using cairo surfaces

[Tommi Sakari Uimonen <tuimonen cc hut fi>]

Hello. I'm trying to create a custom container widget that holds the child 
widgets in a hbox (or scrollarea, after I learn how to use it). The child 
widgets are using cairo for the drawing, and so is the container widget.

I want to optimize the container drawing since the child widgets don't always 
need complete redrawing.

The child drawing is currently done to the container's cairo surface, which is 
passed to each child widget, and childs draw to this surface. Reference to this 
surface is stored and I'm using a private variable in the container widget that 
keeps track of whether the childs need full redraw or can I use the stored 
surface to do quick redraw without the need to call the childs' drawing 
functions.

Now, I want the child widgets to have their own surfaces and each child should 
handle the "smart drawing". So the child widget decides whether it uses the 
previously rendered surface or redraws some parts. The container then just uses 
set_source_surface to draw the child at desired position.

What kind of surface I should create in the child widgets and how do I copy it 
to the container surface?

I've tried creating image surface, but I guess I was doing something wrong, 
because nothing was drawn, or I got segfault. So I still have not found the 
right way of doing it. The documentation is lacking examples, so I have 
proceeded in "trial and error"-basis, and now I'm kind of stuck.


Tommi