# Objective
The documentation for
[`Transform::align`](https://docs.rs/bevy/0.14.0-rc.3/bevy/transform/components/struct.Transform.html#method.align)
mentions a hypothetical ship model. Showing this concretely would be a
nice improvement over using a cube.
> For example, if a spaceship model has its nose pointing in the
X-direction in its own local coordinates and its dorsal fin pointing in
the Y-direction, then align(Dir3::X, v, Dir3::Y, w) will make the
spaceship’s nose point in the direction of v, while the dorsal fin does
its best to point in the direction w.
## Solution
This commit makes the ship less hypothetical by using a kenney ship
model in the example.
The local axes for the ship needed to change to accommodate the gltf, so
the hypothetical in the documentation and this example's local axes
don't necessarily match. Docs use `align(Dir3::X, v, Dir3::Y, w)` and
this example now uses `(Vec3::NEG_Z, *first, Vec3::X, *second)`.
I manually modified the `craft_speederD` Node's `translation` to be
0,0,0 in the gltf file, which means it now differs from kenney's
original model.
Original ship from: https://kenney.nl/assets/space-kit
## Testing
```
cargo run --example align
```
# Objective
- The default font size is too small to be useful in examples or for
debug text.
- Fixes#13587
## Solution
- Updated the default font size value in `TextStyle` from 12px to 24px.
- Resorted to Text defaults in examples to use the default font size in
most of them.
## Testing
- WIP
---
## Migration Guide
- The default font size has been increased to 24px from 12px. Make sure
you set the font to the appropriate values in places you were using
`Default` text style.
# Objective
Since `align` was introduced, it has been reworked to allow the input of
`Dir3` instead of `Vec3`, and we also introduced random sampling for
points on a sphere and then for `Dir3`. Previously, this example rolled
its own random generation, but it doesn't need to any more.
## Solution
Refactor the 'align' example to use `Dir3` instead of `Vec3`, using the
`bevy_math` API for random directions.
# Objective
- There are several redundant imports in the tests and examples that are
not caught by CI because additional flags need to be passed.
## Solution
- Run `cargo check --workspace --tests` and `cargo check --workspace
--examples`, then fix all warnings.
- Add `test-check` to CI, which will be run in the check-compiles job.
This should catch future warnings for tests. Examples are already
checked, but I'm not yet sure why they weren't caught.
## Discussion
- Should the `--tests` and `--examples` flags be added to CI, so this is
caught in the future?
- If so, #12818 will need to be merged first. It was also a warning
raised by checking the examples, but I chose to split off into a
separate PR.
---------
Co-authored-by: François Mockers <francois.mockers@vleue.com>
# Objective
Fixes issue #12613 - the RNG used in examples is _deterministic_, but
its implementation is not _portable_ across platforms. We want to switch
to using a portable RNG that does not vary across platforms, to ensure
certain examples play out the same way every time.
## Solution
Replace all occurences of `rand::rngs::StdRng` with
`rand_chacha::ChaCha8Rng`, as recommended in issue #12613
---
## Changelog
- Add `rand_chacha` as a new dependency (controversial?)
- Replace all occurences of `rand::rngs::StdRng` with
`rand_chacha::ChaCha8Rng`
# Objective
- Closes#11793
- Introduces a general API for aligning local coordinates of Transforms
with given vectors.
## Solution
- We introduce `Transform::align`, which allows a rotation to be
specified by four pieces of alignment data, as explained by the
documentation:
````rust
/// Rotates this [`Transform`] so that the `main_axis` vector, reinterpreted in local coordinates, points
/// in the given `main_direction`, while `secondary_axis` points towards `secondary_direction`.
///
/// For example, if a spaceship model has its nose pointing in the X-direction in its own local coordinates
/// and its dorsal fin pointing in the Y-direction, then `align(Vec3::X, v, Vec3::Y, w)` will make the spaceship's
/// nose point in the direction of `v`, while the dorsal fin does its best to point in the direction `w`.
