mirror of
https://github.com/bevyengine/bevy
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93a131661d
# Objective - Added a bunch of backticks to things that should have them, like equations, abstract variable names, - Changed all small x, y, and z to capitals X, Y, Z. This might be more annoying than helpful; Feel free to refuse this PR.
243 lines
10 KiB
Rust
243 lines
10 KiB
Rust
//! Demonstrates rotating entities in 2D using quaternions.
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use bevy::{math::Vec3Swizzles, prelude::*, time::FixedTimestep};
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const TIME_STEP: f32 = 1.0 / 60.0;
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const BOUNDS: Vec2 = Vec2::new(1200.0, 640.0);
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fn main() {
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App::new()
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.add_plugins(DefaultPlugins)
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.add_startup_system(setup)
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.add_system_set(
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SystemSet::new()
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.with_run_criteria(FixedTimestep::step(TIME_STEP as f64))
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.with_system(player_movement_system)
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.with_system(snap_to_player_system)
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.with_system(rotate_to_player_system),
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)
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.add_system(bevy::window::close_on_esc)
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.run();
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}
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/// player component
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#[derive(Component)]
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struct Player {
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/// linear speed in meters per second
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movement_speed: f32,
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/// rotation speed in radians per second
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rotation_speed: f32,
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}
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/// snap to player ship behavior
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#[derive(Component)]
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struct SnapToPlayer;
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/// rotate to face player ship behavior
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#[derive(Component)]
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struct RotateToPlayer {
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/// rotation speed in radians per second
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rotation_speed: f32,
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}
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/// Add the game's entities to our world and creates an orthographic camera for 2D rendering.
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///
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/// The Bevy coordinate system is the same for 2D and 3D, in terms of 2D this means that:
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///
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/// * `X` axis goes from left to right (`+X` points right)
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/// * `Y` axis goes from bottom to top (`+Y` point up)
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/// * `Z` axis goes from far to near (`+Z` points towards you, out of the screen)
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///
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/// The origin is at the center of the screen.
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fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
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let ship_handle = asset_server.load("textures/simplespace/ship_C.png");
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let enemy_a_handle = asset_server.load("textures/simplespace/enemy_A.png");
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let enemy_b_handle = asset_server.load("textures/simplespace/enemy_B.png");
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// 2D orthographic camera
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commands.spawn_bundle(Camera2dBundle::default());
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let horizontal_margin = BOUNDS.x / 4.0;
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let vertical_margin = BOUNDS.y / 4.0;
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// player controlled ship
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commands
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.spawn_bundle(SpriteBundle {
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texture: ship_handle,
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..default()
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})
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.insert(Player {
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movement_speed: 500.0, // metres per second
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rotation_speed: f32::to_radians(360.0), // degrees per second
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});
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// enemy that snaps to face the player spawns on the bottom and left
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commands
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.spawn_bundle(SpriteBundle {
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texture: enemy_a_handle.clone(),
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transform: Transform::from_xyz(0.0 - horizontal_margin, 0.0, 0.0),
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..default()
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})
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.insert(SnapToPlayer);
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commands
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.spawn_bundle(SpriteBundle {
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texture: enemy_a_handle,
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transform: Transform::from_xyz(0.0, 0.0 - vertical_margin, 0.0),
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..default()
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})
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.insert(SnapToPlayer);
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// enemy that rotates to face the player enemy spawns on the top and right
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commands
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.spawn_bundle(SpriteBundle {
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texture: enemy_b_handle.clone(),
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transform: Transform::from_xyz(0.0 + horizontal_margin, 0.0, 0.0),
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..default()
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})
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.insert(RotateToPlayer {
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rotation_speed: f32::to_radians(45.0), // degrees per second
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});
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commands
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.spawn_bundle(SpriteBundle {
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texture: enemy_b_handle,
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transform: Transform::from_xyz(0.0, 0.0 + vertical_margin, 0.0),
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..default()
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})
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.insert(RotateToPlayer {
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rotation_speed: f32::to_radians(90.0), // degrees per second
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});
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}
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/// Demonstrates applying rotation and movement based on keyboard input.
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fn player_movement_system(
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keyboard_input: Res<Input<KeyCode>>,
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mut query: Query<(&Player, &mut Transform)>,
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) {
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let (ship, mut transform) = query.single_mut();
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let mut rotation_factor = 0.0;
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let mut movement_factor = 0.0;
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if keyboard_input.pressed(KeyCode::Left) {
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rotation_factor += 1.0;
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}
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if keyboard_input.pressed(KeyCode::Right) {
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rotation_factor -= 1.0;
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}
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if keyboard_input.pressed(KeyCode::Up) {
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movement_factor += 1.0;
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}
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// update the ship rotation around the Z axis (perpendicular to the 2D plane of the screen)
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transform.rotate_z(rotation_factor * ship.rotation_speed * TIME_STEP);
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// get the ship's forward vector by applying the current rotation to the ships initial facing vector
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let movement_direction = transform.rotation * Vec3::Y;
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// get the distance the ship will move based on direction, the ship's movement speed and delta time
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let movement_distance = movement_factor * ship.movement_speed * TIME_STEP;
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// create the change in translation using the new movement direction and distance
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let translation_delta = movement_direction * movement_distance;
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// update the ship translation with our new translation delta
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transform.translation += translation_delta;
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// bound the ship within the invisible level bounds
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let extents = Vec3::from((BOUNDS / 2.0, 0.0));
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transform.translation = transform.translation.min(extents).max(-extents);
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}
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/// Demonstrates snapping the enemy ship to face the player ship immediately.
