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@Jondolf Jondolf released this 06 Jul 00:07
v0.1.0
788d94e

Avian Physics 0.1 has been released! 馃

Avian Physics logo

Avian is an ECS-driven physics engine for the Bevy game engine. It is the next evolution of Bevy XPBD, with a completely rewritten contact solver, improved performance, a reworked structure, and numerous other improvements and additions over its predecessor.

See #346 for background on the rebrand.

Highlights

Avian 0.1 has a ton of improvements, additions, and fixes over Bevy XPBD 0.4. Some highlights:

  • A solver rewrite: Avian uses an impulse-based TGS Soft solver instead of XPBD for contacts.
  • A reworked narrow phase: Collision detection is much more performant and reliable.
  • Continuous Collision Detection (CCD): Speculative collision and sweep-based CCD are implemented to prevent tunneling.
  • Optional collision margins: Extra thickness can be added for thin colliders such as trimeshes to improve stability and performance.
  • Improved performance: Overhead for large scenes is significantly smaller, and collision-heavy scenes can have over a 4-6x performance improvement in comparison to Bevy XPBD.
  • Improved runtime collider constructors: It is easier to define colliders and collider hierarchies statically to enable more powerful scene workflows.
  • Structural improvements and polish: The module structure has been heavily reworked, and tons of inconsistencies and bugs have been resolved.
  • Bevy 0.14 support: Avian supports the latest version of Bevy, and internally, it already takes advantage of new features such as observers and component lifecycle hooks.

Check out the announcement blog post for a more in-depth overview of what has changed and why. A more complete changelog can also be found after the migration guide below.

Migration Guide

Note: This guide is for migration from Bevy XPBD 0.4 to Avian 0.1. The entries for migration to Bevy XPBD 0.5 (an easier migration path) still apply and are also listed here.

New Contact Solver #385

The contact solver has been rewritten. In practice, this has the following effects:

  • Collisions should be much more stable.
  • Resolving overlap is no longer nearly as explosive.
  • Less substeps are generally needed for stability.
  • Tunneling is much more rare.
  • Performance is better.

However:

  • Contacts may even be too soft by default for some applications. This can be tuned with the SolverConfig resource.
  • Static friction is currently not considered separately from dynamic friction. This may be fixed in the future.
  • Restitution might not be quite as perfect in some instances (this is a tradeoff for speculative collision to avoid tunneling).
  • 2D applications may need to configure the PhysicsLengthUnit to get the best stability and behavior.

The PhysicsLengthUnit can be thought of a pixels-per-meter scaling factor for the engine's internal length-based tolerances and thresholds, such as the maximum speed at which overlap is resolved, or the speed threshold for allowing bodies to sleep. It does not scale common user-facing inputs or outputs like colliders or velocities.

To configure the PhysicsLengthUnit, you can insert it as a resource, or simply set it while adding PhysicsPlugins:

fn main() {
聽 聽 App::new()
聽 聽 聽 聽 .add_plugins((
聽 聽 聽 聽 聽 聽 DefaultPlugins,
聽 聽 聽 聽 聽 聽 // A 2D game with 20 pixels per meter
聽 聽 聽 聽 聽 聽 PhysicsPlugins::default().with_length_unit(20.0),
聽 聽 聽 聽 ))
聽 聽 聽 聽 .run();
}

Collider Constructor Argument Order #394

To match Bevy's Cylinder, Capsule, and Cone, the order of arguments has changed for some Collider constructors.

  • Use Collider::cylinder(radius, height) instead of Collider::cylinder(height, radius).
  • Use Collider::capsule(radius, height) instead of Collider::capsule(height, radius).
  • Use Collider::capsule_endpoints(radius, a, b) instead of Collider::capsule_endpoints(a, b, radius).
  • Use Collider::cone(radius, height) instead of Collider::cone(height, radius).

This is a very heavily breaking change, but I believe it is important that we align ourselves with Bevy here, and it's better to do it sooner rather than later.

