c++ - 使用 OpenGL 渲染 .obj 文件

Question

我一直在用 opengl 渲染模型时遇到问题。我已经使用 glDrawElements 创建了自己的 obj 解析器和渲染函数，但我看不到问题所在。这是我的解析器函数:

void load_obj(char *nom)
{
FILE *file = fopen(nom, "r");
int iv = 0, in = 0, it = 0, ifa = 0;

if(file != NULL)
{
    while(1)
    {
        char lineHeader[128];
        int res = fscanf(file, "%s", lineHeader);

        if(res == EOF)
            break;

        if(strcmp(lineHeader, "v") == 0)
        {
            float vertex[3] = {0,0,0};
            fscanf(file, "%f %f %f\n", 
                &vertex[0], &vertex[1], &vertex[2]);

            vertices[iv] = vertex[0];
            vertices[iv+1] = vertex[1];
            vertices[iv+2] = vertex[2];
            iv += 3;
        }
        else if(strcmp(lineHeader, "vt") == 0)
        {
            float tex_vert[2] = {0,0};
            fscanf(file, "%f %f\n", 
                &tex_vert[0], &tex_vert[1]);

            texturas[it] = tex_vert[0];
            texturas[it+1] = tex_vert[1];
            it += 2;
        }
        else if(strcmp(lineHeader, "vn") == 0)
        {
            float normal[3] = {0,0,0};
            fscanf(file, "%f %f %f\n", 
                &normal[0], &normal[1], &normal[2]);

            normales[in] = normal[0];
            normales[in+1] = normal[1];
            normales[in+2] = normal[2];
            in += 3;
        }
        else if(strcmp(lineHeader, "f") == 0)
        {
            unsigned int vertexIndex[9] = {0,0,0,0,0,0,0,0,0};
            fscanf(file, "%d/%d/%d %d/%d/%d %d/%d/%d\n", 
                &vertexIndex[0], &vertexIndex[1], &vertexIndex[2],
                &vertexIndex[3], &vertexIndex[4], &vertexIndex[5],
                &vertexIndex[6], &vertexIndex[7], &vertexIndex[8]);

            vertTriangulos[ifa] = vertexIndex[0];
            vertTriangulos[ifa+1] = vertexIndex[1];
            vertTriangulos[ifa+2] = vertexIndex[2];
            vertTriangulos[ifa+3] = vertexIndex[3];
            vertTriangulos[ifa+4] = vertexIndex[4];
            vertTriangulos[ifa+5] = vertexIndex[5];
            vertTriangulos[ifa+6] = vertexIndex[6];
            vertTriangulos[ifa+7] = vertexIndex[7];
            vertTriangulos[ifa+8] = vertexIndex[8];
            ifa += 9;

            nTriangulos++;
        }
    }
 }

这是我的绘制函数:

void draw()
{
        glClear(GL_COLOR_BUFFER_BIT);
        glMatrixMode(GL_MODELVIEW);

        glEnableClientState(GL_VERTEX_ARRAY);
        glEnableClientState(GL_TEXTURE_COORD_ARRAY);
        glEnableClientState(GL_NORMAL_ARRAY);

        glVertexPointer(3, GL_FLOAT, 0, vertices);
        glTexCoordPointer(2, GL_FLOAT, 0, texturas);
        glNormalPointer(GL_FLOAT, 0, normales);

        glDrawElements(GL_TRIANGLES, nTriangulos*9, GL_UNSIGNED_INT, vertTriangulos);

        glDisableClientState(GL_VERTEX_ARRAY);
        glDisableClientState(GL_TEXTURE_COORD_ARRAY);
        glDisableClientState(GL_NORMAL_ARRAY);
   }

作为变量:

    long nTriangulos;
float *vertices, *normales, *texturas;
unsigned int *vertTriangulos;

我正在使用的 obj 文件是一个简单的立方体，但我正在渲染的网格是一个彻头彻尾的灾难。

编辑:我更改了代码，现在解析器如下所示:

    if(strcmp(lineHeader, "f") == 0)
    {
    unsigned int vertexIndex[9] = {0,0,0,0,0,0,0,0,0};
    fscanf(file, "%d/%d/%d %d/%d/%d %d/%d/%d\n", 
        &vertexIndex[0], &vertexIndex[1], &vertexIndex[2],
        &vertexIndex[3], &vertexIndex[4], &vertexIndex[5],
        &vertexIndex[6], &vertexIndex[7], &vertexIndex[8]);

        for(int i = 0; i < 9; i += 3)
        {
            bool cierto = true;
            int pos = 0;

            if(indexbuff.size() > 0)
            {
                for(int i = 0; i < registro.size(); i++)
                {
                    if(vertexIndex[0] == registro[i].in1 
                        && vertexIndex[1] == registro[i].in2 
                        && vertexIndex[2] == registro[i].in3)
                    {
                        cierto = false;
                        pos = i;
                    }
                }
            }

            if(cierto)
            {
                verticebuff.push_back(vertices[vertexIndex[i]]);
                verticebuff.push_back(vertices[vertexIndex[i]+1]);
                verticebuff.push_back(vertices[vertexIndex[i]+2]);

                textbuff.push_back(texturas[vertexIndex[i+1]]);
                textbuff.push_back(texturas[vertexIndex[i+1]+1]);

                normalbuff.push_back(normales[vertexIndex[i+2]]);
                normalbuff.push_back(normales[vertexIndex[i+2]+1]);
                normalbuff.push_back(normales[vertexIndex[i+2]+2]);

                indexbuff.push_back(verticebuff.size()/3);

                index3 indice;
                indice.in1 = vertexIndex[i];
                indice.in2 = vertexIndex[i+1];
                indice.in3 = vertexIndex[i+2];
                registro.push_back(indice);
            }
            else
            {
                indexbuff.push_back(i);
            }
        }
       }

但它似乎不能正常工作。

Answer 1

Classic obj to opengl buffer错误，元素缓冲区索引指向所有属性。换句话说，如果 opengl 看到 0 索引，它会从 all 启用的缓冲区中取出第一个元素，然后移动到下一个索引。在您阅读时，如果不复制数据，就无法直接使用 obj 结构

你面对的代码应该是

if(/*vertexIndex[0..2] triplet has not been seen yet*/){
verticebuff.pushback(vertices[vertexIndex[0]]);
verticebuff.pushback(vertices[vertexIndex[0]+1]);
verticebuff.pushback(vertices[vertexIndex[0]+2]);


textbuff.pushback(texturas[vertexIndex[1]]);
textbuff.pushback(texturas[vertexIndex[1]+1]);

normalbuff.pushback(normales[vertexIndex[2]]);
normalbuff.pushback(normales[vertexIndex[2]+1]);

indexbuff.pushback(verticebuff.size()/3);
} else {
    indexbuff.pushback(/*index of the seen triplet*/);
}

//repeat 3 times

然后你可以用绘制元素来绘制它们。