contains the \texttt{CMakeLists.txt} file. Running this command will launch the CMake command line interface.
Hit the 'c' key to configure the project. There, you can also change some predefined variables (see section \ref{sec:cmakevariables} for more details)
and then, hit the 'c' key again. Once you have set all the values as you like, you can hit the 'g' key to generate the makefiles in the build directory
There are two main ways to use ReactPhysics3D. The first one is to create bodies that you have to manually move so that you can test collision between them. To do this,
you need to create a Collision World with several Collision Bodies in it. The second way is to create bodies and let ReactPhysics3D simulate their motions automatically using the
physics. This is done by creating Rigid Bodies in a Dynamics World instead. In summary, a Collision World is used to simply test collision between bodies that you have to manually move
and a Dynamics World is used to create bodies that will be automatically moved using collisions, joints and forces. \\
The \texttt{CollisionWorld} class represents a Collision World in the ReactPhysics3D library.
\subsection{Creating the Collision World}
If you only have to test collision between bodies, the first thing to do is to create an instance of the \texttt{CollisionWorld} class. \\
Here is how to create a Collision World: \\
\begin{lstlisting}
// Create the collision world
rp3d::CollisionWorld world;
\end{lstlisting}
\subsection{Destroying the Collision World}
Do not forget to destroy the \texttt{CollisionWorld} instance at the end of your program in order to release the allocated memory. If the object has been created
statically, it will be destroyed automatically at the end of the scope in which it has been created. If the object has been created dynamically (using the \texttt{new}
operator), you need to destroy it with the \texttt{delete} operator.
\section{Collision Bodies}
Once the Collision World has been created, you can create Collision Bodies into the world. A Collision Body represents an object in the Collision World.
It has a position, an orientation and one or more collision shapes. It has to be moved manually in the Collision World. You can then
test collisions between the Collision Bodies of the world. In ReactPhysics3D, the \texttt{CollisionBody} class is used to describe a Collision Body. \\
If you do not want to simply test collision between your bodies but want them to move automatically according to the physics, you should use Rigid Bodies in a
Dynamics World instead. See section \ref{sec:dynamicsworld} for more information about the Dynamics World and section \ref{sec:rigidbody} if you would like to know more
about the Rigid Bodies.
\subsection{Creating a Collision Body}
In order to create a Collision Body, you need to specify its transform. The transform describes the initial
position and orientation of the body in the world. You need to create an instance of the \texttt{Transform} class with a vector describing the
initial position and a quaternion for the initial orientation of the body. \\
In order to test collision between your body and other bodies in the world, you need to add one or several collision shapes to your body.
Take a look at section \ref{sec:collisionshapes} to learn about the different collision shapes and how to create them. \\
You need to call the \texttt{CollisionWorld::createCollisionBody()} method to create a Collision Body in the world previously created. This method will return a pointer to the instance
of the \texttt{CollisionBody} class that has been created internally. You will then be able to use that pointer to get or set values of the body. \\
You can see in the following code how to create a Collision Body in the world. \\
\begin{lstlisting}
// Initial position and orientation of the collision body
A Collision Body has to be moved manually in the world. To do that, you need to use the \texttt{CollisionBody::setTransform()} method to set a new position and new
orientation to the body.
\begin{lstlisting}
// New position and orientation of the collision body
In order to destroy a Collision Body from the world, you need to use the \texttt{CollisionWorld::destroyCollisionBody()} method. You need to use the pointer to the body you
want to destroy in argument. Note that after calling that method, the pointer will not be valid anymore and therefore, you should not use it. Note that you must
destroy all the bodies at the end of the simulation before you destroy the world. \\
\end{sloppypar}
Here is how to destroy a Collision Body: \\
\begin{lstlisting}
// Here, world is an instance of the CollisionWorld class
// Destroy the collision body and remove it from the world
world.destroyCollisionBody(body);
\end{lstlisting}
\section{The Dynamics World}
\label{sec:dynamicsworld}
The Collision World of the previous section is used to manually move the bodies and check for collision between them. On the other side, the Dynamics World
is used to automatically simulate the motion of your bodies using the physics. You do not have to move the bodies manually (but you still can if needed).
The Dynamics World will contain the bodies and joints that you create. You will then be able to run your simulation across time by updating the world at each frame.