AsyncCollider and AsyncSceneCollider #378

AsyncCollider, AsyncSceneCollider, and ComputedCollider have been replaced by more powerful ColliderConstructor and ColliderConstructorHierarchy types. They work similarly, but also support primitive shapes and arbitrary hierarchies, not just colliders computed for meshes and scenes.

Additionally, some naming changes have been made to improve consistency, such as renaming TriMesh to Trimesh to be consistent with Collider::trimesh.

  • Remove feature async-collider. If you need to use computed shapes, use the feature collider-from-mesh. If you depend on ColliderConstructorHierarchy waiting for a scene to load, use the feature bevy_scene
  • Remove AsyncCollider and use ColliderConstructor directly
  • Rename AsyncSceneCollider to ColliderConstructorHierarchy
    • Rename AsyncSceneCollider::default_shape to ColliderConstructorHierarchy::default_constructor
    • Rename AsyncSceneCollider::meshes_by_name to ColliderConstructorHierarchy::config
    • Rename AsyncSceneCollider::with_shape_for_name to ColliderConstructorHierarchy::with_constructor_for_name
    • Rename AsyncSceneCollider::without_shape_for_name to ColliderConstructorHierarchy::without_constructor_for_name
  • Rename AsyncSceneColliderData to ColliderConstructorHierarchyConfig
    • Rename AsyncSceneColliderData::shape to ColliderConstructorHierarchyConfig::constructor
  • Rename ComputedCollider to ColliderConstructor.
    • Rename ComputedCollider::TriMesh to ColliderConstructor::TrimeshFromMesh
    • Rename ComputedCollider::TriMeshWithFlags to ColliderConstructor::TrimeshFromMeshWithConfig
    • Rename ComputedCollider::ConvexHull to ColliderConstructor::ConvexHullFromMesh
    • Rename ComputedCollider::ConvexDecomposition to ColliderConstructor::ConvexDecompositionFromMeshWithConfig
  • Rename VHACDParameters to VhacdParameters
  • Rename Collider::halfspace to Collider::half_space

Reworked Module Structure #370

  • The internal module structure has changed significantly, and types have moved around. Most imports from the prelude should work like before, but explicit import paths may be broken.
  • The PhysicsSetupPlugin has been split into PhysicsSchedulePlugin and PhysicsTypeRegistrationPlugin.

Sensor Mass Properties #381

Colliders with the Sensor component no longer contribute to the mass properties of rigid bodies. You can add mass for them by adding another collider that is not a sensor, or by manually adding mass properties with the MassPropertiesBundle or its components.

Additionally, the mass properties of Sensor colliders are no longer updated automatically, unless the Sensor component is removed.

Joints and Custom Constraints #390 and #385

  • SphericalJoint no longer exists in 2D. Use RevoluteJoint instead.
  • AngleLimit properties alpha and beta are now named min and max.
  • apply_positional_correction has been renamed to apply_positional_lagrange_update. There is also an apply_positional_impulse method.
  • apply_angular_correction has been renamed to apply_angular_lagrange_update. There is also an apply_angular_impulse method.
  • compute_lagrange_update no longer takes a slice over gradients. For that, use compute_lagrange_update_with_gradients.
  • Joint::align_orientation has been moved to AngularConstraint.
  • XPBD traits and systems are now located in the dynamics::solver::xpbd module.
  • User constraints should run solve_constraints in SubstepSolverSet::SolveUserConstraints instead of SubstepSet::SolveUserConstraints.

Scheduling Changes #385 and #380

Several scheduling internals have been changed. For example:

  • The narrow phase and PostProcessCollisions schedule are now run in PhysicsStepSet::NarrowPhase instead of SubstepSet::NarrowPhase.
  • Integration is now run in IntegrationSet::Velocity and IntegrationSet::Position instead of SubstepSet::Integrate.
  • SubstepSet has been removed.
    • The solver runs in PhysicsStepSet::Solver.
    • The solver's system sets are in SolverSet.
    • Substepping is performed in SolverSet::Substep.
    • The substepping loop's system sets are in SubstepSolverSet.

