public Cairo.ImageSurface pixbuf2imgsurface(Gdk.Pixbuf pb) {
    var fmt = pb.has_alpha ? Cairo.Format.ARGB32 : Cairo.Format.RGB24;
    var imgsurface = new Cairo.ImageSurface(fmt, pb.width, pb.height);
    var ctx = new Cairo.Context(imgsurface);
    Gdk.cairo_set_source_pixbuf(ctx, pb, 0, 0);
    ctx.paint();
    return imgsurface;
}