XDamage extension over-reports window damage

[Jonathan Lennox]

Hello -- I hope this is the right mailing list.  If not, please let me know
which one I should use.  (I'm not subscribed to it, so please Cc: replies to
me as well as the list.)

I've been experimenting with using the XDamage extension to watch changes to
X windows.  It works nicely, but I've found that it seems to report damage
to windows even when the window I'm monitoring is not changing, and it seems
to over-report damage in areas that don't appear to be changing.

Specifically, I've noticed two problems.  First of all, Xdamage reports
damage if a window *obscured* by the one I'm monitoring is drawn to.  E.g.,
if I have output going to an XTerm that is partially obscured by the window
I'm monitoring, the area of my window that covers the XTerm continually gets
damage reports.

Secondly, wheneve I enter or leave a window, the window's window manager
trim changes, but its contents (normally) don't.  (I'm using fvwm2 with
point-to-focus; I haven't yet experimented with other window managers for
this.)  In this case, with raw or delta damage report types, it seems like
damage reports should be sent just for the area of fvwm2's trim, but instead
I get a rectangle encompassing the entire window.  I imagine this could be
the client actually re-drawing the entire window whenever it regains focus,
but that seems unlikely to me.  Is there an easy way to track this?

I've attached below the program I'm using to play with the xdamage
extension.  It's based on Keith Packard's test program for the xdamage
extension, modified to be able to monitor individual windows as well as the
root.  Compile it with xc/programs/xlsfonts/dsimple.[ch] and -lXdamage.

I'm using the X.Org 6.8.1 release on FreeBSD 5.3p2, built out of the ports
tree.

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-- 
Jonathan Lennox
lennox at cs.columbia.edu