openGL 解析ply文件并且显示三维模型

一、ply文件简介

ply文件是一种用于描述图形结构的文件。一般包括：头部、顶点列表、面片列表、其他元素列表等。

例如下面这个ply文件描述了一个cube。

ply
format ascii 1.0
comment made by anonymous
comment this file is a cube
element vertex 8
property float32 x
property float32 y
property float32 z
element face 12
property list uint8 int32 vertex_index
end_header
0 0 0
0 0 0.01
0 0.01 0.01
0 0.01 0
0.01 0 0
0.01 0 0.01
0.01 0.01 0.01
0.01 0.01 0
3 0 1 2
3 0 3 2
3 7 9 5
3 7 4 5
3 0 4 5
3 0 1 5
3 1 5 6
3 1 2 6
3 2 6 7
3 2 3 7
3 1 7 4
3 3 0 4

二、ply文件的解析及用openGL显示

ply的文件格式比较简单，我们只需要对其中的信息进行提取，在调用openGL中相应的函数就可以实现显示ply模型了。

代码：

#ifndef PLYREADER_H_
#define PLYREADER_H_

#include <GL/glut.h>
#include <GL/glu.h>
#include <GL/gl.h>
#include <vector>
using namespace std;

struct SModelData
{
    vector <float> vecFaceTriangles; // = face * 9
    vector <float> vecFaceTriangleColors; // = face * 9
    int iTotalConnectedTriangles;
};

class CPLYLoader
{
public:
    CPLYLoader();
    bool LoadModel(char * filename);
    void Draw();
private:
    float * mp_vertexXYZ;
    float * mp_vertexRGB;
    int m_totalConnectedQuads;
    int m_totalConnectedPoints;
    int m_totalFaces;
    SModelData m_ModelData;
};

#endif

#include "stdafx.h"
#include "PLYLoader.h"

CPLYLoader::CPLYLoader()
{
    this->m_totalConnectedQuads = 0;
    this->m_totalConnectedPoints = 0;
    this->m_ModelData.iTotalConnectedTriangles = 0;
}

