Ragdolls

Defining a ragdoll

A ragdoll is a physicalized system that controls a skeleton and its skinned mesh. That system is composed of shapes for collision detection and constraints between those shapes. A shape can be used for multiple bones and is large enough to contain the skinned geometry deformed by those bones. Defining a ragdoll consists of listing each physics shape in the system, which bone it is controlling, and some properties such as shape size and rotation axis constraints. The current implementation does not allow automatic size computation.

import { Axis } from "@babylonjs/core/Maths/math.axis";
const config = [
            { bones: ["root"], size: 0.6, boxOffset: 0.1 },
            // Arms.
            {
                bones: ["arm_r", "arm_l"],
                depth: 0.3,
                size: 0.3,
                width: 0.6,
                rotationAxis: Axis.Z,
                min: -1,
                max: 1,
                boxOffset: 0.3,
                boneOffsetAxis: Axis.X
            }
            ...

In this example, 3 shapes are created: 1 for the root bone and 2 for arm_r and arm_l. Because the properties for the arms are the same due to symmetry, there is no need to set 2 entries in the configuration. size property is used if depth, width or height are not set. rotationAxis defines the axis whose angles will be constrained. min and max define those limits. boneOffsetAxis sets the axis used to offset the shape. boxOffset is the world-size value used to shift the shape along that axis. By default, physics shapes are centered on the bone. This offset allows one side of the shape to sit on the bone.

import { Ragdoll } from "@babylonjs/core/Physics/v2/ragdoll";
const ragdoll = new Ragdoll(skeleton, newMeshes[0], config);

The next step is to create the ragdoll instance. This is done in one line, and the user must provide the skeleton, the skinned mesh, and the configuration. Once instantiated, the ragdoll is in Kinematic mode: physicalized bones can interact with other physics bodies, but the animation drives the physics.

At any point after that, to make the ragdoll update dynamically, call:

ragdoll.ragdoll();

Dispose the ragdoll to stop it.

Interactions

Get the aggregate associated with a bone with the getAggregate function. The returned aggregate works like any other aggregate: it is possible to get the shape or body and apply an impulse.

import { Vector3 } from "@babylonjs/core/Maths/math.vector";
ragdoll.getAggregate(0)?.body.applyImpulse(new Vector3(200, 200, 200), Vector3.ZeroReadOnly);

Interactions

A few steps are needed to physicalize a bone:

import { PhysicsPrestepType } from "@babylonjs/core/Physics/v2/IPhysicsEnginePlugin";
// attach sphere to a bone
sph.attachToBone(scene.getBoneByName("bone52"), result.meshes[0]);
// physics sphere is moved to a target (and not teleported) 
boxAggregate2.body.setPrestepType(PhysicsPrestepType.ACTION);
// no feedback from physics to transform
boxAggregate2.body.disableSync = true;

Limitations

Imported glTF/GLB files only work as ragdolls in right-handed scenes. In left-handed scenes, an intermediate transform node is added at the root to perform the handedness conversion described in Coordinate Systems and Handedness. This intermediate transform is not supported by the ragdoll physics-to-bone conversion.