OpenGL网格类不起作用

Question

我已经通过了几个允许抽象网格的解决方案，我已经决定了： RenderObject实例包含指向网格，着色器和纹理的指针。它还包含一个GLuint，它是VAO的ID。

struct RenderObject
{
    GLuint  __vao, bufferStart, length;
    Mesh    *mesh;
    Shader  *shader;
    Texture *tex;

    RenderObject();

    void constructVAO();
};

RenderObject::constructVAO()函数的实现如下：

void RenderObject::constructVAO()
{
    glBindVertexArray(__vao);
    mesh->constructVAO(__vao, false);
    shader->bind();
    tex->push(1, glGetUniformLocation(shader->getID(), "tex_sampler"));
    glBindVertexArray(0);
}

和Mesh::constructVAO(GLuint &id, bool createNew)是这样的：

void Mesh::constructVAO(GLuint &id, bool createNew)
{
    if(createNew)
    {
        if(id != 0) glDeleteVertexArrays(1, &id);
        glGenVertexArrays(1, &id);
    }

    glBindVertexArray(id);
    if(_vertbuf == 0)
    {
        glGenBuffers(1, &_vertbuf);
    }

    glBindBuffer(GL_VERTEX_ARRAY, _vertbuf);
    glBufferData(GL_VERTEX_ARRAY, sizeof(GLfloat) * _vert.size(), &_vert[0], GL_STATIC_DRAW);

    glEnableVertexAttribArray(0);
    glBindBuffer(GL_ARRAY_BUFFER, _vertbuf);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, (void*) 0);
}

使用此代码时我得到的只是一个黑色窗口。但是，如果我像这样手动创建VAO，它可以完美地运行：

GLuint vertex_arr_id;
glGenVertexArrays(1, &vertex_arr_id);

glBindVertexArray(vertex_arr_id);
GLuint vertexbuffer;
glGenBuffers(1, &vertexbuffer);
glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

shader.bind();

glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, (void*) 0);

tex.push(1, glGetUniformLocation(shader.getID(), "tex_sampler"));
glBindVertexArray(0);

ro.__vao = vertex_arr_id;