We want to keep pre-loaded, and invalidated tiles around so that
we have something to render in lots of cases, particularly for
other parts, and slides. However - we need to know that it is
invalid so we can on-demand fetch something better.
It is very important that this invalid state doesn't race with
tile arrivals ie. in a banal way:
invalidate, req, invalidate, req, tile, invalidate, req, tile
it is unclear whether the latest tile is still invalid; similarly,
if we request(req) a tile and there is no change to it we get no
response.
To disambiguate this, use the monotonic wid to check we are in-sync.
Re-factor:
setup debug tile layer more pro-active.y
rename HasContent to NeedsFetch to be more explicit.
Remove:
previous _invalidCount that was perhaps a similar idea.
previous .loaded concept.
previous _pruneTiles concept - now it seems we can be
confident in cached tiles from other slides and sheets.
Change-Id: Ibc6d3b6050e756ace91a9bd53d3e4efe12b023cf
Signed-off-by: Michael Meeks <michael.meeks@collabora.com>
36818e9153