[Dev] Chandler and drawing to the screen

[Grant Baillie]

Yesterday, after Andi's neat demo on "micro" performance in Chandler, I 
started thinking about app performance in general, and remembered an 
easy-to-run "macro" performance test. There are details in

<http://bugzilla.osafoundation.org/show_bug.cgi?id=2714>

but in summary, on the mac you can tell the graphics engine to 
highlight (with a yellow flash) each time a rectangle on screen gets 
drawn. Since drawing, especially when text is involved, can involve 
many CPU cycles, this is a useful thing to look at.

Enabling this for current Chandler shows that there's a lot of extra 
drawing going on: for example, tabbing between the Welcome Note title 
and content causes the entire Summary View to be redrawn.

Anyway, this kind of thing often shows up problems at many levels (eg, 
the model layer may be posting change notifications too often, or with 
too low a granularity; controller-type objects might be reloading 
widgets unnecessarily in response to user events; widgets themselves 
might not be restricting their drawing to dirtied regions, or may 
redraw multiple times).

Right now, the bug is in David S's capable hands for 0.6, but it's 
something that's worth tracking in future releases. It would also be 
interesting to know if similar behaviour can be seen on Windows/Linux.

--Grant