试图渲染GTK +窗口到图像

GTK使用cairo进行绘制。所以我试图创建一个hello world应用程序，它写入图像（svg，png，...）而不是X11。我遇到了两个问题： - 图像为空 - 启动时没有运行X11（这是实际的目标），我得到错误“**（a.out：9021）：警告**：无法打开X显示“试图渲染GTK +窗口到图像

代码是草稿！

#include <string> 
#include <iostream> 
#include <thread> 
#include <chrono> 
#include <cmath> 

#include <cairo.h> 
#include <cairommconfig.h> 
#include <cairomm/context.h> 
#include <cairomm/surface.h> 
#include <gtk/gtk.h> 
#include <gdk-pixbuf/gdk-pixbuf.h> 

int main(int argc, char *argv[]) 
{ 

    gtk_init(&argc, &argv); 
    GtkWidget *window; 
    GtkWidget *button; 
    // GtkWidget *main_window = gtk_initialize(); 

    window = gtk_offscreen_window_new(); 

    button = gtk_button_new_with_label ("Hello World"); 
    gtk_container_add (GTK_CONTAINER (window), button); 
    gtk_widget_show (window); 
    GdkWindow *gdk_window = gtk_widget_get_window(GTK_WIDGET(window)); 
    std::cout << "gdk window: " << gdk_window << std::endl; 
    cairo_surface_t * surfp = gdk_offscreen_window_get_surface(gdk_window); 
    std::cout << "Created Window will now draw to png" << std::endl; 

    std::string filename = "image.svg"; 
    double width = 600; 
    double height = 400; 

    Cairo::SvgSurface srfobj(surfp); 

    Cairo::RefPtr<Cairo::SvgSurface> refptr(&srfobj); 

    Cairo::RefPtr<Cairo::Context> cr = Cairo::Context::create(refptr); 

    cr->save(); // save the state of the context 
    cr->show_page(); 

    std::cout << "Wrote SVG file \"" << filename << "\"" << std::endl; 
    std::chrono::milliseconds dura(200); 
    std::this_thread::sleep_for(dura); 

    return 0; 
}