The \texttt{DynamicsWorld} class (which inherits from the \texttt{CollisionWorld} class) represents a Dynamics World in the ReactPhysics3D library.
The first thing you have to do when you want to simulate the dynamics of rigid bodies in time is to create an instance
of the \texttt{DynamicsWorld}. You need to specify two parameters when constructing the world. The first one is the gravity acceleration vector (in $m / s^2$) in the
world and
the second one is the simulation time step (in seconds). Note that gravity is activated by default when you create the world. The time step is the fixed amount of time
used at each internal
physics tick. Note that multiple internal physics ticks can be taken at each frame. For real-time applications, a time step of $\frac{1}{60}$ seconds (60 Hz) is usually
used. Using a smaller time step makes the simulation more precise but also more expensive to compute. \\
ReactPhysics3D uses an iterative solver to compute the contacts and joints. For contacts, there is a unique velocity solver and for joints there are a velocity and a
position solver. By default, the number of iterations of the velocity solver is 10 and the number of iterations for the position solver is 5. It is possible to
Increasing the number of iterations of the solvers will make the simulation more precise but also more expensive to compute. Therefore, you need to change
The purpose of the sleeping technique is to deactivate resting bodies so that they are not simulated anymore. This is used to save computation time because simulating
many bodies is costly.
A sleeping body (or group of sleeping bodies) is awaken as soon as another body collides with it or a joint in which it is involed is enabled. The sleeping technique
is enabled by default. You can disable it using the following method: \\
Note that it is not recommended to disable the sleeping technique because the simulation might become slower. It is also possible to deactivate the sleeping technique on a
A body is put to sleep when its linear and angular velocity stay under a given velocity threshold for a certain amount of time (one second by default). It is possible to
change the two
linear and angular velocity thresholds using the two methods \texttt{DynamicsWorld::setSleepLinearVelocity()} and \texttt{DynamicsWorld::setSleepAngularVelocity()}.
Note that the velocities must
be specified in meters per second. You can also change the amount of time (in seconds) the velocity of a body needs to stay under the threshold to be considered
Then, each time you have to compute the next frame to render in your application, you need to update the state of the world. To do that, you simply need to call this method: \\
When the \texttt{DynamicsWorld::update()} method is called, collision detection is performed and the position and orientation of the bodies are updated accordingly.
You can also use the \texttt{DynamicsWorld::stop()} method to stop the simulation. You will then be able to start it again and continue updating it. \\
Note that you can get the elapsed time (in seconds) from the beginning of the physics simulation using the \texttt{DynamicsWorld::getPhysicsTime()} method.
Do not forget to destroy the \texttt{DynamicsWorld} instance at the end of your program in order to release the allocated memory. If the object has been created statically, it will
automatically be destroyed at the end of the scope in which it has been created. If the object has been created dynamically (using the \texttt{new} operator), you need to destroy
Once the Dynamics World has been created, you can create rigid bodies into the world. A Rigid Body represents an object that you want to simulate in the world.
It has a mass, a position, an orientation and one or several collision shapes. The Dynamics World will compute collisions between the bodies and will update their position
and orientation accordingly at each time step. You can also create joints between the bodies in the world. In ReactPhysics3D, the \texttt{RigidBody} class
(which inherits from the \texttt{CollisionBody} class) is used to describe a Rigid Body.
