The Raycasting component enables scenes to request raycasting from the game engine. The resulting data will be available in a RaycastResult component associated with the same Entity.
The Raycast component initiates the raycasting process by specifying parameters such as origin, direction, and query type. It is attached to the Entity initiating the raycast.
The RaycastResult component stores the results of the raycasting process, including information about the ray and the intersections with meshes. It is attached to the Entity that initiated the raycast after the raycasting is completed.
Both components PBRaycast and PBRaycastResult are serialized with
protocol buffers.
parameters:
COMPONENT_ID: 1067
COMPONENT_NAME: core::Raycast
CRDT_TYPE: LastWriteWin-Element-Set
parameters:
COMPONENT_ID: 1068
COMPONENT_NAME: core::RaycastResult
CRDT_TYPE: LastWriteWin-Element-Set
message PBRaycast {
// Correlation ID, defined by the scene and used internally by the scene
uint32 timestamp = 1;
// How much to offset the starting point of the ray, relative to the
// entity's transform.
optional Vector3 origin_offset = 2;
oneof direction {
// The direction of the ray in local coordinates (relative to the origin point)
Vector3 local_direction = 3;
// The direction of the ray in global coordinates (relative to origin)
Vector3 global_direction = 4;
// Target coordinates of the raycast, in global coordinates
Vector3 global_target = 5;
// Target entity
uint32 target_entity = 5;
}
// Maximum length of the ray
float max_distance = 6;
// the RaycastQueryType behavior
RaycastQueryType query_type = 7;
// Indicates the renderer to perform the raycast on every scene tick (ADR-148),
// otherwise it will be performed only once
bool continuous = 8;
// Collision mask, by default all bits are 1 (0xFFFF_FFFF)
optional uint32 collision_mask = 9;
}
message PBRaycastResult {
// the timestamp of the Raycast component, used to correlate results
int32 timestamp = 1;
// the starting point of the ray in global coordinates
Vector3 global_origin = 2;
// the direction vector of the ray in global coordinates
Vector3 direction = 3;
// zero or more hits
repeated RaycastHit hits = 4;
}
// RaycastHit contains information about the intersection of a ray with a mesh.
// This RaycastHit structure is also re-used by the PointerEvents component
message RaycastHit {
// Hit position of the raycast in global coordinates
Vector3 position = 1;
// Starting point of the ray in global coordinates
Vector3 global_origin = 2;
// Direction vector of the ray in global coordinates
Vector3 direction = 3;
// Normal of the hit surface in global coordinates
Vector3 normal_hit = 4;
// Distance between the ray origin and the hit position, in virtual meters
float length = 5;
// Mesh name, if collision happened inside a GltfContainer
optional string mesh_name = 6;
// ID of the Entity that has the impacted mesh attached
uint32 entity_id = 7;
}
// RaycastQueryType indicates whether the ray should stop on the first collition,
// or continue until the max_distance is reached
enum RaycastQueryType {
RQT_HIT_FIRST = 0;
RQT_QUERY_ALL = 1;
}
A raycast is a spatial query that uses a ray vector with an origin and
direction to identify intersecting meshes.
How Raycasts work will be left outside of this specification since these are well-known tools in 3D engines.
As defined in (ADR-148)[/adr/ADR-148], raycasts are executed AFTER all the incoming messages from the scene are processed and AFTER all the physics (like gravity and moving platforms) were executed.
That implies that raycast MUST be executed after the "world matrix" of the entity in which they exist is calculated and not dirty. This is of extreme importance, because the ray takes its origin point based on the worldMatrix of the entity. Many interesting properties are inherited from this design, like raycasts that react to billboard rotations or raycasts that are attached to bones and animations of the avatars.
The origin point and global direction are calculated as follow:
// Returns a new Vector3 set with the result of the transformation by the given matrix of the given vector.
declare function TransformCoordinates(position: Vector3, matrix: Matrix): Vector3
// Returns a new Vector3 set with the result of the normal transformation by the given matrix of the given vector.
declare function TransformNormal(normal: Vector3, matrix: Matrix): Vector3
// first calculate the origin of the ray in global coordinates
const globalOrigin = TransformCoordinates(
raycast.originOffset ?? Vector3.Zero(),
entity.getWorldMatrix()
)
// and then calculate the global direction in global coordinates
let globalDirection = Vector3.Forward()
if (raycast.localDirection) {
// then localDirection, is used to detect collisions in a path
// i.e. Vector3.Forward(), it takes into consideration the rotation of
// the entity to perform the raycast in local coordinates
globalDirection = TransformNormal(raycast.localDirection, entity.getWorldMatrix())
} else if (raycast.globalDirection) {
// this is the simplest one, for example Vector3.Down() to evaluate if
// there is a floor and how far it is. No matter the local rotation, tilt or yaw
globalDirection = raycast.globalDirection
} else if (raycast.globalTarget) {
// this one is to make it easy to point towards a pin-pointed element
// in global space, like a fixed tower
globalDirection = Vector3.subtract(raycast.globalTarget, globalOrigin)
} else if (raycast.targetEntity) {
// this one is to make it easy to point towards another entity in space.
// i.e. pointing one laser emitter to a receiver and detect if a user
// collides the laser
const globalTarget = getGlobalPosition(raycast.targetEntity)
globalDirection = Vector3.subtract(globalTarget, globalOrigin)
}
globalDirection.normalizeInPlace()
That depends entirely on the bool continuous property. If set to
true, the raycast MUST execute on every scene tick. Otherwise, the raycast MUST
execute within the scene tick they were added.
In an ideal scenario in which all messages and raycast are processed within the time window/quota defined in (ADR-148)[/adr/ADR-148], the scenes will receive the raycast result on the next update loop of the ECS. Enabling immediate-mode raycasts like the follwing example:
function laserDamageSystem() {
for (const [entity, _turret] of engine.entitiesWith(LaserTurret)) {
const result = raycast(entity, Vector3.Forward())
if (result?.hits.length) {
// apply damage to all hitted entities
}
}
}
// this helper creates sets a Raycast component in the entity and return
// its RaycastResult
function raycast(entity: Entity, direction: Vector3) {
Object.assign(Raycast.getMutableOrCreate(entity), {
// relative to the entity's rotation
localDirection: direction,
continous: true,
queryType: ALL
})
return RaycastResult.getOrNull(entity)
}
timestamp property
The timestamp property is a correlation number, only defined by the scene. The renderer MUST
copy the value of the timestamp from the Raycast component to the RaycastResult
component.
Having multiple continuous raycasts in a scene can significantly impact performance. As a scene developer, it is RECOMMENDED to minimize the number of continuous raycasts. Renderer implementations MUST count the computation of raycasts towards the execution quota of each scene to prevent non-optimized scenes from negatively affecting the overall experience.
The collision_mask parameter allows scene creators to target different layers of
elements, including colliders, avatars, visible meshes, UI elements, and more. The flags for
this mask are defined in the ColliderLayer enum, which is part of the
MeshRenderer component. It is RECOMMENDED that scene creators carefully select
the least amount of flags for each raycast to prevent a performance penalty on the engine.
There are three types of raycasts, as defined by the RaycastQueryType enum:
QUERY_ALL: This type MUST include all intersected elements within the specified
max_distance parameter.
HIT_FIRST: This type MUST include the first intersected element, which is the
closest one to the origin point. It is also subject to the
max_distance parameter filter.
NONE: This type will not intersect any mesh on the renderer, it will provide an
empty result with the final position of the ray and its calculated global direction.
The Raycasting component can be used in various scenarios within a scene, such as:
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 and RFC 8174.