Fl_Scroll initial scroll values - fltk

Question

I'm using FLTK for a project (the version distributed with Debian/sid 1.3.2-6+b1) and I'm having some trouble initializing Fl_Scroll's content scroll values.
I create a Fl_Double_Window and on the right side a vertical panel using Fl_Scroll, it is positioned at left x 600 and top y 24.
Then I set Fl_Scroll's type to Fl_Scroll::VERTICAL and place a Fl_Button inside, everything works fine.
The problem? Fl_Scroll initialize already scrolled with xposition() = 600 and yposition() = 24 (X and Y of the Fl_Scroll's constructor?? Is supposed to work so?), instead I want it to initialize with content scrolled at left and top 0, 0, so I tried scroll_to() in different places, before and after window's show(), on FL_SHOW of the subclassed Fl_Scroll (I didn't really need to subclass Fl_Scroll, just trying to get scroll_to() working), also on overridden draw() after
the parent draw(), even creating Fl_Scroll at 0, 0 then position() at 600, 24, but nothing.
The only way I got scroll_to() working is if I call it from an async event after the application initialize (FL_KEYUP).
Here's the overridden Fl_Double_Window window constructor:
group = new Fl_Group(0, 0, WIN_W, WIN_H);
{
menu = new Fl_Menu_Bar(0, 0, WIN_W, MENU_H);
menu->add("File/Quit", FL_CTRL+'q', cbMenuQuit_i);
glview = new CGLView(0, MENU_H, WIN_W-PROPS_W+1, WIN_H-MENU_H);
group->resizable(glview);
scroll = new CScroll(WIN_W-PROPS_W, MENU_H, PROPS_W-1, WIN_H-MENU_H);
scroll->type(Fl_Scroll::VERTICAL);
{
Fl_Pack *pack = new Fl_Pack(0, 0, PROPS_W-1, WIN_H-1);
{
btnAddLayer = new Fl_Button(0, 0, PROPS_W, 32, "##+ Add Layer");
btnAddLayer->callback(btnAddLayerCb_i, (void *)this);
}
pack->end();
}
scroll->end();
}
group->end();
end();
size_range(WIN_MIN_W, WIN_MIN_H); /* Make the window resizable */
show();

Answer 1

Never mind, got it, two altenative:
create Fl_Scroll at 0, 0 then position() it after scroll->end()
create Fl_Scroll at the wanted position then after scroll->end() use negative values scroll_to(-X, -Y)
In both cases is important that the widgets contained are already added (scroll_to() alter cotained widgets coords)
Isn't clear to me why X and Y of Fl_Scroll's constructor are used.