honeycomb_kernels/triangulation/fan.rs
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180
use crate::triangulation::{
check_requirements, crossp_from_verts, fetch_face_vertices, TriangulateError,
};
use honeycomb_core::cmap::{CMap2, DartIdType, FaceIdType, Orbit2, OrbitPolicy};
use honeycomb_core::geometry::CoordsFloat;
#[allow(clippy::missing_panics_doc)]
/// Triangulates a face using a fan triangulation method.
///
/// This function triangulates a cell (face) in a 2D combinatorial map by creating a fan of
/// triangles from a chosen vertex to all other vertices of the polygon, if such a vertex exist.
///
/// Note that this function will not have any effect if the polygon isn't fannable.
///
/// # Arguments
///
/// - `cmap: &mut CMap2` - A mutable reference to the modified `CMap2`.
/// - `face_id: FaceIdentifier` - Identifier of the face to triangulate within the map.
/// - `new_darts: &[DartIdentifier]` - Identifiers of pre-allocated darts for the new edges;
/// the slice length should match the expected number of edges created by the triangulation. For
/// an `n`-sided polygon, the number of created edge is `n-3`, so the number of dart is `(n-3)*2`.
///
/// # Behavior
///
/// - The function begins by checking if the face has 3 or fewer vertices, in which case
/// it's already triangulated or cannot be further processed.
/// - It verifies if the number of new darts matches the expected number for triangulation.
/// - The function then attempts to find a vertex from which all other vertices can be seen
/// (a star vertex), using the orientation properties of N-maps.
/// - If such a star vertex is found, the function proceeds to create triangles by linking
/// new darts in a fan-like structure from this vertex. Otherwise, the cell is left unchanged
///
/// # Errors
///
/// This function will return an error if the face wasn't triangulated. There can be multiple
/// reason for this:
/// - The face is incompatible with the operation (made of 1, 2 or 3 vertices)
/// - The number of pre-allocated darts did not match the expected number (see [#arguments])
/// - The face contains one or more undefined vertices
/// - The face isn't starrable
///
/// Note that in any of these cases, the face will remain the same as it was before the function
/// call.
pub fn process_cell<T: CoordsFloat>(
cmap: &mut CMap2<T>,
face_id: FaceIdType,
new_darts: &[DartIdType],
) -> Result<(), TriangulateError> {
// fetch darts using a custom orbit so that they're ordered
let darts: Vec<_> =
Orbit2::new(cmap, OrbitPolicy::Custom(&[1]), face_id as DartIdType).collect();
let n = darts.len();
// early checks - check # of darts & face size
check_requirements(n, new_darts.len())?;
// get associated vertices - check for undefined vertices
let vertices = fetch_face_vertices(cmap, &darts)?;
// iterating by ref so that we can still access the list
let star = darts
.iter()
.zip(vertices.iter())
.enumerate()
.find_map(|(id, (d0, v0))| {
let mut tmp = vertices
.windows(2)
.enumerate()
// remove segments directly attached to v0
.filter(|(i_seg, _)| !((n + i_seg) % n == id || (n + i_seg - 1) % n == id))
.map(|(_, val)| {
let [v1, v2] = val else { unreachable!() };
crossp_from_verts(v0, v1, v2)
});
let signum = tmp.next().map(T::signum).unwrap();
for v in tmp {
if v.signum() != signum || v.abs() < T::epsilon() {
return None;
}
}
Some(d0)
});
if let Some(sdart) = star {
// if we found a dart from the previous computations, it means the polygon is "fannable"
// THIS CANNOT BE PARALLELIZED AS IS
let b0_sdart = cmap.beta::<0>(*sdart);
let v0 = cmap.vertex(cmap.vertex_id(*sdart)).unwrap();
cmap.one_unsew(b0_sdart);
let mut d0 = *sdart;
for sl in new_darts.chunks_exact(2) {
let [d1, d2] = sl else { unreachable!() };
let b1_d0 = cmap.beta::<1>(d0);
let b1b1_d0 = cmap.beta::<1>(cmap.beta::<1>(d0));
cmap.one_unsew(b1_d0);
cmap.two_link(*d1, *d2);
cmap.one_link(*d2, b1b1_d0);
cmap.one_sew(b1_d0, *d1);
cmap.one_sew(*d1, d0);
d0 = *d2;
}
cmap.one_sew(cmap.beta::<1>(cmap.beta::<1>(d0)), d0);
cmap.replace_vertex(cmap.vertex_id(*sdart), v0);
} else {
// println!("W: face {face_id} isn't fannable -- skipping triangulation");
return Err(TriangulateError::NonFannable);
}
Ok(())
}
#[allow(clippy::missing_panics_doc)]
/// Triangulates a face using a fan triangulation method.
