Reducing flicker in PDFViewCtrl

Q: If I use pdfview.Update(annot,1) when I create a new Annotation so
it only updates that section of page there is no screen flicker. Now
if I have two Update(annot,1) in the same process then the screen
flickers as it is doing a full screen update. This effect is not very
pleasing. What I'm trying to do is before the new Anno is created I
search through and delete the last Anno created, I use Update(Anno,1)
to refresh the page once the deletion is done, I then, in the same
process create the new anno and Update with that one. Is there a
better way of doing this so I do not get the screen flicker?
A: If the last update is not completed PDFView will do a full Update
(). As a workaround you could perform a union of these rectangles and
call Update only once. Another option to reduce flicker is to disable
progressive rendering (pdfview.SetProgressiveRendering(false))
possibly enabling it latter on (e.g. after Finished rendering callback
is invoked or after certain time interval).