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//! Orbit implementation
//!
//! This module contains all code used to model orbits, a notion defined
//! along the structure of combinatorial maps.
use std::collections::VecDeque;
use rustc_hash::FxHashSet as HashSet;
use crate::cmap::{CMap2, DartIdType, NULL_DART_ID, OrbitPolicy, try_from_fn};
use crate::geometry::CoordsFloat;
use crate::stm::{StmClosureResult, Transaction};
/// **Orbits**
impl<T: CoordsFloat> CMap2<T> {
/// Generic orbit implementation.
///
/// # Arguments
/// - `opolicy: OrbitPolicy` -- Policy used by the orbit for the BFS.
/// - `dart_id: DartIdentifier` -- Dart of which the structure will compute the orbit.
///
/// # The search algorithm
///
/// The search algorithm used to establish the list of dart included in the orbit is a
/// [Breadth-First Search algorithm][WIKIBFS]. This means that:
///
/// - we look at the images of the current dart through all beta functions,
/// adding those to a queue, before moving on to the next dart.
/// - we apply the beta functions in their specified order; This guarantees a consistent and
/// predictable result.
///
/// # Performance
///
/// Currently, orbits use two dynamically allocated structures for computation: a `VecDeque`,
/// and a `HashSet`. There is a possibility to use static thread-local instances to avoid
/// ephemeral allocations, but [it would require a guard mechanism][PR].
///
/// [WIKIBFS]: https://en.wikipedia.org/wiki/Breadth-first_search
/// [PR]: https://github.com/LIHPC-Computational-Geometry/honeycomb/pull/293
#[allow(clippy::needless_for_each)]
pub fn orbit(
&self,
opolicy: OrbitPolicy,
dart_id: DartIdType,
) -> impl Iterator<Item = DartIdType> {
let mut pending = VecDeque::new();
let mut marked: HashSet<DartIdType> = HashSet::default();
pending.push_back(dart_id);
marked.insert(NULL_DART_ID);
marked.insert(dart_id); // we're starting here, so we mark it beforehand
// FIXME: move the match block out of the iterator
std::iter::from_fn(move || {
if let Some(d) = pending.pop_front() {
// I have to define the closure here due to mutability constraints
let mut check = |d: DartIdType| {
if marked.insert(d) {
// if true, we did not see this dart yet
// i.e. we need to visit it later
pending.push_back(d);
}
};
// compute the next images
match opolicy {
OrbitPolicy::Vertex => {
let im1 = self.beta::<1>(self.beta::<2>(d));
let im2 = self.beta::<2>(self.beta::<0>(d));
check(im1);
check(im2);
}
OrbitPolicy::VertexLinear => {
let im = self.beta::<1>(self.beta::<2>(d));
check(im);
}
OrbitPolicy::Edge => {
let im = self.beta::<2>(d);
check(im);
}
OrbitPolicy::Face => {
let im1 = self.beta::<1>(d);
let im2 = self.beta::<0>(d);
check(im1);
check(im2);
}
OrbitPolicy::FaceLinear => {
let im = self.beta::<1>(d);
check(im);
}
OrbitPolicy::Custom(beta_slice) => {
for beta_id in beta_slice {
let im = self.beta_rt(*beta_id, d);
check(im);
}
}
OrbitPolicy::Volume | OrbitPolicy::VolumeLinear => {
unimplemented!("3-cells aren't defined for 2-maps")
}
}
return Some(d);
}
None // queue is empty, we're done
})
}
/// Generic orbit transactional implementation.
#[allow(clippy::needless_for_each)]
pub fn orbit_tx(
&self,
t: &mut Transaction,
opolicy: OrbitPolicy,
dart_id: DartIdType,
) -> impl Iterator<Item = StmClosureResult<DartIdType>> {
let mut pending = VecDeque::new();
let mut marked: HashSet<DartIdType> = HashSet::default();
pending.push_back(dart_id);
marked.insert(NULL_DART_ID);
marked.insert(dart_id); // we're starting here, so we mark it beforehand
try_from_fn(move || {
if let Some(d) = pending.pop_front() {
// I have to define the closure here due to mutability constraints
let mut check = |d: DartIdType| {
if marked.insert(d) {
// if true, we did not see this dart yet
// i.e. we need to visit it later
pending.push_back(d);
}
};
match opolicy {
OrbitPolicy::Vertex => {
let b2 = self.beta_tx::<2>(t, d)?;
let b0 = self.beta_tx::<0>(t, d)?;
let im1 = self.beta_tx::<1>(t, b2)?;
let im2 = self.beta_tx::<2>(t, b0)?;
check(im1);
check(im2);
}
OrbitPolicy::VertexLinear => {
let b2 = self.beta_tx::<2>(t, d)?;
let im = self.beta_tx::<1>(t, b2)?;
check(im);
}
OrbitPolicy::Edge => {
let im = self.beta_tx::<2>(t, d)?;
check(im);
}
OrbitPolicy::Face => {
let im1 = self.beta_tx::<1>(t, d)?;
let im2 = self.beta_tx::<0>(t, d)?;
check(im1);
check(im2);
}
OrbitPolicy::FaceLinear => {
let im = self.beta_tx::<1>(t, d)?;
check(im);
}
OrbitPolicy::Custom(beta_slice) => {
for beta_id in beta_slice {
let im = self.beta_rt_tx(t, *beta_id, d)?;
check(im);
}
}
OrbitPolicy::Volume | OrbitPolicy::VolumeLinear => {
unimplemented!("3-cells aren't defined for 2-maps")
}
}
return Ok(Some(d));
}
Ok(None) // queue is empty, we're done
})
}
/// Return the orbit defined by a dart and its `I`-cell.
///
/// # Usage
///
/// The returned item can be iterated upon to retrieve all dart member of the cell. Note that
/// **the dart passed as an argument is included as the first element of the returned orbit**.
///
/// # Panics
///
/// The method will panic if *I* is not 0, 1 or 2.
#[must_use = "unused return value"]
pub fn i_cell<const I: u8>(&self, dart_id: DartIdType) -> impl Iterator<Item = DartIdType> {
assert!(I < 3);
match I {
0 => self.orbit(OrbitPolicy::Vertex, dart_id),
1 => self.orbit(OrbitPolicy::Edge, dart_id),
2 => self.orbit(OrbitPolicy::Face, dart_id),
_ => unreachable!(),
}
}
}