strafe-project/src/bvh.rs

use crate::aabb::Aabb;

//da algaritum
//lista boxens
//sort by {minx,maxx,miny,maxy,minz,maxz} (6 lists)
//find the sets that minimizes the sum of surface areas
//splitting is done when the minimum split sum of surface areas is larger than the node's own surface area

//start with bisection into octrees because a bad bvh is still 1000x better than no bvh
//sort the centerpoints on each axis (3 lists)
//bv is put into octant based on whether it is upper or lower in each list

enum BvhNodeContent<T>{
	Branch(Vec<BvhNode<T>>),
	Leaf(T),
}
impl<T> Default for BvhNodeContent<T>{
	fn default()->Self{
		Self::Branch(Vec::new())
	}
}
#[derive(Default)]
pub struct BvhNode<T>{
	content:BvhNodeContent<T>,
	aabb:Aabb,
}

impl<T:Copy+Eq+std::hash::Hash> BvhNode<T>{
	pub fn the_tester<F:FnMut(T)>(&self,aabb:&Aabb,f:&mut F){
		match &self.content{
			&BvhNodeContent::Leaf(model)=>f(model),
			BvhNodeContent::Branch(children)=>for child in children{
				//this test could be moved outside the match statement
				//but that would test the root node aabb
				//you're probably not going to spend a lot of time outside the map,
				//so the test is extra work for nothing
				if aabb.intersects(&child.aabb){
					child.the_tester(aabb,f);
				}
			},
		}
	}
}

pub fn generate_bvh<T:Copy+Eq+std::hash::Hash>(boxen:Vec<(T,Aabb)>)->BvhNode<T>{
	generate_bvh_node(boxen,false)
}

fn generate_bvh_node<T:Copy+Eq+std::hash::Hash>(boxen:Vec<(T,Aabb)>,force:bool)->BvhNode<T>{
	let n=boxen.len();
	if force||n<20{
		let mut aabb=Aabb::default();
		let nodes=boxen.into_iter().map(|b|{
			aabb.join(&b.1);
			BvhNode{
				content:BvhNodeContent::Leaf(b.0),
				aabb:b.1,
			}
		}).collect();
		BvhNode{
			content:BvhNodeContent::Branch(nodes),
			aabb,
		}
	}else{
		let mut octant=std::collections::HashMap::with_capacity(n);//this ids which octant the boxen is put in
		let mut sort_x=Vec::with_capacity(n);
		let mut sort_y=Vec::with_capacity(n);
		let mut sort_z=Vec::with_capacity(n);
		for (i,aabb) in boxen.iter(){
			let center=aabb.center();
			octant.insert(*i,0);
			sort_x.push((*i,center.x()));
			sort_y.push((*i,center.y()));
			sort_z.push((*i,center.z()));
		}
		sort_x.sort_by(|tup0,tup1|tup0.1.cmp(&tup1.1));
		sort_y.sort_by(|tup0,tup1|tup0.1.cmp(&tup1.1));
		sort_z.sort_by(|tup0,tup1|tup0.1.cmp(&tup1.1));
		let h=n/2;
		let median_x=sort_x[h].1;
		let median_y=sort_y[h].1;
		let median_z=sort_z[h].1;
		for (i,c) in sort_x{
			if median_x<c{
				octant.insert(i,octant[&i]+1<<0);
			}
		}
		for (i,c) in sort_y{
			if median_y<c{
				octant.insert(i,octant[&i]+1<<1);
			}
		}
		for (i,c) in sort_z{
			if median_z<c{
				octant.insert(i,octant[&i]+1<<2);
			}
		}
		//generate lists for unique octant values
		let mut list_list=Vec::with_capacity(8);
		let mut octant_list=Vec::with_capacity(8);
		for (i,aabb) in boxen.into_iter(){
			let octant_id=octant[&i];
			let list_id=if let Some(list_id)=octant_list.iter().position(|&id|id==octant_id){
				list_id
			}else{
				let list_id=list_list.len();
				octant_list.push(octant_id);
				list_list.push(Vec::new());
				list_id
			};
			list_list[list_id].push((i,aabb));
		}
		let mut aabb=Aabb::default();
		if list_list.len()==1{
			generate_bvh_node(list_list.remove(0),true)
		}else{
			BvhNode{
				content:BvhNodeContent::Branch(
					list_list.into_iter().map(|b|{
						let node=generate_bvh_node(b,false);
						aabb.join(&node.aabb);
						node
					}).collect()
				),
				aabb,
			}
		}
	}
}