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Introduction

Atlas Engine provides a comprehensive physics system through the Bezel abstraction layer, which is powered by Jolt Physics - a high-performance, multi-threaded physics engine.
Bezel provides a backend-agnostic interface for rigid bodies, colliders, joint constraints, and vehicle simulation. When BEZEL_NATIVE is not defined, this implementation is backed by Jolt Physics.

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Architecture

The physics system consists of several layers:
  • atlas/physics.h - High-level physics components for the Atlas engine
  • bezel/bezel.h - Backend-agnostic physics abstraction layer
  • Jolt Physics - Underlying physics engine implementation

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Core Components

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PhysicsWorld

The PhysicsWorld manages the entire physics simulation: 
bezel::PhysicsWorld world;
world.init();

// Set global gravity
world.setGravity({0.0f, -9.81f, 0.0f});

// Update simulation
world.update(deltaTime);

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Rigidbody Component

The Rigidbody component binds physics to a GameObject: 
auto rb = std::make_shared<Rigidbody>();
rb->setMotionType(MotionType::Dynamic);
rb->setMass(5.0f);
rb->addBoxCollider({0.5f, 0.5f, 0.5f});
rb->setFriction(0.8f);

// Optional tagging for filtered queries
rb->addTag("Player");

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Motion Types

Rigidbodies can have three motion types: 
enum class MotionType {
    Static,    // Immovable objects (terrain, walls)
    Dynamic,   // Fully simulated objects affected by forces
    Kinematic  // Movable but not affected by forces
};

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Usage Example

// Static ground
auto ground = std::make_shared<Rigidbody>();
ground->setMotionType(MotionType::Static);
ground->addBoxCollider({10.0f, 0.1f, 10.0f});

// Dynamic ball
auto ball = std::make_shared<Rigidbody>();
ball->setMotionType(MotionType::Dynamic);
ball->setMass(1.0f);
ball->addSphereCollider(0.5f);
ball->applyImpulse({0.0f, 10.0f, 0.0f});

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Physics Properties

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Mass and Damping

// Set mass (in kilograms)
rigidbody->setMass(10.0f);

// Set linear and angular damping
rigidbody->setDamping(0.05f, 0.1f);

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Material Properties

// Set friction coefficient (0.0 to 1.0)
rigidbody->setFriction(0.5f);

// Set restitution/bounciness (0.0 to 1.0)
rigidbody->setRestitution(0.7f);

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Applying Forces

// Apply continuous force
rigidbody->applyForce({0.0f, 100.0f, 0.0f});

// Apply force at a specific point
rigidbody->applyForceAtPoint({10.0f, 0.0f, 0.0f}, {0.0f, 1.0f, 0.0f});

// Apply instantaneous impulse
rigidbody->applyImpulse({0.0f, 0.0f, 20.0f});

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Velocity Control

// Set linear velocity
rigidbody->setLinearVelocity({5.0f, 0.0f, 0.0f});

// Add to linear velocity
rigidbody->addLinearVelocity({0.0f, 2.0f, 0.0f});

// Set angular velocity
rigidbody->setAngularVelocity({0.0f, 1.0f, 0.0f});

// Get velocities
Velocity3d linearVel = rigidbody->getLinearVelocity();
Velocity3d angularVel = rigidbody->getAngularVelocity();

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Velocity Limits

// Set maximum velocities to prevent instability
rigidbody->setMaxLinearVelocity(50.0f);
rigidbody->setMaxAngularVelocity(10.0f);

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Sensors (Triggers)

Sensors detect overlaps without physical collision: 
auto sensor = std::make_shared<Sensor>();
sensor->addSphereCollider(1.0f);
sensor->setSignal("EnteredTrigger");

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Physics Queries

Atlas provides several query types:
  • Raycast - Cast a ray and detect hits
  • Overlap - Check for overlapping objects
  • Sweep - Predict movement collisions
// Raycast from rigidbody
rigidbody->raycast({0.0f, -1.0f, 0.0f}, 100.0f);

// Raycast from world position
rigidbody->raycastWorld({0.0f, 10.0f, 0.0f}, {0.0f, -1.0f, 0.0f}, 100.0f);

// Results delivered via Component::onQueryReceive(QueryResult&)

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Next Steps

Colliders

Learn about collision shapes and collider types

Rigidbodies

Deep dive into rigidbody physics

Joints

Connect objects with physics constraints

Vehicles

Build realistic vehicle physics

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Additional Resources

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