Re: gdk_pixbuf_composite_color() help needed.

[Tim Evans <t evans aranz com>]

Dave Andruczyk wrote:

> I'm trying to overlay my application's logo over an empty space in my gtk+2
> prog (MegaTunix).  In this mostly empty window exists a label and a
> drawingarea, bothed packed into a vbox.  I've successfully setup the
> expose/configure events modeling after the "testpixbuf" demo from the gtk+
> source code. For the most part it works, EXCEPT I want to be able to display
> the logo and have it blend in smoothly with the window no matter what color the
> window may be (User may have a theme with different BG colors than mine, or a
> pixmap background)
>
> The only way I found thus far, was to retrieve the style of the parent widget
> (the vbox in this case) and extract the bgcolor from it, the problem is it's a
> GdkColor which stores the colors in 16 bit formats.  The
> gdk_pixbuf_composite_color() accepts two colors  with 8 bits per component only
> (I use the same color for each to avoid a checkerpattern) but in RGB packed
> format (only 8 bits per R, G or B component).  In my conversion from 16 to 8, I
> loose resolution and the composition ends up having a rectangular box (the size
> of the drawingarea) that is close, but not exactly the same color as the rest
> of the applications background color.  It works (with the slight color
> mismatch) with theme changes as long as the theme doesn't use a pixmap
> background (instead ofa solid color).
>
> I want to be able to display my logo (which has an alpha channel) on one of my
> app's panes (gtk_notebook used) and have it blend into the background properly
> no matter if the user is running a pixmap style theme or an arbritrary color
> schemed theme..  (it almost works for the latter, I have no idea how to do the
> former..)
>
> Anyone got any ideas?  I'm currently stuck at this point.

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.

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