bevy/examples/movement/smooth_follow.rs
Joona Aalto 54006b107b
Migrate meshes and materials to required components (#15524)
# Objective

A big step in the migration to required components: meshes and
materials!

## Solution

As per the [selected
proposal](https://hackmd.io/@bevy/required_components/%2Fj9-PnF-2QKK0on1KQ29UWQ):

- Deprecate `MaterialMesh2dBundle`, `MaterialMeshBundle`, and
`PbrBundle`.
- Add `Mesh2d` and `Mesh3d` components, which wrap a `Handle<Mesh>`.
- Add `MeshMaterial2d<M: Material2d>` and `MeshMaterial3d<M: Material>`,
which wrap a `Handle<M>`.
- Meshes *without* a mesh material should be rendered with a default
material. The existence of a material is determined by
`HasMaterial2d`/`HasMaterial3d`, which is required by
`MeshMaterial2d`/`MeshMaterial3d`. This gets around problems with the
generics.

Previously:

```rust
commands.spawn(MaterialMesh2dBundle {
    mesh: meshes.add(Circle::new(100.0)).into(),
    material: materials.add(Color::srgb(7.5, 0.0, 7.5)),
    transform: Transform::from_translation(Vec3::new(-200., 0., 0.)),
    ..default()
});
```

Now:

```rust
commands.spawn((
    Mesh2d(meshes.add(Circle::new(100.0))),
    MeshMaterial2d(materials.add(Color::srgb(7.5, 0.0, 7.5))),
    Transform::from_translation(Vec3::new(-200., 0., 0.)),
));
```

If the mesh material is missing, previously nothing was rendered. Now,
it renders a white default `ColorMaterial` in 2D and a
`StandardMaterial` in 3D (this can be overridden). Below, only every
other entity has a material:

![Näyttökuva 2024-09-29
181746](https://github.com/user-attachments/assets/5c8be029-d2fe-4b8c-ae89-17a72ff82c9a)

![Näyttökuva 2024-09-29
181918](https://github.com/user-attachments/assets/58adbc55-5a1e-4c7d-a2c7-ed456227b909)

Why white? This is still open for discussion, but I think white makes
sense for a *default* material, while *invalid* asset handles pointing
to nothing should have something like a pink material to indicate that
something is broken (I don't handle that in this PR yet). This is kind
of a mix of Godot and Unity: Godot just renders a white material for
non-existent materials, while Unity renders nothing when no materials
exist, but renders pink for invalid materials. I can also change the
default material to pink if that is preferable though.

## Testing

I ran some 2D and 3D examples to test if anything changed visually. I
have not tested all examples or features yet however. If anyone wants to
test more extensively, it would be appreciated!

## Implementation Notes

- The relationship between `bevy_render` and `bevy_pbr` is weird here.
`bevy_render` needs `Mesh3d` for its own systems, but `bevy_pbr` has all
of the material logic, and `bevy_render` doesn't depend on it. I feel
like the two crates should be refactored in some way, but I think that's
out of scope for this PR.
- I didn't migrate meshlets to required components yet. That can
probably be done in a follow-up, as this is already a huge PR.
- It is becoming increasingly clear to me that we really, *really* want
to disallow raw asset handles as components. They caused me a *ton* of
headache here already, and it took me a long time to find every place
that queried for them or inserted them directly on entities, since there
were no compiler errors for it. If we don't remove the `Component`
derive, I expect raw asset handles to be a *huge* footgun for users as
we transition to wrapper components, especially as handles as components
have been the norm so far. I personally consider this to be a blocker
for 0.15: we need to migrate to wrapper components for asset handles
everywhere, and remove the `Component` derive. Also see
https://github.com/bevyengine/bevy/issues/14124.

---

## Migration Guide

Asset handles for meshes and mesh materials must now be wrapped in the
`Mesh2d` and `MeshMaterial2d` or `Mesh3d` and `MeshMaterial3d`
components for 2D and 3D respectively. Raw handles as components no
longer render meshes.

Additionally, `MaterialMesh2dBundle`, `MaterialMeshBundle`, and
`PbrBundle` have been deprecated. Instead, use the mesh and material
components directly.

Previously:

```rust
commands.spawn(MaterialMesh2dBundle {
    mesh: meshes.add(Circle::new(100.0)).into(),
    material: materials.add(Color::srgb(7.5, 0.0, 7.5)),
    transform: Transform::from_translation(Vec3::new(-200., 0., 0.)),
    ..default()
});
```

Now:

```rust
commands.spawn((
    Mesh2d(meshes.add(Circle::new(100.0))),
    MeshMaterial2d(materials.add(Color::srgb(7.5, 0.0, 7.5))),
    Transform::from_translation(Vec3::new(-200., 0., 0.)),
));
```

If the mesh material is missing, a white default material is now used.
Previously, nothing was rendered if the material was missing.

