feat(lambda-rs): Add 2D physics world for managing physics in 2D environments

Cargo.toml

@@ -11,6 +11,7 @@ members = [
  "tools/lambda_audio",
  # Demo crates (not built by default; see `default-members`).
  "demos/audio",
+ "demos/physics",
  "demos/render",
  "demos/minimal",
 ]

crates/lambda-rs-platform/Cargo.toml

@@ -29,6 +29,7 @@ symphonia = { version = "=0.5.5", optional = true, default-features = false, fea
  "wav",
  "pcm",
 ] }
+rapier2d = { version = "=0.32.0", optional = true }
 
 # Force windows crate to 0.62 to unify wgpu-hal and gpu-allocator dependencies.
 # Both crates support this version range, but Cargo may resolve to different
@@ -65,3 +66,8 @@ audio = ["audio-device", "audio-decode-wav", "audio-decode-vorbis"]
 audio-device = ["dep:cpal"]
 audio-decode-wav = ["dep:symphonia"]
 audio-decode-vorbis = ["dep:symphonia"]
+
+# --------------------------------- PHYSICS -----------------------------------
+
+# Umbrella features (disabled by default)
+physics-2d = ["dep:rapier2d"]

crates/lambda-rs-platform/src/lib.rs

@@ -23,3 +23,6 @@ pub mod winit;
  feature = "audio-decode-vorbis"
 ))]
 pub mod audio;
+
+#[cfg(feature = "physics-2d")]
+pub mod physics;

crates/lambda-rs-platform/src/physics/mod.rs

@@ -0,0 +1,9 @@
+//! Internal physics backends.
+//!
+//! This module contains physics backend implementations that support the
+//! higher-level `lambda-rs` physics APIs without exposing vendor types from
+//! `lambda-rs` itself.
+
+pub mod rapier2d;
+
+pub use rapier2d::PhysicsBackend2D;

crates/lambda-rs-platform/src/physics/rapier2d.rs

@@ -0,0 +1,110 @@
+//! Rapier-backed 2D physics backend.
+//!
+//! This module provides a minimal wrapper around `rapier2d` to support the
+//! higher-level `lambda-rs` physics APIs without exposing vendor types outside
+//! of the platform layer.
+
+use rapier2d::prelude::*;
+
+/// A 2D physics backend powered by `rapier2d`.
+///
+/// This type is an internal implementation detail used by `lambda-rs`.
+pub struct PhysicsBackend2D {
+ gravity: Vector,
+ integration_parameters: IntegrationParameters,
+ islands: IslandManager,
+ broad_phase: BroadPhaseBvh,
+ narrow_phase: NarrowPhase,
+ bodies: RigidBodySet,
+ colliders: ColliderSet,
+ impulse_joints: ImpulseJointSet,
+ multibody_joints: MultibodyJointSet,
+ ccd_solver: CCDSolver,
+ pipeline: PhysicsPipeline,
+}
+
+impl PhysicsBackend2D {
+ /// Creates a new empty 2D physics backend.
+ ///
+ /// # Arguments
+ /// - `gravity`: The gravity vector in meters per second squared.
+ /// - `timestep_seconds`: The fixed integration timestep in seconds.
+ ///
+ /// # Returns
+ /// Returns a new `PhysicsBackend2D` with no bodies, colliders, or joints.
+ pub fn new(gravity: [f32; 2], timestep_seconds: f32) -> Self {
+ let gravity_vector = Vector::new(gravity[0], gravity[1]);
+
+ let integration_parameters = IntegrationParameters {
+ dt: timestep_seconds,
+ ..Default::default()
+ };
+
+ return Self {
+ gravity: gravity_vector,
+ integration_parameters,
+ islands: IslandManager::new(),
+ broad_phase: BroadPhaseBvh::new(),
+ narrow_phase: NarrowPhase::new(),
+ bodies: RigidBodySet::new(),
+ colliders: ColliderSet::new(),
+ impulse_joints: ImpulseJointSet::new(),
+ multibody_joints: MultibodyJointSet::new(),
+ ccd_solver: CCDSolver::new(),
+ pipeline: PhysicsPipeline::new(),
+ };
+ }
+
+ /// Returns the gravity vector used by this backend.
+ ///
+ /// # Returns
+ /// Returns the gravity vector in meters per second squared.
+ pub fn gravity(&self) -> [f32; 2] {
+ return [self.gravity.x, self.gravity.y];
+ }
+
+ /// Returns the fixed integration timestep in seconds.
+ ///
+ /// # Returns
+ /// Returns the timestep used for each simulation step.
+ pub fn timestep_seconds(&self) -> f32 {
+ return self.integration_parameters.dt;
+ }
+
+ /// Advances the simulation by one fixed timestep.
+ ///
+ /// # Returns
+ /// Returns `()` after applying integration and constraint solving for the
+ /// configured timestep.
+ pub fn step(&mut self) {
+ return self.step_with_timestep_seconds(self.integration_parameters.dt);
+ }
+
+ /// Advances the simulation by the given timestep.
+ ///
+ /// # Arguments
+ /// - `timestep_seconds`: The timestep used for this step.
+ ///
+ /// # Returns
+ /// Returns `()` after applying integration and constraint solving.
+ pub fn step_with_timestep_seconds(&mut self, timestep_seconds: f32) {
+ self.integration_parameters.dt = timestep_seconds;
+
+ self.pipeline.step(
+ self.gravity,
+ &self.integration_parameters,
+ &mut self.islands,
+ &mut self.broad_phase,
+ &mut self.narrow_phase,
+ &mut self.bodies,
+ &mut self.colliders,
+ &mut self.impulse_joints,
+ &mut self.multibody_joints,
+ &mut self.ccd_solver,
+ &(),
+ &(),
+ );
+
+ return;
+ }
+}

crates/lambda-rs/Cargo.toml

@@ -89,6 +89,11 @@ render-validation-encoder = []
 render-validation-instancing = []
 render-validation-render-targets = []
 
+# --------------------------------- PHYSICS -----------------------------------
+
+# Umbrella features (disabled by default)
+physics-2d = ["lambda-rs-platform/physics-2d"]
+
 
 # ---------------------------- PLATFORM DEPENDENCIES ---------------------------
 

crates/lambda-rs/src/lib.rs

@@ -29,6 +29,9 @@ pub mod util;
 ))]
 pub mod audio;
 
+#[cfg(feature = "physics-2d")]
+pub mod physics;
+
 /// The logging module provides a simple logging interface for Lambda
 /// applications.
 pub use logging;