You need to call the \texttt{DynamicsWorld::createRigidBody()} method to create a Rigid Body in the world previously created. This method will return a pointer to the
instance of the \texttt{RigidBody} object that has been created internally. You will then be able to use that pointer to get or set values of the body. \\
Once your Rigid Body has been created in the world, you need to add one or several collision shapes to it. Take a look at section \ref{sec:collisionshapes} to learn
about the different collision shapes and how to create them. \\
There are three types of bodies: \emph{static}, \emph{kinematic} and \emph{dynamic}. A \emph{static} body has infinite mass, zero velocity but its position can be
changed manually. Moreover, a static body does not collide with other static or kinematic bodies. On the other side, a \emph{kinematic} body has infinite mass, its velocity can be
changed manually and its position is computed by the physics engine. A kinematic body does not collide with other static or kinematic bodies. Finally, A \emph{dynamic} body
has non-zero mass, non-zero velocity determined by forces and its position is determined by the physics engine. Moreover, a dynamic body can collide with other dynamic, static or
When you create a new body in the world, it is of dynamic type by default. You can change the type of the body using the \texttt{CollisionBody::setType()}
By default, all the rigid bodies with react to the gravity force of the world. If you do not want the gravity to be applied to a given body, you can disable
it using the \texttt{RigidBody::enableGravity()} method as in the following example : \\
The material of a rigid body is used to describe the physical properties it is made of. The \texttt{Material} class represents the material of a body. Each body that
you create will have a default material. You can get the material of the rigid body using the \texttt{RigidBody::getMaterial()} method. Then, you will be able to change some
properties. \\
For instance, you can change the bounciness of the rigid body. The bounciness is a value between 0 and 1. The value 1 is used for a very bouncy object and the value 0 means that
the body will not be bouncy at all. To change the bounciness of the material, you can use the \texttt{Material::setBounciness()} method. \\
You are also able to change the friction coefficient of the body. This value needs to be between 0 and 1. If the value is 0, no friction will be applied when the body is in contact with
another body. However, if the value is 1, the friction force will be high. You can change the friction coefficient of the material with the
Damping is the effect of reducing the velocity of the rigid body during the simulation to simulate effects like air friction for instance. By default, no damping
is applied. However, you can choose to damp the linear or/and the angular velocity of a rigid body. For instance, without angular damping a pendulum will never come
to rest. You need to use the \texttt{RigidBody::setLinearDamping()} and \texttt{RigidBody::setAngularDamping()} methods to change the damping values. The damping
value has to be positive and a value of zero means no damping at all.
As described in section \ref{sec:sleeping}, the sleeping technique is used to disable the simulation of resting bodies. By default, the bodies are allowed to sleep
when they come to rest. However, if you do not want a given body to be put to sleep, you can use the \texttt{Body::setIsAllowedToSleep()} method as in the next example : \\
\subsubsection{Applying Force or Torque to a Rigid Body}
During the simulation, you can apply a force or a torque to a given rigid body. First, you can apply a force to the center of mass of the rigid body using the
\texttt{RigidBody::applyForceToCenter()} method. You need to specify the force vector (in Newton) as a parameter. If the force is applied to the center of mass, no
You can also apply a force to any given point (in world-space) using the \texttt{RigidBody::applyForce()} method. You need to specify the force vector (in Newton) and the point
(in world-space) where to apply the given force. Note that if the point is not the center of mass of the body, applying a force will generate some torque and therefore, the
angular motion of the body will be affected as well. \\
It is also possible to apply a torque to a given body using the \texttt{RigidBody::applyTorque()} method. You simply need to specify the torque vector (in Newton $\cdot$ meter) as
Note that when you call the previous methods, the specified force/torque will be added to the total force/torque applied to the rigid body and that at the end of each call to the
\texttt{DynamicsWorld::update()}, the total force/torque of all the rigid bodies will be reset to zero. Therefore, you need to call the previous methods during several frames
When you call the \texttt{DynamicsWorld::update()} method, the collisions between the bodies are computed and the joints are evaluated. Then, the bodies position
are updated accordingly. After calling this method, you can get the updated position and orientation of each body to render it. To do that, you simply need to use the
\texttt{RigidBody::getInterpolatedTransform()} method to get the interpolated transform. This transform represents the current local-to-world-space transformation
If you need the array with the corresponding $4\times4$ OpenGL transformation matrix, you can use the \texttt{Transform::getOpenGLMatrix()} method as in the
It is really simple to destroy a rigid body. You simply need to use the \texttt{DynamicsWorld::destroyRigidBody()} method. You need to use the pointer to the body you
want to destroy as a parameter. Note that after calling that method, the pointer will not be valid anymore and therefore, you should not use it. Note that you must
destroy all the rigid bodies at the end of the simulation before you destroy the world. When you destroy a rigid body that was part of a joint, that joint will be
Once you have created a Collision Body or a Rigid Body in the world, you need to add one or more collision shapes into it so that it is able to collide with other bodies.
The Collision Shapes are also the way to represent the mass of a Rigid Body. Whenever you add a collision shape to a Rigid Body, you need to specify the mass of the shape.
