如何在openGL中渲染屏幕

Question

我有一个任务是在openGL中在屏幕外渲染事物。我必须在帧缓冲区中渲染东西，但不需要在openGL窗口上显示它。

我尝试了以下代码。它没有任何错误或崩溃，但它在帧缓冲区上没有呈现任何内容。

glGenTextures(1, &textureId);
     glBindTexture(GL_TEXTURE_2D, textureId);
     glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
     glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,GL_LINEAR_MIPMAP_LINEAR);
     glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
     glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
     glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP, GL_TRUE); // automatic mipmap
     glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, TEXTURE_WIDTH, TEXTURE_HEIGHT, 0,GL_RGBA, GL_UNSIGNED_BYTE, 0);
     glBindTexture(GL_TEXTURE_2D, 0);

     //create a renderbuffer object to store depth info
    GLuint rboId;
    glGenRenderbuffers(1, &rboId);
    glBindRenderbuffer(GL_RENDERBUFFER, rboId);
    glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT,TEXTURE_WIDTH, TEXTURE_HEIGHT);
    glBindRenderbuffer(GL_RENDERBUFFER, 0);

    // create a framebuffer object
    GLuint fboId;
    glGenFramebuffers(1, &fboId);
    glBindFramebuffer(GL_FRAMEBUFFER, fboId);

    // attach the texture to FBO color attachment point
    glFramebufferTexture2D(GL_FRAMEBUFFER,        // 1. fbo target: GL_FRAMEBUFFER 
                       GL_COLOR_ATTACHMENT0,  // 2. attachment point
                       GL_TEXTURE_2D,         // 3. tex target: GL_TEXTURE_2D
                       textureId,             // 4. tex ID
                       0);   

    // attach the renderbuffer to depth attachment point
    glFramebufferRenderbuffer(GL_FRAMEBUFFER,      // 1. fbo target: GL_FRAMEBUFFER
                          GL_DEPTH_ATTACHMENT, // 2. attachment point
                          GL_RENDERBUFFER,     // 3. rbo target: GL_RENDERBUFFER
                          rboId);              // 4. rbo ID


    // check FBO status
    GLenum status = glCheckFramebufferStatus(GL_FRAMEBUFFER);
    if(status != GL_FRAMEBUFFER_COMPLETE)
    bool fboUsed = false;

    glBindFramebuffer(GL_FRAMEBUFFER, 0);

     // set rendering destination to FBO
    glBindFramebuffer(GL_FRAMEBUFFER, fboId);

     // clear buffers
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

     // draw a scene to a texture directly
    //draw();

     // unbind FBO
    glBindFramebuffer(GL_FRAMEBUFFER, 0);

     // trigger mipmaps generation explicitly
     // NOTE: If GL_GENERATE_MIPMAP is set to GL_TRUE, then glCopyTexSubImage2D()
     // triggers mipmap generation automatically. However, the texture attached
    // onto a FBO should generate mipmaps manually via glGenerateMipmap().
    glBindTexture(GL_TEXTURE_2D, textureId);
    glGenerateMipmap(GL_TEXTURE_2D);
    glBindTexture(GL_TEXTURE_2D, 0);