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 these shapes. A shape can be used for multiple bones and is big enough to contain the skinned geometry deformed this these bones. Defining a ragdoll consists in listing each physic shape in the system, which bone it's controlling and some properties like shape size, rotation axis constraint. Current implementation does not allow automatic size computation.

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: BABYLON.Axis.Z,
                min: -1,
                max: 1,
                boxOffset: 0.3,
                boneOffsetAxis: BABYLON.Axis.X
            }
            ...

In this example, 3 shapes are created: 1 for root bone, 2 for arm_r and arm_l. As properties for arms are the same because symmetrical, 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 that will be constrained in angles. min and max define these limits. boneOffsetAxis set the axis used to offset the shape on. boxOffset is the world size value to shift the shape along the axis. By default, physics shapes are centered on the bone. This offset allows to have the shape to have one of its side on the bone.

const ragdoll = new BABYLON.Ragdoll(skeleton, newMeshes[0], config);

Next step is to create the ragdoll instance. This is done in 1 line and 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 body but it's the animation that drives the physics.

At any moment after, to make the ragdoll dynamically updated, call:

ragdoll.ragdoll();

Dispose the ragdoll to stop it.

Interactions

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

ragdoll.getAggregate(0)?.body.applyImpulse(new BABYLON.Vector3(200,200,200), BABYLON.Vector3.ZeroReadOnly);

Interactions

Few steps are needed to physicalize a bone:

// 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(BABYLON.PhysicsPrestepType.ACTION);
// no feedback from physics to transform
boxAggregate2.body.disableSync = true;

Limitations

Imported .GLTF/.GLB will only work as ragdoll in Right Handed scenes. In Left Handed scenes, an intermediate Transform Node is added at the root to emulate the LH/RH coordinate switch. This intermediate transform is not supported by the ragdoll physics to bone conversion.