Then the Rigid Body will recompute its total mass, its center of mass and its inertia tensor taking into account all its collision shapes. Therefore, you do not have to compute
those things by yourself. However, if needed, you can also specify your own center of mass or inertia tensor. Note that the inertia tensor is a $3\times3$ matrix describing
how the mass is distributed inside the rigid body which will be used to calculate its rotation. The inertia tensor depends on the mass and the shape of the body. \\
For instance, if you want to create a box shape with dimensions of 4 meters, 6 meters and 10 meters along the X, Y and Z axis respectively, you need to use the
The \texttt{BoxShape} has a collision margin that is added to the box dimension you define. Therefore, the actual box shape will be a little bit larger that the one you define.
It is recommended that you use the default margin. In case, you really need to change the collision margin of your box shape (if the dimension of your box is small compared
to the default collision margin for instance), you can pass the length of the new collision margin (in meters) as a second parameter of the \texttt{BoxShape} constructor. \\
The \texttt{SphereShape} class describes a sphere collision shape centered at the origin of the shape local space. You only need to specify the radius of the sphere to create it. \\
The collision margin of the \texttt{SphereShape} is integrated into the sphere you define. Therefore, you do not need to worry about it and you cannot change it.
The \texttt{ConeShape} has a collision margin that is added to the cone dimension that you define. Therefore, the actual cone shape will be a little bit larger that the size you define.
It is recommended that you use the default margin. In case you really need to change the collision margin of your cone shape (if the dimension of your cone is small compared
to the default collision margin for instance), you can pass the length of the new collision margin (in meters) as a third parameter of the \texttt{ConeShape} constructor. \\
The \texttt{CylinderShape} class describes a cylinder collision shape centered at the origin of the shape local-space. The cylinder is aligned along the Y axis.
In order to create a cylinder shape, you need to specify the radius of its base and its height (along the Y axis). \\
The \texttt{CylinderShape} has a collision margin that is added to the cylinder dimension that you define. Therefore, the actual cylinder shape will be a little bit larger that the one you define.
It is recommended that you use the default margin. In case you really need to change the collision margin of your cylinder shape (if the dimension of your cylinder is small compared
to the default collision margin for instance), you can pass the length of the new collision margin (in meters) as a third parameter of the \texttt{CylinderShape} constructor. \\
The \texttt{CapsuleShape} class describes a capsule collision shape around the Y axis and centered at the origin of the shape local-space. It is the convex hull of two
spheres. It can also be seen as an elongated sphere. In order to create it, you only need to specify the radius of the two spheres and the height of the
capsule (distance between the centers of the two spheres). \\
The \texttt{ConvexMeshShape} class can be used to describe the shape of a convex mesh. In order to create a convex mesh shape, you need to supply the array with the coordinates of
the vertices of the mesh. The array is supposed to start with the three X, Y and Z coordinates of the first vertex, then the X, Y and Z coordinates of the second vertex and so on.
The first parameter of the \texttt{ConvexMeshShape} constructor is a pointer to the array of the vertices coordinates, the second parameter is the number of vertices in the array and
the third parameter is the size (in bytes) of the data needed for a single vertex in the array (data used by all the three coordinates of a single vertex). \\
The following example shows how to create a convex mesh shape: \\
The collision detection test with a convex mesh shape runs in $O(n)$ where $n$ is the number of vertices in the mesh. Collision detection can become expensive if there are
too many vertices in the mesh. It is possible to speed up the collision detection by providing information about the edges of the convex mesh. If you provide edges information, the collision detection will run in almost constant time at the cost of a little extra memory to store the edges information. In order to provide the edges
information, you need to call the \texttt{ConvexMeshShape::addEdge()} method for each edge of the mesh. The first parameter is the index of the first vertex of the edge and the
second parameter is the index of the second vertex. Do not worry about calling this method multiple times for the same edge, the edge information will be added only
Do not forget to enable the fast collision detection by asking the collision shape to use the edges information you have just provided. To do this, you need to
\subsection{Adding a Collision Shape to a body - The Proxy Shape concept}
\begin{sloppypar}
Now that you know how to create a collision shape, we will see how to add it to a given body. \\
First, note that when you add a collision shape to a body, the collision shape object that you gave as a parameter
will be copied internally. Therefore, you can destroy the collision shape object right after it has been added to the body. \\
In order to add a collision shape to a body, you need to use the \texttt{CollisionBody::addCollisionShape()} method for a Collision Body and the
\texttt{RigidBody::addCollisionShape()} method for a Rigid Body. You will have to provide the collision shape transform in parameter. This is the
transformation mapping the local-space of the collision shape to the local-space of the body. For a Rigid Body, you will also have to provide the
mass of the shape you want to add. As explained before, this is used to automatically compute the center of mass, total mass and inertia tensor of the body. \\
The \texttt{addCollisionShape()} method returns a pointer to a Proxy Shape. A Proxy Shape is what links a given collision shape to the body it has been added.
