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SirVer
SirVer

Reputation: 1527

Using a pyqt widget from a linearly running console application

My scenario here is the following: I am using a pyqt widget to display a solid color fullscreen on a second display and observe this display with a camera that is continuously capturing images. I do some processing with the images and this is the data I am interested in. This works great when used interactively with ipython and matplotlib using the qt4agg backend like so

% ipython -pylab
# ... import PatternDisplay, starting camera
pd = PatternDisplay(); pd.show(); pd.showColor(r=255,g=255,b=255)
imshow(cam.current_image)

I need a similar behavior now in a console script though: it should display the PatternDisplay widget, capture an image, than change the color on the PatternDisplay and take a new image and so on.

The problem is now that the PatternDisplay is never updated/redrawn in my script, likely because PyQt never gets a chance to run it's event queue. I had no luck trying to move the linear worker part of my script into a QThread because I cannot communicate with the PatternDisplay Widget from another Thread any longer. I tried to replicate the implementation of ipython/matplotlib, but I didn't fully understand it, it is quite complicated - it avoids running the QApplication main loop via monkey patching and somehow moves QT into it's own thread. It then checks periodically using a QTimer if a new command was entered by the user.

Isn't there an easy way to achieve what I want to do? I am gladly providing more information if needed. Thanks for any help!

Upvotes: 0

Views: 759

Answers (2)

eudoxos
eudoxos

Reputation: 19065

I solved the same problem (i.e. interactive ipython console in terminal, and GUI thread running independently) in the following way with ipython 0.10 (code here) 1. Construct QApplication object, but don't enter its event loop explicitly 2. Run the embedded IPython instance 3. Run the UI code you need by instantiating your window and calling show() on it (like here with the yade.qt.Controller(), which I aliased to F12. (I did not find a way how to ask the embedded shell to run a command at the start of the session, as if the user had typed it)

(You can also show() your window first, then run the embedded ipython. It will provide event loop for Qt.)

(BTW I also tried running Qt4 from a background thread (using both python threads module, and Qt4.QThreads), but it refuses to run in such way stubbornly. Don't bother going that way.)

The disadvantage is that UI will be blocked while ipython is busy. I hope to finding something better for 0.11, which should have much better threading facilities (I asked on ipython-users about how to unblock the UI).

HTH, v.

Upvotes: 1

Thomas K
Thomas K

Reputation: 40330

What you need is easier than IPython's job - IPython makes the Qt application and the command line interactive at the same time.

I think the way to do it in Qt is to use a timer which fires at regular intervals, and connect the signal to the 'slot' representing your function that gets the new image and puts it in the widget. So you're pulling it in from the event loop, rather than trying to push it.

I've not used Qt much, so I can't give specifics, but the more I think about it, the more I think that's the right way to do it.

Upvotes: 2

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