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use na::RealField;
use std::collections::HashMap;

//use crate::bounding_volume::AABB;
use crate::math::{Point, Vector, DIM};

#[derive(PartialEq, Debug, Clone)]
pub struct HGrid<N: RealField, T> {
    cells: HashMap<Point<i64>, Vec<T>>,
    cell_width: N,
}

impl<N: RealField, T> HGrid<N, T> {
    pub fn new(cell_width: N) -> Self {
        Self {
            cells: HashMap::new(),
            cell_width,
        }
    }

    fn quantify(value: N, cell_width: N) -> i64 {
        na::try_convert::<N, f64>((value / cell_width).floor()).unwrap() as i64
    }

    fn key(point: &Point<N>, cell_width: N) -> Point<i64> {
        Point::from(point.coords.map(|e| Self::quantify(e, cell_width)))
    }

    pub fn clear(&mut self) {
        self.cells.clear();
    }

    pub fn insert(&mut self, point: &Point<N>, elt: T) {
        let key = Self::key(point, self.cell_width);
        self.cells.entry(key).or_insert(Vec::new()).push(elt)
    }

    pub fn elements_close_to_point<'a>(
        &'a self,
        point: &Point<N>,
        radius: N,
    ) -> impl Iterator<Item = &T> {
        let key = Self::key(point, self.cell_width);
        // FIXME: we could sometimes avoid the `+ 1` by taking into account the point location on the cell.
        let quantified_radius = Self::quantify(radius, self.cell_width) + 1;
        let range = -(quantified_radius as i64)..=(quantified_radius as i64);
        let cells = &self.cells;

        NeighborCellsIterator::new(key, quantified_radius)
            .flat_map(move |cell| cells.get(&cell).into_iter())
            .flat_map(|cells| cells.iter())
    }

    //    pub fn elements_intersecting_aabb<'a>(&'a self, aabb: &AABB<N>) -> impl Iterator<Item = &T> {
    //        self.cells.values().flat_map(|v| v)
    //    }

    pub fn elements_containing_point(&self, point: &Point<N>) -> impl Iterator<Item = &T> {
        std::iter::empty()
    }
}

struct NeighborCellsIterator {
    start: Point<i64>,
    end: Point<i64>,
    curr: Point<i64>,
    done: bool,
}

impl NeighborCellsIterator {
    fn new(center: Point<i64>, radius: i64) -> Self {
        let start = center - Vector::repeat(radius as i64);
        Self {
            start,
            end: center + Vector::repeat(radius as i64),
            curr: start,
            done: false,
        }
    }
}

impl Iterator for NeighborCellsIterator {
    type Item = Point<i64>;

    fn next(&mut self) -> Option<Self::Item> {
        if self.done {
            return None;
        }

        if self.curr == self.end {
            self.done = true;
            Some(self.curr)
        } else {
            let result = self.curr;

            for i in 0..DIM {
                self.curr[i] += 1;

                if self.curr[i] > self.end[i] {
                    self.curr[i] = self.start[i];
                } else {
                    break;
                }
            }

            Some(result)
        }
    }
}

#[cfg(test)]
mod test {
    #[test]
    #[cfg(feature = "dim2")]
    fn grid_neighbor_iterator() {
        use super::NeighborCellsIterator;
        use crate::math::Point;

        let expected = [
            Point::new(-1, 0),
            Point::new(0, 0),
            Point::new(1, 0),
            Point::new(2, 0),
            Point::new(3, 0),
            Point::new(-1, 1),
            Point::new(0, 1),
            Point::new(1, 1),
            Point::new(2, 1),
            Point::new(3, 1),
            Point::new(-1, 2),
            Point::new(0, 2),
            Point::new(1, 2),
            Point::new(2, 2),
            Point::new(3, 2),
            Point::new(-1, 3),
            Point::new(0, 3),
            Point::new(1, 3),
            Point::new(2, 3),
            Point::new(3, 3),
        ];

        let iter = NeighborCellsIterator::new(Point::new(1, 2), 2);

        assert!(iter.zip(expected.into_iter()).all(|(a, b)| a == *b))
    }
}