Question

I am writing a C++ application using GTK and OpenGL. I have a GTK builder which reads an XML file and builds itself. I need to add an “OpenGL window area” into it. How do I do this?

Answer 1

The way I do it (gtkmm / C++ code) is like this:

#include <gtkmm.h>
#include <gtkglmm.h>

class GLWidget : public Gtk::GL::DrawingArea {
    public:
    GLWidget(Glib::RefPtr<Gdk::GL::Config> glconfig)
        : Gtk::GL::DrawingArea(glconfig) {}
    ~GLWidget() {}
    virtual bool on_expose_event(GdkEventExpose* event);
};

bool GLWidget::on_expose_event(GdkEventExpose* event)
{
    Glib::RefPtr<Gdk::GL::Drawable> d = get_gl_drawable();
    d->gl_begin(get_gl_context());

    // make this as complex as you need
    glClear(GL_COLOR_BUFFER_BIT);

    d->swap_buffers();
    d->gl_end();
    return true;
}

int main(int argc, char **argv)
{
    Gtk::Main kit(argc, argv);
    Gtk::GL::init(argc, argv);

    Glib::RefPtr<Gtk::Builder> builder = Gtk::Builder::create_from_file("ui.glade");

    Gtk::Window* mainWindow;
    Gtk::Alignment* container;

    builder->get_widget("mainWindow", mainWindow);
    builder->get_widget("Box", container);

    if (mainWindow == NULL || container == NULL) {
        g_critical("Gtk Builder failed to load mainWindow and/or container !\n");
        return -1;
    }

    Glib::RefPtr<Gdk::GL::Config> glconfig;

    glconfig = Gdk::GL::Config::create(Gdk::GL::MODE_RGBA | Gdk::GL::MODE_DOUBLE);
    if (!glconfig)
        glconfig = Gdk::GL::Config::create(Gdk::GL::MODE_RGB);
    if (!glconfig) {
        g_critical("Cannot create OpenGL-capable config\n");
        return -1;
    }

    GLWidget drawingArea(glconfig);

    drawingArea.set_size_request(640, 480);
    drawingArea.show();
    container->add(drawingArea);

    kit.run(*mainWindow);

    return 0;

I.e. I’m simply loading a UI that contains an empty container widget, get the handle to that by name, then create the GL-enabled drawing area in code and add it to the empty container. Supposedly, it’s possible to “load-time” substitute an ordinary Gtk DrawingArea for a GtkGL one (see this posting) but that method didn’t work for me; the above, programmatically creating it, always did.

You need gtkglext / gtkglextmm for the GL Drawingarea widget.