Status of backing store support?

[Peter Åstrand]

Can anyone tell me about the status of the backing store support these 
days? I wonder:

* Should miInitializeBackingStore() be used? I've found the comment in 
mibstore.c:

  "There is no longer an mi implementation of backing store.  This function
  is only for source compatibility with old drivers."

However, the function is not an no-op, and there are still servers that 
calls this function. This includes Xvfb, Xwin, kdrive and DMX.


* Assuming that Composite can provide backing store support, why is 
backing store disabled by default, even if Composite is used? If a server 
such as Xvfb or Xvnc wants to enable backing store by default, does it 
have to do anything else than just set "pScreen->backingStoreSupport=Always"?


* Backing store doesn't really seem to work reliable; it would be nice if 
http://bugs.freedesktop.org/show_bug.cgi?id=19654 could get some 
attention.


My primary objective is to make sure Xvnc in TigerVNC can properly run 
KDE4. The easy solution is to simply remove 
"pScreen->backingStoreSupport=Always", but I'd like to know if this is the 
"correct" way of doing it. Of course, it will still crash if "+bs" is 
manually specified, just like the normal Xorg, due to the bug above.


Best regards, 
---
Peter Åstrand		ThinLinc Chief Developer
Cendio AB		http://www.cendio.com
Wallenbergs gata 4
583 30 Linköping	Phone: +46-13-21 46 00