Helper script for importing magicavoxel files into c#

MagicaVoxelFormatHelper.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using System.IO;

[System.Serializable]
public class MagicaVoxelModel_PACK : MagicaVoxelChunk
{
    public int numModels; // num of SIZE and SYZI chunks 

    public bool TryFillFromBuffer(byte[] buffer, ref int startIndex)
    {
        base.FillFromBuffer(buffer, ref startIndex);

        var matching = Id[0] == 'P' && Id[1] == 'A' && Id[2] == 'C' && Id[3] == 'K';
        if (!matching)
        {
            startIndex -= 4; // char[4]
            startIndex -= 4; // int
            startIndex -= 4; // int 

            return false; 
        }

        numModels = MathExtensions.ReadFromStreamReversed(buffer, ref startIndex);

        return true; 
    }
}

[System.Serializable]
public class MagicaVoxelModel_SIZE : MagicaVoxelChunk
{
    public int size_x;
    public int size_y;
    public int size_z; // gravity direction 

    public override void FillFromBuffer(byte[] buffer, ref int startIndex)
    {
        base.FillFromBuffer(buffer, ref startIndex);

        MathExtensions.ReadFromStreamReversed(buffer, ref startIndex);
        MathExtensions.ReadFromStreamReversed(buffer, ref startIndex);
        MathExtensions.ReadFromStreamReversed(buffer, ref startIndex);
    }
}

[System.Serializable]
public class MagicaVoxelVoxel
{
    public byte x;
    public byte y;
    public byte z;
    public byte colorIndex;

    public void FillFromBuffer(byte[] buffer, ref int startIndex)
    {
        x = MathExtensions.ReadFromStreamByte(buffer, ref startIndex);
        y = MathExtensions.ReadFromStreamByte(buffer, ref startIndex);
        z = MathExtensions.ReadFromStreamByte(buffer, ref startIndex);
        colorIndex = MathExtensions.ReadFromStreamByte(buffer, ref startIndex);
    }
}

[System.Serializable]
public class MagicaVoxelModel_XYZI : MagicaVoxelChunk
{
    public int numVoxels;
    public MagicaVoxelVoxel[] voxels; 

    public override void FillFromBuffer(byte[] buffer, ref int startIndex)
    {
        base.FillFromBuffer(buffer, ref startIndex);

        numVoxels = MathExtensions.ReadFromStreamReversed(buffer, ref startIndex);

        if(numVoxels < 0)
        {
            Debug.LogWarningFormat("Tried to make voxel buffer size: {0}", numVoxels);
            voxels = new MagicaVoxelVoxel[0];
            return;
        }

        voxels = new MagicaVoxelVoxel[numVoxels];

        for(var i = 0; i < numVoxels; ++i)
        {
            var voxel = new MagicaVoxelVoxel();
            voxel.FillFromBuffer(buffer, ref startIndex);
            voxels[i] = voxel; 
        }
    }
}

[System.Serializable]
public class MagicaVoxelPalleteEntry
{
    public byte r; 
    public byte g; 
    public byte b; 
    public byte a;

    public void FillFromBuffer(byte[] buffer, ref int startIndex)
    {
        r = MathExtensions.ReadFromStreamByte(buffer, ref startIndex);
        g = MathExtensions.ReadFromStreamByte(buffer, ref startIndex);
        b = MathExtensions.ReadFromStreamByte(buffer, ref startIndex);
        a = MathExtensions.ReadFromStreamByte(buffer, ref startIndex);
    }
}

[System.Serializable]
public class MagicaVoxelModel_RGBA : MagicaVoxelChunk
{
    public MagicaVoxelPalleteEntry[] Pallette = new MagicaVoxelPalleteEntry[256]; // (R, G, B, A) : 1 byte for each component

    public bool TryFillFromBuffer(byte[] buffer, ref int startIndex)
    {
        base.FillFromBuffer(buffer, ref startIndex);

        var matching = Id[0] == 'R' && Id[1] == 'G' && Id[2] == 'B' && Id[3] == 'A';
        if (!matching)
        {
            startIndex -= 4; // char[4]
            startIndex -= 4; // int
            startIndex -= 4; // int 

            return false;
        }

        for (var i = 0; i < Pallette.Length; ++i)
        {
            var entry = new MagicaVoxelPalleteEntry();
            entry.FillFromBuffer(buffer, ref startIndex);
            Pallette[i] = entry; 
        } 

        return true; 
    }
}

[System.Serializable]
public class MagicaVoxelModel_MATT : MagicaVoxelChunk
{
    public int MatId;
    public int materialType;
    public int materialWeight;
    public int propertyBits;
    public float[] normalizedPropertyValue; // (N)

    // danger, not overloading 
    public bool TryFillFromBuffer(byte[] buffer, ref int startIndex)
    {
        base.FillFromBuffer(buffer, ref startIndex);

        var matching = Id[0] == 'M' && Id[1] == 'A' && Id[2] == 'T' && Id[3] == 'T';
        if (!matching)
        {
            startIndex -= 4; // char[4]
            startIndex -= 4; // int
            startIndex -= 4; // int 

            return false;
        }

        MatId = MathExtensions.ReadFromStreamReversed(buffer, ref startIndex); 
        materialType = MathExtensions.ReadFromStreamReversed(buffer, ref startIndex); 
        materialWeight = MathExtensions.ReadFromStreamReversed(buffer, ref startIndex); 
        propertyBits = MathExtensions.ReadFromStreamReversed(buffer, ref startIndex);

        normalizedPropertyValue = new float[numBytesOfChunkContent];
        for (var i = 0; i < numBytesOfChunkContent; ++i)
        {
            normalizedPropertyValue[i] = MathExtensions.ReadFromStreamFloatReversed(buffer, ref startIndex); 
        }

        return true; 
    }
}

[System.Serializable]
public class MagicaVoxelChunk
{
    public char[] Id = new char[4];
    public int numBytesOfChunkContent; // (N)
    public int numBytesOfChildrenChunks; // (M)

    public virtual void FillFromBuffer(byte[] buffer, ref int startIndex)
    {
        MathExtensions.ReadFromStreamCharBuffer(buffer, Id, 0, Id.Length, ref startIndex);
        numBytesOfChunkContent = MathExtensions.ReadFromStreamReversed(buffer, ref startIndex);
        numBytesOfChildrenChunks = MathExtensions.ReadFromStreamReversed(buffer, ref startIndex);

        Debug.LogFormat("{0}{1}{2}{3}: {4}, {5}", 
            Id[0], Id[1], Id[2], Id[3], numBytesOfChunkContent, numBytesOfChildrenChunks);
    }
}

[System.Serializable]
public class MagicaVoxelFile
{
    public char[] Id = new char[4];
    public int Version;

    public MagicaVoxelChunk ChunkMain = new MagicaVoxelChunk();

    public List<MagicaVoxelModel_SIZE> SizeChunks = new List<MagicaVoxelModel_SIZE>();
    public List<MagicaVoxelModel_XYZI> XYZIChunks = new List<MagicaVoxelModel_XYZI>();

    public MagicaVoxelModel_RGBA RGBAChunk = new MagicaVoxelModel_RGBA();

    public List<MagicaVoxelModel_MATT> MattChunks = new List<MagicaVoxelModel_MATT>();

    // not from file, dont serialize 
    public bool HasRGBAChunk; 

    public static MagicaVoxelFile ReadFromBuffer(byte[] buffer, ref int startIndex)
    {
        // file info 
        var magicaVoxelFile = new MagicaVoxelFile();
        MathExtensions.ReadFromStreamCharBuffer(buffer, magicaVoxelFile.Id, 0, magicaVoxelFile.Id.Length, ref startIndex);
        magicaVoxelFile.Version = MathExtensions.ReadFromStreamReversed(buffer, ref startIndex);

        // main chunk 
        magicaVoxelFile.ChunkMain.FillFromBuffer(buffer, ref startIndex);

        var targetIndex = startIndex + magicaVoxelFile.ChunkMain.numBytesOfChildrenChunks - sizeof(int) * 256 - 4 - 4 - 4;
        while(startIndex < targetIndex && startIndex < buffer.Length) // danger zone 
        {
            Debug.LogFormat("startIndex: {0} / targetIndex: {1}", startIndex, targetIndex);
            var sizeChunk = new MagicaVoxelModel_SIZE();
            sizeChunk.FillFromBuffer(buffer, ref startIndex);
            magicaVoxelFile.SizeChunks.Add(sizeChunk);

            var xyziChunk = new MagicaVoxelModel_XYZI();
            xyziChunk.FillFromBuffer(buffer, ref startIndex);
            magicaVoxelFile.XYZIChunks.Add(xyziChunk);
        }

        magicaVoxelFile.HasRGBAChunk = magicaVoxelFile.RGBAChunk.TryFillFromBuffer(buffer, ref startIndex);
        if (magicaVoxelFile.HasRGBAChunk)
        {
            // might be more matts, not checking yet 
        }
        
