collide-mesh 0.1.0

Triangle mesh collider for the collide crate (3D)
Documentation 
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use crate::Aabb;

pub struct Bvh {
    root: Option<Node>,
}

enum Node {
    Leaf {
        item_index: usize,
    },
    Branch {
        bounds: Aabb,
        left: Box<Self>,
        right: Box<Self>,
    },
}

impl Bvh {
    pub fn build(bounds: &[Aabb]) -> Self {
        if bounds.is_empty() {
            return Self { root: None };
        }
        let mut indices: Vec<usize> = (0..bounds.len()).collect();
        Self {
            root: Some(build_node(bounds, &mut indices)),
        }
    }

    pub fn overlapping(&self, query: &Aabb) -> Vec<usize> {
        let mut results = Vec::new();
        if let Some(root) = &self.root {
            collect_overlapping(root, query, &mut results);
        }
        results
    }

    pub fn ray_overlapping(
        &self,
        origin: [f32; 3],
        inverse_direction: [f32; 3],
        max_distance: f32,
    ) -> Vec<usize> {
        let mut results = Vec::new();
        if let Some(root) = &self.root {
            collect_ray_overlapping(root, origin, inverse_direction, max_distance, &mut results);
        }
        results
    }
}

fn build_node(bounds: &[Aabb], indices: &mut [usize]) -> Node {
    if let [single] = indices {
        return Node::Leaf {
            item_index: *single,
        };
    }

    let combined = indices.iter().fold(Aabb::EMPTY, |accumulated, &index| {
        accumulated.merged(&bounds[index])
    });
    let split_axis = largest_axis(&combined);

    indices.sort_unstable_by(|&a, &b| {
        let center_a = f32::midpoint(bounds[a].min[split_axis], bounds[a].max[split_axis]);
        let center_b = f32::midpoint(bounds[b].min[split_axis], bounds[b].max[split_axis]);
        center_a.total_cmp(&center_b)
    });

    let middle = indices.len() / 2;
    let (left_indices, right_indices) = indices.split_at_mut(middle);

    Node::Branch {
        bounds: combined,
        left: Box::new(build_node(bounds, left_indices)),
        right: Box::new(build_node(bounds, right_indices)),
    }
}

fn largest_axis(bounds: &Aabb) -> usize {
    let extents = [
        bounds.max[0] - bounds.min[0],
        bounds.max[1] - bounds.min[1],
        bounds.max[2] - bounds.min[2],
    ];
    if extents[0] >= extents[1] && extents[0] >= extents[2] {
        0
    } else if extents[1] >= extents[2] {
        1
    } else {
        2
    }
}

fn collect_overlapping(node: &Node, query: &Aabb, results: &mut Vec<usize>) {
    match node {
        Node::Leaf { item_index } => results.push(*item_index),
        Node::Branch {
            bounds,
            left,
            right,
        } => {
            if bounds.overlaps(query) {
                collect_overlapping(left, query, results);
                collect_overlapping(right, query, results);
            }
        }
    }
}

fn collect_ray_overlapping(
    node: &Node,
    origin: [f32; 3],
    inverse_direction: [f32; 3],
    max_distance: f32,
    results: &mut Vec<usize>,
) {
    match node {
        Node::Leaf { item_index } => results.push(*item_index),
        Node::Branch {
            bounds,
            left,
            right,
        } => {
            if ray_hits(bounds, origin, inverse_direction, max_distance) {
                collect_ray_overlapping(left, origin, inverse_direction, max_distance, results);
                collect_ray_overlapping(right, origin, inverse_direction, max_distance, results);
            }
        }
    }
}

fn ray_hits(
    bounds: &Aabb,
    origin: [f32; 3],
    inverse_direction: [f32; 3],
    max_distance: f32,
) -> bool {
    let mut entry = 0.0_f32;
    let mut exit = max_distance;
    for axis in 0..3 {
        let near = (bounds.min[axis] - origin[axis]) * inverse_direction[axis];
        let far = (bounds.max[axis] - origin[axis]) * inverse_direction[axis];
        entry = entry.max(near.min(far));
        exit = exit.min(near.max(far));
    }
    entry <= exit
}