docs/bevy/examples/2d/rotate_to_cursor.rs 2.2 K · 59 lines · raw · history

1 //! Demonstrates rotating sprites to face the cursor.
2
3 use bevy::prelude::*;
4 use std::f32::consts::FRAC_PI_2;
5
6 fn main() {
7 App::new()
8 .add_plugins(DefaultPlugins)
9 .add_systems(Startup, setup)
10 .add_systems(FixedUpdate, player_movement_system)
11 .run();
12 }
13
14 /// Player component
15 #[derive(Component)]
16 struct Player;
17
18 /// Add the game's entities to our world and create an orthographic camera for 2D rendering.
19 ///
20 /// The Bevy coordinate system is the same for 2D and 3D, in terms of 2D this means that:
21 ///
22 /// * `X` axis goes from left to right (`+X` points right)
23 /// * `Y` axis goes from bottom to top (`+Y` point up)
24 /// * `Z` axis goes from far to near (`+Z` points towards you, out of the screen)
25 ///
26 /// The world origin in this case is at the center of the screen, but the camera could
27 /// move in which case the world origin would not be the center of the screen
28 fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
29 let ship_handle = asset_server.load("textures/simplespace/ship_C.png");
30
31 commands.spawn(Camera2d);
32
33 // Player controlled ship
34 commands.spawn((Sprite::from_image(ship_handle), Player));
35 }
36
37 /// Demonstrates applying rotation and movement based on keyboard input.
38 fn player_movement_system(
39 mut player: Single<&mut Transform, With<Player>>,
40 camera_query: Single<(&Camera, &GlobalTransform)>,
41 window: Single<&Window>,
42 ) {
43 let (camera, camera_transform) = *camera_query;
44
45 if let Some(cursor_position) = window.cursor_position()
46 // Calculate a world position based on the cursor's position.
47 && let Ok(cursor_world_pos) = camera.viewport_to_world_2d(camera_transform, cursor_position)
48 {
49 // The angle an entity needs to rotate to face a point is defined
50 // by the vector between the two points (Vec2 - Vec2), which we can then
51 // turn into radians using to_angle.
52 //
53 // FRAC_PI_2 is because our sprite's ship is facing "up" so we rotate it an additional 90 degrees
54 // so that it faces the cursor.
55 player.rotation = Quat::from_rotation_z(
56 (cursor_world_pos - player.translation.xy()).to_angle() - FRAC_PI_2,
57 );
58 }
59 }