,
width: Val::Px(200.),
..default()
})
.with_children(|parent| {
// Title
parent.spawn((
Text::new("Nested Scrolling Lists"),
TextFont {
font: asset_server.load("fonts/FiraSans-Bold.ttf"),
font_size: FONT_SIZE,
..default()
},
Label,
));
// Outer, horizontal scrolling container
parent
.spawn((
Node {
column_gap: Val::Px(20.),
flex_direction: FlexDirection::Row,
align_self: AlignSelf::Stretch,
height: Val::Percent(50.),
overflow: Overflow::scroll_x(), // n.b.
..default()
},
BackgroundColor(Color::srgb(0.10, 0.10, 0.10)),
))
.with_children(|parent| {
// Inner, scrolling columns
for oi in 0..30 {
parent
.spawn((
Node {
flex_direction: FlexDirection::Column,
align_self: AlignSelf::Stretch,
overflow: Overflow::scroll_y(),
..default()
},
BackgroundColor(Color::srgb(0.05, 0.05, 0.05)),
))
.insert(PickingBehavior {
should_block_lower: false,
..default()
})
.with_children(|parent| {
for i in 0..25 {
parent
.spawn((
Text(format!("Item {}", (oi * 25) + i)),
TextFont {
font: asset_server.load(
"fonts/FiraSans-Bold.ttf",
),
..default()
},
Label,
AccessibilityNode(Accessible::new(
Role::ListItem,
)),
))
.insert(PickingBehavior {
should_block_lower: false,
..default()
});
}
});
}
});
});
});
});
}
/// Updates the scroll position of scrollable nodes in response to mouse input
pub fn update_scroll_position(
mut mouse_wheel_events: EventReader<MouseWheel>,
hover_map: Res<HoverMap>,
mut scrolled_node_query: Query<&mut ScrollPosition>,
keyboard_input: Res<ButtonInput<KeyCode>>,
) {
for mouse_wheel_event in mouse_wheel_events.read() {
let (mut dx, mut dy) = match mouse_wheel_event.unit {
MouseScrollUnit::Line => (
mouse_wheel_event.x * LINE_HEIGHT,
mouse_wheel_event.y * LINE_HEIGHT,
),
MouseScrollUnit::Pixel => (mouse_wheel_event.x, mouse_wheel_event.y),
};
if keyboard_input.pressed(KeyCode::ControlLeft)
|| keyboard_input.pressed(KeyCode::ControlRight)
{
std::mem::swap(&mut dx, &mut dy);
}
for (_pointer, pointer_map) in hover_map.iter() {
for (entity, _hit) in pointer_map.iter() {
if let Ok(mut scroll_position) = scrolled_node_query.get_mut(*entity) {
scroll_position.offset_x -= dx;
scroll_position.offset_y -= dy;
}
}
}
}
}