How to ensure a child actor in a sub-class is drawn on top of all actors in derived class

[Stephan Haller <nomad froevel de>]

Hi,

I'm using Clutter in my project 'xfdashboard' which is similar to Gnome 
Shell but for other desktop environments. It is working pretty well but 
now I want something special ;)

The question is: Is there a way to draw one child actor above the other 
in a compounded actor if this actor may be used as a sub-class? I know 
you need more explaination ;)

I have a background actor (XfdashboardBackground) which draws the 
background of an actor. A lot of other visual actors are derived from 
this class, like buttons, popup-menus etc. They all use this background 
actor as sub-class.

The background actor also allows to draw an outline if requested. 
Therefore an effect (XfdashboardOutlineEffect) is added to this actor to 
ensure it is drawn at last regardless if the actor is a directly 
instanciated XfdashboardBackground object or any derived one (buttons 
etc.). This has the drawback that I have to duplicate all outline 
related properties like line width, color and so on - once in the 
background actor and once in the effect class. But it is working great 
...

... but now I want sub-classes (especially the pop-up menu actors) to 
override the drawing functions to provide a different path to draw the 
background and outline. If I follow the coding style I would have to 
implement two virtual functions - one in the background actor and one in 
the effect class - and I have to ensure that overiding the virtual 
function in the background function would also override the one in the 
effect class.

My idea now is to get rid of the effect in the background actor but I do 
not find a way to ensure that the outline is draw last. The paint_node() 
function of pop-up menu would add all paint nodes of the background 
first and then add the paint nodes of the pop-up menu. So the pop-up 
menu overrides the background. That is just one way I tried. I also 
tried to create a cairo-based canvas object which contains the outline 
and which is added as child to the background actor but this does not 
work well.

So is there a way to ensure that a base class, which is used as 
sub-class at other actors, to ensure that one child is drawn at last?

Thanks for any hints.

Regards,
Stephan