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fn snap_to_player_system(
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mut query: Query<&mut Transform, (With<SnapToPlayer>, Without<Player>)>,
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player_query: Query<&Transform, With<Player>>,
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) {
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let player_transform = player_query.single();
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// get the player translation in 2D
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let player_translation = player_transform.translation.xy();
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for mut enemy_transform in &mut query {
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// get the vector from the enemy ship to the player ship in 2D and normalize it.
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let to_player = (player_translation - enemy_transform.translation.xy()).normalize();
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// get the quaternion to rotate from the initial enemy facing direction to the direction
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// facing the player
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let rotate_to_player = Quat::from_rotation_arc(Vec3::Y, to_player.extend(0.));
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// rotate the enemy to face the player
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enemy_transform.rotation = rotate_to_player;
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}
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}
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/// Demonstrates rotating an enemy ship to face the player ship at a given rotation speed.
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///
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/// This method uses the vector dot product to determine if the enemy is facing the player and
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/// if not, which way to rotate to face the player. The dot product on two unit length vectors
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/// will return a value between -1.0 and +1.0 which tells us the following about the two vectors:
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///
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/// * If the result is 1.0 the vectors are pointing in the same direction, the angle between them
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/// is 0 degrees.
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/// * If the result is 0.0 the vectors are perpendicular, the angle between them is 90 degrees.
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/// * If the result is -1.0 the vectors are parallel but pointing in opposite directions, the angle
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/// between them is 180 degrees.
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/// * If the result is positive the vectors are pointing in roughly the same direction, the angle
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/// between them is greater than 0 and less than 90 degrees.
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/// * If the result is negative the vectors are pointing in roughly opposite directions, the angle
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/// between them is greater than 90 and less than 180 degrees.
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///
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/// It is possible to get the angle by taking the arc cosine (`acos`) of the dot product. It is
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/// often unnecessary to do this though. Beware than `acos` will return `NaN` if the input is less
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/// than -1.0 or greater than 1.0. This can happen even when working with unit vectors due to
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/// floating point precision loss, so it pays to clamp your dot product value before calling
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/// `acos`.
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fn rotate_to_player_system(
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mut query: Query<(&RotateToPlayer, &mut Transform), Without<Player>>,
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player_query: Query<&Transform, With<Player>>,
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) {
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let player_transform = player_query.single();
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// get the player translation in 2D
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let player_translation = player_transform.translation.xy();
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for (config, mut enemy_transform) in &mut query {
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// get the enemy ship forward vector in 2D (already unit length)
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let enemy_forward = (enemy_transform.rotation * Vec3::Y).xy();
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// get the vector from the enemy ship to the player ship in 2D and normalize it.
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let to_player = (player_translation - enemy_transform.translation.xy()).normalize();
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// get the dot product between the enemy forward vector and the direction to the player.
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let forward_dot_player = enemy_forward.dot(to_player);
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// if the dot product is approximately 1.0 then the enemy is already facing the player and
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// we can early out.
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if (forward_dot_player - 1.0).abs() < f32::EPSILON {
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continue;
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}
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// get the right vector of the enemy ship in 2D (already unit length)
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let enemy_right = (enemy_transform.rotation * Vec3::X).xy();
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// get the dot product of the enemy right vector and the direction to the player ship.
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// if the dot product is negative them we need to rotate counter clockwise, if it is
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// positive we need to rotate clockwise. Note that `copysign` will still return 1.0 if the
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// dot product is 0.0 (because the player is directly behind the enemy, so perpendicular
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// with the right vector).
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let right_dot_player = enemy_right.dot(to_player);
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// determine the sign of rotation from the right dot player. We need to negate the sign
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// here as the 2D bevy co-ordinate system rotates around +Z, which is pointing out of the
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// screen. Due to the right hand rule, positive rotation around +Z is counter clockwise and
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// negative is clockwise.
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let rotation_sign = -f32::copysign(1.0, right_dot_player);
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// limit rotation so we don't overshoot the target. We need to convert our dot product to
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// an angle here so we can get an angle of rotation to clamp against.
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let max_angle = forward_dot_player.clamp(-1.0, 1.0).acos(); // clamp acos for safety
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// calculate angle of rotation with limit
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let rotation_angle = rotation_sign * (config.rotation_speed * TIME_STEP).min(max_angle);
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// rotate the enemy to face the player
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enemy_transform.rotate_z(rotation_angle);
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}
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}
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