When a Wikipedia article is already cached, this change reduces the
amount of sent and received network data almost tenfold.
Setting up a network disk cache in the same way for dictNetMgr does not
noticeably impact the amount of network traffic. Either this network
access manager sends and receives very little data or the data is never
the same. So dictNetMgr does not need a disk cache.
Use QNetworkDiskCache's default maximum size of 50 MiB as the default
network cache size. This size is large enough to accommodate tens of
huge MediaWiki articles. It is also small enough that the user is
unlikely to run out of disk space because of the cache.
Clear network cache on exit by default because most users probably
don't load the same online articles after restarting GoldenDict. Plus
storing the network cache on disk indefinitely by default would be a new
and unexpected to the users privacy risk.
Nikita Moor came up with the idea and wrote an initial network disk
cache implementation in #1310.
My tests in many desktop environments and window managers indicate that
no single configuration works perfectly in all environments. There are
also behavior differences between Qt::Popup and Qt::Tool flags, which
are not exactly bugs, so I suppose users might subjectively prefer
different options.
Customizing the flags allows the user to prevent unpinned scan popup
window flickering with Qt5 on Linux. In a way adding these options fixes
issue #645, which is: the scan popup window blinks rapidly, barely
noticeably in some applications, such as Calibre ebook-viewer
and Chromium. In this case the scan popup window usually ends up hidden
when selection ends, unless it was finished with a jerk.
I have tested the new options in 9 desktop environments and window
managers: at least one configuration for each eliminates #645 and makes
the scan popup window work the same as with Qt4 in this regard:
the popup window remains visible, text in the popup's translation line
keeps up with the text selection in the external application,
and the selected text is being translated on the fly.
Moreover, for each tested DE/WM, at least one configuration makes
the scan popup window work perfectly as far as I am concerned.
This issue was partially worked around with a 200ms scan popup delay
timer in the recent commit 58e41fe3ce
for the duplicate issue #854. However the timer solution is incomplete
because it requires the user to select text quickly and without delays.
If global mouse selection does not change for 200ms while the left mouse
button is held down, the user will likely not see the scan popup when
(s)he finishes selection, and will have to try selecting again -
hopefully faster this time.
The 200ms delay is no longer critically important after this commit,
but it is still beneficial: the lookup query changes less often,
which in turn reduces article definition update frequency.
So the delay improves the UI (perhaps subjectively) and performance.