bool CPLYLoader::LoadModel(char * filename)
{
    printf("Loading %s...
", filename);
    char * pch = strstr(filename, ".ply");
    if (pch != NULL)
    {
        FILE * file = fopen(filename, "r");
        if (!file)
        {
            printf("load PLY file %s failed
", filename);
            return false;
        }
        fseek(file, 0, SEEK_END);
        long fileSize = ftell(file);
        try
        {
            mp_vertexXYZ = (float*)malloc(fileSize);
            mp_vertexRGB = (float*)malloc(fileSize);
        }
        catch (char *)
        {
            return false;
        }
        if (mp_vertexXYZ == NULL || mp_vertexRGB == NULL) return false;
        fseek(file, 0, SEEK_SET);
        if (file)
        {
            char buffer[1000];
            fgets(buffer, 300, file);            
            //READ HEADER
            while (strncmp("element vertex", buffer, strlen("element vertex")) != 0)
            {
                fgets(buffer, 300, file);        
            }
            strcpy(buffer, buffer + strlen("element vertex"));
            sscanf(buffer, "%i", &this->m_totalConnectedPoints);
            printf("first we get %d vertexs
", this->m_totalConnectedPoints);
            //Find the number of vertexes
            fseek(file, 0, SEEK_SET);
            while (strncmp("element face", buffer, strlen("element face")) != 0)
            {
                fgets(buffer, 300, file);        
            }
            strcpy(buffer, buffer + strlen("element face"));
            sscanf(buffer, "%i", &this->m_totalFaces);
            printf("second we get %d faces
", this->m_totalFaces);
            //Go to end_header
            while (strncmp("end_header", buffer, strlen("end_header")) != 0)
            {
                fgets(buffer, 300, file);            
            }
            //Read vertices
            int i = 0;
            for (int iterator = 0; iterator < this->m_totalConnectedPoints; iterator++)
            {
                fgets(buffer, 300, file);
                sscanf(buffer, "%f %f %f", &mp_vertexXYZ[i], &mp_vertexXYZ[i + 1], &mp_vertexXYZ[i + 2]);
                i += 3;
            }
            //Read faces
            for (int iterator = 0; iterator < this->m_totalFaces; iterator++)
            {
                fgets(buffer, 300, file);
                //Triangular patch
                if (buffer[0] == '3')
                {
                    int vertex1 = 0, vertex2 = 0, vertex3 = 0;
                    buffer[0] = ' ';
                    sscanf(buffer, "%i%i%i", &vertex1, &vertex2, &vertex3);
                    //point
                    m_ModelData.vecFaceTriangles.push_back(mp_vertexXYZ[3 * vertex1]);
                    m_ModelData.vecFaceTriangles.push_back(mp_vertexXYZ[3 * vertex1 + 1]);
                    m_ModelData.vecFaceTriangles.push_back(mp_vertexXYZ[3 * vertex1 + 2]);
                    m_ModelData.vecFaceTriangles.push_back(mp_vertexXYZ[3 * vertex2]);
                    m_ModelData.vecFaceTriangles.push_back(mp_vertexXYZ[3 * vertex2 + 1]);
                    m_ModelData.vecFaceTriangles.push_back(mp_vertexXYZ[3 * vertex2 + 2]);
                    m_ModelData.vecFaceTriangles.push_back(mp_vertexXYZ[3 * vertex3]);
                    m_ModelData.vecFaceTriangles.push_back(mp_vertexXYZ[3 * vertex3 + 1]);
                    m_ModelData.vecFaceTriangles.push_back(mp_vertexXYZ[3 * vertex3 + 2]);
                    //color
                    m_ModelData.vecFaceTriangleColors.push_back(1.0);
                    m_ModelData.vecFaceTriangleColors.push_back(1.0);
                    m_ModelData.vecFaceTriangleColors.push_back(1.0);
                    m_ModelData.vecFaceTriangleColors.push_back(1.0);
                    m_ModelData.vecFaceTriangleColors.push_back(1.0);
                    m_ModelData.vecFaceTriangleColors.push_back(1.0);
                    m_ModelData.vecFaceTriangleColors.push_back(1.0);
                    m_ModelData.vecFaceTriangleColors.push_back(1.0);
                    m_ModelData.vecFaceTriangleColors.push_back(1.0);
                    m_ModelData.iTotalConnectedTriangles += 3;
                }
            }
            fclose(file);
            printf("%s Loaded!
", filename);
            return true;
        }
        else
        {
            printf("File can't be opened
");
            return false;
        }
    }
    else
    {
        printf("File does not have a ply extension.
");
        return false;
    }
}

void CPLYLoader::Draw() //implemented in GLPainter, not called again
{
    glVertexPointer(3, GL_FLOAT, 0, m_ModelData.vecFaceTriangles.data());
    glColorPointer(3, GL_FLOAT, 0, m_ModelData.vecFaceTriangleColors.data());
    glDrawArrays(GL_TRIANGLES, 0, m_ModelData.iTotalConnectedTriangles);
}

#include "stdafx.h"
#include "PlyLoader.h"
#include <gl/glut.h>

CPLYLoader plyLoader;

void init()
{
    glClearColor(0, 0, 0, 0);
    glEnableClientState(GL_VERTEX_ARRAY);
    glEnable(GL_COLOR_ARRAY);
    plyLoader.LoadModel("dragon.ply");
}

void display()
{
    glClear(GL_COLOR_BUFFER_BIT);
    plyLoader.Draw();
    glFlush();
}

int _tmain(int argc, _TCHAR* argv[])
{
    glutInit(&argc, (char **)argv);
    glutInitWindowSize(500, 500);
    glutInitWindowPosition(100, 100);
    glutCreateWindow("load model");
    init();
    glutDisplayFunc(display);
    glutMainLoop();
    return 0;
}

代码参考来源于互联网。