为什么OpenGL 4.5中的以下帧缓冲区不完整？

Question

我正在尝试创建一个立方体贴图纹理来渲染阴影贴图的深度信息。我遇到过我的帧缓冲区不完整。特别是，它会返回一个GL_FRAMEBUFFER_INCOMPLETE_MISSING_ATTACHMENT，根据文档意味着它上面没有附加至少一个图像。

代码是：

GLuint depth_map;
GLuint FramebufferName;
void Renderer::create_shadow_map()
{
    //TODO: change render program here
    glUseProgram(0);
    FramebufferName = 0;
    glGenFramebuffers(1, &FramebufferName);

    glBindFramebuffer(GL_FRAMEBUFFER, FramebufferName);

    glGenBuffers(1, &depth_map);

    const unsigned int SHADOW_WIDTH = 1024, SHADOW_HEIGHT = 1024;
    glBindTexture(GL_TEXTURE_CUBE_MAP, depth_map);
    for (unsigned int i = 0; i < 6; ++i)
            glTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_X + i, 0, GL_DEPTH_COMPONENT, 
                            SHADOW_WIDTH, SHADOW_HEIGHT, 0, GL_DEPTH_COMPONENT, GL_FLOAT, NULL); 

    glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_R, GL_CLAMP_TO_EDGE);  

    glFramebufferTexture(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, depth_map, 0);

    glDrawBuffer(GL_NONE); // No color buffer is drawn to.
    glReadBuffer(GL_NONE);

    if(glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
    {
        if(glCheckFramebufferStatus(GL_FRAMEBUFFER)==GL_FRAMEBUFFER_INCOMPLETE_MISSING_ATTACHMENT)
            cerr << "shadow map not ok" << endl;
        exit(0);
    }
    glBindFramebuffer(GL_FRAMEBUFFER, 0);
}

致电glGetError()后，我就可以确定问题是glFrameBufferTexture()行。

所以我假设我要么没有正确生成缓冲区，要么我没有将它连接到帧缓冲区。