You can use the returned Proxy Shape to get or set parameters of the given collision shape in that particular body. This concept is also called \emph{fixture} in some
other physics engines. In ReactPhysics3D, a Proxy Shape is represented by the \texttt{ProxyShape} class. \\
When you create a collision shape, you can add it to multiple bodies. You do not need to create several times the same collision shape. \\
The following example shows how to add a sphere collision shape with a given mass to a rigid body and also how to remove it from the body using the Proxy Shape pointer. \\
\end{sloppypar}
\begin{lstlisting}
// Create the sphere collision shape
rp3d::decimal radius = rp3d::decimal(3.0)
const rp3d::BoxShape shape(radius);
// Transform of the collision shape
// Place the shape at the origin of the body local-space
// If you want to remove the collision shape from the body
// at some point, you need to use the proxy shape
body->removeCollisionShape(proxyShape);
\end{lstlisting}
\vspace{0.6cm}
As you can see, you can use the \texttt{removeCollisionShape()} method to remove a collision shape from a body by using the Proxy Shape. Note that
after removing a collision shape, the corresponding Proxy Shape pointer will not be valid anymore. It is not necessary to manually remove all the collision shapes from
a body at the end of your application. They will automatically be removed when you destroy the body.
\subsection{Collision filtering}
\label{sec:collisionfiltering}
By default all the collision shapes of all your bodies are able to collide with each other in the world. However, sometimes we want a body to collide only with a given
group of bodies and not with other bodies. This is called collision filtering. The idea is to group the collision shapes of bodies into categories. Then we can specify
for each collision shape against which categories it will be able to collide. \\
ReactPhysics3D uses bits mask to represent categories. The first thing to do is to assign a category to the collision shapes of your body. To do this, you need to
call the \texttt{ProxyShape::setCollisionCategoryBits()} method on the corresponding Proxy Shape as in the following example. Here we consider that we have four bodies
where each one has a single collision shape. \\
\begin{lstlisting}
// Enumeration for categories
enum Category {
CATEGORY1 = 0x0001,
CATEGORY2 = 0x0002,
CATEGORY3 = 0x0004
};
// Set the collision category for each proxy shape of
As you can see, the collision shape of body 1 will be part of the category 1, the collision shape of body 2 will be part of the category 2 and the collision shapes of bodies 3 and 4 will be
Now, for each collision shape, we need to specify with which categories the shape is allowed to collide with. To do this, you need to use the \texttt{ProxyShape::setCollideWithMaskBits()}
method of the Proxy Shape. Note that you can specify one or more categories using the bitwise OR operator. The following example shows how to specify with which categories the
As you can see, we specify that the body 1 will be allowed to collide with bodies from the categorie 3. We also indicate that the body 2 will be allowed to collide with bodies from the
category 1 and 3 (using the bitwise OR operator). Finally, we specify that bodies 3 and 4 will be allowed to collide against bodies of the category 2. \\
A collision shape is able to collide with another only if you have specify that the category mask of the first shape is part of the \emph{collide with} mask of the second shape. It
is also important to understand that this condition must be satisfied in both directions. For instance in the previous example, the body 1 (of category 1) says that it wants to collide
against bodies of the category 3 (for instance against body 3). However, body 1 and body 3 will not be able to collide because the body 3 does not say that it wants to collide
with bodies from category 1. Therefore, in the previous example, the body 2 is allowed to collide against bodies 3 and 4 but no other collision is allowed. \\
In the same way, you can perform this filtering for ray casting (described in section \ref{sec:raycasting}). For instance, you can perform a ray cast test
against a given subset of categories of collision shapes only.
