最近在學習OpenGL如何讀入obj模型的時候，發現百度出來，相應的示例程式要麼跑不通、要麼較複雜，初學者的我想找到個簡單易懂的示例程式愣是沒找到。只好自己通過谷歌學習之後，寫了個簡單的示例程式，實現了基本的讀入obj模型的功能，希望對於初學OpenGL的朋友有一些幫助。

第一，配置VS2015 + OpenGL開發環境

• 這裡我是參考的簡書作者@fan2b，直通車，這位作者寫的非常詳細，而且配置出來的程式能直接整個工程拷走執行，很贊

第二，開始正題

1、新建 ObjLoader.h

#include "Dependencies\glew\glew.h"
#include "Dependencies\freeglut\freeglut.h"
 

#include <vector>
#include <string>
using namespace std;
class ObjLoader{
public:
    ObjLoader(string filename);//建構函式
    void Draw();//繪製函式
private:
    vector<vector<GLfloat>>vSets;//存放頂點(x,y,z)座標
    vector<vector<GLint>>fSets;//存放面的三個頂點索引
};

2、新建ObjLoader.cpp

#include "ObjLoader.h"
 

#include <fstream>
#include <iostream>
using namespace std;

ObjLoader::ObjLoader(string filename)
{
    string line;
    fstream f;
    f.open(filename, ios::in);
    if (!f.is_open()){
        cout << "Something Went Wrong When Opening Objfiles" << endl;
    }

    while (!f.eof()){
        getline(f, line);//拿到obj檔案中一行，作為一個字串
 

        vector<string>parameters;
        string tailMark = " ";
        string ans = "";

        line = line.append(tailMark);
        for (int i = 0; i < line.length(); i++) {
            char ch = line[i];
            if (ch != ' ') {
                ans+=ch;
            }
            else {
                parameters.push_back(ans); //取出字串中的元素，以空格切分
                ans = "";
            }
        }
        //cout << parameters.size() << endl;
        if (parameters.size() != 4) {
            cout << "the size is not correct" << endl;
        }
        else {
            if (parameters[0] == "v") {   //如果是頂點的話
                vector<GLfloat>Point;
                for (int i = 1; i < 4; i++) {   //從1開始，將頂點的xyz三個座標放入頂點vector
                    GLfloat xyz = atof(parameters[i].c_str());
                    Point.push_back(xyz);
                }
                vSets.push_back(Point);
            }

            else if (parameters[0] == "f") {   //如果是面的話，存放三個頂點的索引
                vector<GLint>vIndexSets;
                for (int i = 1; i < 4; i++){
                    string x = parameters[i];
                    string ans = "";
                    for (int j = 0; j < x.length(); j++) {   //跳過‘/’
                        char ch = x[j];
                        if (ch != '/') { 
                            ans += ch;
                        }
                        else {
                            break;
                        }
                    }
                    GLint index = atof(ans.c_str());
                    index = index--;//因為頂點索引在obj檔案中是從1開始的，而我們存放的頂點vector是從0開始的，因此要減1
                    vIndexSets.push_back(index);
                }
                fSets.push_back(vIndexSets);
            }
        }
    }
    f.close();
}

void ObjLoader::Draw(){

    glBegin(GL_TRIANGLES);//開始繪製
    for (int i = 0; i < fSets.size(); i++) {
        GLfloat VN[3];
        //三個頂點
        GLfloat SV1[3];
        GLfloat SV2[3];
        GLfloat SV3[3];

        if ((fSets[i]).size() != 3) {
            cout << "the fSetsets_Size is not correct" << endl;
        }
        else {
                GLint firstVertexIndex = (fSets[i])[0];//取出頂點索引
                GLint secondVertexIndex = (fSets[i])[1];
                GLint thirdVertexIndex = (fSets[i])[2];

                SV1[0] = (vSets[firstVertexIndex])[0];//第一個頂點
                SV1[1] = (vSets[firstVertexIndex])[1];
                SV1[2] = (vSets[firstVertexIndex])[2];

                SV2[0] = (vSets[secondVertexIndex])[0]; //第二個頂點
                SV2[1] = (vSets[secondVertexIndex])[1];
                SV2[2] = (vSets[secondVertexIndex])[2];

                SV3[0] = (vSets[thirdVertexIndex])[0]; //第三個頂點
                SV3[1] = (vSets[thirdVertexIndex])[1];
                SV3[2] = (vSets[thirdVertexIndex])[2];


