Systems

LifeCycle

Streamables

Prioritization

Scene bounds checker

Bounds are described by 4 planes:

public readonly struct SceneCircumscribedPlanes
{
    public readonly float MinX;
    public readonly float MaxX;
    public readonly float MinZ;
    public readonly float MaxZ;
}

It means that effectively parcels a scene consists of are circumscribed (approximated by a rectangular area).

Rendering

The capability of culling meshes as they go out of scene bounds is provided by Scene.shader:

_PlaneClipping("PlaneClipping", Vector) = (-2147483648, 2147483648, -2147483648, 2147483648)

_PlaneClipping is set only once on initialization of GLTFContainer or MeshPrimitive. For empty scenes planes always have the default value.

Clipping is performed on the shader side for each pass via a simple algorithm, effectively leading to zero overhead.

static const float3 _PlaneX = float3(1.0, 0.0, 0.0);
static const float3 _PlaneY = float3(0.0, 0.0, 1.0);

void ClipFragmentViaPlaneTests(const float3 _positionWS, const float _PlaneClippingPosX, const float _PlaneClippingNegX, const float _PlaneClippingPosZ, const float _PlaneClippingNegZ)
{
    float distanceX = dot(_positionWS, _PlaneX);
    clip(distanceX - _PlaneClippingPosX);
    clip(-distanceX + _PlaneClippingNegX);

    float distanceZ = dot(_positionWS, _PlaneY);
    clip(distanceZ - _PlaneClippingPosZ);
    clip(-distanceZ + _PlaneClippingNegZ);
}

Colliders

Unlike meshes, colliders can't be clipped partially. Therefore, if collider bounds intersect scene bounds it gets fully disabled.

collider.enabled = sceneGeometry.CircumscribedPlanes.Intersects(collider.bounds);

CheckColliderBoundsSystem is responsible for this logic:

• Both Primitive Colliders and Colliders originated from GLTF assets are checked
• This check is performed only for assets in the 0 partition bucket (the closest ones including the scene the player is currently on)
• Execution is throttled once per fixed frame