Re: Wheelbarrow example with Gtkmm on DirectFB

[José Alburquerque <jaalburquerque cox net>]

Reposting to list with additional comments:

José Alburquerque said the following:
> Phoenix Revived said the following:
> > Yes, I am able to get it to work on X11. I need some help in making 
> > it work on DirectFB.
> >   
>
> The problem could be a difference in how the video drivers handle 
> transparency and may not even be related to gtkmm.  You might try 
> using the C API and seeing if there's a difference.  You could then 
> ask on the gtk list and see if they have some insight.

To help a little more, the following lines that appear in the 
constructor seem to be relevant:

1  realize(); // the widget must be realized to create the GDK window
2  const Glib::RefPtr<const Gdk::Drawable> drawable = get_window();
3  const Gdk::Color transparent = 
Gtk::Widget::get_default_style()->get_bg(Gtk::STATE_NORMAL);

4  Glib::RefPtr<Gdk::Bitmap>       mask;
5  const Glib::RefPtr<Gdk::Pixmap> pixmap =
     Gdk::Pixmap::create_from_xpm(drawable, mask, transparent, 
wheelbarrow_xpm);

6  Gtk::Image *const image = new Gtk::Image(pixmap, mask);
7  add(*Gtk::manage(image));

 ...

 // Mask out transparent parts of the pixmap.
8  shape_combine_mask(mask, 0, 0);

The ones that are interesting are the getting of the "transparent" color 
with the default style[1] (line 3 above), and the creating of the 
"pixmap" with Gdk::Pixmap::create_from_xpm[2] (line 5 above), which sets 
the "mask" parameter to a mask that can be used to create a Gtk::Image 
(line 6 above) and for transparent windows (line 8 above).  Also 
interesting is the actual "masking out" of the background color with the 
call to Gtk::Widget::shape_combine_mask[3] (line 8 above).

You could try different things with those lines and see if things work 
for your setup.  For example,  the Gtk::Style class has methods such as 
get_white[4] which might do something interesting in your case.  The 
trick might be to understand what the lines do.  For that you might look 
into Gtk::Style, Gdk::Pixmap[5] and the methods in Gtk::widget[6] that 
deal with masks like the one in line 8 above.

[1] 
http://www.gtkmm.org/docs/gtkmm-2.4/docs/reference/html/classGtk_1_1Style.html
[2] 
http://www.gtkmm.org/docs/gtkmm-2.4/docs/reference/html/classGdk_1_1Pixmap.html#0c8f0c29a699ff740c23414d49598516
[3] 
http://www.gtkmm.org/docs/gtkmm-2.4/docs/reference/html/classGtk_1_1Widget.html#62b87786cfecfaf40239a3bdc9118866
[4] 
http://www.gtkmm.org/docs/gtkmm-2.4/docs/reference/html/classGtk_1_1Style.html#c21a682c9fddadb11bf38b0a71fec915
[5] 
http://www.gtkmm.org/docs/gtkmm-2.4/docs/reference/html/classGdk_1_1Pixmap.html
[6] 
http://www.gtkmm.org/docs/gtkmm-2.4/docs/reference/html/classGtk_1_1Widget.html
> > Cheers,
> >     ---AK
> >   

--
José Alburquerque
jaalburquerque cox net