OBJLoader.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace SortRenderWithCSharp {
    /// <summary>
    /// 读取一个OBJ，
    /// 并将其的顶点序列放到vertices数组中，
    /// 将其的纹理坐标序列放到uvs数组中，
    /// 将其的法线序列放到normals数组中，
    /// 将其的顶点索引序列放到triangle中，
    /// 最后再根据它的uv索引和法线索引给这个顶点赋值
    /// 
    /// PS:
    ///     1个顶点可能同时在obj文件中对应多个纹理坐标和法线(这是因为使用顶点索引复用顶点造成的),
    ///     这时该顶点的纹理坐标和法线等于该顶点所邻接的所有三角面的纹理坐标和法线的均值
    /// </summary>
    public class OBJLoader {
        /// <summary>
        /// 根据OBJ文件的文件名来读取他
        /// </summary>
        /// <param name="fileName"></param>
        public static Mesh LoadOBJ(string fileName) {
            List<Vertex> tVertex = new List<Vertex>();
            List<Vector3> tpos = new List<Vector3>();
            List<Vector3> tNormals = new List<Vector3>();
            List<Vector2> tuvs = new List<Vector2>();
            List<int> ttriangles = new List<int>();

            // 存储多点共面的法线,key是该顶点的triangle值,即该顶点在vertex数组的下标值,value是该vertex所共面的所有法线
            Dictionary<int, List<Vector3>> differentNormals = new Dictionary<int, List<Vector3>>();
            // 存储多点共面的uv
            Dictionary<int, List<Vector2>> differentUvs = new Dictionary<int, List<Vector2>>();

            StreamReader reader = new StreamReader(fileName);
            string line;
            string[] param;
            while ((line=reader.ReadLine())!=null) {

                if (line.Length <= 2) continue;

                string anotherCommand = line.Substring(0, 2);
                // 转为全大写
                anotherCommand = anotherCommand.ToUpper();
                if (anotherCommand == "VT" || anotherCommand == "TU" || anotherCommand == "TV") {
                    // 表示输入的是纹理坐标
                    param = line.Split(' ');
                    float u = float.Parse(param[1]);
                    float v = float.Parse(param[2]);
                    tuvs.Add(new Vector2(u, v));

                    continue;
                } else if (anotherCommand == "VN") {
                    // 表示输入的是法向量
                    param = line.Split(' ');
                    float x = float.Parse(param[1]);
                    float y = float.Parse(param[2]);
                    float z = float.Parse(param[3]);
                    tNormals.Add(new Vector3(x, y, z));

                    continue;
                }

                char command = line[0];

                switch (command) {
                    // 表示这是个顶点
                    // 顶点后面跟着三个浮点数，表示该顶点在模型空间下的坐标
                    case 'v':
                    case 'V':
                        param = line.Split(' ');
                        float x = float.Parse(param[1]);
                        float y = float.Parse(param[2]);
                        float z = float.Parse(param[3]);
                        Vector3 ttpos = (new Vector3(x,y,z));
                        tVertex.Add(new Vertex(ttpos,Color01.White,0,0));
                        break;
                    case 'f':
                    case 'F':
                        // 表示读取的是一个三角面
                        // 这个三角面的格式如下:
                        // f Vertex1/Texture1/Normal1 Vertex2/Texture2/Normal2 Vertex3/Texture3/Normal3
                        
                        param = line.Split(' ');

                        for (int i = 1; i < 4; i++) {
                            string[] ps = param[i].Split('/');
                            if (ps.Length != 3) continue;
                            // 需要注意的是输入的索引是从1开始的,这里要将其-1

                            // 顶点索引
                            int triangle = int.Parse(ps[0])-1;
                            // uv索引
                            int uvIndex = int.Parse(ps[1])-1;
                            // 法线索引
                            int normalIndex = int.Parse(ps[2])-1;

                            // 获得目标顶点
                            Vertex v = tVertex[triangle];

                            // 设置法线
                            v.normal = tNormals[normalIndex];

                            if (!differentNormals.ContainsKey(triangle)) differentNormals[triangle] = new List<Vector3>();
                            differentNormals[triangle].Add(tNormals[normalIndex]);

                            // 设置uv
                            v.u = tuvs[uvIndex].u;
                            v.v = tuvs[uvIndex].v;

                            if (!differentUvs.ContainsKey(triangle)) differentUvs[triangle] = new List<Vector2>();
                            differentUvs[triangle].Add(tuvs[uvIndex]);

                            // 添加进索引中
                            ttriangles.Add(triangle);

                        }

                        break;
                }
            }

            foreach (int triangle in differentNormals.Keys) {
                Vertex vertex = tVertex[triangle];

                Vector3 normal = Vector3.Zero;
                foreach (Vector3 n in differentNormals[triangle]) normal += n;
                normal /= differentNormals[triangle].Count;

                Vector2 uv = new Vector2(0, 0);
                foreach (Vector2 tuv in differentUvs[triangle]) {
                    uv.u += tuv.u;
                    uv.v += tuv.v;
                }
                uv.u /= differentUvs[triangle].Count; uv.v /= differentUvs[triangle].Count;

                vertex.normal = normal;
                vertex.u = uv.u;
                vertex.v = uv.v;
            }

            return new Mesh(tVertex.ToArray(), ttriangles.ToArray(), tNormals.ToArray());
        }
    }
}