Pros of Bullet

• Open-source and free for commercial use
• More flexible and customizable
• Supports a wider range of platforms and programming languages

Cons of Bullet

• Less optimized for high-performance scenarios
• Smaller community and less documentation compared to PhysX
• Fewer advanced features out-of-the-box

Code Comparison

Bullet

btDefaultCollisionConfiguration* collisionConfiguration = new btDefaultCollisionConfiguration();
btCollisionDispatcher* dispatcher = new btCollisionDispatcher(collisionConfiguration);
btBroadphaseInterface* overlappingPairCache = new btDbvtBroadphase();
btSequentialImpulseConstraintSolver* solver = new btSequentialImpulseConstraintSolver;
btDiscreteDynamicsWorld* dynamicsWorld = new btDiscreteDynamicsWorld(dispatcher, overlappingPairCache, solver, collisionConfiguration);

PhysX

PxDefaultAllocator allocator;
PxDefaultErrorCallback errorCallback;
PxFoundation* foundation = PxCreateFoundation(PX_PHYSICS_VERSION, allocator, errorCallback);
PxPhysics* physics = PxCreatePhysics(PX_PHYSICS_VERSION, *foundation, PxTolerancesScale());
PxScene* scene = physics->createScene(PxSceneDesc(physics->getTolerancesScale()));

Both libraries offer similar functionality, but PhysX provides a more streamlined API with fewer lines of code required for basic setup. Bullet offers more granular control over the simulation components, which can be beneficial for advanced users but may require more initial setup.

Pros of Box2D

• Lightweight and easy to integrate into smaller projects
• Simpler API, making it more accessible for beginners
• Open-source with a permissive license (zlib)

Cons of Box2D

• Limited to 2D physics simulations
• Less advanced features compared to PhysX
• Smaller community and fewer resources available

Code Comparison

Box2D:

b2World world(gravity);
b2BodyDef bodyDef;
bodyDef.type = b2_dynamicBody;
b2Body* body = world.CreateBody(&bodyDef);
world.Step(timeStep, velocityIterations, positionIterations);

PhysX:

PxPhysics* physics = PxCreatePhysics(PX_PHYSICS_VERSION, *foundation, PxTolerancesScale());
PxScene* scene = physics->createScene(sceneDesc);
PxRigidDynamic* body = physics->createRigidDynamic(PxTransform(PxVec3(0, 0, 0)));
scene->addActor(*body);
scene->simulate(timeStep);

Box2D is more straightforward and requires less setup, while PhysX offers more advanced features and 3D capabilities. Box2D is ideal for 2D games and simpler projects, whereas PhysX is better suited for complex 3D simulations and AAA game development.

Pros of LiquidFun

• Specialized for fluid and soft body simulations
• Lightweight and optimized for mobile devices
• Open-source with a permissive Apache 2.0 license

Cons of LiquidFun

• Limited feature set compared to PhysX
• Less active development and community support
• Primarily focused on 2D physics

Code Comparison

LiquidFun:

b2World world(gravity);
b2ParticleSystemDef particleSystemDef;
b2ParticleSystem* particleSystem = world.CreateParticleSystem(&particleSystemDef);
b2ParticleGroupDef pd;
pd.flags = b2_waterParticle;
particleSystem->CreateParticleGroup(pd);

PhysX:

PxPhysics* physics = PxCreatePhysics(PX_PHYSICS_VERSION, *gFoundation, PxTolerancesScale());
PxScene* scene = physics->createScene(sceneDesc);
PxRigidDynamic* body = physics->createRigidDynamic(PxTransform(PxVec3(0, 0, 0)));
scene->addActor(*body);

Summary

LiquidFun excels in fluid simulations and mobile optimization but has a narrower focus. PhysX offers a more comprehensive physics engine with broader platform support and features. The choice depends on specific project requirements and target platforms.

Pros of JoltPhysics

• Better performance, especially for large-scale simulations
• More modern codebase with C++17 support
• Easier to integrate and use in projects

Cons of JoltPhysics

• Less mature and battle-tested compared to PhysX
• Smaller community and ecosystem
• Fewer advanced features and specialized solvers

Code Comparison

JoltPhysics:

JPH::BodyInterface &body_interface = physics_system.GetBodyInterface();
JPH::Body *body = body_interface.CreateAndAddBody(body_creation_settings, JPH::EActivation::Activate);

PhysX:

PxRigidDynamic* body = PxCreateDynamic(*gPhysics, transform, geometry, *gMaterial, 10.0f);
gScene->addActor(*body);

Both libraries offer similar functionality for creating and adding physics bodies, but JoltPhysics uses a more modern C++ approach with its interface design. PhysX relies more on global objects and pointers, while JoltPhysics uses references and a more object-oriented style.

JoltPhysics generally requires less boilerplate code and has a more intuitive API, which can lead to cleaner and more maintainable physics implementations in game projects.