OBJ file format vertex color importer for Unity

.ObjFileFormatVertexColorImporter.cs.md

(Unity) vertex color importer for MeshLab's OBJ files

ObjFileFormatVertexColorImporter.cs

/// src* https://gist.github.com/andrew-raphael-lukasik/3559728d022a4c96f491924f8285e1bf
///
/// Copyright (C) 2023 Andrzej Rafał Łukasik (also known as: Andrew Raphael Lukasik)
///
/// This program is free software: you can redistribute it and/or modify
/// it under the terms of the GNU General Public License as published by
/// the Free Software Foundation, version 3 of the License.
///
/// This program is distributed in the hope that it will be useful,
/// but WITHOUT ANY WARRANTY; without even the implied warranty of
/// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
/// See the GNU General Public License for details https://www.gnu.org/licenses/
///
#if UNITY_EDITOR
using System.Collections.Generic;
using UnityEditor;
using UnityEngine;

using IO = System.IO;
using NumberStyles = System.Globalization.NumberStyles;
using CultureInfo = System.Globalization.CultureInfo;

public class ObjFileFormatVertexColorImporter : AssetPostprocessor
{
    
    Dictionary<string,Color[]> _colorData = new Dictionary<string,Color[]>();

    void OnPreprocessModel ()
    {
        if( !assetPath.EndsWith(".obj") ) return;
        
        var stopwatch = System.Diagnostics.Stopwatch.StartNew();

        // read obj data
        var current_sourceColor = new List<Color>();
        var current_geometryIndices = new List<int>();
        var current_sourceNormalHash = new Dictionary<int,int>();
        var current_sourceUvHash = new Dictionary<int,int>();
        var current_geometrySharedVerticesDetector = new HashSet<Vector3Int>();
        var geometryIndices = new Dictionary<string,List<int>>() { { "default" , current_geometryIndices } };
        var sourceColor = new Dictionary<string,List<Color>>() { { "default" , current_sourceColor } };
        var sourceNormalHash = new Dictionary<string,Dictionary<int,int>>() { { "default" , current_sourceNormalHash } };
        var sourceUvHash = new Dictionary<string,Dictionary<int,int>>() { { "default" , current_sourceUvHash } };
        var geometrySharedVerticesDetector = new Dictionary<string,HashSet<Vector3Int>>() { { "default" , current_geometrySharedVerticesDetector } };
        string line, g = null, o = null, meshName = "default";
        int numVertexColorVertices = 0;
        int v_index = 1, vn_index = 1, vt_index = 1;
        var reader = IO.File.OpenText( Application.dataPath + assetPath.Replace("Assets","") );
        while( (line = reader.ReadLine())!=null )
        {
            string[] words = line.Split(' ');

            byte wordsLength = (byte)words.Length;
            byte is_o = words[0]=="o" ? (byte)1 : (byte)0;
            byte is_g = words[0]=="g" ? (byte)1 : (byte)0;
            byte is_v = words[0]=="v" && wordsLength==7 ? (byte)1 : (byte)0;
            byte is_vt = words[0]=="vt" && wordsLength==3 ? (byte)1 : (byte)0;
            byte is_vn = words[0]=="vn" && wordsLength==4 ? (byte)1 : (byte)0;
            byte is_f = words[0]=="f" && wordsLength>1 ? (byte)1 : (byte)0;

            // parse o
            if( is_o==1 )
            {
                o = line.Substring(1).Trim(' ').Replace(' ','_');
            }

            // parse g
            if( is_g==1 )
            {
                g = line.Substring(1).Trim(' ').Replace(' ','_');
                meshName = g;

                current_sourceColor = new List<Color>();
                current_geometryIndices = new List<int>();
                current_sourceNormalHash = new Dictionary<int,int>();
                current_sourceUvHash = new Dictionary<int,int>();
                current_geometrySharedVerticesDetector = new HashSet<Vector3Int>();

                sourceColor.Add( meshName , current_sourceColor );
                geometryIndices.Add( meshName , current_geometryIndices );
                sourceNormalHash.Add( meshName , current_sourceNormalHash );
                sourceUvHash.Add( meshName , current_sourceUvHash );
                geometrySharedVerticesDetector.Add( meshName , current_geometrySharedVerticesDetector );

                v_index = 1;
                vn_index = 1;
                vt_index = 1;
            }

            // parse face data
            if( is_f==1 )
            {
                for( int i=1 ; i<wordsLength ; i++ )
                {
                    string[] v_vt_vn = words[i].Split('/');
                    if( v_vt_vn.Length==3 )
                    {
                        string v = v_vt_vn[0];
                        string vt = v_vt_vn[1];
                        string vn = v_vt_vn[2];

                        int vertexIndex = int.Parse( v , NumberStyles.Number , CultureInfo.InvariantCulture );
                            
                        int normalHash;
                        if( vn.Length!=0 )
                        {
                            int normalIndex = int.Parse( vn , NumberStyles.Number , CultureInfo.InvariantCulture );
                            normalHash = current_sourceNormalHash[normalIndex];
                        }
                        else normalHash = -1;// vertex with no normal data

