gather

Builds a column from another column and a run of indices: element i of the result is element index[i] of src. An index below 0 or past the end of src gives zeros. The element type is the T specialization (f32, i32, and two to four lanes of either); a three-lane column is read and written tightly packed, twelve bytes an element.

Dispatch over n, the number of indices. Exact: each result element has one writer. It declares fusion: (the value of element i is element(i), a thread runs where skip(i) is false), so a chain of fused kernels evaluates it inside one dispatch.

Most nodes that reorder, select or copy elements read their columns through it: core.select, core.concat, core.make, core.weld, attribute.gather, attribute.promote, elements.sort and the geometry nodes among them.

Over a live count (COUNT=device, see the abi README) n is the capacity and the first domain_count slots are live: a slot at or past it holds zeros. It binds 4 storage buffers (3 in the plain variant), and dst holds n elements.