Rigid Bodies
In Babylon.js, the rigid bodies are objects that maintain its shape and size when forces act upon theme. Unlike soft bodies, which can deform, rigid bodies only move, rotate, or collide without bending or stretching. A rigid body consists of two key components:
- Bodies - define an objects motion, mass, velocity, and interactions
- Shapes - determine its collision geometry.
Together, they enable realistic physics-based behavior in a scene.
Body
The PhysicsBody it is virtual object that represents a physical object in a simulation. It used to define the physical properties and behavior of objects in a scene. Below is an overview of its key properties:
Mass
It represents how the object responds to forces and torques. It is composed by:
mass- its resistance to acceleration when forces ar applied (how heavy is and object)centerOfMass- the point releative to the object where the forces act (also the point that a body spins around)inertia- a tensor what defines how the object resist angular acceleration based on its shape and mass distribution (how far away the mass is distributed from the center of the mass affecting rotations)inertiaOrientation- the rotation of the inertia tensor relative to the object’s local coordinate system (the axes that a body spins around)
Some physics engines, such as Havok, can automatically determine the mass properties of a body from the body’s shape, so it is very common to supply only the mass parameter and allow the rest of the properties to be derived by the engine.
Position
It represents the world-space location of the body. It is dynamically updated as the physics simulation progresses.
Velocity
It defines the rate of change of position over time. It includes linear velocity (movement in the space) and angular velocity (rotation).
Motion Type
It determines how the physics engine updates the object’s motion. It can be:
PhysicsMotionType.STATIC- the object doesn’t move and is unaffected by forces but it affects other bodies in the engine (e.g: terrain, walls, floors)PhysicsMotionType.DYNAMIC- the object moves freely under physics forces like gravity and collisionsPhysicsMotionType.ANIMATED- the object follows a user-defined animation while interacting with physics (it causes collisions but it isn’t affected by, e.g: an elevator which should always reach the correct floor, no matter how many other bodies are inside the elevator)
Sleep Mode
To optimize performance, the physics engine can put objects to sleep when they are at rest. The engine will skip they calculations until they should collide with another body or if a force il applied (the physics engine will automatically put bodies to sleep when they have come to rest and wake those bodies up when appropriate).
Shape
The PhysicsShape is a virtual rapresentation of the collision geometry of a physics body, used for collision detection and response. In order to collide with other object, a body needs a shape.
Material
A material holds friction and restitution and is associated with a PhysicsShape:
friction, how much resistance to sliding exists between two objects in contactrestitution(elasticity or bounciness), how much energy is conserved in a collision between two objects. It describes how much an object will bounce back after a collision, relative to how much it was moving before the collision. Restitution is often used to model the behavior of objects bouncing, colliding, or deforming.
Shapes
Shapes are geometries that the bodis will have when interacting with the world. Depending on the chosen shape, the body will react differently to colliding with other objects. There are several types of shapes:
PhysicsShapeSphere- a spherical collision shape defined by a center point and radius.PhysicsShapeCylinder- a cylinder shape defined by the positions of its bottom and top ends, and radius.PhysicsShapeCapsule- a capsule shape defined by two points (start and end) and a radius.PhysicsShapeBox- a box shape defined by a center point, rotation, and dimensions.PhysicsShapeConvexHull- a convex hull shape generated from a mesh, with the engine calculating the convex part for concave meshes.PhysicsShapeMesh- a mesh-based shape suitable for concave meshes.PhysicsShapeContainer- a container shape that can hold multiple child shapes for complex collision structures.PhysicsShapeHeightField- a height field shape used for creating terrains from heightmaps.
If multiple bodies share the same or the similar enough geometry, the same shape can be reused for all of them, greatly increasing the performance.
Aggregates
The aggregates provide a streamlined way to add physics to objects by automatically creating physics bodies, assigning collision shapes, setting motion types, and managing properties like mass, friction, restitution, and damping. They simplify the integration of rigid body dynamics, allowing objects to interact with forces, collisions, and constraints without requiring manual physics setup.
Learn More
For advanced use cases and customizations, please refer to Babylon.js documentation:
