JoltPhysics/HelloWorld/HelloWorld.cpp

// SPDX-FileCopyrightText: 2021 Jorrit Rouwe
// SPDX-License-Identifier: MIT

// Jolt includes
#include <Jolt.h>
#include <RegisterTypes.h>
#include <Core/TempAllocator.h>
#include <Core/JobSystemThreadPool.h>
#include <Physics/PhysicsSettings.h>
#include <Physics/PhysicsSystem.h>
#include <Physics/Collision/Shape/BoxShape.h>
#include <Physics/Collision/Shape/SphereShape.h>
#include <Physics/Body/BodyCreationSettings.h>
#include <Physics/Body/BodyActivationListener.h>

// STL includes
#include <iostream>
#include <cstdarg>
#include <thread>

// All Jolt symbols are in the JPH namespace
using namespace JPH;

// We're also using STL classes in this example
using namespace std;

// Callback for traces, connect this to your own trace function if you have one
static void TraceImpl(const char *inFMT, ...)
{ 
	// Format the message
	va_list list;
	va_start(list, inFMT);
	char buffer[1024];
	vsnprintf(buffer, sizeof(buffer), inFMT, list);

	// Print to the TTY
	cout << buffer << endl;
}

#ifdef JPH_ENABLE_ASSERTS

// Callback for asserts, connect this to your own assert handler if you have one
static bool AssertFailedImpl(const char *inExpression, const char *inMessage, const char *inFile, uint inLine)
{ 
	// Print to the TTY
	cout << inFile << ":" << inLine << ": (" << inExpression << ") " << (inMessage != nullptr? inMessage : "") << endl;

	// Breakpoint
	return true;
};

#endif // JPH_ENABLE_ASSERTS

// Layer that objects can be in, determines which other objects it can collide with
// Typically you at least want to have 1 layer for moving bodies and 1 layer for static bodies, but you can have more
// layers if you want. E.g. you could have a layer for high detail collision (which is not used by the physics simulation
// but only if you do collision testing).
namespace Layers
{
	static constexpr uint8 NON_MOVING = 0;
	static constexpr uint8 MOVING = 1;
	static constexpr uint8 NUM_LAYERS = 2;
};

// Function that determines if two object layers can collide
bool MyObjectCanCollide(ObjectLayer inObject1, ObjectLayer inObject2)
{
	switch (inObject1)
	{
	case Layers::NON_MOVING:
		return inObject2 == Layers::MOVING; // Non moving only collides with moving
	case Layers::MOVING:
		return true; // Moving collides with everything
	default:
		JPH_ASSERT(false);
		return false;
	}
};

// Each broadphase layer results in a separate bounding volume tree in the broad phase. You at least want to have
// a layer for non-moving and moving objects to avoid having to update a tree full of static objects every frame.
// You can have a 1-on-1 mapping between object layers and broadphase layers (like in this case) but if you have
// many object layers you'll be creating many broad phase trees, which is not efficient. If you want to fine tune
// your broadphase layers define JPH_TRACK_BROADPHASE_STATS and look at the stats reported on the TTY.
namespace BroadPhaseLayers
{
	static constexpr BroadPhaseLayer NON_MOVING(0);
	static constexpr BroadPhaseLayer MOVING(1);
};

// Function that determines if two broadphase layers can collide
bool MyBroadPhaseCanCollide(ObjectLayer inLayer1, BroadPhaseLayer inLayer2)
{
	switch (inLayer1)
	{
	case Layers::NON_MOVING:
		return inLayer2 == BroadPhaseLayers::MOVING;
	case Layers::MOVING:
		return true;	
	default:
		JPH_ASSERT(false);
		return false;
	}
}

// An example contact listener
class MyContactListener : public ContactListener
{
public:
	// See: ContactListener
	virtual ValidateResult	OnContactValidate(const Body &inBody1, const Body &inBody2, const CollideShapeResult &inCollisionResult) override
	{
		cout << "Contact validate callback" << endl;

