Because the lua reader is single threaded on which both user inputloop
and background page rendering is processed. Although there is a pretty
good precache system to save user's time spending on waiting for the
rendering when going to the next page, user input is indeed blocked when
running the precache thing. The situation is even worse in koptreader as
reflowing on page would usually take several second, in this period
users cannot move to the next page view even it's already in the cache.
This patch will let precache run in the background in a seperate thread
so that the koptreader is still responsive when precaching the next
page. Now it only just works. Welcome to find out bugs in it.
Reflow can be configured to use bbox which could remove
side comments and defects in the margin and get much better reflowed
page in some documents. Currently the bbox is only set in PDFReader or
DJVUReader reader. But eventually there will be bbox setting routines in
KOPTReader.
Thirdparty should be cleaned and refetched and remake to get
this feature in operation.