        return magicaVoxelFile;
    }

    public static uint[] default_palette = new uint[256] {
        0x00000000, 0xffffffff, 0xffccffff, 0xff99ffff, 0xff66ffff, 0xff33ffff, 0xff00ffff, 0xffffccff, 0xffccccff, 0xff99ccff, 0xff66ccff, 0xff33ccff, 0xff00ccff, 0xffff99ff, 0xffcc99ff, 0xff9999ff,
        0xff6699ff, 0xff3399ff, 0xff0099ff, 0xffff66ff, 0xffcc66ff, 0xff9966ff, 0xff6666ff, 0xff3366ff, 0xff0066ff, 0xffff33ff, 0xffcc33ff, 0xff9933ff, 0xff6633ff, 0xff3333ff, 0xff0033ff, 0xffff00ff,
        0xffcc00ff, 0xff9900ff, 0xff6600ff, 0xff3300ff, 0xff0000ff, 0xffffffcc, 0xffccffcc, 0xff99ffcc, 0xff66ffcc, 0xff33ffcc, 0xff00ffcc, 0xffffcccc, 0xffcccccc, 0xff99cccc, 0xff66cccc, 0xff33cccc,
        0xff00cccc, 0xffff99cc, 0xffcc99cc, 0xff9999cc, 0xff6699cc, 0xff3399cc, 0xff0099cc, 0xffff66cc, 0xffcc66cc, 0xff9966cc, 0xff6666cc, 0xff3366cc, 0xff0066cc, 0xffff33cc, 0xffcc33cc, 0xff9933cc,
        0xff6633cc, 0xff3333cc, 0xff0033cc, 0xffff00cc, 0xffcc00cc, 0xff9900cc, 0xff6600cc, 0xff3300cc, 0xff0000cc, 0xffffff99, 0xffccff99, 0xff99ff99, 0xff66ff99, 0xff33ff99, 0xff00ff99, 0xffffcc99,
        0xffcccc99, 0xff99cc99, 0xff66cc99, 0xff33cc99, 0xff00cc99, 0xffff9999, 0xffcc9999, 0xff999999, 0xff669999, 0xff339999, 0xff009999, 0xffff6699, 0xffcc6699, 0xff996699, 0xff666699, 0xff336699,
        0xff006699, 0xffff3399, 0xffcc3399, 0xff993399, 0xff663399, 0xff333399, 0xff003399, 0xffff0099, 0xffcc0099, 0xff990099, 0xff660099, 0xff330099, 0xff000099, 0xffffff66, 0xffccff66, 0xff99ff66,
        0xff66ff66, 0xff33ff66, 0xff00ff66, 0xffffcc66, 0xffcccc66, 0xff99cc66, 0xff66cc66, 0xff33cc66, 0xff00cc66, 0xffff9966, 0xffcc9966, 0xff999966, 0xff669966, 0xff339966, 0xff009966, 0xffff6666,
        0xffcc6666, 0xff996666, 0xff666666, 0xff336666, 0xff006666, 0xffff3366, 0xffcc3366, 0xff993366, 0xff663366, 0xff333366, 0xff003366, 0xffff0066, 0xffcc0066, 0xff990066, 0xff660066, 0xff330066,
        0xff000066, 0xffffff33, 0xffccff33, 0xff99ff33, 0xff66ff33, 0xff33ff33, 0xff00ff33, 0xffffcc33, 0xffcccc33, 0xff99cc33, 0xff66cc33, 0xff33cc33, 0xff00cc33, 0xffff9933, 0xffcc9933, 0xff999933,
        0xff669933, 0xff339933, 0xff009933, 0xffff6633, 0xffcc6633, 0xff996633, 0xff666633, 0xff336633, 0xff006633, 0xffff3333, 0xffcc3333, 0xff993333, 0xff663333, 0xff333333, 0xff003333, 0xffff0033,
        0xffcc0033, 0xff990033, 0xff660033, 0xff330033, 0xff000033, 0xffffff00, 0xffccff00, 0xff99ff00, 0xff66ff00, 0xff33ff00, 0xff00ff00, 0xffffcc00, 0xffcccc00, 0xff99cc00, 0xff66cc00, 0xff33cc00,
        0xff00cc00, 0xffff9900, 0xffcc9900, 0xff999900, 0xff669900, 0xff339900, 0xff009900, 0xffff6600, 0xffcc6600, 0xff996600, 0xff666600, 0xff336600, 0xff006600, 0xffff3300, 0xffcc3300, 0xff993300,
        0xff663300, 0xff333300, 0xff003300, 0xffff0000, 0xffcc0000, 0xff990000, 0xff660000, 0xff330000, 0xff0000ee, 0xff0000dd, 0xff0000bb, 0xff0000aa, 0xff000088, 0xff000077, 0xff000055, 0xff000044,
        0xff000022, 0xff000011, 0xff00ee00, 0xff00dd00, 0xff00bb00, 0xff00aa00, 0xff008800, 0xff007700, 0xff005500, 0xff004400, 0xff002200, 0xff001100, 0xffee0000, 0xffdd0000, 0xffbb0000, 0xffaa0000,
        0xff880000, 0xff770000, 0xff550000, 0xff440000, 0xff220000, 0xff110000, 0xffeeeeee, 0xffdddddd, 0xffbbbbbb, 0xffaaaaaa, 0xff888888, 0xff777777, 0xff555555, 0xff444444, 0xff222222, 0xff111111
    };
}

public class MagicaVoxelFormatHelper : MonobehaviorSingleton<MagicaVoxelFormatHelper>
{
    public MagicaVoxelFile file = new MagicaVoxelFile();
    public Mesh tempMesh;

    public string magicaVoxelFilename = "default.vox";
    public string saveChunkDataAs = "magicaToChunkData.world";
}

note for the missing extension helper:

public static byte ReadFromStreamByte(byte[] buffer, ref int startIndex)
    {
        return buffer[startIndex++];
    }

public static int ReadFromStreamReversed(byte[] buffer, ref int startIndex)
    {
        int value = 0;

        value += buffer[startIndex + 0] << 00;
        value += buffer[startIndex + 1] << 08;
        value += buffer[startIndex + 2] << 16;
        value += buffer[startIndex + 3] << 24;

        startIndex += 4;

        return value;
    }