Prepare a labelled surface for parcel rendering — prepare_surface

Precomputes the per-geometry quantities used by [render_surface_parcels()]: outward vertex normals, a normalized anatomical underlay, and smoothed label memberships that let parcel boundaries follow smooth curves through mesh triangles instead of stair-stepping along triangle edges. Reuse the result across cameras and value maps.

Usage

prepare_surface_parcels(
  geometry,
  labels,
  anatomy_metric = NULL,
  cortex_mask = NULL,
  boundary_smooth = 3L,
  boundary_method = c("membership", "smooth"),
  t_clamp = c(0.1, 0.9)
)

Arguments

geometry: Display `SurfaceGeometry` (typically inflated).
labels: Integer parcel label per vertex; 0 marks the medial wall.
anatomy_metric: Optional sulcal-depth or curvature value per vertex, larger on gyri. `NULL` gives a neutral underlay.
cortex_mask: Optional logical per vertex; `FALSE` vertices are treated as medial wall. Defaults to `labels != 0`.
boundary_smooth: Laplacian iterations applied to label memberships. 0 gives piecewise-linear boundaries through triangle edge midpoints.
boundary_method: "membership" (default) retains the original per-face interpolated-membership argmax. "smooth" prepares the shared vertex-preserving partition used by [find_roi_boundaries()].
t_clamp: Symmetric edge bounds for "smooth"; see [find_roi_boundaries()]. Ignored by "membership".

Value

A `surface_parcel_prep` object.

Details

In smooth mode, labels must be nonnegative integers. The cortex mask is applied before partition construction; preservation refers to these effective labels. The prepared object retains labelled face cells, boundary paths and their provenance in partition. Rendering reuses this partition across cameras and value maps. The partition does not reproduce the unconstrained membership argmax. Existing input behaviour is retained in membership mode, except that fractional smoothing counts are rejected rather than truncated.