The `WithMesh2d` and `WithMesh3d` query filter type aliases have also
been removed. Simply use `With<Mesh2d>` or `With<Mesh3d>`.

---------

Co-authored-by: Tim Blackbird <justthecooldude@gmail.com>
Co-authored-by: Carter Anderson <mcanders1@gmail.com>
2024-10-01 21:33:17 +00:00

136 lines
4.2 KiB
Rust

//! This example demonstrates how to use interpolation to make one entity smoothly follow another.
use bevy::{
math::{prelude::*, vec3, NormedVectorSpace},
prelude::*,
};
use rand::SeedableRng;
use rand_chacha::ChaCha8Rng;
fn main() {
App::new()
.add_plugins(DefaultPlugins)
.add_systems(Startup, setup)
.add_systems(Update, (move_target, move_follower).chain())
.run();
}
// The sphere that the following sphere targets at all times:
#[derive(Component)]
struct TargetSphere;
// The speed of the target sphere moving to its next location:
#[derive(Resource)]
struct TargetSphereSpeed(f32);
// The position that the target sphere always moves linearly toward:
#[derive(Resource)]
struct TargetPosition(Vec3);
// The decay rate used by the smooth following:
#[derive(Resource)]
struct DecayRate(f32);
// The sphere that follows the target sphere by moving towards it with nudging:
#[derive(Component)]
struct FollowingSphere;
/// The source of randomness used by this example.
#[derive(Resource)]
struct RandomSource(ChaCha8Rng);
fn setup(
mut commands: Commands,
mut meshes: ResMut<Assets<Mesh>>,
mut materials: ResMut<Assets<StandardMaterial>>,
) {
// A plane:
commands.spawn((
Mesh3d(meshes.add(Plane3d::default().mesh().size(12.0, 12.0))),
MeshMaterial3d(materials.add(Color::srgb(0.3, 0.15, 0.3))),
Transform::from_xyz(0.0, -2.5, 0.0),
));
// The target sphere:
commands.spawn((
Mesh3d(meshes.add(Sphere::new(0.3))),
MeshMaterial3d(materials.add(Color::srgb(0.3, 0.15, 0.9))),
TargetSphere,
));
// The sphere that follows it:
commands.spawn((
Mesh3d(meshes.add(Sphere::new(0.3))),
MeshMaterial3d(materials.add(Color::srgb(0.9, 0.3, 0.3))),
Transform::from_translation(vec3(0.0, -2.0, 0.0)),
FollowingSphere,
));
// A light:
commands.spawn((
PointLight {
intensity: 15_000_000.0,
shadows_enabled: true,
..default()
},
Transform::from_xyz(4.0, 8.0, 4.0),
));
// A camera:
commands.spawn(Camera3dBundle {
transform: Transform::from_xyz(-2.0, 3.0, 5.0).looking_at(Vec3::ZERO, Vec3::Y),
..default()
});
// Set starting values for resources used by the systems:
commands.insert_resource(TargetSphereSpeed(5.0));
commands.insert_resource(DecayRate(2.0));
commands.insert_resource(TargetPosition(Vec3::ZERO));
commands.insert_resource(RandomSource(ChaCha8Rng::seed_from_u64(68941654987813521)));
}
fn move_target(
mut target: Query<&mut Transform, With<TargetSphere>>,
target_speed: Res<TargetSphereSpeed>,
mut target_pos: ResMut<TargetPosition>,
time: Res<Time>,
mut rng: ResMut<RandomSource>,
) {
let mut target = target.single_mut();
match Dir3::new(target_pos.0 - target.translation) {
// The target and the present position of the target sphere are far enough to have a well-
// defined direction between them, so let's move closer:
Ok(dir) => {
let delta_time = time.delta_seconds();
let abs_delta = (target_pos.0 - target.translation).norm();
// Avoid overshooting in case of high values of `delta_time`:
let magnitude = f32::min(abs_delta, delta_time * target_speed.0);
target.translation += dir * magnitude;
}
// The two are really close, so let's generate a new target position:
Err(_) => {
let legal_region = Cuboid::from_size(Vec3::splat(4.0));
*target_pos = TargetPosition(legal_region.sample_interior(&mut rng.0));
}
}
}
fn move_follower(
mut following: Query<&mut Transform, With<FollowingSphere>>,
target: Query<&Transform, (With<TargetSphere>, Without<FollowingSphere>)>,
decay_rate: Res<DecayRate>,
time: Res<Time>,
) {
let target = target.single();
let mut following = following.single_mut();
let decay_rate = decay_rate.0;
let delta_time = time.delta_seconds();
// Calling `smooth_nudge` is what moves the following sphere smoothly toward the target.
following
.translation
.smooth_nudge(&target.translation, decay_rate, delta_time);
}