Re: gdk_pixbuf_composite_color() help needed.

[Tim Evans <t evans aranz com>]

>> Why not just create a GtkImage widget and use that to display your
> > pixbuf?  GtkImage is a subclass of GtkMisc, just like GtkLabel, so 
> > it's basically a label that displays an image instead of some text. 
> > Use gtk_image_new_from_pixbuf to easily create the widget and set it
> > to display your pixbuf.
>
> I did that originally,  but the logo has an alpha channel and a 
> gentle fade at the edges,  since X11 doesn't natively handle alpha 
> channels, the GtkImage clips it and make the logo look like crap. 
> (sharp edge) By compositing it with the color of the background it 
> has a nice smooth transition,  the problem comes with getting the 
> background color in the same format that gdk_pixbuf_composite_color 
> accepts (I get the color back in 16 bit,  the gdk call wants it in 
> packed 8 bit,  the resolution loss causes errors and leaves unwated 
> artifacts onscreen.
>
> If I could find the code to actually take a screenshot of the empty 
> space on my app before the pixmap is placed and use that as my 
> compositing source, that would solve all of my problems.  Thus far I
> haven't figured out how to do that.

The attached screenshot shows a GtkImage displaying a png image with an 
alpha channel (the glade icon).  The shadow on the icon is an alpha 
channel and the GtkImage widget renders it correctly.  The code (in 
Python) was:

import gtk
w = gtk.Window()
i = gtk.Image()
i.set_from_file('glade.png')
w.add(i)
w.show_all()
gtk.main()

Perhaps you need to upgrade your version of GTK, I'm using 2.2.2

--
Tim Evans
Applied Research Associates NZ
http://www.aranz.com/