///
/// This function triangulates a cell (face) in a 2D combinatorial map by creating a fan of
/// triangles from a the first vertex of
///
/// **Note that this function assumes the polygon is convex and correctly defined (i.e. all vertices
/// are) and may fail or produce incorrect results if called on a cell that does not verify these
/// requirements**.
///
/// # Arguments
///
/// - `cmap: &mut CMap2` - A mutable reference to the modified `CMap2`.
/// - `face_id: FaceIdentifier` - Identifier of the face to triangulate within the map.
/// - `new_darts: &[DartIdentifier]` - Identifiers of pre-allocated darts for the new edges;
/// the slice length should match the expected number of edges created by the triangulation. For
/// an `n`-sided polygon, the number of created edge is `n-3`, so the number of dart is `(n-3)*2`.
///
/// # Behavior
///
/// - The function begins by checking if the face has 3 or fewer vertices, in which case
/// it's already triangulated or cannot be further processed.
/// - It verifies if the number of new darts matches the expected number for triangulation.
/// - The function creates triangles by linking new darts in a fan-like structure to the first
/// vertex of the polygon. **This is done unconditionnally, whether the polygon is convex or not**.
///
/// # Errors
///
/// This function will return an error if the face wasn't triangulated. There can be multiple
/// reason for this:
/// - The face is incompatible with the operation (made of 1, 2 or 3 vertices)
/// - The number of pre-allocated darts did not match the expected number (see [#arguments])
///
/// Note that in any of these cases, the face will remain the same as it was before the function
/// call.
pub fn process_convex_cell<T: CoordsFloat>(
cmap: &mut CMap2<T>,
face_id: FaceIdType,
new_darts: &[DartIdType],
) -> Result<(), TriangulateError> {
let n = Orbit2::new(cmap, OrbitPolicy::Custom(&[1]), face_id as DartIdType).count();
// early rets
check_requirements(n, new_darts.len())?;
// we assume the polygon is convex (== starrable from any vertex)
let sdart = face_id as DartIdType;
// THIS CANNOT BE PARALLELIZED AS IS
let b0_sdart = cmap.beta::<0>(sdart);
let v0 = cmap.vertex(cmap.vertex_id(sdart)).unwrap();
cmap.one_unsew(b0_sdart);
let mut d0 = sdart;
for sl in new_darts.chunks_exact(2) {
let [d1, d2] = sl else { unreachable!() };
let b1_d0 = cmap.beta::<1>(d0);
let b1b1_d0 = cmap.beta::<1>(cmap.beta::<1>(d0));
cmap.one_unsew(b1_d0);
cmap.two_link(*d1, *d2);
cmap.one_link(*d2, b1b1_d0);
cmap.one_sew(b1_d0, *d1);
cmap.one_sew(*d1, d0);
d0 = *d2;
}
cmap.one_sew(cmap.beta::<1>(cmap.beta::<1>(d0)), d0);
cmap.replace_vertex(cmap.vertex_id(sdart), v0);
Ok(())
}