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[Launchpad Bug Tracker <1598173@xxxxxxxxxxxxxxxxxx>]

This bug was fixed in the package qtbase-opensource-src - 5.5.1+dfsg-
16ubuntu7.5

---------------
qtbase-opensource-src (5.5.1+dfsg-16ubuntu7.5) xenial; urgency=medium

  * Backport upstream change to fix behavior of QMenuBar::isNativeMenuBar()
    method (fix_isNativeMenuBar.diff). This should finally fix LP: #1380702.

 -- Dmitry Shachnev <mitya57@xxxxxxxxxx>  Wed, 03 May 2017 22:22:47
+0300

** Changed in: qtbase-opensource-src (Ubuntu Xenial)
       Status: Fix Committed => Fix Released

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https://bugs.launchpad.net/bugs/1598173

Title:
  Please consider SRU of "xcb: Compress mouse motion and touch update
  events"

Status in qtbase-opensource-src package in Ubuntu:
  Fix Released
Status in qtbase-opensource-src source package in Xenial:
  Fix Released

Bug description:
  Mouse event compression stopped working in Qt 5, a regression from Qt
  4:

     https://bugreports.qt.io/browse/QTBUG-40889

  The bug was fixed in Qt 5.6 https://codereview.qt-
  project.org/#/c/126136/ where the fix has been thoroughly tested by
  now.

  Attached is a debdiff against 5.5.1+dfsg-16ubuntu7.2 which includes a
  backport of the 5.6 patch (only one trivial hunk failed, which was
  easily fixed).

  [Impact]

  The bug affects any program that relies on the event compression Qt
  normally performs. For example, VTK programs (ParaView, Tomviz, ...)
  do their rendering in response to mouse events during camera
  movements, and with event compression at the Qt level suddenly gone,
  camera movements become very slow, since the application is now
  flooded with mouse events and the rendering lags behind.

  The problem is not limited to these programs however; it can be
  observed by simply putting two regular, slightly slow-to-render,
  widgets into a QSplitter and moving the splitter handle. The result is
  a syrup-like experience as the widgets try to keep up with the
  onslaught of resize events due to the lack of mouse event compression.

  [Test Case]

  The attached test application can be used to check if event
  compression is functioning. It performs some artificial work on each
  mouse move and prints a message. Click and drag the mouse a little.
  After releasing the mouse, you'll notice that the printouts keeps
  coming for quite a while, as the program is catching up with the flood
  of events.

  With the attached patch (and with Qt 4), the problem is gone - the
  mouse event stream is compressed and the printouts are no longer
  lagging behind.

  [Regression Potential]

  There's a small risk that some applications have made workarounds for
  the faulty behavior, and that unwanted behavior is introduced if this
  bug is fixed. But chances are high that such workarounds will keep
  working, as the obvious workaround is to do timer based rendering
  instead of event based. The workarounds will then simply become
  unnecessary, but shouldn't cause problems.

  I'm asking for someone to nominate this bug for an SRU of 16.04 LTS.

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