Add helper methods for rotating Transforms (bevyengine#5151)

# Objective
Users often ask for help with rotations as they struggle with `Quat`s.
`Quat` is rather complex and has a ton of verbose methods.

## Solution
Add rotation helper methods to `Transform`.


Co-authored-by: devil-ira <justthecooldude@gmail.com>

crates/bevy_animation/src/lib.rs

@@ -262,8 +262,8 @@ pub fn animation_player(
                                     rot_end = -rot_end;
                                 }
                                 // Rotations are using a spherical linear interpolation
-                                transform.rotation = Quat::from_array(rot_start.normalize().into())
-                                    .slerp(Quat::from_array(rot_end.normalize().into()), lerp);
+                                transform.rotation =
+                                    rot_start.normalize().slerp(rot_end.normalize(), lerp);
                             }
                             Keyframes::Translation(keyframes) => {
                                 let translation_start = keyframes[step_start];

crates/bevy_gltf/src/loader.rs

@@ -368,7 +368,7 @@ async fn load_gltf<'a, 'b>(
                         scale,
                     } => Transform {
                         translation: bevy_math::Vec3::from(translation),
-                        rotation: bevy_math::Quat::from_vec4(rotation.into()),
+                        rotation: bevy_math::Quat::from_array(rotation),
                         scale: bevy_math::Vec3::from(scale),
                     },
                 },

crates/bevy_transform/src/components/transform.rs

@@ -195,20 +195,81 @@ impl Transform {
         self.local_z()
     }
 
-    /// Rotates the transform by the given rotation.
+    /// Rotates this [`Transform`] by the given rotation.
     #[inline]
     pub fn rotate(&mut self, rotation: Quat) {
         self.rotation = rotation * self.rotation;
     }
 
-    /// Rotates this [`Transform`] around a point in space.
-    /// If the point is a zero vector, this will rotate around the parent (if any) or the origin.
+    /// Rotates this [`Transform`] around the given `axis` by `angle` (in radians).
+    ///
+    /// If this [`Transform`] has a parent, the `axis` is relative to the rotation of the parent.
+    #[inline]
+    pub fn rotate_axis(&mut self, axis: Vec3, angle: f32) {
+        self.rotate(Quat::from_axis_angle(axis, angle));
+    }
+
+    /// Rotates this [`Transform`] around the X axis by `angle` (in radians).
+    ///
+    /// If this [`Transform`] has a parent, the axis is relative to the rotation of the parent.
+    #[inline]
+    pub fn rotate_x(&mut self, angle: f32) {
+        self.rotate(Quat::from_rotation_x(angle));
+    }
+
+    /// Rotates this [`Transform`] around the Y axis by `angle` (in radians).
+    ///
+    /// If this [`Transform`] has a parent, the axis is relative to the rotation of the parent.
+    #[inline]
+    pub fn rotate_y(&mut self, angle: f32) {
+        self.rotate(Quat::from_rotation_y(angle));
+    }
+
+    /// Rotates this [`Transform`] around the Z axis by `angle` (in radians).
+    ///
+    /// If this [`Transform`] has a parent, the axis is relative to the rotation of the parent.
+    #[inline]
+    pub fn rotate_z(&mut self, angle: f32) {
+        self.rotate(Quat::from_rotation_z(angle));
+    }
+
+    /// Rotates this [`Transform`] around its X axis by `angle` (in radians).
+    #[inline]
+    pub fn rotate_local_x(&mut self, angle: f32) {
+        self.rotate_axis(self.local_x(), angle);
+    }
+
+    /// Rotates this [`Transform`] around its Y axis by `angle` (in radians).
+    #[inline]
+    pub fn rotate_local_y(&mut self, angle: f32) {
+        self.rotate_axis(self.local_y(), angle);
+    }
+
+    /// Rotates this [`Transform`] around its Z axis by `angle` (in radians).
+    #[inline]
+    pub fn rotate_local_z(&mut self, angle: f32) {
+        self.rotate_axis(self.local_z(), angle);
+    }
+
+    /// Rotates this [`Transform`] around a `point` in space.
+    ///
+    /// If this [`Transform`] has a parent, the `point` is relative to the [`Transform`] of the parent.
     #[inline]
     pub fn rotate_around(&mut self, point: Vec3, rotation: Quat) {
         self.translation = point + rotation * (self.translation - point);
         self.rotation *= rotation;
     }
 
