我正在尝试渲染一个帧缓冲区内的3D金字塔，以便在ImGui窗口中显示它。但深度测试失败了，我得到了这样的结论：

这就是我所拥有的：

glEnable(GL_DEPTH_TEST);
while (!glfwWindowShouldClose(mainwin))
{
    glClearColor(0.5f, 0.5f, 0.5f, 1.0f);

    ImGui_ImplOpenGL3_NewFrame();
    ImGui_ImplGlfw_NewFrame();
    ImGui::NewFrame();

    glEnable(GL_DEPTH_TEST);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    fbo.bind();//framebufferobject bind

    glClearColor(0.8f, 0.8f, 0.8f, 1.0f);

    glEnable(GL_DEPTH_TEST);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    /* Render here */       
    defaultshader.Activate();

    // Handles camera inputs
    camera1.Inputs(mainwin);
    // Updates and exports the camera matrix to the Vertex Shader
    camera1.Matrix(45.0f, 0.1f, 100.0f, defaultshader, "camMatrix");

    tex1.Bind();
    VAO1.Bind();
    // Draw primitives, number of indices, datatype of indices, index of indices
    glDrawElements(GL_TRIANGLES, sizeof(indices) / sizeof(int), GL_UNSIGNED_INT, 0);
    //---------------------------------------------------------------------------------------------------------------------------
    fbo.unbind();

    ImGui::Begin("Viewport");

    AppImguiAddImage(fbtex.FBtexID);//adds image to imgui drawlist

    ImGui::End();

    AppImguiFrameEnd();

    /* Swap front and back buffers */
    glfwSwapBuffers(mainwin);

    /* Poll for and process events */
    glfwPollEvents();

}

注：我从https://gamedev.stackexchange.com/questions/150214/render-in-a-imgui-window获得了AppImguiAddImage()和Clear()
为了得到相同的结果，我尝试了不同的颜色透明和深度透明的组合，以使While循环中的两个Clear()函数达到相同的效果。
到底出了什么问题？