From a942e10554e638e54e66838885a50773763415b3 Mon Sep 17 00:00:00 2001
From: Quaternions <krakow20@gmail.com>
Date: Thu, 5 Oct 2023 20:32:25 -0700
Subject: [PATCH] bvh

---
 src/aabb.rs | 17 +++++++++-
 src/bvh.rs  | 94 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/main.rs |  1 +
 3 files changed, 111 insertions(+), 1 deletion(-)
 create mode 100644 src/bvh.rs

diff --git a/src/aabb.rs b/src/aabb.rs
index 194ba83..ef728e9 100644
--- a/src/aabb.rs
+++ b/src/aabb.rs
@@ -33,7 +33,10 @@ impl Aabb {
 		self.min=self.min.min(point);
 		self.max=self.max.max(point);
 	}
-
+	pub fn join(&mut self, aabb:&Aabb){
+		self.min=self.min.min(aabb.min);
+		self.max=self.max.max(aabb.max);
+	}
 	pub fn normal(face:AabbFace) -> glam::Vec3 {
 		match face {
 			AabbFace::Right => glam::vec3(1.,0.,0.),
@@ -60,4 +63,16 @@ impl Aabb {
 		}
 		return aabb;
 	}
+	pub fn center(&self)->glam::Vec3{
+		return (self.min+self.max)/2.0
+	}
+	//probably use floats for area & volume because we don't care about precision
+	pub fn area_weight(&self)->f32{
+		let d=self.max-self.min;
+		d.x*d.y+d.y*d.z+d.z*d.x
+	}
+	pub fn volume(&self)->f32{
+		let d=self.max-self.min;
+		d.x*d.y*d.z
+	}
 }
\ No newline at end of file
diff --git a/src/bvh.rs b/src/bvh.rs
new file mode 100644
index 0000000..62eadc9
--- /dev/null
+++ b/src/bvh.rs
@@ -0,0 +1,94 @@
+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
+
+pub struct BvhNode{
+	children:Vec<Self>,
+	models:Vec<u32>,
+	aabb:Aabb,
+}
+
+pub fn generate_bvh(boxen:Vec<Aabb>)->BvhNode{
+	generate_bvh_node(boxen.into_iter().enumerate().collect())
+}
+
+fn generate_bvh_node(boxen:Vec<(usize,Aabb)>)->BvhNode{
+	let n=boxen.len();
+	if n<20{
+		let mut aabb=Aabb::new();
+		let models=boxen.into_iter().map(|b|{aabb.join(&b.1);b.0 as u32}).collect();
+		BvhNode{
+			children:Vec::new(),
+			models,
+			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.partial_cmp(&tup1.1).unwrap());
+		sort_y.sort_by(|tup0,tup1|tup0.1.partial_cmp(&tup1.1).unwrap());
+		sort_z.sort_by(|tup0,tup1|tup0.1.partial_cmp(&tup1.1).unwrap());
+		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::new();
+		let children=list_list.into_iter().map(|b|{
+			let node=generate_bvh_node(b);
+			aabb.join(&node.aabb);
+			node
+		}).collect();
+		BvhNode{
+			children,
+			models:Vec::new(),
+			aabb,
+		}
+	}
+}
diff --git a/src/main.rs b/src/main.rs
index 3263905..3b5c70e 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -4,6 +4,7 @@ use model::{Vertex,ModelInstance,ModelGraphicsInstance};
 use physics::{InputInstruction, PhysicsInstruction};
 use instruction::{TimedInstruction, InstructionConsumer};
 
+mod bvh;
 mod aabb;
 mod model;
 mod zeroes;