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Fix incorrect rotation in Transform::rotate_around. (#5300)

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Someone noted that the `rotate_around` method did not give the results they expected: [discord thread](https://discord.com/channels/691052431525675048/996497295325544479)
I tested `rotate_around` and their workaround and it seems like it was indeed incorrect.

Here is a scene with some cubes at different angles all being rotated around the center on the Y axis.

https://user-images.githubusercontent.com/29694403/178598432-407d7e80-1caf-4b17-b69b-66d9156c81e1.mp4

Interestingly, the middle cube rotates as you might expect. This threw me for a bit of a loop before I added the other cubes to the test haha.

Here is the same scene with the order multiplication of the quaternions flipped in `rotate_around`.

https://user-images.githubusercontent.com/29694403/178598446-a98026f3-524c-448b-8437-4d0d3175c6ca.mp4

That looks better :)

## Changelog

* Fixed `rotate_around` rotating the wrong way around
* Added `translate_around`. - Split out the translation code from `rotate_around`.
* Simplified/optimized `rotate_local_*` methods. - Yep, That works somehow.

<sup>Quaternions sure are wacky. Do not ask me how this works exactly, haha.</sup>

Co-authored-by: devil-ira <justthecooldude@gmail.com>
This commit is contained in:
ira 2022-07-13 15:10:43 +00:00
parent 2f9a886c55
commit 56d69c1427
2 changed files with 33 additions and 9 deletions
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2
crates/bevy_transform/src/components/global_transform.rs
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@ -202,7 +202,7 @@ impl GlobalTransform {
#[inline] #[inline]
pub fn rotate_around(&mut self, point: Vec3, rotation: Quat) { pub fn rotate_around(&mut self, point: Vec3, rotation: Quat) {
self.translation = point + rotation * (self.translation - point); self.translation = point + rotation * (self.translation - point);
self.rotation *= rotation; self.rotate(rotation);
} }
/// Multiplies `self` with `transform` component by component, returning the /// Multiplies `self` with `transform` component by component, returning the

40
crates/bevy_transform/src/components/transform.rs
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@ -196,6 +196,8 @@ impl Transform {
} }
/// Rotates this [`Transform`] by the given rotation. /// Rotates this [`Transform`] by the given rotation.
///
/// If this [`Transform`] has a parent, the `rotation` is relative to the rotation of the parent.
#[inline] #[inline]
pub fn rotate(&mut self, rotation: Quat) { pub fn rotate(&mut self, rotation: Quat) {
self.rotation = rotation * self.rotation; self.rotation = rotation * self.rotation;
@ -233,22 +235,44 @@ impl Transform {
self.rotate(Quat::from_rotation_z(angle)); self.rotate(Quat::from_rotation_z(angle));
} }
/// Rotates this [`Transform`] around its `X` axis by `angle` (in radians). /// Rotates this [`Transform`] by the given `rotation`.
///
/// The `rotation` is relative to this [`Transform`]'s current rotation.
#[inline]
pub fn rotate_local(&mut self, rotation: Quat) {
self.rotation *= rotation;
}
/// Rotates this [`Transform`] around its local `axis` by `angle` (in radians).
#[inline]
pub fn rotate_local_axis(&mut self, axis: Vec3, angle: f32) {
self.rotate_local(Quat::from_axis_angle(axis, angle));
}
/// Rotates this [`Transform`] around its local `X` axis by `angle` (in radians).
#[inline] #[inline]
pub fn rotate_local_x(&mut self, angle: f32) { pub fn rotate_local_x(&mut self, angle: f32) {
self.rotate_axis(self.local_x(), angle); self.rotate_local(Quat::from_rotation_x(angle));
} }
/// Rotates this [`Transform`] around its `Y` axis by `angle` (in radians). /// Rotates this [`Transform`] around its local `Y` axis by `angle` (in radians).
#[inline] #[inline]
pub fn rotate_local_y(&mut self, angle: f32) { pub fn rotate_local_y(&mut self, angle: f32) {
self.rotate_axis(self.local_y(), angle); self.rotate_local(Quat::from_rotation_y(angle));
} }
/// Rotates this [`Transform`] around its `Z` axis by `angle` (in radians). /// Rotates this [`Transform`] around its local `Z` axis by `angle` (in radians).
#[inline] #[inline]
pub fn rotate_local_z(&mut self, angle: f32) { pub fn rotate_local_z(&mut self, angle: f32) {
self.rotate_axis(self.local_z(), angle); self.rotate_local(Quat::from_rotation_z(angle));
}
/// Translates 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 translate_around(&mut self, point: Vec3, rotation: Quat) {
self.translation = point + rotation * (self.translation - point);
} }
/// Rotates this [`Transform`] around a `point` in space. /// Rotates this [`Transform`] around a `point` in space.
@ -256,8 +280,8 @@ impl Transform {
/// If this [`Transform`] has a parent, the `point` is relative to the [`Transform`] of the parent. /// If this [`Transform`] has a parent, the `point` is relative to the [`Transform`] of the parent.
#[inline] #[inline]
pub fn rotate_around(&mut self, point: Vec3, rotation: Quat) { pub fn rotate_around(&mut self, point: Vec3, rotation: Quat) {
self.translation = point + rotation * (self.translation - point); self.translate_around(point, rotation);
self.rotation *= rotation; self.rotate(rotation);
} }
/// Rotates this [`Transform`] so that its local negative `Z` direction is toward /// Rotates this [`Transform`] so that its local negative `Z` direction is toward