+    /// Rotates this [`Transform`] so that its local negative z direction is toward
+    /// `target` and its local y direction is toward `up`.
+    #[inline]
+    pub fn look_at(&mut self, target: Vec3, up: Vec3) {
+        let forward = Vec3::normalize(self.translation - target);
+        let right = up.cross(forward).normalize();
+        let up = forward.cross(right);
+        self.rotation = Quat::from_mat3(&Mat3::from_cols(right, up, forward));
+    }
+
     /// Multiplies `self` with `transform` component by component, returning the
     /// resulting [`Transform`]
     #[inline]
@@ -239,16 +300,6 @@ impl Transform {
     pub fn apply_non_uniform_scale(&mut self, scale_factor: Vec3) {
         self.scale *= scale_factor;
     }
-
-    /// Rotates this [`Transform`] so that its local z direction is toward
-    /// `target` and its local y direction is toward `up`.
-    #[inline]
-    pub fn look_at(&mut self, target: Vec3, up: Vec3) {
-        let forward = Vec3::normalize(self.translation - target);
-        let right = up.cross(forward).normalize();
-        let up = forward.cross(right);
-        self.rotation = Quat::from_mat3(&Mat3::from_cols(right, up, forward));
-    }
 }
 
 impl Default for Transform {

examples/2d/rotation.rs

@@ -134,10 +134,8 @@ fn player_movement_system(
         movement_factor += 1.0;
     }
 
-    // create the change in rotation around the Z axis (perpendicular to the 2D plane of the screen)
-    let rotation_delta = Quat::from_rotation_z(rotation_factor * ship.rotation_speed * TIME_STEP);
-    // update the ship rotation with our rotation delta
-    transform.rotation *= rotation_delta;
+    // update the ship rotation around the Z axis (perpendicular to the 2D plane of the screen)
+    transform.rotate_z(rotation_factor * ship.rotation_speed * TIME_STEP);
 
     // get the ship's forward vector by applying the current rotation to the ships initial facing vector
     let movement_direction = transform.rotation * Vec3::Y;
@@ -168,7 +166,7 @@ fn snap_to_player_system(
 
         // get the quaternion to rotate from the initial enemy facing direction to the direction
         // facing the player
-        let rotate_to_player = Quat::from_rotation_arc(Vec3::Y, Vec3::from((to_player, 0.0)));
+        let rotate_to_player = Quat::from_rotation_arc(Vec3::Y, to_player.extend(0.));
 
         // rotate the enemy to face the player
         enemy_transform.rotation = rotate_to_player;
@@ -243,11 +241,7 @@ fn rotate_to_player_system(
         // calculate angle of rotation with limit
         let rotation_angle = rotation_sign * (config.rotation_speed * TIME_STEP).min(max_angle);
 
-        // get the quaternion to rotate from the current enemy facing direction towards the
-        // direction facing the player
-        let rotation_delta = Quat::from_rotation_z(rotation_angle);
-
         // rotate the enemy to face the player
-        enemy_transform.rotation *= rotation_delta;
+        enemy_transform.rotate_z(rotation_angle);
     }
 }

