gtkmm-3.0和Cairomm，透明窗口不起作用

Question

I've been trying for the last hour to make this work. The idea es Dock is a class whose base is Gtk::Window, and upon the signal_draw() being emited, the given context should be painted by CairoMM to be transparent.. Instead I see a black window. Here goes the code:

Dock::Dock() : Gtk::Window()
{
    set_decorated(false);
    set_default_size(200,200);  
    set_app_paintable(true);
    signal_draw().connect(sigc::mem_fun(*this,&Dock::dibujar));

}

bool Dock::dibujar(const Cairo::RefPtr<Cairo::Context>& contexto)
{

    contexto->set_source_rgba(1.0,1.0,1.0,0.0);
    contexto->set_operator(Cairo::OPERATOR_SOURCE);
    contexto->paint();
    return false;
}

Shouldn't it be enough to make the window transparent?

Answer 1

Your draw handler doesn't have access to the information about what else should be painted on the window, so your paint() call paints a transparent layer above what is, I guess by default, a black background.

Luckily there is a method to achieve what you want: Gtk::Widget::set_opacity()