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//! Shows how `Time<Virtual>` can be used to pause, resume, slow down
//! and speed up a game.
use std::time::Duration;
use bevy::{
input::common_conditions::input_just_pressed, prelude::*,
time::common_conditions::on_real_timer,
};
fn main() {
App::new()
.add_plugins(DefaultPlugins)
.add_systems(Startup, setup)
.add_systems(
Update,
(
move_virtual_time_sprites,
move_real_time_sprites,
toggle_pause.run_if(input_just_pressed(KeyCode::Space)),
change_time_speed::<1>.run_if(input_just_pressed(KeyCode::ArrowUp)),
change_time_speed::<-1>.run_if(input_just_pressed(KeyCode::ArrowDown)),
(update_virtual_time_info_text, update_real_time_info_text)
// update the texts on a timer to make them more readable
// `on_timer` run condition uses `Virtual` time meaning it's scaled
// and would result in the UI updating at different intervals based
// on `Time<Virtual>::relative_speed` and `Time<Virtual>::is_paused()`
.run_if(on_real_timer(Duration::from_millis(250))),
),
)
.run();
}
/// `Real` time related marker
#[derive(Component)]
struct RealTime;
/// `Virtual` time related marker
#[derive(Component)]
struct VirtualTime;
/// Setup the example
fn setup(mut commands: Commands, asset_server: Res<AssetServer>, mut time: ResMut<Time<Virtual>>) {
// start with double `Virtual` time resulting in one of the sprites moving at twice the speed
// of the other sprite which moves based on `Real` (unscaled) time
time.set_relative_speed(2.);
commands.spawn(Camera2dBundle::default());
let virtual_color = Color::GOLD;
let sprite_scale = Vec2::splat(0.5).extend(1.);
let texture_handle = asset_server.load("branding/icon.png");
// the sprite moving based on real time
commands.spawn((
SpriteBundle {
texture: texture_handle.clone(),
transform: Transform::from_scale(sprite_scale),
..default()
},
RealTime,
));
// the sprite moving based on virtual time
commands.spawn((
SpriteBundle {
texture: texture_handle,
sprite: Sprite {
color: virtual_color,
..default()
},
transform: Transform {
scale: sprite_scale,
translation: Vec3::new(0., -160., 0.),
..default()
},
..default()
},
VirtualTime,
));
// info UI
let font_size = 40.;
commands
.spawn(NodeBundle {
style: Style {
display: Display::Flex,
justify_content: JustifyContent::SpaceBetween,
width: Val::Percent(100.),
position_type: PositionType::Absolute,
top: Val::Px(0.),
padding: UiRect::all(Val::Px(20.0)),
..default()
},
..default()
})
.with_children(|builder| {
// real time info
builder.spawn((
TextBundle::from_section(
"",
TextStyle {
font_size,
..default()
},
),
RealTime,
));
// keybindings
builder.spawn(
TextBundle::from_section(
"CONTROLS\nUn/Pause: Space\nSpeed+: Up\nSpeed-: Down",
TextStyle {
font_size,
color: Color::rgb(0.85, 0.85, 0.85),
..default()
},
)
.with_text_justify(JustifyText::Center),
);
// virtual time info
builder.spawn((
TextBundle::from_section(
"",
TextStyle {
font_size,
color: virtual_color,
..default()
},
)
.with_text_justify(JustifyText::Right),
VirtualTime,
));
});
}
/// Move sprites using `Real` (unscaled) time
fn move_real_time_sprites(
mut sprite_query: Query<&mut Transform, (With<Sprite>, With<RealTime>)>,
// `Real` time which is not scaled or paused
time: Res<Time<Real>>,
) {
for mut transform in sprite_query.iter_mut() {
// move roughly half the screen in a `Real` second
// when the time is scaled the speed is going to change
// and the sprite will stay still the the time is paused
transform.translation.x = get_sprite_translation_x(time.elapsed_seconds());
}
}
/// Move sprites using `Virtual` (scaled) time
fn move_virtual_time_sprites(
mut sprite_query: Query<&mut Transform, (With<Sprite>, With<VirtualTime>)>,
// the default `Time` is either `Time<Virtual>` in regular systems
// or `Time<Fixed>` in fixed timestep systems so `Time::delta()`,
// `Time::elapsed()` will return the appropriate values either way
time: Res<Time>,
) {
for mut transform in sprite_query.iter_mut() {
// move roughly half the screen in a `Virtual` second
// when time is scaled using `Time<Virtual>::set_relative_speed` it's going
// to move at a different pace and the sprite will stay still when time is
// `Time<Virtual>::is_paused()`
transform.translation.x = get_sprite_translation_x(time.elapsed_seconds());
}
}
fn get_sprite_translation_x(elapsed: f32) -> f32 {
elapsed.sin() * 500.
}
/// Update the speed of `Time<Virtual>.` by `DELTA`
fn change_time_speed<const DELTA: i8>(mut time: ResMut<Time<Virtual>>) {
let time_speed = (time.relative_speed() + DELTA as f32)
.round()
.clamp(0.25, 5.);
// set the speed of the virtual time to speed it up or slow it down
time.set_relative_speed(time_speed);
}
/// pause or resume `Relative` time
fn toggle_pause(mut time: ResMut<Time<Virtual>>) {
if time.is_paused() {
time.unpause();
} else {
time.pause();
}
}
/// Update the `Real` time info text
fn update_real_time_info_text(time: Res<Time<Real>>, mut query: Query<&mut Text, With<RealTime>>) {
for mut text in &mut query {
text.sections[0].value = format!(
"REAL TIME\nElapsed: {:.1}\nDelta: {:.5}\n",
time.elapsed_seconds(),
time.delta_seconds(),
);
}
}
/// Update the `Virtual` time info text
fn update_virtual_time_info_text(
time: Res<Time<Virtual>>,
mut query: Query<&mut Text, With<VirtualTime>>,
) {
for mut text in &mut query {
text.sections[0].value = format!(
"VIRTUAL TIME\nElapsed: {:.1}\nDelta: {:.5}\nSpeed: {:.2}",
time.elapsed_seconds(),
time.delta_seconds(),
time.relative_speed()
);
}
}