examples/3d/lighting.rs

@@ -34,7 +34,7 @@ fn setup(
 
     // left wall
     let mut transform = Transform::from_xyz(2.5, 2.5, 0.0);
-    transform.rotate(Quat::from_rotation_z(std::f32::consts::FRAC_PI_2));
+    transform.rotate_z(std::f32::consts::FRAC_PI_2);
     commands.spawn_bundle(PbrBundle {
         mesh: meshes.add(Mesh::from(shape::Box::new(5.0, 0.15, 5.0))),
         transform,
@@ -47,7 +47,7 @@ fn setup(
     });
     // back (right) wall
     let mut transform = Transform::from_xyz(0.0, 2.5, -2.5);
-    transform.rotate(Quat::from_rotation_x(std::f32::consts::FRAC_PI_2));
+    transform.rotate_x(std::f32::consts::FRAC_PI_2);
     commands.spawn_bundle(PbrBundle {
         mesh: meshes.add(Mesh::from(shape::Box::new(5.0, 0.15, 5.0))),
         transform,
@@ -214,7 +214,7 @@ fn animate_light_direction(
     mut query: Query<&mut Transform, With<DirectionalLight>>,
 ) {
     for mut transform in query.iter_mut() {
-        transform.rotate(Quat::from_rotation_y(time.delta_seconds() * 0.5));
+        transform.rotate_y(time.delta_seconds() * 0.5);
     }
 }
 

examples/3d/parenting.rs

@@ -18,7 +18,7 @@ struct Rotator;
 /// rotates the parent, which will result in the child also rotating
 fn rotator_system(time: Res<Time>, mut query: Query<&mut Transform, With<Rotator>>) {
     for mut transform in query.iter_mut() {
-        transform.rotation *= Quat::from_rotation_x(3.0 * time.delta_seconds());
+        transform.rotate_x(3.0 * time.delta_seconds());
     }
 }
 

examples/3d/render_to_texture.rs

@@ -145,15 +145,15 @@ fn setup(
 /// Rotates the inner cube (first pass)
 fn rotator_system(time: Res<Time>, mut query: Query<&mut Transform, With<FirstPassCube>>) {
     for mut transform in query.iter_mut() {
-        transform.rotation *= Quat::from_rotation_x(1.5 * time.delta_seconds());
-        transform.rotation *= Quat::from_rotation_z(1.3 * time.delta_seconds());
+        transform.rotate_x(1.5 * time.delta_seconds());
+        transform.rotate_z(1.3 * time.delta_seconds());
     }
 }
 
 /// Rotates the outer cube (main pass)
 fn cube_rotator_system(time: Res<Time>, mut query: Query<&mut Transform, With<MainPassCube>>) {
     for mut transform in query.iter_mut() {
-        transform.rotation *= Quat::from_rotation_x(1.0 * time.delta_seconds());
-        transform.rotation *= Quat::from_rotation_y(0.7 * time.delta_seconds());
+        transform.rotate_x(1.0 * time.delta_seconds());
+        transform.rotate_y(0.7 * time.delta_seconds());
     }
 }

examples/3d/shapes.rs

@@ -53,6 +53,7 @@ fn setup(
                         2.0,
                         0.0,
                     ),
+                    rotation: Quat::from_rotation_x(-std::f32::consts::PI / 4.),
                     ..default()
                 },
                 ..default()
@@ -86,8 +87,7 @@ fn setup(
 
 fn rotate(mut query: Query<&mut Transform, With<Shape>>, time: Res<Time>) {
     for mut transform in query.iter_mut() {
-        transform.rotation = Quat::from_rotation_y(time.seconds_since_startup() as f32 / 2.)
-            * Quat::from_rotation_x(-std::f32::consts::PI / 4.);
+        transform.rotate_y(time.delta_seconds() / 2.);
     }
 }
 

examples/ecs/hierarchy.rs

@@ -94,14 +94,14 @@ fn rotate(
     let angle = std::f32::consts::PI / 2.0;
     for (parent, children) in parents_query.iter_mut() {
         if let Ok(mut transform) = transform_query.get_mut(parent) {
-            transform.rotate(Quat::from_rotation_z(-angle * time.delta_seconds()));
+            transform.rotate_z(-angle * time.delta_seconds());
         }
 