///
/// More precisely, the [`Transform::rotation`] produced will be such that:
/// * applying it to `main_axis` results in `main_direction`
/// * applying it to `secondary_axis` produces a vector that lies in the half-plane generated by `main_direction` and
/// `secondary_direction` (with positive contribution by `secondary_direction`)
///
/// [`Transform::look_to`] is recovered, for instance, when `main_axis` is `Vec3::NEG_Z` (the [`Transform::forward`]
/// direction in the default orientation) and `secondary_axis` is `Vec3::Y` (the [`Transform::up`] direction in the default
/// orientation). (Failure cases may differ somewhat.)
///
/// In some cases a rotation cannot be constructed. Another axis will be picked in those cases:
/// * if `main_axis` or `main_direction` is zero, `Vec3::X` takes its place
/// * if `secondary_axis` or `secondary_direction` is zero, `Vec3::Y` takes its place
/// * if `main_axis` is parallel with `secondary_axis` or `main_direction` is parallel with `secondary_direction`,
/// a rotation is constructed which takes `main_axis` to `main_direction` along a great circle, ignoring the secondary
/// counterparts
///
/// Example
/// ```
/// # use bevy_math::{Vec3, Quat};
/// # use bevy_transform::components::Transform;
/// let mut t1 = Transform::IDENTITY;
/// let mut t2 = Transform::IDENTITY;
/// t1.align(Vec3::ZERO, Vec3::Z, Vec3::ZERO, Vec3::X);
/// t2.align(Vec3::X, Vec3::Z, Vec3::Y, Vec3::X);
/// assert_eq!(t1.rotation, t2.rotation);
///
/// t1.align(Vec3::X, Vec3::Z, Vec3::X, Vec3::Y);
/// assert_eq!(t1.rotation, Quat::from_rotation_arc(Vec3::X, Vec3::Z));
/// ```
pub fn align(
&mut self,
main_axis: Vec3,
main_direction: Vec3,
secondary_axis: Vec3,
secondary_direction: Vec3,
) { //... }
````
- We introduce `Transform::aligned_by`, the returning-Self version of
`align`:
````rust
pub fn aligned_by(
mut self,
main_axis: Vec3,
main_direction: Vec3,
secondary_axis: Vec3,
secondary_direction: Vec3,
) -> Self { //... }
````
- We introduce an example (examples/transforms/align.rs) that shows the
usage of this API. It is likely to be mathier than most other
`Transform` APIs, so when run, the example demonstrates what the API
does in space:
<img width="1440" alt="Screenshot 2024-03-12 at 11 01 19 AM"
src="https://github.com/bevyengine/bevy/assets/2975848/884b3cc3-cbd9-48ae-8f8c-49a677c59dfe">
---
## Changelog
- Added methods `align`, `aligned_by` to `Transform`.
- Added transforms/align.rs to examples.
---
## Discussion
### On the form of `align`
The original issue linked above suggests an API similar to that of the
existing `Transform::look_to` method:
````rust
pub fn align_to(&mut self, direction: Vec3, up: Vec3) { //... }
````
Not allowing an input axis of some sort that is to be aligned with
`direction` would not really solve the problem in the issue, since the
user could easily be in a scenario where they have to compose with
another rotation on their own (undesirable). This leads to something
like:
````rust
pub fn align_to(&mut self, axis: Vec3, direction: Vec3, up: Vec3) { //... }
````
However, this still has two problems:
- If the vector that the user wants to align is parallel to the Y-axis,
then the API basically does not work (we cannot fully specify a
rotation)
- More generally, it does not give the user the freedom to specify which
direction is to be treated as the local "up" direction, so it fails as a
general alignment API
Specifying both leads us to the present situation, with two local axis
inputs (`main_axis` and `secondary_axis`) and two target directions
(`main_direction` and `secondary_direction`). This might seem a little
cumbersome for general use, but for the time being I stand by the
decision not to expand further without prompting from users. I'll expand
on this below.