The \texttt{BallAndSocketJoint} class describes a ball and socket joint between two bodies. In a ball and socket joint, the two bodies cannot translate with respect to each other.
However, they can rotate freely around a common anchor point. This joint has three degrees of freedom and can be used to simulate a chain of bodies for instance. \\
In order to create a ball and socket joint, you first need to create an instance of the \texttt{BallAndSocketJointInfo} class with the necessary information. You need to provide the pointers to the
two rigid bodies and also the coordinates of the anchor point (in world-space). At the joint creation, the world-space anchor point will be converted into the local-space of the two rigid
bodies and then, the joint will make sure that the two local-space anchor points match in world-space. Therefore, the two bodies need to be in a correct position at the joint creation. \\
The \texttt{HingeJoint} class describes a hinge joint (or revolute joint) between two rigid bodies. The hinge joint only allows rotation around an anchor point and
around a single axis (the hinge axis). This joint can be used to simulate doors or pendulums for instance. \\
In order to create a hinge joint, you first need to create a \texttt{HingeJointInfo} object with the necessary information. You need to provide the pointers to the
two rigid bodies, the coordinates of the anchor point (in world-space) and also the hinge rotation axis (in world-space). The two bodies need to be in a correct position
With the hinge joint, you can constrain the motion range using limits. The limits of the hinge joint are the minimum and maximum angle of rotation allowed with respect to the initial
angle between the bodies when the joint is created. The limits are disabled by default. If you want to use the limits, you first need to enable them by setting the
\texttt{isLimitEnabled} variable of the \texttt{HingeJointInfo} object to \emph{true} before you create the joint. You also have to specify the minimum and maximum limit
angles (in radians) using the \texttt{minAngleLimit} and \texttt{maxAngleLimit} variables of the joint info object. Note that the minimum limit angle must be in the
range $[-2\pi; 0]$ and the maximum limit angle must be in the range $[0; 2\pi]$. \\
It is also possible to use the \texttt{HingeJoint::enableLimit()}, \texttt{HingeJoint::setMinAngleLimit()} and \texttt{HingeJoint::setMaxAngleLimit()} methods to specify
the limits of the joint after its creation. See the API documentation for more information.
A motor is also available for the hinge joint. It can be used to rotate the bodies around the hinge axis at a given angular speed and such that the torque applied to
rotate the bodies does not exceed a maximum allowed torque. The motor is disabled by default. If you want to use it, you first have to activate it using the
\texttt{isMotorEnabled} boolean variable of the \texttt{HingeJointInfo} object before you create the joint. Then, you need to specify the angular motor speed (in radians/seconds)
using the \texttt{motorSpeed} variable and also the maximum allowed torque (in Newton $\cdot$ meters) with the \texttt{maxMotorTorque} variable. \\
It is also possible to use the \texttt{HingeJoint::enableMotor()}, \texttt{HingeJoint::setMotorSpeed()} and \texttt{HingeJoint::setMaxMotorTorque()} methods to
enable the motor of the joint after its creation. See the API documentation for more information.
The \texttt{SliderJoint} class describes a slider joint (or prismatic joint) that only allows relative translation along a single direction. It has a single degree of freedom and allows no
relative rotation. In order to create a slider joint, you first need to specify the anchor point (in world-space) and the slider axis direction (in world-space). The constructor of the
\texttt{SliderJointInfo} object needs two pointers to the bodies of the joint, the anchor point and the axis direction. Note that the two bodies have to be in a correct initial position when
It is also possible to control the range of the slider joint motion using limits. The limits are disabled by default. In order to use the limits when the joint is created, you first
need to activate them using the \texttt{isLimitEnabled} variable of the \texttt{SliderJointInfo} class. Then, you need to specify the minimum and maximum translation limits
(in meters) using the \texttt{minTranslationLimit} and \texttt{maxTranslation\-Limit} variables. Note that the initial position of the two bodies when the joint is created
corresponds to a translation of zero. Therefore, the minimum limit must be smaller or equal to zero and the maximum limit must be larger or equal to zero. \\
You can also use the \texttt{SliderJoint::enableLimit()}, \texttt{SliderJoint::\-setMinTranslationLimit()} and \texttt{SliderJoint::setMaxTranslationLimit()} methods to
enable the limits of the joint after its creation. See the API documentation for more information.
