axiolid_arrangement/
entity.rs

1// SPDX-License-Identifier: MPL-2.0
2
3//! Arena records for the arrangement.
4//!
5//! Records hold only topology and position. Anything derived -- area,
6//! outline, adjacency -- is computed in `query.rs` rather than cached here,
7//! because a cached derivative is a second source of truth that edits have to
8//! remember to invalidate.
9
10use axiolid_core::Point2;
11
12use crate::id::{FaceId, HalfEdgeId, VertexId};
13
14impl FaceId {
15    /// The unbounded face, which every arrangement has from creation.
16    pub const OUTER: Self = Self::outer();
17}
18
19/// A point in the plane, with one outgoing half-edge as an entry into the
20/// edges around it.
21#[derive(Debug, Clone, Copy, PartialEq)]
22pub struct Vertex {
23    /// Where the vertex is.
24    pub position: Point2,
25    /// Any half-edge whose origin is this vertex, or `None` if isolated.
26    ///
27    /// Isolated vertices are legal: an edit can remove the last edge touching
28    /// a vertex without the vertex itself becoming invalid.
29    pub outgoing: Option<HalfEdgeId>,
30}
31
32/// One direction of an edge.
33///
34/// The twin runs the other way along the same geometric segment. Storing both
35/// directions is what makes "the face on the other side" a constant-time
36/// question rather than a search.
37#[derive(Debug, Clone, Copy, PartialEq)]
38pub struct HalfEdge {
39    /// Vertex this half-edge leaves from.
40    pub origin: VertexId,
41    /// The opposite half-edge along the same segment.
42    pub twin: HalfEdgeId,
43    /// Next half-edge counter-clockwise around `face`.
44    pub next: HalfEdgeId,
45    /// Previous half-edge around `face`.
46    pub prev: HalfEdgeId,
47    /// Face lying to the left of this half-edge.
48    pub face: FaceId,
49}
50
51/// A region of the plane bounded by a cycle of half-edges.
52#[derive(Debug, Clone, Copy, PartialEq)]
53pub struct Face {
54    /// Any half-edge on this face's outer boundary.
55    ///
56    /// `None` only for the unbounded face of an arrangement with no edges.
57    pub boundary: Option<HalfEdgeId>,
58}
axiolid_arrangement/entity.rs

axiolid_arrangement/
entity.rs