Systems running in PostProcessCollisions may need to be modified to account for it being moved outside of the substepping loop.

Some PrepareSet system sets have also changed order.

Before:

  1. PreInit
  2. PropagateTransforms
  3. InitRigidBodies
  4. InitMassProperties
  5. InitColliders
  6. InitTransforms
  7. Finalize

After:

  1. PreInit
  2. InitRigidBodies
  3. InitColliders
  4. PropagateTransforms
  5. InitMassProperties
  6. InitTransforms
  7. Finalize

ColliderHierarchyPlugin #377

Hierarchy and transform logic for colliders has been extracted from the ColliderBackendPlugin into a new ColliderHierarchyPlugin, which by default is included in the PhysicsPlugins plugin group.

If you are adding plugins manually, make sure you have both if you want that functionality.

Rotation Component #370

The Rotation component has been updated to match the API of Bevy's new Rot2 type more closely.

The primary breaking changes are that rotate and mul have been deprecated in favor of Mul implementations, and the 2D from_radians and from_degrees have been renamed to just radians and degrees.

// Before
let rotation = Rotation::from_degrees(45.0);
assert_eq!(rotation.mul(rotation).rotate(Vec2::X), Vec2::Y);

// After
let rotation = Rotation::degrees(45.0);
assert_eq!(rotation * rotation * Vec2::X, Vec2::Y);

Add and Sub implementations have also been removed, as adding or subtracting quaternions in 3D is not quite equivalent to performing rotations, which can be a footgun, and having the 2D version function differently would also be inconsistent.

What's Changed

Note: These are changes made between Bevy XPBD 0.4 and Avian 0.1.

  • Fix time of impact description in ShapeHits by @Jondolf in #340
  • Fix 2D heightfield scale and docs by @Jondolf in #343
  • Fix 3D ShapeCaster global_rotation by @ramon-oliveira in #344
  • Normalize rotations after solving constraints in solver by @Jondolf in #345
  • Add feature to examples_common to enable PhysicsDebugPlugin by @jpedrick in #339
  • Use compile_error! macro instead of panicking in PhysicsLayer derive macro by @doonv in #347
  • Fix some doc tests by @yrns in #354
  • various fixes in the prepare/init_transforms system by @exoexo-dev in #360
  • Implement RegularPolygon colliders with a custom shape by @Jondolf in #367
  • Rework module structure, and improve documentation and Rotation by @Jondolf in #370
  • Improve trimesh docs by @janhohenheim in #373
  • Apply collider scale before physics instead of afterwards by @Jondolf in #374
  • Fix collider scale for child rigid bodies by @Jondolf in #375
  • Update bevy-0.14 branch to crates.io release of nalgebra by @gmorenz in #372
  • Speed up ColliderTransform propagation and extract collider hierarchy logic into ColliderHierarchyPlugin by @Jondolf in #377
  • Refactor and speed up transform propagation and hierarchies further by @Jondolf in #380
  • Make sensors not contribute to mass properties by @Jondolf in #381
  • Rework deferred collider initialization by @janhohenheim in #378
  • Fix angular corrections for some 3D joints by @Jondolf in #388
  • Rework contact solver and collision detection, implement speculative collision by @Jondolf in #385
  • Clean up and refactor joint logic by @Jondolf in #390
  • Implement sweep-based CCD by @Jondolf in #391
  • Fix inconsistency between collider constructors and Bevy's primitives by @Jondolf in #394
  • Implement collision margin by @Jondolf in #393
  • Add #[reflect(Serialize, Deserialize)] and register more types by @Jondolf in #395

New Contributors

Full Changelog: xpbd-v0.4.0...v0.1.0

Contributors

yrns, gmorenz, and 6 other contributors
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