### Additional APIs?
Presently, this PR introduces only `align` and `aligned_by`. Other
potentially useful bundles of API surface arrange into a few different
categories:
1. Inferring direction from position, a la `Transform::look_at`, which
might look something like this:
````rust
pub fn align_at(&mut self, axis: Vec3, target: Vec3, up: Vec3) {
self.align(axis, target - self.translation, Vec3::Y, up);
}
````
(This is simple but still runs into issues when the user wants to point
the local Y-axis somewhere.)
2. Filling in some data for the user for common use-cases; e.g.:
````rust
pub fn align_x(&mut self, direction: Vec3, up: Vec3) {
self.align(Vec3::X, direction, Vec3::Y, up);
}
````
(Here, use of the `up` vector doesn't lose any generality, but it might
be less convenient to specify than something else. This does naturally
leave open the question of what `align_y` would look like if we provided
it.)
Morally speaking, I do think that the `up` business is more pertinent
when the intention is to work with cameras, which the `look_at` and
`look_to` APIs seem to cover pretty well. If that's the case, then I'm
not sure what the ideal shape for these API functions would be, since it
seems like a lot of input would have to be baked into the function
definitions. For some cases, this might not be the end of the world:
````rust
pub fn align_x_z(&mut self, direction: Vec3, weak_direction: Vec3) {
self.align(Vec3::X, direction, Vec3::Z, weak_direction);
}
````
(However, this is not symmetrical in x and z, so you'd still need six
API functions just to support the standard positive coordinate axes, and
if you support negative axes then things really start to balloon.)
The reasons that these are not actually produced in this PR are as
follows:
1. Without prompting from actual users in the wild, it is unknown to me
whether these additional APIs would actually see a lot of use. Extending
these to our users in the future would be trivial if we see there is a
demand for something specific from the above-mentioned categories.
2. As discussed above, there are so many permutations of these that
could be provided that trying to do so looks like it risks unduly
ballooning the API surface for this feature.
3. Finally, and most importantly, creating these helper functions in
user-space is trivial, since they all just involve specializing `align`
to particular inputs; e.g.:
````rust
fn align_ship(ship_transform: &mut Transform, nose_direction: Vec3, dorsal_direction: Vec3) {
ship_transform.align(Ship::NOSE, nose_direction, Ship::DORSAL, dorsal_direction);
}
````
With that in mind, I would prefer instead to focus on making the
documentation and examples for a thin API as clear as possible, so that
users can get a grip on the tool and specialize it for their own needs
when they feel the desire to do so.
### `Dir3`?
As in the case of `Transform::look_to` and `Transform::look_at`, the
inputs to this function are, morally speaking, *directions* rather than
vectors (actually, if we're being pedantic, the input is *really really*
a pair of orthonormal frames), so it's worth asking whether we should
really be using `Dir3` as inputs instead of `Vec3`. I opted for `Vec3`
for the following reasons:
1. Specifying a `Dir3` in user-space is just more annoying than
providing a `Vec3`. Even in the most basic cases (e.g. providing a
vector literal), you still have to do error handling or call an unsafe
unwrap in your function invocations.
2. The existing API mentioned above uses `Vec3`, so we are just adhering
to the same thing.
Of course, the use of `Vec3` has its own downsides; it can be argued
that the replacement of zero-vectors with fixed ones (which we do in
`Transform::align` as well as `Transform::look_to`) more-or-less amounts
to failing silently.
### Future steps
The question of additional APIs was addressed above. For me, the main
thing here to handle more immediately is actually just upstreaming this
API (or something similar and slightly mathier) to `glam::Quat`. The
reason that this would be desirable for users is that this API currently
only works with `Transform`s even though all it's actually doing is
specifying a rotation. Upstreaming to `glam::Quat`, properly done, could
buy a lot basically for free, since a number of `Transform` methods take
a rotation as an input. Using these together would require a little bit
of mathematical savvy, but it opens up some good things (e.g.
`Transform::rotate_around`).
