CDT: Multiple constraint edge insertion (outer + holes)

[mkofler96]

Context

Part of the CDT implementation. Depends on Issues #1–#5. A polygon with holes has multiple boundary rings. All edges from all rings must be inserted as constraints. Order: outer boundary first, then holes. Within each ring, edges can be processed in any order without affecting correctness.

Problem

Implement the loop that iterates over all n edges of each boundary ring and calls insert_constraint for each. Inserting a constraint that already exists must be a no-op (idempotent).

Acceptance Criteria

• A polygon with outer boundary and one rectangular hole produces a triangulation where all 4 outer edges AND all 4 hole edges are present as triangle edges.
• Inserting the same constraint twice is a no-op (no panic, no duplicate triangles).
• All boundary ring edges present after full insertion pass.

Red-Green Tests

#[test]
fn all_outer_edges_present_after_insertion() {
    let outer = vec![
        Point2::new(0.0, 0.0), Point2::new(3.0, 0.0),
        Point2::new(3.0, 3.0), Point2::new(0.0, 3.0),
    ];
    let mesh = triangulate_constrained(&outer, &[]);
    // All 4 boundary edges must appear
    assert!(has_edge(&mesh.triangles, 0, 1));
    assert!(has_edge(&mesh.triangles, 1, 2));
    assert!(has_edge(&mesh.triangles, 2, 3));
    assert!(has_edge(&mesh.triangles, 3, 0));
}

#[test]
fn hole_edges_present_after_insertion() {
    let outer = vec![
        Point2::new(0.0, 0.0), Point2::new(4.0, 0.0),
        Point2::new(4.0, 4.0), Point2::new(0.0, 4.0),
    ];
    let hole = vec![
        Point2::new(1.0, 1.0), Point2::new(3.0, 1.0),
        Point2::new(3.0, 3.0), Point2::new(1.0, 3.0),
    ];
    let mesh = triangulate_constrained(&outer, &[hole.as_slice()]);
    // Hole vertices are indices 4-7 in the combined point array
    // All 4 hole edges must be present
    let n = outer.len(); // 4
    assert!(has_edge(&mesh.triangles, n,   n+1));
    assert!(has_edge(&mesh.triangles, n+1, n+2));
    assert!(has_edge(&mesh.triangles, n+2, n+3));
    assert!(has_edge(&mesh.triangles, n+3, n));
}

#[test]
fn duplicate_constraint_is_noop() {
    let outer = vec![
        Point2::new(0.0, 0.0), Point2::new(2.0, 0.0),
        Point2::new(1.0, 2.0),
    ];
    // triangulate_constrained inserts each edge once; calling it again on
    // the same polygon must produce the same result.
    let mesh1 = triangulate_constrained(&outer, &[]);
    let mesh2 = triangulate_constrained(&outer, &[]);
    assert_eq!(mesh1.triangles.len(), mesh2.triangles.len());
}

Location

crates/kofem-mesh/src/cdt.rs — constraint insertion loop in triangulate_constrained