         // To iterate through the entities children, just treat the Children component as a Vec
         // Alternatively, you could query entities that have a Parent component
         for child in children.iter() {
             if let Ok(mut transform) = transform_query.get_mut(*child) {
-                transform.rotate(Quat::from_rotation_z(angle * 2.0 * time.delta_seconds()));
+                transform.rotate_z(angle * 2.0 * time.delta_seconds());
             }
         }
 

examples/games/alien_cake_addict.rs

@@ -348,7 +348,7 @@ fn spawn_bonus(
 fn rotate_bonus(game: Res<Game>, time: Res<Time>, mut transforms: Query<&mut Transform>) {
     if let Some(entity) = game.bonus.entity {
         if let Ok(mut cake_transform) = transforms.get_mut(entity) {
-            cake_transform.rotate(Quat::from_rotation_y(time.delta_seconds()));
+            cake_transform.rotate_y(time.delta_seconds());
             cake_transform.scale = Vec3::splat(
                 1.0 + (game.score as f32 / 10.0 * time.seconds_since_startup().sin() as f32).abs(),
             );

examples/games/contributors.rs

@@ -301,7 +301,7 @@ fn move_system(time: Res<Time>, mut query: Query<(&Velocity, &mut Transform)>) {
 
     for (velocity, mut transform) in query.iter_mut() {
         transform.translation += delta * velocity.translation;
-        transform.rotate(Quat::from_rotation_z(velocity.rotation * delta));
+        transform.rotate_z(velocity.rotation * delta);
     }
 }
 

examples/shader/post_processing.rs

@@ -158,8 +158,8 @@ fn main_camera_cube_rotator_system(
     mut query: Query<&mut Transform, With<MainCube>>,
 ) {
     for mut transform in query.iter_mut() {
-        transform.rotation *= Quat::from_rotation_x(0.55 * time.delta_seconds());
-        transform.rotation *= Quat::from_rotation_z(0.15 * time.delta_seconds());
+        transform.rotate_x(0.55 * time.delta_seconds());
+        transform.rotate_z(0.15 * time.delta_seconds());
     }
 }
 

examples/stress_tests/many_cubes.rs

@@ -149,8 +149,9 @@ fn spherical_polar_to_cartesian(p: DVec2) -> DVec3 {
 // System for rotating the camera
 fn move_camera(time: Res<Time>, mut camera_query: Query<&mut Transform, With<Camera>>) {
     let mut camera_transform = camera_query.single_mut();
-    camera_transform.rotate(Quat::from_rotation_z(time.delta_seconds() * 0.15));
-    camera_transform.rotate(Quat::from_rotation_x(time.delta_seconds() * 0.15));
+    let delta = time.delta_seconds() * 0.15;
+    camera_transform.rotate_z(delta);
+    camera_transform.rotate_x(delta);
 }
 
 // System for printing the number of meshes on every tick of the timer

examples/stress_tests/many_foxes.rs

@@ -204,9 +204,7 @@ fn update_fox_rings(
     let dt = time.delta_seconds();
     for (ring, rotation_direction, mut transform) in rings.iter_mut() {
         let angular_velocity = foxes.speed / ring.radius;
-        transform.rotate(Quat::from_rotation_y(
-            rotation_direction.sign() * angular_velocity * dt,
-        ));
+        transform.rotate_y(rotation_direction.sign() * angular_velocity * dt);
     }
 }
 

examples/stress_tests/many_lights.rs

@@ -124,8 +124,9 @@ fn spherical_polar_to_cartesian(p: DVec2) -> DVec3 {
 // System for rotating the camera
 fn move_camera(time: Res<Time>, mut camera_query: Query<&mut Transform, With<Camera>>) {
     let mut camera_transform = camera_query.single_mut();
-    camera_transform.rotate(Quat::from_rotation_z(time.delta_seconds() * 0.15));
-    camera_transform.rotate(Quat::from_rotation_x(time.delta_seconds() * 0.15));
+    let delta = time.delta_seconds() * 0.15;
+    camera_transform.rotate_z(delta);
+    camera_transform.rotate_x(delta);
 }
 