                GLfloat vec1[3], vec2[3], vec3[3];//計算法向量
                //(x2-x1,y2-y1,z2-z1)
                vec1[0] = SV1[0] - SV2[0];
                vec1[1] = SV1[1] - SV2[1];
                vec1[2] = SV1[2] - SV2[2];

                //(x3-x2,y3-y2,z3-z2)
                vec2[0] = SV1[0] - SV3[0];
                vec2[1] = SV1[1] - SV3[1];
                vec2[2] = SV1[2] - SV3[2];

                //(x3-x1,y3-y1,z3-z1)
                vec3[0] = vec1[1] * vec2[2] - vec1[2] * vec2[1];
                vec3[1] = vec2[0] * vec1[2] - vec2[2] * vec1[0];
                vec3[2] = vec2[1] * vec1[0] - vec2[0] * vec1[1];

                GLfloat D = sqrt(pow(vec3[0], 2) + pow(vec3[1], 2) + pow(vec3[2], 2));

                VN[0] = vec3[0] / D;
                VN[1] = vec3[1] / D;
                VN[2] = vec3[2] / D;

                glNormal3f(VN[0], VN[1], VN[2]);//繪製法向量

                glVertex3f(SV1[0], SV1[1], SV1[2]);//繪製三角面片
                glVertex3f(SV2[0], SV2[1], SV2[2]);
                glVertex3f(SV3[0], SV3[1], SV3[2]); 
        }
    }
    glEnd();
}

3、最後，新建main.cpp

#include "ObjLoader.h"
using namespace std;
//模型路徑
string filePath = "data/monkey.obj";

ObjLoader objModel = ObjLoader(filePath);
//實現移動滑鼠觀察模型所需變數
static float c = 3.1415926 / 180.0f;
static float r = 1.0f;
static int degree = 90;
static int oldPosY = -1;
static int oldPosX = -1;

//安置光源
void setLightRes() {
    GLfloat lightPosition[] = { 0.0f, 0.0f, 1.0f, 0.0f };
    glLightfv(GL_LIGHT0, GL_POSITION, lightPosition);
    glEnable(GL_LIGHTING); //啟用光源
    glEnable(GL_LIGHT0);   //使用指定燈光
}

//初始化
void init() {
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
    glutInitWindowSize(500, 500);
    glutCreateWindow("ObjLoader");
    glEnable(GL_DEPTH_TEST);
    glShadeModel(GL_SMOOTH);
    setLightRes();
    glEnable(GL_DEPTH_TEST);
}

void display()
{
    glColor3f(1.0, 1.0, 1.0);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glMatrixMode(GL_MODELVIEW);                            
    glLoadIdentity();                                     
    glTranslatef(0.0f, 0.0f, -5.0f);                                                            
    setLightRes();
    glPushMatrix();

    gluLookAt(r*cos(c*degree), 0, r*sin(c*degree), 0.0f, 0.0f, 0.0f, 0.0f, 1.0f, 0.0f);

    objModel.Draw();//繪製obj模型
    glPopMatrix();
    glutSwapBuffers();
}

void reshape(int width, int height)
{
    glViewport(0, 0, width, height);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(60.0f, (GLdouble)width / (GLdouble)height, 1.0f, 200.0f);
    glMatrixMode(GL_MODELVIEW);
}

//移動滑鼠360觀察模型
void moseMove(int button, int state, int x, int y)
{
    if (state == GLUT_DOWN) {
        oldPosX = x; oldPosY = y;
    }
}
void changeViewPoint(int x, int y)
{
    int temp = x - oldPosX;
    degree += temp;
    oldPosX = x;
    oldPosY = y;
}

void myIdle()
{
    glutPostRedisplay();
}

int main(int argc, char* argv[])
{
    glutInit(&argc, argv);
    init();
    glutDisplayFunc(display);
    glutReshapeFunc(reshape);
    glutMouseFunc(moseMove);
    glutMotionFunc(changeViewPoint);
    glutIdleFunc(myIdle);
    glutMainLoop();
    return 0;
}

總結

• 這份程式碼比較小白，也是我初學的水平，但好在比較簡單易懂，針對複雜的obj檔案讀取，比如說頂點法向量和紋理的載入等，可在之基礎上進行改進。整個工程可在此下載
• 執行效果：
  

許可協議

• 商業用途轉載請聯絡 Chen.Jiayang [AT] foxmail.com