How to use Gtk::Viewport?

[abris (Abraham Zsombor Nagy)]

I have a large widget that I would like to fit into a small place and make it scrollable. For this, I have an example code as follows.

• I have a Gtk::Window with default size 100x100.

• It has a Gtk::Box that contains a Gtk::Viewport and a Gtk::Scrollbar.

• The Gtk::Viewport widget contains a “large” widget with size 100x200.

Unfortunately, the viewport’s size grows to 100x200.

How can I make the viewport stay 100x100 to allow the scrolling?

#include <gtkmm.h>

class LargeWidget : public Gtk::DrawingArea {
public:
    LargeWidget(int width, int height) {
        set_content_width(width);
        set_content_height(height);
    }
};


class Window : public Gtk::Window {
    Gtk::Box box;
    Gtk::Scrollbar scrollbar;
    Glib::RefPtr<Gtk::Adjustment> h, v;
    Gtk::Viewport viewport;
    LargeWidget large_widget;

public:
    Window() : h(Gtk::Adjustment::create(0, 0, 100)),
               v(Gtk::Adjustment::create(0, 0, 200)),
               viewport(h, v),
               large_widget(100, 200) {
        scrollbar.set_orientation(Gtk::Orientation::VERTICAL);
        scrollbar.set_adjustment(viewport.get_vadjustment());

        viewport.set_child(large_widget);

        box.set_orientation(Gtk::Orientation::HORIZONTAL);
        box.append(viewport);
        box.append(scrollbar);

        set_default_size(100, 100);
        set_child(box);
    }
};


int main(int argc, char **argv) {
    auto app = Gtk::Application::create("hu.aszn.playground");
    return app->make_window_and_run<Window>(argc, argv);
}

I tried:

viewport.size_allocate(Gtk::Allocation(0, 0, 100, 100), 0);

and

viewport.set_size_request(100, 100);

Thank you for your help.

[abris (Abraham Zsombor Nagy)]

Thank you, it was answered here: c++ - How to use Gtk::Viewport in GTKMM4? - Stack Overflow

[ebassi (Emmanuele Bassi)]

A viewport is a scrollable widget; the thing that scrolls is GtkScrolledWindow. This means you need to set the size of the scrolled window, not the viewport.