 // System for printing the number of meshes on every tick of the timer

examples/stress_tests/many_sprites.rs

@@ -74,7 +74,7 @@ fn setup(mut commands: Commands, assets: Res<AssetServer>) {
 // System for rotating and translating the camera
 fn move_camera(time: Res<Time>, mut camera_query: Query<&mut Transform, With<Camera>>) {
     let mut camera_transform = camera_query.single_mut();
-    camera_transform.rotate(Quat::from_rotation_z(time.delta_seconds() * 0.5));
+    camera_transform.rotate_z(time.delta_seconds() * 0.5);
     *camera_transform = *camera_transform
         * Transform::from_translation(Vec3::X * CAMERA_SPEED * time.delta_seconds());
 }

examples/tools/scene_viewer.rs

@@ -14,6 +14,8 @@ use bevy::{
     scene::InstanceId,
 };
 
+use std::f32::consts::TAU;
+
 #[derive(Debug, Hash, PartialEq, Eq, Clone, SystemLabel)]
 struct CameraControllerCheckSystem;
 
@@ -327,8 +329,8 @@ fn update_lights(
             transform.rotation = Quat::from_euler(
                 EulerRot::ZYX,
                 0.0,
-                time.seconds_since_startup() as f32 * std::f32::consts::TAU / 30.0,
-                -std::f32::consts::FRAC_PI_4,
+                time.seconds_since_startup() as f32 * TAU / 30.0,
+                -TAU / 8.,
             );
         }
     }

examples/transforms/3d_rotation.rs

@@ -1,10 +1,8 @@
-//! Illustrates how to (constantly) rotate an object around an axis.
+//! Illustrates how to rotate an object around an axis.
 
 use bevy::prelude::*;
 
-use std::f32::consts::PI;
-
-const FULL_TURN: f32 = 2.0 * PI;
+use std::f32::consts::TAU;
 
 // Define a component to designate a rotation speed to an entity.
 #[derive(Component)]
@@ -41,19 +39,19 @@ fn setup(
         ..default()
     });
 
-    // Add a light source for better 3d visibility.
+    // Add a light source so we can see clearly.
     commands.spawn_bundle(PointLightBundle {
         transform: Transform::from_translation(Vec3::ONE * 3.0),
         ..default()
     });
 }
 
-// This system will rotate any entity in the scene with an assigned Rotatable around its z-axis.
+// This system will rotate any entity in the scene with a Rotatable component around its y-axis.
 fn rotate_cube(mut cubes: Query<(&mut Transform, &Rotatable)>, timer: Res<Time>) {
     for (mut transform, cube) in cubes.iter_mut() {
-        // The speed is taken as a percentage of a full 360 degree turn.
-        // The timers delta_seconds is used to smooth out the movement.
-        let rotation_change = Quat::from_rotation_y(FULL_TURN * cube.speed * timer.delta_seconds());
-        transform.rotate(rotation_change);
+        // The speed is first multiplied by TAU which is a full rotation (360deg) in radians,
+        // and then multiplied by delta_seconds which is the time that passed last frame.
+        // In other words. Speed is equal to the amount of rotations per second.
+        transform.rotate_y(cube.speed * TAU * timer.delta_seconds());
     }
 }

examples/transforms/transform.rs

@@ -60,8 +60,8 @@ fn setup(
     // Define a start transform for an orbiting cube, that's away from our central object (sphere)
     // and rotate it so it will be able to move around the sphere and not towards it.
     let angle_90 = PI / 2.0;
-    let mut cube_spawn = Transform::from_translation(Vec3::Z * -10.0);
-    cube_spawn.rotation = Quat::from_rotation_y(angle_90);
+    let cube_spawn =
+        Transform::from_translation(Vec3::Z * -10.0).with_rotation(Quat::from_rotation_y(angle_90));
     commands
         .spawn_bundle(PbrBundle {
             mesh: meshes.add(Mesh::from(shape::Cube { size: 1.0 })),