eased_motion/
eased_motion.rs

1//! Demonstrates the application of easing curves to animate a transition.
2
3use std::f32::consts::FRAC_PI_2;
4
5use bevy::{
6    animation::{animated_field, AnimationTarget, AnimationTargetId},
7    color::palettes::css::{ORANGE, SILVER},
8    math::vec3,
9    prelude::*,
10};
11
12fn main() {
13    App::new()
14        .add_plugins(DefaultPlugins)
15        .add_systems(Startup, setup)
16        .run();
17}
18
19fn setup(
20    mut commands: Commands,
21    mut meshes: ResMut<Assets<Mesh>>,
22    mut materials: ResMut<Assets<StandardMaterial>>,
23    mut animation_graphs: ResMut<Assets<AnimationGraph>>,
24    mut animation_clips: ResMut<Assets<AnimationClip>>,
25) {
26    // Create the animation:
27    let AnimationInfo {
28        target_name: animation_target_name,
29        target_id: animation_target_id,
30        graph: animation_graph,
31        node_index: animation_node_index,
32    } = AnimationInfo::create(&mut animation_graphs, &mut animation_clips);
33
34    // Build an animation player that automatically plays the animation.
35    let mut animation_player = AnimationPlayer::default();
36    animation_player.play(animation_node_index).repeat();
37
38    // A cube together with the components needed to animate it
39    let cube_entity = commands
40        .spawn((
41            Mesh3d(meshes.add(Cuboid::from_length(2.0))),
42            MeshMaterial3d(materials.add(Color::from(ORANGE))),
43            Transform::from_translation(vec3(-6., 2., 0.)),
44            animation_target_name,
45            animation_player,
46            AnimationGraphHandle(animation_graph),
47        ))
48        .id();
49
50    commands.entity(cube_entity).insert(AnimationTarget {
51        id: animation_target_id,
52        player: cube_entity,
53    });
54
55    // Some light to see something
56    commands.spawn((
57        PointLight {
58            shadows_enabled: true,
59            intensity: 10_000_000.,
60            range: 100.0,
61            ..default()
62        },
63        Transform::from_xyz(8., 16., 8.),
64    ));
65
66    // Ground plane
67    commands.spawn((
68        Mesh3d(meshes.add(Plane3d::default().mesh().size(50., 50.))),
69        MeshMaterial3d(materials.add(Color::from(SILVER))),
70    ));
71
72    // The camera
73    commands.spawn((
74        Camera3d::default(),
75        Transform::from_xyz(0., 6., 12.).looking_at(Vec3::new(0., 1.5, 0.), Vec3::Y),
76    ));
77}
78
79// Holds information about the animation we programmatically create.
80struct AnimationInfo {
81    // The name of the animation target (in this case, the text).
82    target_name: Name,
83    // The ID of the animation target, derived from the name.
84    target_id: AnimationTargetId,
85    // The animation graph asset.
86    graph: Handle<AnimationGraph>,
87    // The index of the node within that graph.
88    node_index: AnimationNodeIndex,
89}
90
91impl AnimationInfo {
92    // Programmatically creates the UI animation.
93    fn create(
94        animation_graphs: &mut Assets<AnimationGraph>,
95        animation_clips: &mut Assets<AnimationClip>,
96    ) -> AnimationInfo {
97        // Create an ID that identifies the text node we're going to animate.
98        let animation_target_name = Name::new("Cube");
99        let animation_target_id = AnimationTargetId::from_name(&animation_target_name);
100
101        // Allocate an animation clip.
102        let mut animation_clip = AnimationClip::default();
103
104        // Each leg of the translation motion should take 3 seconds.
105        let animation_domain = interval(0.0, 3.0).unwrap();
106
107        // The easing curve is parametrized over [0, 1], so we reparametrize it and
108        // then ping-pong, which makes it spend another 3 seconds on the return journey.
109        let translation_curve = EasingCurve::new(
110            vec3(-6., 2., 0.),
111            vec3(6., 2., 0.),
112            EaseFunction::CubicInOut,
113        )
114        .reparametrize_linear(animation_domain)
115        .expect("this curve has bounded domain, so this should never fail")
116        .ping_pong()
117        .expect("this curve has bounded domain, so this should never fail");
118
119        // Something similar for rotation. The repetition here is an illusion caused
120        // by the symmetry of the cube; it rotates on the forward journey and never
121        // rotates back.
122        let rotation_curve = EasingCurve::new(
123            Quat::IDENTITY,
124            Quat::from_rotation_y(FRAC_PI_2),
125            EaseFunction::ElasticInOut,
126        )
127        .reparametrize_linear(interval(0.0, 4.0).unwrap())
128        .expect("this curve has bounded domain, so this should never fail");
129
130        animation_clip.add_curve_to_target(
131            animation_target_id,
132            AnimatableCurve::new(animated_field!(Transform::translation), translation_curve),
133        );
134        animation_clip.add_curve_to_target(
135            animation_target_id,
136            AnimatableCurve::new(animated_field!(Transform::rotation), rotation_curve),
137        );
138
139        // Save our animation clip as an asset.
140        let animation_clip_handle = animation_clips.add(animation_clip);
141
142        // Create an animation graph with that clip.
143        let (animation_graph, animation_node_index) =
144            AnimationGraph::from_clip(animation_clip_handle);
145        let animation_graph_handle = animation_graphs.add(animation_graph);
146
147        AnimationInfo {
148            target_name: animation_target_name,
149            target_id: animation_target_id,
150            graph: animation_graph_handle,
151            node_index: animation_node_index,
152        }
153    }
154}
eased_motion/eased_motion.rs

eased_motion/
eased_motion.rs
