SoundTool/Assets/Scripts/VoxelOctree/VoxelTreeBuilder.cs

using UnityEngine;
using System;
using System.Collections.Generic;
using System.Linq;

public class VoxelTreeBuilder
{
    private int maxDepth;
    private float minNodeSize;

    public VoxelTreeBuilder(int maxDepth, float minNodeSize)
    {
        this.maxDepth = maxDepth;
        this.minNodeSize = minNodeSize;
    }

    public OctreeNode Build(Bounds bounds, Func<Vector3, float, IsSolidNodeAnswere> isSolid)
    {
        return BuildNode(bounds, isSolid, 0);
    }

    private OctreeNode BuildNode(Bounds bounds, Func<Vector3, float, IsSolidNodeAnswere> isSolid, int depth)
    {
        OctreeNode node = new OctreeNode(bounds);
        IsSolidNodeAnswere answere;

        // Stop subdivision if we reached the maximum depth or smallest size
        if (depth >= maxDepth)
        {
            // Check the voxel state at the center
            answere = isSolid(bounds.center, bounds.size.x);
            node.isOccupied = answere.isSolid;
            node.penetrationFactor = answere.penetrationFactor;
            node.reflexionFactor = answere.reflexionFactor;
            return node;
        }

        if( bounds.size.x <= minNodeSize )
        {
            bool allSolid = true;
            bool allEmpty = true;

            foreach (Vector3 corner in GetCorners(bounds))
            {
                answere = isSolid(corner, bounds.size.x);
                bool solid = answere.isSolid;
                
                node.penetrationFactor = answere.penetrationFactor;
                node.reflexionFactor = answere.reflexionFactor;

                allSolid &= solid;
                allEmpty &= !solid;
            }

            // Check if the entire cube is homogeneous (either fully solid or empty)
            if (depth >= maxDepth || allSolid)
            {
                // If homogeneous, stop subdivision
                if (allSolid || allEmpty)
                {
                    if (allSolid)
                    {
                        answere = isSolid(bounds.center, bounds.size.x);
                        node.isOccupied = answere.isSolid;
                        node.penetrationFactor = answere.penetrationFactor;
                        node.reflexionFactor = answere.reflexionFactor;
                        node.isOccupied = allSolid;
                    }
                    
                    return node;
                }
            }   
        }

        // Otherwise, subdivide into 8 child nodes
        node.isLeaf = false;
        int arrayIndex = 0;

        foreach (var (i, subBounds) in GetSubBounds(bounds).Select((b, i) => (i, b)))
        {
            OctreeNode childrenNode = BuildNode(subBounds, isSolid, depth + 1);

            if (childrenNode.isOccupied == true || childrenNode.hasChildrenOccupied == true)
            {
                node.hasChildrenOccupied = true;
                node.children[arrayIndex] = childrenNode;
            }
            else
            {
                node.children[arrayIndex] = null;
            }
            arrayIndex++;
        }

        if (arrayIndex == 0)
            node.isLeaf = true;

        return node;
    }

    private IEnumerable<Bounds> GetSubBounds(Bounds parent)
    {
        // Generate 8 sub-bounds for the octree subdivision
        Vector3 size = parent.size / 2f;
        Vector3 min = parent.min;
        for (int x = 0; x < 2; x++)
            for (int y = 0; y < 2; y++)
                for (int z = 0; z < 2; z++)
                {
                    Vector3 center = min + Vector3.Scale(new Vector3(x + 0.5f, y + 0.5f, z + 0.5f), size);
                    yield return new Bounds(center, size);
                }
    }

    private IEnumerable<Vector3> GetCorners(Bounds b)
    {
        // Return all 8 corners of the bounding box
        Vector3 min = b.min;
        Vector3 max = b.max;
        for (int x = 0; x <= 1; x++)
            for (int y = 0; y <= 1; y++)
                for (int z = 0; z <= 1; z++)
                    yield return new Vector3(
                        x == 0 ? min.x : max.x,
                        y == 0 ? min.y : max.y,
                        z == 0 ? min.z : max.z);
    }
}