		// Allows you to ignore a contact before it is created (using layers to not make objects collide is cheaper!)
		return ValidateResult::AcceptAllContactsForThisBodyPair;
	}

	virtual void			OnContactAdded(const Body &inBody1, const Body &inBody2, const ContactManifold &inManifold, ContactSettings &ioSettings) override
	{
		cout << "A contact was added" << endl;
	}

	virtual void			OnContactPersisted(const Body &inBody1, const Body &inBody2, const ContactManifold &inManifold, ContactSettings &ioSettings) override
	{
		cout << "A contact was persisted" << endl;
	}

	virtual void			OnContactRemoved(const SubShapeIDPair &inSubShapePair) override
	{ 
		cout << "A contact was removed" << endl;
	}
};

// An example activation listener
class MyBodyActivationListener : public BodyActivationListener
{
public:
	virtual void		OnBodyActivated(const BodyID &inBodyID, void *inBodyUserData) override
	{
		cout << "A body got activated" << endl;
	}

	virtual void		OnBodyDeactivated(const BodyID &inBodyID, void *inBodyUserData) override
	{
		cout << "A body went to sleep" << endl;
	}
};

// Program entry point
int main(int argc, char** argv)
{
	// Install callbacks
	Trace = TraceImpl;
	JPH_IF_ENABLE_ASSERTS(AssertFailed = AssertFailedImpl;)

	// Register all Jolt physics types
	RegisterTypes();

	// We need a temp allocator for temporary allocations during the physics update. We're
	// pre-allocating 10 MB to avoid having to do allocations during the physics update. 
	// B.t.w. 10 MB is way too much for this example but it is a typical value you can use.
	// If you don't want to pre-allocate you can also use TempAllocatorMalloc to fall back to
	// malloc / free.
	TempAllocatorImpl temp_allocator(10 * 1024 * 1024);

	// We need a job system that will execute physics jobs on multiple threads. Typically
	// you would implement the JobSystem interface yourself and let Jolt Physics run on top
	// of your own job scheduler. JobSystemThreadPool is an example implementation.
	JobSystemThreadPool job_system(cMaxPhysicsJobs, cMaxPhysicsBarriers, thread::hardware_concurrency() - 1);

	// This is the max amount of rigid bodies that you can add to the physics system. If you try to add more you'll get an error.
	const uint cMaxBodies = 1024;

	// This determines how many mutexes to allocate to protect rigid bodies from concurrent access. Set it to 0 for the default settings.
	const uint cNumBodyMutexes = 0;

	// This is the max amount of body pairs that can be queued at any time (the broad phase will detect overlapping
	// body pairs based on their bounding boxes and will insert them into a queue for the narrowphase). If you make this buffer
	// too small the queue will fill up and the broad phase jobs will start to do narrow phase work. This is slightly less efficient.
	const uint cMaxBodyPairs = 1024;

	// This is the maximum size of the contact constraint buffer. If more contacts (collisions between bodies) are detected than this
	// number then these contacts will be ignored and bodies will start interpenetrating / fall through the world.
	const uint cMaxContactConstraints = 1024;

	// Create mapping table from object layer to broadphase layer
	ObjectToBroadPhaseLayer object_to_broadphase;
	object_to_broadphase.resize(Layers::NUM_LAYERS);
	object_to_broadphase[Layers::NON_MOVING] = BroadPhaseLayers::NON_MOVING;
	object_to_broadphase[Layers::MOVING] = BroadPhaseLayers::MOVING;

	// Now we can create the actual physics system.
	PhysicsSystem physics_system;
	physics_system.Init(cMaxBodies, cNumBodyMutexes, cMaxBodyPairs, cMaxContactConstraints, object_to_broadphase, MyBroadPhaseCanCollide, MyObjectCanCollide);

	// A body activation listener gets notified when bodies activate and go to sleep
	// Note that this is called from a job so whatever you do here needs to be thread safe.
	// Registering one is entirely optional.
	MyBodyActivationListener body_activation_listener;
	physics_system.SetBodyActivationListener(&body_activation_listener);

