GdkPixbuf *pixbuf = NULL;
  GdkPixmap *pixmap = NULL;
  GtkWidget *image = NULL;
  GdkPixbuf* scaled = NULL;


      gtk_widget_set_app_paintable(window,TRUE);
      gtk_widget_realize (window);

      /* load background */
      pixbuf = gdk_pixbuf_new_from_file (background,NULL);
      image = gtk_image_new_from_pixbuf (pixbuf);

      int src_w = gdk_pixbuf_get_width(pixbuf);
      int src_h = gdk_pixbuf_get_height(pixbuf);
      int dest_w = gdk_screen_get_width(gtk_widget_get_screen(window));
      int dest_h = gdk_screen_get_height(gtk_widget_get_screen(window));

      if( src_w != dest_w || src_h != dest_h )
      {
              scaled = gdk_pixbuf_scale_simple( pixbuf, dest_w, dest_h, GDK_INTERP_BILINEAR );
              g_object_unref( pixbuf );
              pixbuf = scaled;
      }

      pixmap = gdk_pixmap_new (window->window, dest_w, dest_h, -1);
      gdk_pixbuf_render_to_drawable(pixbuf, pixmap,
                      (window)->style->fg_gc[GTK_STATE_NORMAL],
                      0,0,0,0,
                      dest_w,
                      dest_h,
                      GDK_RGB_DITHER_NORMAL,0,0);
      g_object_unref(pixbuf);
      gdk_window_set_back_pixmap ( (GtkWidget*)window->window, pixmap, FALSE);

  gdk_window_clear( window->window );
  gtk_widget_queue_draw(window);



用这种方法给window背景绘图，程序运行正常，可是当改变linux主题的时候或出现背景图变成白色的情况，为什么会这样？怎么解决，谢谢

是因为你的Linux系统没有安装gd库   如果是CentOS使用  yum install gd gd-devel    

然后编译PHP时加上--with-gd 就可以了