                        int uvHash;
                        if( vt.Length!=0 )
                        {
                            int uvIndex = int.Parse( vt , NumberStyles.Number , CultureInfo.InvariantCulture );
                            uvHash = current_sourceUvHash[uvIndex];
                        }
                        else uvHash = -1;// vertex with no uv data
                            
                        if( current_geometrySharedVerticesDetector.Add(new Vector3Int(vertexIndex,uvHash,normalHash)) )
                        {
                            //Debug.Log($"new vertex index added: ( {vertexIndex} #{uvHash} , #{normalVectorHash} )");
                            current_geometryIndices.Add(vertexIndex);
                        }
                        //else Debug.Log($"ignoring vertex as shared: ( {vertexIndex} , #{normalVectorHash} )");
                    }
                }
            }

            // parse vertex data (vertex color only)
            if( is_v==1 )
            {
                float red = float.Parse( words[4] , NumberStyles.Number , CultureInfo.InvariantCulture );
                float green = float.Parse( words[5] , NumberStyles.Number , CultureInfo.InvariantCulture );
                float blue = float.Parse( words[6] , NumberStyles.Number , CultureInfo.InvariantCulture );
                current_sourceColor.Add( new Color(red,green,blue) );
                v_index++;
                numVertexColorVertices++;
            }

            // parse vertex normal data
            if( is_vn==1 )
            {
                int hash = 17;
                unchecked
                {
                    hash = hash * 23 + words[1].GetHashCode();
                    hash = hash * 23 + words[2].GetHashCode();
                    hash = hash * 23 + words[3].GetHashCode();
                }
                //Debug.Log($"vn #{vn_index} ( {words[1]} , {words[2]} , {words[3]} ) added as #{hash}");
                current_sourceNormalHash.Add( vn_index++ , hash );
            }

            // parse texture UV data
            if( is_vt==1 )
            {
                int hash = 17;
                unchecked
                {
                    hash = hash * 23 + words[1].GetHashCode();
                    hash = hash * 23 + words[2].GetHashCode();
                }
                //Debug.Log($"vt #{vn_index} ( {words[1]} , {words[2]} ) added as #{hash}");
                current_sourceUvHash.Add( vt_index++ , hash );
            }
        }
        reader.Dispose();

        if( numVertexColorVertices!=0 )// was any vertex color data found ?
        {
            // change importer settings
            var importer = (ModelImporter)assetImporter;
            importer.optimizeMeshVertices = false;
            importer.optimizeMeshPolygons = false;
            importer.weldVertices = false;
            importer.importNormals = ModelImporterNormals.Import;
            importer.importTangents = ModelImporterTangents.CalculateMikk;
            importer.importAnimation = false;
            importer.animationType = ModelImporterAnimationType.None;
            importer.materialImportMode = ModelImporterMaterialImportMode.None;

            // prepare final color array
            foreach( string nextMeshName in sourceColor.Keys )
            {
                List<int> nextMeshIndices = geometryIndices[nextMeshName];
                int numIndices = nextMeshIndices.Count;
                    
                List<Color> unpreparedColorArray = sourceColor[nextMeshName];
                Color[] finalColorArray = new Color[numIndices];
                    
                for( int i=0 ; i<numIndices ; i++ )
                {
                    finalColorArray[i] = unpreparedColorArray[nextMeshIndices[i]-1];
                }

                _colorData.Add( nextMeshName , finalColorArray );
            }
        }

        double totalSeconds = new System.TimeSpan(stopwatch.ElapsedTicks).TotalSeconds;
        if( totalSeconds>0.1 ) Debug.LogWarning($"{GetType().Name}::{nameof(OnPreprocessModel)}() took {totalSeconds:0.00} seconds, `{assetPath}` asset");
    }

    void OnPostprocessModel ( GameObject gameObject )
    {
        if( !assetPath.EndsWith(".obj") ) return;

        var stopwatch = System.Diagnostics.Stopwatch.StartNew();

        if( _colorData.Count!=0 )
        {
            MeshFilter[] meshFilters = gameObject.GetComponentsInChildren<MeshFilter>();
            //Debug.Log($"meshFilters:{meshFilters.Length}, _colorData.Count:{_colorData.Count}",gameObject);
            foreach( var mf in meshFilters )
            {
                Mesh mesh = mf.sharedMesh;
                var vertexColor = _colorData[ mesh.name ];
                if( vertexColor.Length!=mesh.vertexCount ) Debug.LogError($"Invalid color data length! mesh.name:'{mesh.name}', vertexColor.Length:{vertexColor.Length}, mesh.vertexCount:{mesh.vertexCount}",gameObject);
                mesh.SetColors( vertexColor );
            }
        }

        double totalSeconds = new System.TimeSpan(stopwatch.ElapsedTicks).TotalSeconds;
        if( totalSeconds>0.1 ) Debug.LogWarning($"{GetType().Name}::{nameof(OnPostprocessModel)}() took {totalSeconds:0.00} seconds, `{assetPath}` asset",gameObject);
    }

}
#endif

Thank you @andrew-raphael-lukasik . I got a lot of help thanks to your code.