[cairo] basic question?

[Bill Spitzak]

The advantage of back buffers is that they can be drawn to directly 
without context switches. This is why they are faster. For the normal 
displays Cairo has to be able to get the display to be up to date after 
every single cairo call.

I feel that Cairo could automatically be as fast as possible with the 
addition of some cairo flush() call that indicates that you actually 
want the display to update. This does not guarantee back buffering, but 
allows the driver to use it if it is faster. The flush() means that you 
want the display to be updated now. It could also be used to queue up 
driver requests locally.

Tying this to the xlib flush is problematic as there are far too many 
xlib calls that do it and that programs find it hard to avoid. A 
reliable check for the window state, for instance, will flush, and 
typically this is not wanted.

I am aware that Cairo does not have a flush now, but one method to be 
compatible is to not require flush() until after the first time it is 
called. From then on it can assume flush() will be sent when the program 
wants the display up to date.