Edyn (pronunciation: "eh-dyin'") stands for Entity Dynamics and it is a real-time physics engine organized as an ECS (Entity-Component System) using the amazing EnTT library. The main goals of this library is to be multi-threaded and to support networked and distributed physics simulation of large dynamic worlds.

Examples are located in a separate repository: Edyn Testbed

Build Instructions

Edyn is a compiled library.

Requirements

A compiler with C++17 support is required, along with CMake version 3.12.4 or above.

Dependencies:

• EnTT (installed via Conan)

Steps

In the terminal, in the Edyn directory, run:

$ mkdir build
$ cd build
$ conan install ..
$ cmake ..
$ make

Then you should find the library under edyn/build/lib/. Optionally, you can use make install to neatly package the library, in which case the files will be placed under edyn/build/package.

It's also possible to use Conan to build the library:

$ mkdir build
$ cd build
$ conan install ..
$ conan build ..
$ make

This will build the library in Release mode by default. Other build modes can be specified in the conan build command, e.g. to build it in Debug mode with assertions enabled:

$ conan install .. -s build_type=Debug -o enable_assert=True
$ conan build ..
$ make

Windows and Visual Studio 2019

After running cmake .., the Edyn.sln solution should be in the build directory. Open it and it should be ready to build the library. It's important to note whether you want to build it as a static or dynamic library. It's is set to dynamic by default in VS2019. If you want to build it as a static library, you'll have to open the project properties (Alt Enter) and under Configuration Properties > C/C++ > Code Generation > Runtime Library select Multi-threaded Debug (/MTd) for debug builds and Multi-thread (/MT) for release builds.

When linking your application against Edyn you'll also have to link winmm.lib because it needs the timeGetTime() function.

Integration

To use Edyn in your project you'll have to link it with libEdyn (or libEdyn_d for debug builds) which can be found in edyn/build/lib/ after it's built. On Linux, you'll also have to link pthread. On Windows, you'll additionally have to link winmm.lib.

The paths to edyn/include and edyn/build/include must be added to your include paths.

The ECS approach

Typical physics engines will offer explicit means to create objects such as rigid bodies, whereas in Edyn object creation is implicit due to the entity-component design. A rigid body is created from the bottom up, by associating its parts to a single entity, such as:

entt::registry registry;
auto entity = registry.create();
registry.emplace<edyn::dynamic_tag>(entity);
registry.emplace<edyn::position>(entity, 0, 3, 0);
registry.emplace<edyn::orientation>(entity, edyn::quaternion_axis_angle({0, 1, 0}, edyn::to_radians(30)));
registry.emplace<edyn::linvel>(entity, edyn::vector3_zero);
registry.emplace<edyn::angvel>(entity, 0, 0.314, 0);
auto mass = edyn::scalar{50};
registry.emplace<edyn::mass>(entity, mass);
auto &shape = registry.emplace<edyn::box_shape>(entity, 0.5, 0.2, 0.4); // Box half-extents.
registry.emplace<edyn::inertia>(entity, edyn::moment_of_inertia(shape, mass));
registry.emplace<edyn::material>(entity, 0.2, 0.9); // Restitution and friction.
registry.emplace<edyn::gravity>(entity, edyn::gravity_earth);

There's no explicit mention of a rigid body in the code, but during the physics update all entities that have a combination of the components assigned above will be treated as a rigid body and their state will be updated over time as expected. Then, the rigid body motion may be updated as follows:

// Apply gravity acceleration, increasing linear velocity
auto view = registry.view<edyn::linvel, edyn::gravity, edyn::dynamic_tag>();
for (auto [entity, vel, g] : view.each()) {
  vel += g * dt;
}
// ...
// Move entity with its linear velocity
auto view = registry.view<edyn::position, edyn::linvel, edyn::dynamic_tag>();
for (auto [entity, pos, vel] : view.each()) {
  pos += vel * dt;
}
// ...
// Rotate entity with its angular velocity
auto view = registry.view<edyn::orientation, edyn::angvel, edyn::dynamic_tag>();
for (auto [entity, orn, vel] : view.each()) {
  orn = edyn::integrate(orn, vel, dt);
}

Assigning each component to every rigid body entity individually quickly becomes a daunting task which is prone to errors, thus utility functions are provided for common tasks such as creating rigid bodies:

