[BUG]: Clipped Polygon must be CCW for Voronoi

[skygering]

Describe the bug

In the case below, the clipping polygon only works if the boundary is CCW, which isn't in the documentation.

Reproducer

using DelaunayTriangulation
using Random
using CairoMakie

rng = Xoshiro(0)

points = [(0.25, 0.25), (0.75, 0.25), (0.75, 0.75), (0.25, 0.75), (0.5, 0.5)]
boundary1 = (((0.0, 0.0), (0.0, 1.0), (1.0, 1.0), (1.0, 0.0), (0.0, 0.0)), (1, 2, 3, 4, 1))
boundary2 = (((0.0, 0.0), (1.0, 0.0), (1.0, 1.0), (0.0, 1.0), (0.0, 0.0)), (1, 2, 3, 4, 1))

tri = triangulate(points; rng)
vorn1 = voronoi(tri, clip = true, clip_polygon = boundary1)
voronoiplot(vorn1)

vorn2 = voronoi(tri, clip = true, clip_polygon = boundary2)
voronoiplot(vorn2)

For boundary1, I get the following:

while for boundary2, I get the correct result:

Environment information

Post the result of doing

using InteractiveUtils
versioninfo()

Julia Version 1.11.5
Commit 760b2e5b739 (2025-04-14 06:53 UTC)
Build Info:
  Official https://julialang.org/ release
Platform Info:
  OS: macOS (arm64-apple-darwin24.0.0)
  CPU: 8 × Apple M3
  WORD_SIZE: 64
  LLVM: libLLVM-16.0.6 (ORCJIT, apple-m2)
Threads: 1 default, 0 interactive, 1 GC (on 4 virtual cores)
Environment:
  JULIA_PKG_USE_CLI_GIT = true

and

using Pkg
Pkg.status()

julia> Pkg.status()
Project GeometryOps v0.1.30
Status `~/.julia/dev/GeometryOps/Project.toml`
  [1520ce14] AbstractTrees v0.4.5
  [35492f91] AdaptivePredicates v1.2.0
  [150eb455] CoordinateTransformations v0.6.4
  [9a962f9c] DataAPI v1.16.0
  [927a84f5] DelaunayTriangulation v1.6.4
  [429591f6] ExactPredicates v2.2.9
  [411431e0] Extents v0.1.6
  [68eda718] GeoFormatTypes v0.4.4
  [cf35fbd7] GeoInterface v1.6.0
  [05efe853] GeometryOpsCore v0.1.7
  [746ee33f] SortTileRecursiveTree v0.1.4
  [90137ffa] StaticArrays v1.9.15
  [10745b16] Statistics v1.11.1
  [bd369af6] Tables v1.12.1
  [37e2e46d] LinearAlgebra v1.11.0
  [9a3f8284] Random v1.11.0

[DanielVandH]

I think it is mentioned in the docstring:

    •  clip_polygon=nothing: If clip=true, then this is the polygon to clip the Voronoi tessellation to. If
       nothing, the convex hull of the triangulation is used. The polygon should be defined as a Tuple of the
       form (points, boundary_nodes) where the boundary_nodes are vertices mapping to coordinates in points,
       adhering to the usual conventions for defining boundaries.

specifically the "usual conventions for defining boundaries" part. But yeah it should probably link back to the documentation to make that clearer, and also be mentioned upfront in https://juliageometry.github.io/DelaunayTriangulation.jl/dev/tutorials/clipped_polygon/...

[DanielVandH]

Do the changes in #230 seem sufficient to you @skygering? Was there another place you were looking?

Hope it didn't cause you too much trouble - I was probably too used to always thinking in terms of everything counter-clockwise, at the time of writing, that I missed it :)