Raycasting

Raycasting

core/raycaster.mojo. A Raycaster carries a Ray through a scene and returns everything it meets, nearest first: meshes, skinned meshes, lines, points and sprites. Use it to find what is under a pixel.

three.js: Raycaster, setFromCamera, intersectObject, intersectObjects, Mesh.raycast, SkinnedMesh.raycast, Line.raycast, Points.raycast, Sprite.raycast.

Construct one

var caster = Raycaster(origin, direction)
var ranged = Raycaster(origin, direction, Length(0.1, METER), Length(50.0, METER))

Argument	Type	Default	Meaning
origin	Vector3	required	Where the ray starts, in world space.
direction	Vector3	required	Which way it goes. Any length but zero.
near	Length	zero	Hits nearer than this are dropped.
far	Length	unbounded	Hits further than this are dropped.

The two distances are lengths. A bare number does not compile. near must not be negative, far must not be below near, and neither can be NaN.

Field	Default	Meaning
line_threshold	1 m	How near a line the ray must pass to meet it. three.js: params.Line.threshold.
points_threshold	1 m	How near a point the ray must pass to meet it. three.js: params.Points.threshold.

Both thresholds are a meter by default, as in three.js. That is wide for a small scene. Set them to what a pointer must reach. A negative threshold, or one that is not a number, raises when it is used.

caster.layers is a Layers, on layer zero by default. An object whose node shares no layer with it is not tested. See Scene graph.

Aim it

Method	Meaning
set(origin, direction)	A new ray.
set_from_camera(coords, camera, scene)	Through a point of the camera's image. coords is a Vector2 in normalized device coordinates: -1 to 1 each way, y up.
set_from_pixel(x, y, width, height, camera, scene)	Through a pixel of an image the camera would render at width by height. y counts down from the top. The center of pixel (i, j) is (i + 0.5, j + 0.5).

A perspective camera's ray leaves the camera's position toward the point. An orthographic camera's ray starts on the camera's own plane and goes the way the camera looks. Every orthographic ray is parallel. Both are three.js's choices.

set_from_camera and set_from_pixel also keep the camera, three.js's Raycaster.camera. A sprite faces the camera, so a sprite is picked only after one of them. A later set keeps the camera.

The camera can ride a scene node. The scene must be updated. See Cameras.

Ask the scene

var hits = caster.intersect_scene(scene, assets)
if len(hits) > 0:
    print(hits[0].mesh.node, hits[0].point)

Method	Meaning
intersect_scene(scene, assets) -> List[Hit]	Every hit on everything the scene holds that can be picked, nearest first. Sprites are left out until a camera is kept.
intersect_mesh(scene, assets, index) -> List[Hit]	Every hit on scene.meshes[index], nearest first.
intersect_instanced_mesh(scene, assets, index) -> List[Hit]	Every hit on every instance of scene.instanced_meshes[index].
intersect_batched_mesh(scene, assets, index) -> List[Hit]	Every hit on every instance of scene.batched_meshes[index].
intersect_lod(scene, assets, index) -> List[Hit]	Every hit on the level of scene.lods[index] that the ray's origin picks.
intersect_skinned_mesh(scene, assets, index) -> List[Hit]	Every hit on scene.skinned_meshes[index], where its bones carry it.
intersect_line(scene, assets, index) -> List[Hit]	Every segment of scene.lines[index] within line_threshold of the ray.
intersect_points(scene, assets, index) -> List[Hit]	Every point of scene.points[index] within points_threshold of the ray.
intersect_sprite(scene, assets, index) -> List[Hit]	The hit on scene.sprites[index], if any.
intersect_wide_line(scene, assets, index, camera, width, height) -> List[Hit]	Every segment of scene.wide_lines[index] that the ray passes within half the line's width of. See wide lines.

Hit

Field	Meaning
distance	Meters from the ray's origin.
point	Where, in world space.
normal	The face's front in world space, unit length. The face as wound, whichever side the ray came from. Zero for a line, points or a sprite, which have no face. For a wide line, the way back along the ray.
kind	A HitKind: which list index counts in. MESH_HIT, INSTANCED_HIT, BATCHED_HIT, LOD_HIT, SKINNED_HIT, LINE_HIT, POINTS_HIT, SPRITE_HIT or WIDE_LINE_HIT.
index	The object's position in that list.
instance	Which instance of an instanced or batched mesh, or which level of an LOD. -1 for a plain mesh. three.js's instanceId and batchId.
mesh	The shape struck as a Mesh: its node, geometry and material. For a plain mesh, the mesh itself. For a mesh that wears a list, material is the material of the group struck. A sprite has no geometry, so its geometry is -1.
triangle	Which of the geometry's triangles, from zero. For a line or a wide line, which segment. For points, which point. For a sprite, which of its two halves. three.js's faceIndex and index.
uv, uv1	The texture coordinates at the point, as an Optional[Vector2]. None when the geometry has no such attribute. A sprite's uv runs from 0 to 1 across it.
vertex_normal	The geometry's normals mixed at the point, as an Optional[Vector3]. three.js's normal. None when the geometry has no normals.
face	The triangle struck, as an Optional[HitFace]. three.js's face.
barycoord	The point's weights on the face's three corners, as an Optional[Vector3]. They add up to one.
point_on_line	For a wide line, the point on the segment nearest the ray, as an Optional[Vector3]. three.js's pointOnLine.

