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, AnimatedBy, 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
51        .entity(cube_entity)
52        .insert((animation_target_id, AnimatedBy(cube_entity)));
53
54    // Some light to see something
55    commands.spawn((
56        PointLight {
57            shadow_maps_enabled: true,
58            intensity: 10_000_000.,
59            range: 100.0,
60            ..default()
61        },
62        Transform::from_xyz(8., 16., 8.),
63    ));
64
65    // Ground plane
66    commands.spawn((
67        Mesh3d(meshes.add(Plane3d::default().mesh().size(50., 50.))),
68        MeshMaterial3d(materials.add(Color::from(SILVER))),
69    ));
70
71    // The camera
72    commands.spawn((
73        Camera3d::default(),
74        Transform::from_xyz(0., 6., 12.).looking_at(Vec3::new(0., 1.5, 0.), Vec3::Y),
75    ));
76}
77
78// Holds information about the animation we programmatically create.
79struct AnimationInfo {
80    // The name of the animation target (in this case, the text).
81    target_name: Name,
82    // The ID of the animation target, derived from the name.
83    target_id: AnimationTargetId,
84    // The animation graph asset.
85    graph: Handle<AnimationGraph>,
86    // The index of the node within that graph.
87    node_index: AnimationNodeIndex,
88}
89
90impl AnimationInfo {
91    // Programmatically creates the UI animation.
92    fn create(
93        animation_graphs: &mut Assets<AnimationGraph>,
94        animation_clips: &mut Assets<AnimationClip>,
95    ) -> AnimationInfo {
96        // Create an ID that identifies the text node we're going to animate.
97        let animation_target_name = Name::new("Cube");
98        let animation_target_id = AnimationTargetId::from_name(&animation_target_name);
99
100        // Allocate an animation clip.
101        let mut animation_clip = AnimationClip::default();
102
103        // Each leg of the translation motion should take 3 seconds.
104        let animation_domain = interval(0.0, 3.0).unwrap();
105
106        // The easing curve is parametrized over [0, 1], so we reparametrize it and
107        // then ping-pong, which makes it spend another 3 seconds on the return journey.
108        let translation_curve = EasingCurve::new(
109            vec3(-6., 2., 0.),
110            vec3(6., 2., 0.),
111            EaseFunction::CubicInOut,
112        )
113        .reparametrize_linear(animation_domain)
114        .expect("this curve has bounded domain, so this should never fail")
115        .ping_pong()
116        .expect("this curve has bounded domain, so this should never fail");
117
118        // Something similar for rotation. The repetition here is an illusion caused
119        // by the symmetry of the cube; it rotates on the forward journey and never
120        // rotates back.
121        let rotation_curve = EasingCurve::new(
122            Quat::IDENTITY,
123            Quat::from_rotation_y(FRAC_PI_2),
124            EaseFunction::ElasticInOut,
125        )
126        .reparametrize_linear(interval(0.0, 4.0).unwrap())
127        .expect("this curve has bounded domain, so this should never fail");
128
129        animation_clip.add_curve_to_target(
130            animation_target_id,
131            AnimatableCurve::new(animated_field!(Transform::translation), translation_curve),
132        );
133        animation_clip.add_curve_to_target(
134            animation_target_id,
135            AnimatableCurve::new(animated_field!(Transform::rotation), rotation_curve),
136        );
137
138        // Save our animation clip as an asset.
139        let animation_clip_handle = animation_clips.add(animation_clip);
140
141        // Create an animation graph with that clip.
142        let (animation_graph, animation_node_index) =
143            AnimationGraph::from_clip(animation_clip_handle);
144        let animation_graph_handle = animation_graphs.add(animation_graph);
145
146        AnimationInfo {
147            target_name: animation_target_name,
148            target_id: animation_target_id,
149            graph: animation_graph_handle,
150            node_index: animation_node_index,
151        }
152    }
153}
eased_motion/eased_motion.rs

eased_motion/
eased_motion.rs
