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flex_layout.rs:
//! Demonstrates how the `AlignItems` and `JustifyContent` properties can be composed to layout text.
use bevy::prelude::*;
const ALIGN_ITEMS_COLOR: Color = Color::srgb(1., 0.066, 0.349);
const JUSTIFY_CONTENT_COLOR: Color = Color::srgb(0.102, 0.522, 1.);
const MARGIN: Val = Val::Px(12.);
fn main() {
App::new()
.add_plugins(DefaultPlugins.set(WindowPlugin {
primary_window: Some(Window {
title: "Bevy Flex Layout Example".to_string(),
..Default::default()
}),
..Default::default()
}))
.add_systems(Startup, spawn_layout)
.run();
}
fn spawn_layout(mut commands: Commands, asset_server: Res<AssetServer>) {
let font = asset_server.load("fonts/FiraSans-Bold.ttf");
commands.spawn(Camera2dBundle::default());
commands
.spawn(NodeBundle {
style: Style {
// fill the entire window
width: Val::Percent(100.),
height: Val::Percent(100.),
flex_direction: FlexDirection::Column,
align_items: AlignItems::Center,
padding: UiRect::all(MARGIN),
row_gap: MARGIN,
..Default::default()
},
background_color: BackgroundColor(Color::BLACK),
..Default::default()
})
.with_children(|builder| {
// spawn the key
builder
.spawn(NodeBundle {
style: Style {
flex_direction: FlexDirection::Row,
..Default::default()
},
..Default::default()
})
.with_children(|builder| {
spawn_nested_text_bundle(
builder,
font.clone(),
ALIGN_ITEMS_COLOR,
UiRect::right(MARGIN),
"AlignItems",
);
spawn_nested_text_bundle(
builder,
font.clone(),
JUSTIFY_CONTENT_COLOR,
UiRect::default(),
"JustifyContent",
);
});
builder
.spawn(NodeBundle {
style: Style {
width: Val::Percent(100.),
height: Val::Percent(100.),
flex_direction: FlexDirection::Column,
row_gap: MARGIN,
..Default::default()
},
..Default::default()
})
.with_children(|builder| {
// spawn one child node for each combination of `AlignItems` and `JustifyContent`
let justifications = [
JustifyContent::FlexStart,
JustifyContent::Center,
JustifyContent::FlexEnd,
JustifyContent::SpaceEvenly,
JustifyContent::SpaceAround,
JustifyContent::SpaceBetween,
];
let alignments = [
AlignItems::Baseline,
AlignItems::FlexStart,
AlignItems::Center,
AlignItems::FlexEnd,
AlignItems::Stretch,
];
for align_items in alignments {
builder
.spawn(NodeBundle {
style: Style {
width: Val::Percent(100.),
height: Val::Percent(100.),
flex_direction: FlexDirection::Row,
column_gap: MARGIN,
..Default::default()
},
..Default::default()
})
.with_children(|builder| {
for justify_content in justifications {
spawn_child_node(
builder,
font.clone(),
align_items,
justify_content,
);
}
});
}
});
});
}
fn spawn_child_node(
builder: &mut ChildBuilder,
font: Handle<Font>,
align_items: AlignItems,
justify_content: JustifyContent,
) {
builder
.spawn(NodeBundle {
style: Style {
flex_direction: FlexDirection::Column,
align_items,
justify_content,
width: Val::Percent(100.),
height: Val::Percent(100.),
..Default::default()
},
background_color: BackgroundColor(Color::srgb(0.25, 0.25, 0.25)),
..Default::default()
})
.with_children(|builder| {
let labels = [
(format!("{align_items:?}"), ALIGN_ITEMS_COLOR, 0.),
(format!("{justify_content:?}"), JUSTIFY_CONTENT_COLOR, 3.),
];
for (text, color, top_margin) in labels {
// We nest the text within a parent node because margins and padding can't be directly applied to text nodes currently.
spawn_nested_text_bundle(
builder,
font.clone(),
color,
UiRect::top(Val::Px(top_margin)),
&text,
);
}
});
}
fn spawn_nested_text_bundle(
builder: &mut ChildBuilder,
font: Handle<Font>,
background_color: Color,
margin: UiRect,
text: &str,
) {
builder
.spawn(NodeBundle {
style: Style {
margin,
padding: UiRect::axes(Val::Px(5.), Val::Px(1.)),
..Default::default()
},
background_color: BackgroundColor(background_color),
..Default::default()
})
.with_children(|builder| {
builder.spawn(TextBundle::from_section(
text,
TextStyle {
font,
font_size: 24.0,
color: Color::BLACK,
},
));
});
}