honeycomb_kernels/remeshing/
swap.rs

1use honeycomb_core::{
2    cmap::{CMap2, DartIdType, EdgeIdType, NULL_DART_ID, NULL_EDGE_ID, SewError},
3    geometry::CoordsFloat,
4    stm::{Transaction, TransactionClosureResult, abort, try_or_coerce},
5};
6
7/// Error-modeling enum for edge swap routine.
8#[derive(thiserror::Error, Debug, PartialEq, Eq)]
9pub enum EdgeSwapError {
10    /// A core operation failed.
11    #[error("core operation failed: {0}")]
12    FailedCoreOp(#[from] SewError),
13    /// The edge passed as argument is null.
14    #[error("cannot swap null edge")]
15    NullEdge,
16    /// The edge passed as argument is made of single dart, hence doesn't have a cell on each side.
17    #[error("cannot swap an edge adjacent to a single cell")]
18    IncompleteEdge,
19    /// One or both of the cells adjacent to the edge are not triangles.
20    #[error("cannot swap an edge adjacent to a non-triangular cell")]
21    BadTopology,
22}
23
24/// Tip over an edge shared by two triangles.
25///
26/// The edge is tipped in the clockwise direction. Vertices that were shared become exclusive
27/// to each new triangle and vice versa:
28///
29/// ```text
30///
31///       +                   +
32///      / \                 /|\
33///     /   \               / | \
34///    /     \             /  |  \
35///   /       \           /   |   \
36///  /         \         /    |    \
37/// +-----------+  -->  +     |     +
38///  \    e    /         \    |    /
39///   \       /           \   |   /
40///    \     /             \  |  /
41///     \   /               \ | /
42///      \ /                 \|/
43///       +                   +
44///
45/// ```
46///
47/// This function expects to operate on a triangular mesh. At the moment, calling it on another type
48/// of mesh may result in non-explicit errors (e.g. an internal sew operation will consistently fail
49/// due to a dart being non-free) as there is no check on each faces' degree.
50///
51/// # Arguments
52///
53/// - `t: &mut Transaction` -- Associated transaction.
54/// - `map: &mut CMap2` -- Edited map.
55/// - `e: EdgeIdType` -- Edge to move.
56///
57/// # Panics
58///
59/// This function will panic if there is no cell on one side of the edge.
60///
61/// # Errors
62///
63/// This function will abort and raise an error if:
64/// - the transaction cannot be completed,
65/// - one internal sew operation fails.
66///
67/// The returned error can be used in conjunction with transaction control to avoid any
68/// modifications in case of failure at attribute level. The user can then choose to retry or
69/// abort as he wishes using `Transaction::with_control_and_err`.
70#[inline]
71pub fn swap_edge<T: CoordsFloat>(
72    t: &mut Transaction,
73    map: &CMap2<T>,
74    e: EdgeIdType,
75) -> TransactionClosureResult<(), EdgeSwapError> {
76    if e == NULL_EDGE_ID {
77        abort(EdgeSwapError::NullEdge)?;
78    }
79    let (l, r) = (e as DartIdType, map.beta_transac::<2>(t, e as DartIdType)?);
80    if r == NULL_DART_ID {
81        abort(EdgeSwapError::IncompleteEdge)?;
82    }
83
84    let (b1l, b1r) = (map.beta_transac::<1>(t, l)?, map.beta_transac::<1>(t, r)?);
85    let (b0l, b0r) = (map.beta_transac::<0>(t, l)?, map.beta_transac::<0>(t, r)?);
86    if map.beta_transac::<1>(t, b1l)? != b0l || map.beta_transac::<1>(t, b1r)? != b0r {
87        abort(EdgeSwapError::BadTopology)?;
88    }
89
90    try_or_coerce!(map.unsew::<1>(t, l), EdgeSwapError);
91    try_or_coerce!(map.unsew::<1>(t, r), EdgeSwapError);
92    try_or_coerce!(map.unsew::<1>(t, b0l), EdgeSwapError);
93    try_or_coerce!(map.unsew::<1>(t, b0r), EdgeSwapError);
94    try_or_coerce!(map.unsew::<1>(t, b1l), EdgeSwapError);
95    try_or_coerce!(map.unsew::<1>(t, b1r), EdgeSwapError);
96
97    try_or_coerce!(map.sew::<1>(t, l, b0r), EdgeSwapError);
98    try_or_coerce!(map.sew::<1>(t, b0r, b1l), EdgeSwapError);
99    try_or_coerce!(map.sew::<1>(t, b1l, l), EdgeSwapError);
100    try_or_coerce!(map.sew::<1>(t, r, b0l), EdgeSwapError);
101    try_or_coerce!(map.sew::<1>(t, b0l, b1r), EdgeSwapError);
102    try_or_coerce!(map.sew::<1>(t, b1r, r), EdgeSwapError);
103
104    Ok(())
105}
honeycomb_kernels/remeshing/swap.rs

honeycomb_kernels/remeshing/
swap.rs