The slider joint also has a motor. You can use it to translate the bodies along the slider axis at a given linear speed and such that the force applied to
move the bodies does not exceed a maximum allowed force. The motor is disabled by default. If you want to use it when the joint is created, you first have to activate it using the
\texttt{isMotorEnabled} boolean variable of the \texttt{SliderJointInfo} object before you create the joint. Then, you need to specify the linear motor speed (in meters/seconds)
using the \texttt{motorSpeed} variable and also the maximum allowed force (in Newtons) with the \texttt{maxMotorForce} variable. \\
It is also possible to use the \texttt{SliderJoint::enableMotor()}, \texttt{SliderJoint::setMotorSpeed()} and \texttt{SliderJoint::setMaxMotorForce()} methods to enable the
motor of the joint after its creation. See the API documentation for more information.
The \texttt{FixedJoint} class describes a fixed joint between two bodies. In a fixed joint, there is no degree of freedom, the bodies are not allowed to translate
or rotate with respect to each other. In order to create a fixed joint, you simply need to specify an anchor point (in world-space) to create the \texttt{FixedJointInfo}
\subsection{Collision between the bodies of a Joint}
By default the two bodies involved in a joint are able to collide with each other. However, it is possible to disable the collision between the two bodies that are part
of the joint. To do it, you simply need to set the variable \texttt{isCollisionEnabled} of the joint info object to \emph{false} when you create the joint. \\
For instance, when you create a \texttt{HingeJointInfo} object in order to construct a hinge joint, you can disable the collision between the two bodies of the joint as in the
rigid body involved in a joint will automatically destroy that joint.
\section{Ray casting}
\label{sec:raycasting}
You can use ReactPhysics3D to test intersection between a ray and the bodies of the world you have created. Ray casting can be performed against multiple bodies, a single body or
any proxy shape of a given body. \\
The first thing you need to do is to create a ray using the \texttt{Ray} class of ReactPhysics3D. As you can see in the following example, this is very easy. You
simply need to specify the point where the ray starts and the point where the ray ends (in world-space coordinates). \\
\begin{lstlisting}
// Start and end points of the ray
rp3d::Vector3 startPoint(0.0, 5.0, 1.0);
rp3d::Vector3 endPoint(0.0, 5.0, 30);
// Create the ray
rp3d::Ray ray(startPoint, endPoint);
\end{lstlisting}
\vspace{0.6cm}
Any ray casting test that will be described in the following sections returns a \texttt{RaycastInfo} object in case of intersection with the ray.
This structure contains the following attributes: \\
\begin{description}
\item[worldPoint] Hit point in world-space coordinates
\item[worldNormal] Surface normal of the proxy shape at the hit point in world-space coordinates
\item[hitFraction] Fraction distance of the hit point between \emph{startPoint} and \emph{endPoint} of the ray. The hit point \emph{p} is such that
\item[body] Pointer to the Collision Body or Rigid Body that has been hit by the ray
\item[proxyShape] Pointer to the Proxy Shape that has been hit by the ray
\end{description}
Note that you can also use collision filtering with ray casting in order to only test ray intersection with specific proxy shapes.
Collision filtering is described in section \ref{sec:collisionfiltering}.
\subsection{Ray casting against multiple bodies}
This ray casting query will return all the proxy shapes of all bodies in the world that are intersected by a given ray.
\subsubsection{The RaycastCallback class}
First, you have to implement your own class that inherits from the \texttt{RaycastCallback} class. Then, you need to override the
\texttt{RaycastCallback::notifyRaycastHit()} method in your own class. An instance of your class have to be provided as a parameter
of the raycast method and the \texttt{notifyRaycastHit()} method will be called for each proxy shape that is hit by the ray. You will receive, as a parameter
of this method, a \texttt{RaycastInfo} object that will contain the information about the raycast hit (hit point, hit surface normal, hit body, hit proxy shape, \dots). \\
In your \texttt{notifyRaycastHit()} method, you need to return a fraction value that will specify the continuation of the ray cast after a hit.
