TraverseTree visits the parent before the children. When performing
the automatic redirection updates, the children must be visited before
the parent.
If there are automatically redirected windows on multiple levels of the
tree, updating the parents before the children would cause the parent
updates to use stale data for areas covered by the children. Also
updating the damaged children would re-damage the parent, which would
cause additional walks over the tree.
In the worst case with an unbroken chain of automatically redirected
subwindows, all of which are damaged, only the leaf window would be
properly updated on the first round. Then it's parent would be properly
updated on the second round, and so on. And on every round all of the
ancestor windows would be updated as well, but with stale data.
So with N damaged windows you would end up with (N^2+N)/2 updates,
instead of the expected N.
This reverts commit 648c8871c9.
Signed-off-by: Ville Syrjälä <ville.syrjala@nokia.com>
Reviewed-by: Keith Packard <keithp@keithp.com>
Reviewed-by: Daniel Stone <daniel@fooishbar.org>
Signed-off-by: Keith Packard <keithp@keithp.com>
a5dc3531e1