Function layout_reingold_tilford 

pub fn layout_reingold_tilford(
    graph: &Graph,
    root: Option<VertexId>,
    mode: RtMode,
) -> IgraphResult<Vec<[f64; 2]>>

Compute the Reingold-Tilford tree layout.

Places vertices in a layered hierarchy with the root at level 0. Y-coordinate is the depth in the tree; X-coordinate is computed using the contour-merging algorithm to keep subtrees compact.

If the graph is not a tree, a BFS spanning tree from root is used. Unreachable vertices are connected to the root before layout.

Arguments

• graph — input graph.
• root — root vertex for the tree layout. If None, automatically selects the vertex with highest degree.
• mode — edge traversal direction.

Returns (x, y) pairs for each vertex.

Examples

use rust_igraph::{Graph, layout_reingold_tilford, RtMode};

// Binary tree: 0 -> {1, 2}, 1 -> {3, 4}
let mut g = Graph::with_vertices(5);
g.add_edge(0, 1).unwrap();
g.add_edge(0, 2).unwrap();
g.add_edge(1, 3).unwrap();
g.add_edge(1, 4).unwrap();

let pos = layout_reingold_tilford(&g, Some(0), RtMode::All).unwrap();
assert_eq!(pos.len(), 5);
// Root should be at level 0
assert!((pos[0][1]).abs() < 1e-10);