A hit on a mesh of any kind has face and barycoord, and uv, uv1 and vertex_normal where the geometry has them. Anything else leaves them None, as three.js leaves them out. The values agree with three.js 0.180 to a part in 10,000.

HitFace field	Meaning
a, b, c	The vertices at the triangle's corners, through the index if there is one.
normal	The triangle's unit normal, from its corners as wound. Zero for a triangle with no area.
material_index	A MaterialIndex: the index of the group struck on a mesh that wears a list of materials. Zero for a mesh with one material, as in three.js.

vertex_normal and face.normal are in the mesh's own space, as three.js gives them. Carry them to the world with the node's world matrix. normal is already in world space. vertex_normal is not made unit length. It is turned to face the ray, so a hit from behind has it reversed. face.normal is not turned.

The two normals and the weights come from the triangle as picked. A morphed, skinned or displaced mesh gives them from where its corners were carried. The texture coordinates and the vertex normals are read from the geometry, as three.js reads them.

A HitKind is a type. A bare integer does not compile.

What it sees

The mesh as it is drawn, not as it was modelled. A mesh wearing a morph target is picked where the target has carried it, because picking and the renderer both ask core/deform.mojo the same question.

They did not always. Rendering wore the targets and picking did not. The drawn shape could not be hit, and the modelled one could be hit where nothing was.

An instanced mesh is picked instance by instance. Each instance is tested at the node's transform times its own. A batched mesh is picked the same way, with each instance's own geometry. An LOD is picked on one level. That level is the one the distance from the ray's origin to the node picks with no memory, as three.js's LOD.raycast does.

A skinned mesh is picked where its bones carry it, after its morph targets. The renderer and the raycaster both ask core/deform.mojo for the posed bones and the matrix that carries each vertex.

A mesh whose material names a displacement map is picked where the map moved it, after its morph targets and its bones. three.js picks the geometry and ignores the map. This port picks what the renderer draws.

Lines, points and sprites

A line is met where the ray passes within line_threshold of a segment. The hit's point is on the segment, and its distance is to the ray's nearest point, as three.js reports them. A strip, a loop and a list of segments are all read as the renderer reads them.

Points are met where the ray passes within points_threshold of a point. The hit's point is the ray's point nearest that point.

The gap is measured in world space. three.js divides the threshold by the object's average scale and measures in the object's own space. The two agree under an even scale. Under an uneven scale, this port is exact and three.js is not.

A sprite is met on its two triangles, laid flat to the kept camera with its center, rotation and size, as the renderer lays them.

Rules

A mesh is tested in three steps. First its bounding sphere, in world space. Then its bounding box, in its own space. Then every triangle. A mesh the ray misses at the first step costs six multiplies.

The material's side decides which faces count. A FRONT_SIDE mesh is not picked through its back. A BACK_SIDE mesh is picked only on its back. A DOUBLE_SIDE mesh is picked on both. What the renderer draws, the raycaster hits. See Materials.

A mesh that wears a list of materials is tested group by group. Each group uses the side of its own material. A group that is not drawn is not hit. The hit's face.material_index is the index of the group, three.js's face.materialIndex.

A mirrored mesh is hit on the face the renderer draws. Its hit normal is turned back, as the renderer turns its geometric normal.

The ray is carried into a mesh's own space by the inverse of its world matrix. That inverse is set to be exactly affine. Before, a turned and stretched mesh could round the inverse's bottom row off (0, 0, 0, 1), and the pick raised.

A geometry of lines or points must not be indexed, as for the renderer.

A wide line is picked by intersect_wide_line alone, because a width in pixels needs a camera and an image size. intersect_scene has neither.

Errors

• An index that names no object in its list raises.
• A sprite pick with no kept camera raises.
• A negative threshold, or one that is not a number, raises.
• An indexed line or points geometry raises.
• A mesh that names a missing node, geometry or material raises. A geometry with no positions raises.
• A stale scene raises. Call scene.update() first.
• A mesh whose world transform flattens a dimension raises. It has no inverse to carry the ray through.
• set_from_pixel raises for an image with no size.

Example

var caster = Raycaster(Vector3(0, 0, 0), Vector3(0, 0, -1))
caster.set_from_pixel(160.5, 120.5, 320, 240, camera, scene)
for hit in caster.intersect_scene(scene, assets):
    print(hit.index, hit.distance)

See Math for the Ray the raycaster carries.