Guis not staying in front of main workbench window

[Matthew-Andrew]

The new ISIS SANS GUI is not currently staying in front of the Mantidplot window. This is due to a difference in behavior between python and C++ interfaces.

Having investigated the following seems to be the case:

• On windows the C++ interfaces are set as children of the main window and then have their parent removed and reset when the window is minimized or maximized. This is taking advantage of the fact that on windows child widgets always stay in front of their parents. This is the behavior most of the scientists are used to. An example of how it is achieved can be found here https://github.com/mantidproject/mantid/blob/master/MantidPlot/src/FloatingWindow.cpp#L85.
• On Ubuntu child widgets do not stay on top of their parents. So interfaces always drop behind the main Mantidplot window. This is currently worked around by having interfaces docked by default. You cannot currently dock python interfaces however and making it so you can may be difficult.
• I think getting the expected behaviour on windows is most important here as not many users are on Ubuntu and there is a workaround to pin a window to the front.

[TTitcombe]

This is behaviour is wanted by several interfaces on Mantid, so any solution should be discussed with the wider Mantid team. It is also necessary for the solution to provide the same behaviour on all platforms Mantid supports.

I have found a solution which keeps the SANS gui on top of mantid, but removes its minimise/maximise buttons. In ISIS_SANS.py
Add the following imports

from qtpy.QtCore import Qt

from mantid.gui_helper import get_application

We then get the MantidPlot/Workbench object:

mainapp, _ = get_qapplication()
mainwindow = main.appactiveWindow()

We set the workbench/mantidplot object as the parent of the SANS gui, and give it the flag "Tool"

ui = sans_data_processor_gui.SANSDataProcessorGui(mainwindow)
flags = ui.windowFlags() | Qt.Tool
ui.setWindowFlags(flags)

This requires SANSDataProcessorGui to be changed in the following way:

def __init__(self, parent=None):
    super(QMainWindow, self).__init__(parent=parent)

Adding flags such as WindowMinimizeButtonHint does not provide the buttons we need. It should be confirmed whether this solution works on other operating systems, as I can find no reference online to Qt::Tool taking away minimise/maximise functionality

[TTitcombe]

Some sources state this as a difficult problem to solve for Mac, at least (fredrikaverpil/pyvfx-boilerplate#12). The pertinent bit is :

This is really difficult to solve unfortunately. The Qt documentation for QWidget says that parenting a window to another will make it float above the other window, but the documentation is wrong and the behaviour is dependent on the window management policy for your platform. Having a floating window which doesn't get hidden when the application goes to the background is deemed un-Mac-like behaviour and not allowed. The only ways to get windows to float are to use Qt.Tool or Qt.WindowStaysOnTopHint which both have problems. In particular, Qt.WindowStaysOnTopHint makes the window stay on top of all windows even when the application is in the background. Nuke gets round this problem by manipulating the Qt.WindowStaysOnTopHint during application activation and deactivation, but to do this correctly requires writing Objective-C code and can't be done from Python (the equivalent Qt events don't get delivered at the correct time for this).

[TTitcombe]

Moved from a SANS issue to workbench as behaviour wanted by several groups

[dtasev]

Note that the Ubuntu pinning is not by default part of the GNOME 3 GUI for 18.04/19.04

[NickDraper]

@hsautessella Can you drop Matthew some hints about what you did for the plot windows

[ghost]

The best I could do on Linux for the plot windows was look out for QApplication.focusWindowChanged events, checking if the focus has been switched to the main window (which has a specific objectName), and raising the plot window if so. See #27049 for the code.

As stated in the PR, this is not perfect behaviour as the window is hidden briefly and then brought forward. This causes a slight flicker effect. But, as hinted by Tom above, this doesn't seem to be a problem with a perfect solution.

That said, if the window doesn't need a minimize/maximize button, then passing it the Qt.Tool flag will keep it on top.

[Matthew-Andrew]

@gemmaguest I am closing this for now as this is a long running issue with most interfaces on workbench.