The return value is the next maxFraction value to use. If you return a fraction of 0.0, it means that the raycast should terminate. If you return a
fraction of 1.0, it indicates that the ray is not clipped and the ray cast should continue as if no hit occurred. If you return the fraction in the
parameter (hitFraction value in the \texttt{RaycastInfo} object), the current ray will be clipped to this fraction in the next queries. If you return -1.0, it will
ignore this ProxyShape and continue the ray cast. Note that no assumption can be done about the order of the calls of the \texttt{notifyRaycastHit()} method. \\
Here is an example about creating your own raycast callback class that inherits from the \texttt{RaycastCallback} class and how to override the
\texttt{notifyRaycastHit()} method: \\
\begin{lstlisting}
// Class WorldRaycastCallback
class MyCallbackClass : public rp3d::RaycastCallback {
Now that you have your own raycast callback class, you can use the \texttt{raycast()} method to perform a ray casting test
on a Collision World or a Dynamics World. \\
The first parameter of this method is a reference to the \texttt{Ray} object representing the ray you need to test intersection with. The second parameter is a pointer to
the object of your raycast callback object. You can specify an optional third parameter which is the bit mask for collision filtering.
It can be used to raycast only against selected categories of proxy shapes as described in section \ref{sec:collisionfiltering}. \\
\begin{lstlisting}
// Create the ray
rp3d::Vector3 startPoint(1 , 2, 10);
rp3d::Vector3 endPoint(1, 2, -20);
Ray ray(startPoint, endPoint);
// Create an instance of your callback class
MyCallbackClass callbackObject;
// Raycast test
world->raycast(ray, &callbackObject);
\end{lstlisting}
\vspace{0.6cm}
\subsection{Ray casting against a single body}
\begin{sloppypar}
You can also perform ray casting against a single specific Collision Body or Rigid Body of the world. To do this, you need to use the
\texttt{CollisionBody::raycast()} method. This method takes two parameters. The first one is a reference to the \texttt{Ray} object and the second one
is a reference to the \texttt{RaycastInfo} object that will contain hit information if the ray hits the body. This method returns true if the ray hits the
body. The \texttt{RaycastInfo} object will only be valid if the returned value is \emph{true} (a hit occured). \\
\end{sloppypar}
The following example shows how test ray intersection with a body: \\
\begin{lstlisting}
// Create the ray
rp3d::Vector3 startPoint(1 , 2, 10);
rp3d::Vector3 endPoint(1, 2, -20);
Ray ray(startPoint, endPoint);
// Create the raycast info object for the
// raycast result
RaycastInfo raycastInfo;
// Raycast test
bool isHit = body->raycast(ray, raycastInfo);
\end{lstlisting}
\vspace{0.6cm}
\subsection{Ray casting against the proxy shape of a body}
You can also perform ray casting against a single specific Proxy Shape of a Collision Body or Rigid Body of the world. To do this, you need to use the
\texttt{ProxyShape::raycast()} method of the given Proxy Shape. This method takes two parameters. The first one is a reference to the \texttt{Ray}
object and the second one is a reference to the \texttt{RaycastInfo} object that will contain hit information if the ray hits the body. This method returns
true if the ray hits the body. The \texttt{RaycastInfo} object will only be valid if the returned value is \emph{true} (a hit occured). \\
The following example shows how to test ray intersection with a given Proxy Shape: \\
Sometimes, you want to receive notifications from the physics engine when a given event happens. The \texttt{EventListener} class can be used for that purpose. In order to use
it, you need to create a new class that inherits from the \texttt{EventListener} class and overrides some methods that will be called by the ReactPhysics3D library when some events
If you want to be notified when two bodies that were separated before become in contact, you need to override the \texttt{EventListener::beginContact()} method in your event
listener class. Then, this method will be called when the two separated bodies becomes in contact. \\
If you receive a notification when a new contact between two bodies is found, you need to override the \texttt{EventListener::newContact()} method in your event listener class. Then, this
method will be called when a new contact is found.
If you build the library with the \texttt{PROFILING\_ENABLED} variable enabled (see section \ref{sec:cmakevariables}), a real-time profiler will collect information while the application
is running. Then, at the end of your application, when the destructor of the \texttt{DynamicsWorld} class is called, information about the running time of the library will be displayed in the
standard output. This can be useful to know where time is spent in the different parts of the ReactPhysics3D library in case your application is too slow.
