occt render to texture without window

Hi,

I want to use occt + glfw + imgui to program a app.

Here is how I init occt and render 

void OCCTRenderer::initViewer(GLFWwindow* win)
{
	if (m_Display.IsNull())
		m_Display = new Aspect_DisplayConnection;
	Handle(OpenGl_GraphicDriver) aGraphicDriver = new OpenGl_GraphicDriver (m_Display, false);
	Handle(V3d_Viewer) aViewer = new V3d_Viewer (aGraphicDriver);
	aViewer->SetDefaultLights();
	aViewer->SetLightOn();
	aViewer->SetDefaultTypeOfView (V3d_PERSPECTIVE);
	aViewer->ActivateGrid (Aspect_GT_Rectangular, Aspect_GDM_Lines);
	m_View = aViewer->CreateView();
	m_ctx = new OpenGl_Context;
	if (m_ctx->Init(glfwGetWin32Window(win), GetDC(glfwGetWin32Window(win)), glfwGetWGLContext(win))) {
		Handle(OpenGl_FrameBuffer) fbo = new OpenGl_FrameBuffer;
		if (fbo->Init(m_ctx, 800, 600, GL_RGBA8, GL_DEPTH24_STENCIL8)) {
			m_View->View()->SetFBO(fbo);
		    m_Texture = fbo->ColorTexture();
		}
	}
	m_View->SetImmediateUpdate (false);
	m_View->ChangeRenderingParams().ToShowStats = true;
	m_Context = new AIS_InteractiveContext (aViewer);
	m_Context->SetDisplayMode(AIS_Shaded, true);
}

void OCCTRenderer::Render(void)
{
	if (!m_View.IsNull()) {
		m_ctx->MakeCurrent();
		if (m_View->IsInvalidated()){
			m_View->Redraw();
		} else if (m_ToRedraw){
			m_View->RedrawImmediate();
		}
	}
	m_ToRedraw = false;
}

and render like this

    while (!glfwWindowShouldClose(window))
    {
        // Poll and handle events (inputs, window resize, etc.)
        // You can read the io.WantCaptureMouse, io.WantCaptureKeyboard flags to tell if dear imgui wants to use your inputs.
        // - When io.WantCaptureMouse is true, do not dispatch mouse input data to your main application.
        // - When io.WantCaptureKeyboard is true, do not dispatch keyboard input data to your main application.
        // Generally you may always pass all inputs to dear imgui, and hide them from your application based on those two flags.
        glfwPollEvents();

		renderer.Render();

        // Start the Dear ImGui frame
        ImGui_ImplOpenGL3_NewFrame();
        ImGui_ImplGlfw_NewFrame();
        ImGui::NewFrame();

		renderer.Draw();

        // Rendering
        ImGui::Render();
        int display_w, display_h;
        glfwGetFramebufferSize(window, &display_w, &display_h);
        glViewport(0, 0, display_w, display_h);
        glClearColor(clear_color.x, clear_color.y, clear_color.z, clear_color.w);
        glClear(GL_COLOR_BUFFER_BIT);


        ImGui_ImplOpenGL3_RenderDrawData(ImGui::GetDrawData());
    	
        glfwSwapBuffers(window);
    }

void OCCTRenderer::Draw()
{
	ImGui::SetNextWindowSize(ImVec2(800, 600));
	ImGui::Begin(u8"OCCT Viewer");
	ImGui::Image((ImTextureID)m_Texture->TextureId(), m_Size, ImVec2(0, 1), ImVec2(1, 0));
	ImGui::End();
}

But all I got is a black image.

So, how to render occt into a texture ?

Thanks