How to draw through the points: 'polyline' joins them with straight segments (orthogonal routes), 'spline' reads them as cubic Bézier control points (3k + 1 of them).
points
readonly
Float64Array
Flat [x0, y0, x1, y1, …] in layout units, from the source to the target (both ends are the node centers or the points on the nodes' outlines the layout chose).