无法将法线添加到.obj网格

我已经在Blender中创建了一个形状（已经确保对三角剖分并添加了法线），并已将其导出为.obj格式以在openframeworks项目中使用。我还编写了一个小类来解析此.obj文件。形状绘制得很完美，但是我似乎无法正确使用法线。

导出仅包含顶点，法线和面。如.obj格式所指示：我将顶点添加到网格中，并使用提供的索引绘制面。法线和法线索引以类似的方式提供。由下图所示，我没有正确应用它们。

这是我的模型加载器脚本：

modelLoader.h

#ifndef _WAVEFRONTLOADER
#define _WAVEFRONTLOADER

#include "ofMain.h"

class waveFrontLoader {

public:

ofMesh mesh;

waveFrontLoader();
~waveFrontLoader();

void loadFile(char *fileName);
ofMesh generateMesh();

private:

typedef struct
{
    ofIndexType v1,v2,v3;
    ofIndexType vn1,vn2,vn3;
}
Index;

std::vector<ofVec3f> vertices;
std::vector<ofVec3f> normals;
std::vector<Index> indices;

void parseLine(char *line);
void parseVertex(char *line);
void parseNormal(char *line);
void parseFace(char *line);
};

#endif

modelLoader.cpp

#include "waveFrontLoader.h"

waveFrontLoader::waveFrontLoader()
{

}

void waveFrontLoader::loadFile(char *fileName)
{
ifstream file;
char line[255];

//open file in openframeworks data folder
file.open(ofToDataPath(fileName).c_str());

if (file.is_open())
{
    while (file.getline(line,255))
    {
        parseLine(line);
    }
}
}

void waveFrontLoader::parseLine(char *line)
{
//If empty, don't do anything with it
if(!strlen(line))
{
    return;
}

//get line type identifier from char string
char *lineType = strtok(strdup(line), " ");

//parse line depending on type
if (!strcmp(lineType, "v")) // Vertices
{
    parseVertex(line);
}
else if (!strcmp(lineType, "vn")) // Normals
{
    parseNormal(line);
}
else if (!strcmp(lineType, "f")) // Indices (Faces)
{
    parseFace(line);
}
}

void waveFrontLoader::parseVertex(char *line)
{
float x;
float y;
float z;

vertices.push_back(ofVec3f(x,y,z));

//get coordinates from vertex line and assign
sscanf(line, "v %f %f %f", &vertices.back().x, &vertices.back().y, &vertices.back().z);
}

void waveFrontLoader::parseNormal(char *line)
{
float x;
float y;
float z;

normals.push_back(ofVec3f(x,y,z));

//get coordinates from normal line and assign
sscanf(line, "vn %f %f %f", &normals.back().x, &normals.back().y, &normals.back().z);
}

void waveFrontLoader::parseFace(char *line)
{
indices.push_back(Index());

//get vertex and normal indices
sscanf(line, "f %d//%d %d//%d %d//%d",
       &indices.back().v1,
       &indices.back().vn1,
       &indices.back().v2,
       &indices.back().vn2,
       &indices.back().v3,
       &indices.back().vn3);
}

ofMesh waveFrontLoader::generateMesh()
{
//add vertices to mesh
for (std::vector<ofVec3f>::iterator i = vertices.begin(); i != vertices.end(); ++i)
{
    mesh.addVertex(*i);
}

//add indices to mesh
for (std::vector<Index>::iterator i = indices.begin(); i != indices.end(); ++i)
{
    // -1 to count from 0
    mesh.addIndex((i->v1) - 1);
    mesh.addIndex((i->v2) - 1);
    mesh.addIndex((i->v3) - 1);

    mesh.addNormal(normals[(i->vn1) - 1]);
    mesh.addNormal(normals[(i->vn2) - 1]);
    mesh.addNormal(normals[(i->vn3) - 1]);

}

return mesh;
}

waveFrontLoader::~waveFrontLoader()
{

}

我也尝试过添加这样的法线（这很有意义，因为它是每张脸的一个法线）：

mesh.addNormal(normals[(i->vn1) - 1]);

我还尝试了每绘制两个三角形仅添加一次法线，并尝试在索引之前添加索引和法线。这些都不起作用。

testApp.h

#pragma once

#include "ofMain.h"
#include "waveFrontLoader.h"

class testApp : public ofBaseApp{

public:
    void setup();
    void update();
    void draw();
    void exit();

    waveFrontLoader *objectLoader;
    ofMesh mesh;
    ofEasyCam camera;
    ofLight light;
};

testApp.cpp

#include "testApp.h"

//--------------------------------------------------------------
void testApp::setup()
{
glEnable(GL_DEPTH_TEST);
glEnable(GL_LIGHTING);

ofBackground(10, 10, 10);

camera.setDistance(10);
light.setPosition(10,30,-25);

objectLoader = new waveFrontLoader();
objectLoader->loadFile("test.obj");
mesh = objectLoader->generateMesh();
}

//--------------------------------------------------------------
void testApp::update()
{

}

//--------------------------------------------------------------
void testApp::draw()
{
camera.begin();
light.enable();
mesh.draw();
light.disable();
camera.end();
}

void testApp::exit()
{
delete objectLoader;
}