topology.islands (procNode)

A geometry's connected components labelled: a per-primitive island id, and for each point the lowest island id among the faces using it. connectivity joins faces across a shared edge or a shared point. Ids run from 0 in order of the first face that carries them. Faces a group leaves out, and points no participating face uses, carry -1.

Inputs

• geometry (Geometry): the geometry whose connected pieces are labelled.
• group (String, default ""): names a 0/1 attribute on class restricting which faces take part; empty, the whole mesh takes part. A name the class does not carry is refused.
• class (String, default "primitive"): the class group lives on: "edge", "point", "primitive" or "vertex".
• promote (String, default "all"): how a group on a class other than "primitive" becomes a face set: "all" takes the faces every one of whose elements of that class is in the group, "any" the faces at least one is.
• connectivity (String, default "edge"): what joins two faces into one island: "edge", a shared edge, or "point", a shared point.
• attribute (String, default "island"): the name the island id is written under, per primitive and per point, plus a detail attribute <attribute>Count holding how many islands there are.

Outputs

A call answers a record by output name.

• geometry (Geometry): the input with the island ids and the count written.
• islands (Data): count, sizes (faces per island, in id order), faceCount, connectivity and attribute.

Example

local a = g.sdf.sphere({ radius = 0.4, center = vector.create(-1, 0, 0) })
local b = g.sdf.sphere({ radius = 0.4, center = vector.create(1, 0, 0) })
local pair = g.sdf.mesh({ sdf = g.sdf.union({ a = a, b = b }), resolution = 24 }).geometry
local labelled = g.topology.islands({ geometry = pair })
local count = g.value.get({ data = labelled.islands, path = "count" })