// Equivalent to example above.
auto def = edyn::rigidbody_def();
def.kind = edyn::rigidbody_kind::rb_dynamic;
def.position = {0, 3, 0};
def.orientation = edyn::quaternion_axis_angle({0, 1, 0}, edyn::to_radians(30));
def.linvel = edyn::vector3_zero;
def.angvel = {0, 0.314, 0};
def.mass = 50;
def.shape = edyn::box_shape{0.5, 0.2, 0.4}; // Shape is optional.
def.material->restitution = 0.2; // Material is also optional.
def.material->friction = 0.9;
def.gravity = edyn::gravity_earth;
auto entity = edyn::make_rigidbody(registry, def);

You are free to assign other components of your own to the returned entity. An existing entity can be passed to edyn::make_rigidbody as well, such as:

auto entity = registry.create();
registry.emplace<MyCustomComponent>(entity, ...); // Assign your own components to it.
edyn::make_rigidbody(entity, registry, def);

Basic setup

Edyn is built as a multi-threaded library from the ground up which requires initializing its worker threads on start-up invoking edyn::init(), and then it must be attached to an entt::registry before setting up the scene:

#include <entt/entt.hpp>
#include <edyn/edyn.hpp>

entt::registry registry;
edyn::init();
edyn::attach(registry);

// Create rigid bodies as shown above...

// Call `edyn::update()` periodically in your main loop somewhere.
for (;;) {
  edyn::update(registry);
  // Do something with the results, e.g. render scene.
  // ...
}

When edyn::update() is called, it processes any pending changes, creates/destroys workers if needed, dispatches messages to workers, reads and processes messages from workers which are merged into the entt::registry, preparing the entities and components to be rendered right after.

Due to its multi-threaded nature, all changes to relevant components in the main entt::registry need to be propagated to the worker threads. Edyn doesn't automatically pick up these changes, thus it's necessary to notify it either by calling edyn::refresh() or assigning a edyn::dirty component to the entity and calling some of its functions such as edyn::dirty::updated() (e.g. registry.emplace<edyn::dirty>(entity).updated<edyn::position, edyn::linvel>()).

Features

Following is a list containing the current major features:

• Dynamic, static and kinematic rigid bodies.
• Broad-phase collision detection using a dynamic bounding volume tree.
• Narrow-phase collision detection using specialized code for each permutation of shape types. Most closest point calculation is done using SAT.
• Closest point calculation can be done explicitly using the edyn::collide function and a pair of shapes, outside of a physics simulation.
• Shapes: sphere, cylinder, capsule, box, convex polyhedron, compound, plane, concave triangle mesh, paged triangle mesh which loads chunks in the background on demand.
• Constraints: distance, soft distance, hinge, point, gravity, generic, CV-joint, cone.
• Hinge constraint limits beyond the [-π, π] range, limit restitution, bump stops, friction, damping and spring.
• Ability to easily change the center of mass, without affecting constraint pivot points.
• Amorphous rigid bodies, i.e. rigid bodies without a shape which do not take part in collision detection and can be connected to other bodies via constraints.
• Rigid bodies which do not collide yet generate collision events, aka sensors.
• Raycasting.
• Ragdolls.
• Collision filtering using the typical group and mask bitsets and the more advanced collision exclusion list for greater control.
• Collision events.
• Material ids and material properties to be used when a specific pair of materials interact.
• Per-vertex material properties in triangle mesh shapes.
• Rolling and spinning friction.
• Internal edge collision avoidance in triangle mesh shapes using Voronoi regions.
• Sequential impulses constraint solver with warm-starting.
• Proper restitution propagation using a specialized restitution solver.
• Parallel simulation using islands.
• Networked physics using a client-server model. Edyn performs client state application in the server-side using a jitter buffer and does extrapolation on the client-side in a background thread. It generates packets containing physics state which just needs to be sent over the network and once received in the other side it must be fed into the engine. It handles serialization, deserialization and processing of all packets.

Games

• Exhibition of Speed: Build your own car and go racing.

Documentation and Support

Check out the wiki where the user manual can be found.

Check out Edyn Testbed for concrete examples.

See the design document for information about the internals and planned features.

Questions can be asked on discussions and the author can also be reached on the EnTT Discord under the same username and avatar.

Follow progress on Trello where you can see the to-do list and what's being currently worked on.