	// A contact listener gets notified when bodies (are about to) collide, and when they separate again.
	// Note that this is called from a job so whatever you do here needs to be thread safe.
	// Registering one is entirely optional.
	MyContactListener contact_listener;
	physics_system.SetContactListener(&contact_listener);

	// The main way to interact with the bodies in the physics system is through the body interface. There is a locking and a non-locking
	// variant of this. We're going to use the locking version (even though we're not planning to access bodies from multiple threads)
	BodyInterface &body_interface = physics_system.GetBodyInterface();

	// Next we can create a rigid body to serve as the floor, we make a large box
	// Create the settings for the collision volume (the shape). 
	// Note that for simple shapes (like boxes) you can also directly construct a BoxShape.
	BoxShapeSettings floor_shape_settings(Vec3(100.0f, 1.0f, 100.0f));

	// Create the shape
	ShapeSettings::ShapeResult floor_shape_result = floor_shape_settings.Create();
	ShapeRefC floor_shape = floor_shape_result.Get(); // We don't expect an error here, but you can check floor_shape_result for HasError() / GetError()

	// Create the settings for the body itself. Note that here you can also set other properties like the restitution / friction.
	BodyCreationSettings floor_settings(floor_shape, Vec3(0.0f, -1.0f, 0.0f), Quat::sIdentity(), EMotionType::Static, Layers::NON_MOVING);

	// Create the actual rigid body
	Body *floor = body_interface.CreateBody(floor_settings); // Note that if we run out of bodies this can return nullptr

	// Add it to the world
	body_interface.AddBody(floor->GetID(), EActivation::DontActivate);

	// Now create a dynamic body to bounce on the floor
	// Note that this uses the shorthand version of creating and adding a body to the world
	BodyCreationSettings sphere_settings(new SphereShape(0.5f), Vec3(0.0f, 2.0f, 0.0f), Quat::sIdentity(), EMotionType::Dynamic, Layers::MOVING);
	BodyID sphere_id = body_interface.CreateAndAddBody(sphere_settings, EActivation::Activate);

	// Now you can interact with the dynamic body, in this case we're going to give it a velocity.
	// (note that if we had used CreateBody then we could have set the velocity straight on the body before adding it to the physics system)
	body_interface.SetLinearVelocity(sphere_id, Vec3(0.0f, -5.0f, 0.0f));

	// We simulate the physics world in discrete time steps. 60 Hz is a good rate to update the physics system.
	const float cDeltaTime = 1.0f / 60.0f;

	// Now we're ready to simulate the body, keep simulating until it goes to sleep
	uint step = 0;
	while (body_interface.IsActive(sphere_id))
	{
		// Next step
		++step;

		// Output current position and velocity of the sphere
		Vec3 position = body_interface.GetCenterOfMassPosition(sphere_id);
		Vec3 velocity = body_interface.GetLinearVelocity(sphere_id);
		cout << "Step " << step << ": Position = (" << position.GetX() << ", " << position.GetY() << ", " << position.GetZ() << "), Velocity = (" << velocity.GetX() << ", " << velocity.GetY() << ", " << velocity.GetZ() << ")" << endl;

		// If you take larger steps than 1 / 60th of a second you need to do multiple collision steps in order to keep the simulation stable. Do 1 collision step per 1 / 60th of a second (round up).
		const int cCollisionSteps = 1;

		// If you want more accurate step results you can do multiple sub steps within a collision step. Usually you would set this to 1.
		const int cIntegrationSubSteps = 1;

		// Step the world
		physics_system.Update(cDeltaTime, cCollisionSteps, cIntegrationSubSteps, &temp_allocator, &job_system);
	}

	// Remove the sphere from the physics system. Note that the sphere itself keeps all of its state and can be re-added at any time.
	body_interface.RemoveBody(sphere_id);

	// Destroy the sphere. After this the sphere ID is no longer valid.
	body_interface.DestroyBody(sphere_id);

	// Remove and destroy the floor
	body_interface.RemoveBody(floor->GetID());
	body_interface.DestroyBody(floor->GetID());

	return 0;
}