最近在学习 OpenGL 如何读入 obj模型 的时候，发现百度出来，相应的示例程序要么跑不通、要么较复杂，初学者的我想找到个简单易懂的示例程序愣是没找到。只好自己通过谷歌学习之后，写了个简单的示例程序，实现了基本的读入 obj模型 的功能，希望对于初学 OpenGL 的朋友有一些帮助。
第一，配置VS2015 + OpenGL开发环境
这里我是参考的简书作者 @fan2b，直通车，这位作者写的非常详细，而且配置出来的程序能直接整个工程拷走运行，很赞
第二，开始正题
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);//构造函数
void Draw();//绘制函数
private:
vector<vector<GLfloat>>vSets;//存放顶点(x,y,z)坐标
vector<vector<GLint>>fSets;//存放面的三个顶点索引
};
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文件中一行，作为一个字符串
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); //取出字符串中的元素，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") { //如果是顶点的话
vector<GLfloat>Point;
for (int i = 1; i < 4; i++) { //从1开始，将顶点的xyz三个坐标放入顶点vector
GLfloat xyz = atof(parameters[i].c_str());
Point.push_back(xyz);
}
vSets.push_back(Point);
}
else if (parameters[0] == "f") { //如果是面的话，存放三个顶点的索引
vector<GLint>vIndexSets;
for (int i = 1; i < 4; i++){
string x = parameters[i];
string ans = "";
for (int j = 0; j < x.length(); j++) { //跳过‘/’
char ch = x[j];
if (ch != '/') {
ans += ch;
}
else {
break;
}
}
GLint index = atof(ans.c_str());
index = index--;//因为顶点索引在obj文件中是从1开始的，而我们存放的顶点vector是从0开始的，因此要减1
vIndexSets.push_back(index);
}
fSets.push_back(vIndexSets);
}
}
}
f.close();
}
void ObjLoader::Draw(){
glBegin(GL_TRIANGLES);//开始绘制
for (int i = 0; i < fSets.size(); i++) {
GLfloat VN[3];
//三个顶点
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];//取出顶点索引
GLint secondVertexIndex = (fSets[i])[1];
GLint thirdVertexIndex = (fSets[i])[2];
SV1[0] = (vSets[firstVertexIndex])[0];//第一个顶点
SV1[1] = (vSets[firstVertexIndex])[1];
SV1[2] = (vSets[firstVertexIndex])[2];
SV2[0] = (vSets[secondVertexIndex])[0]; //第二个顶点
SV2[1] = (vSets[secondVertexIndex])[1];
SV2[2] = (vSets[secondVertexIndex])[2];
SV3[0] = (vSets[thirdVertexIndex])[0]; //第三个顶点
SV3[1] = (vSets[thirdVertexIndex])[1];
SV3[2] = (vSets[thirdVertexIndex])[2];
GLfloat vec1[3], vec2[3], vec3[3];//计算法向量
//(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]);//绘制法向量
glVertex3f(SV1[0], SV1[1], SV1[2]);//绘制三角面片
glVertex3f(SV2[0], SV2[1], SV2[2]);
glVertex3f(SV3[0], SV3[1], SV3[2]);
}
}
glEnd();
}
3、最后，新建main.cpp
#include "ObjLoader.h"
using namespace std;
//模型路径
string filePath = "data/monkey.obj";
ObjLoader objModel = ObjLoader(filePath);
//实现移动鼠标观察模型所需变量
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); //启用光源
glEnable(GL_LIGHT0); //使用指定灯光
}
//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();//绘制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);
}
//移动鼠标360观察模型
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;
}
总结
这份代码比较小白，也是我初学的水平，但好在比较简单易懂，针对复杂的 obj文件 读取，比如说顶点法向量和纹理的载入等，可在之基础上进行改进。整个工程可在此下载
运行效果：
许可协议
- 本文遵守创作共享 CC BY-NC-SA 3.0协议
- 封面图片来自 unsplash
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