Its quite easy to reproduce:
Stick a "qDebug("DATA() CALLED");" into ResultsModel::data(), and keep
scrolling one scope up and down. Those message don't seem to stop for
me.
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https://bugs.launchpad.net/bugs/1395994
Title:
UI lags when scrolling through scopes
Status in “unity8” package in Ubuntu:
New
Bug description:
Some causes ruled out:
1. OA in scopes can't be to blame as I have tested with and without it
enabled, and with and without it present in the code
(https://bugs.launchpad.net/ubuntu/+source/unity-scopes-
api/+bug/1392615/comments/4).
2. Location can't be blamed either (for the same reasons as above, as
well as removing location service usage from the shell plugin itself).
3. When profiling the QML and C++ code, I saw no indication that the
shell plugin was doing anything process intensive enough to cause any
hold up. In fact, it seems to be doing a pretty good job handling
calls from the UI thread asynchronously.
Observations made when profiling unity8:
1. The QML ListView component updates its current item index when the
next item reaches half-way across the screen (therefore, in mid
animation between scopes). There doesn't look to be any serious
blocking actions taking place during the onIsCurrentChange, setActive,
etc. methods that I could find, but we should keep this in mind.
2. ResultsModel::data() seems to be called constantly while scrolling
a scope up and down. I assume this should only be called once per
result item (This doesn't explain the horizontal scrolling lag, but it
may explain some vertical lag).
3. If you pull down to refresh any scope, then continuously move the
dash left and right, the dash movement is smooth until results start
showing up in the scope, at which point you see a lag as they appear.
The lag observed here is almost definitely the same lag we see when
scrolling through scopes (jittering as results start to pop up in
scopes as they populate).
(NOTE: All of the above points were observed with and without the
latest unity8 performance fixes in rtm silo 8)
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