build_leader_grob: Build the polyline leader for an exterior tag, or...

In eulerr: Area-Proportional Euler and Venn Diagrams

Build the polyline leader for an exterior tag, or grid::nullGrob() for interior / missing-tether placements.

Description

Draws the polyline ⁠tether → waypoints[1..] → leader_end⁠. For straight leaders (raycast / force-directed) ⁠waypoints_*⁠ are empty, so the polyline collapses to the single ⁠tether → leader_end⁠ segment. For elbow leaders eunoia emits one knee waypoint, producing the orthogonal ⁠tether → knee → leader_end⁠ bend.

Usage

build_leader_grob(
  ax,
  ay,
  kind,
  tx,
  ty,
  lend_x,
  lend_y,
  waypoints_x = numeric(0),
  waypoints_y = numeric(0),
  leader_gp_list,
  fallback_gp,
  name
)

Arguments

ax, ay	the tag anchor, in native units
kind	the placement kind eunoia returned; anything other than "interior" gets a leader
tx, ty	the tether point on the shape, in native units
lend_x, lend_y	the leader endpoint on the tag bbox, in native units
waypoints_x, waypoints_y	intermediate leader vertices, in native units
leader_gp_list	grid::gpar() for the leader line, or NULL
fallback_gp	grid::gpar() used when leader_gp_list is NULL
name	name to give the returned grob

Details

Terminates at ⁠(lend_x, lend_y)⁠ — the point on the label box AABB edge supplied by eunoia (LabelPlacement::leader_end). Falls back to the anchor when the leader endpoint isn't finite so older / partial placement results still draw something sensible.

eulerr documentation built on Aug. 22, 2026, 1:09 a.m.