Feature Request: Ability to render Polyscope viewer in multiple ImGui windows

先從 issue 中的 main.cpp ImGui、GLFW 和 OpenGL3 範例開始，接著檢查 Polyscope 目前如何管理其視窗和事件迴圈。確定在多個 ImGui 視窗中渲染個別視覺化所需的架構進入點；當所要求的多視窗渲染 API 能在單一 GUI 中運作時，即表示完成。

Hello Polyscope maintainers and community,

I'm using Polyscope to visualize point cloud data within a GUI application.

Currently, Polyscope encapsulates its own window and event loop and doesn't provide an API to render into multiple ImGui windows. In my case, I would like to show the 3D data in one window alongside 2 other windows to show the two 2D cameras windows. Specifically, I'm looking to render different Polyscope visualizations in separate ImGui windows within the same GUI.

I understand that this feature might involve significant changes to Polyscope's architecture, but I believe the added flexibility would benefit many users and use cases. I look forward to hearing your thoughts on this suggestion.

Thank you for your time and the excellent work on Polyscope!

This is the implementation of two different windows in the same GUI using ImGUI, GLFW and OpenGL3:

// main.cpp
#include "imgui.h"
#include "imgui_impl_glfw.h"
#include "imgui_impl_opengl3.h"
#include <GLFW/glfw3.h>

int main() {
    // Set up window
    glfwInit();
    GLFWwindow* window = glfwCreateWindow(1280, 720, "Hello", NULL, NULL);
    glfwMakeContextCurrent(window);
    glfwSwapInterval(1); // Enable vsync

    // Set up Dear ImGui context
    IMGUI_CHECKVERSION();
    ImGui::CreateContext();
    ImGuiIO& io = ImGui::GetIO();

    // Set up Platform/Renderer bindings
    ImGui_ImplGlfw_InitForOpenGL(window, true);
    ImGui_ImplOpenGL3_Init("#version 130");

    while (!glfwWindowShouldClose(window)) {
        glfwPollEvents();

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

        // Here we construct our GUI
        ImGui::SetNextWindowPos(ImVec2(0, 0));
        ImGui::SetNextWindowSize(ImVec2(640, 720));
        ImGui::Begin("Window 1");
        ImGui::Text("This is window 1");
        ImGui::End();

        ImGui::SetNextWindowPos(ImVec2(640, 0));
        ImGui::SetNextWindowSize(ImVec2(640, 720));
        ImGui::Begin("Window 2");
        ImGui::Text("This is window 2");
        ImGui::End();

        // Render ImGui frame
        ImGui::Render();
        int display_w, display_h;
        glfwGetFramebufferSize(window, &display_w, &display_h);
        glViewport(0, 0, display_w, display_h);
        glClearColor(0.45f, 0.55f, 0.60f, 1.00f);
        glClear(GL_COLOR_BUFFER_BIT);
        ImGui_ImplOpenGL3_RenderDrawData(ImGui::GetDrawData());

        glfwSwapBuffers(window);
    }

    // Cleanup
    ImGui_ImplOpenGL3_Shutdown();
    ImGui_ImplGlfw_Shutdown();
    ImGui::DestroyContext();

    glfwDestroyWindow(window);
    glfwTerminate();

    return 0;
}