Re: [Matplotlib-users] Simple animation with Qt4 backend
On 11/21/10 9:43 AM, Gael Varoquaux wrote: Yes, I can confirm that adding processEvents in places to facilitate redraws is a good way to lead to segfaults. I have seen this in many places other than matplotlib. The reason Tk does not have this problem is that it deals with event loops in a fundementally different way that Wx or Qt. wx has Yield() which sounds a lot like QT's processEvents. But it also has SafeYield() which can (in theory, anyway) be called safetly within an event handler. Does QT have anything similar? -Chris -- Christopher Barker, Ph.D. Oceanographer Emergency Response Division NOAA/NOS/ORR(206) 526-6959 voice 7600 Sand Point Way NE (206) 526-6329 fax Seattle, WA 98115 (206) 526-6317 main reception chris.bar...@noaa.gov -- Increase Visibility of Your 3D Game App Earn a Chance To Win $500! Tap into the largest installed PC base get more eyes on your game by optimizing for Intel(R) Graphics Technology. Get started today with the Intel(R) Software Partner Program. Five $500 cash prizes are up for grabs. http://p.sf.net/sfu/intelisp-dev2dev ___ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
[Matplotlib-users] Simple animation with Qt4 backend
Hi all, Following a discussion with a Spyder user regarding simple animations with Matplotlib, I took a very quick look at the Qt4's backend source code to see if it was possible to make the following code work (which is working with the TkAgg backend but not the Qt4 backend): http://www.scipy.org/Cookbook/Matplotlib/Animations#head-e50abcca4333d3d76b3f2bb66ef00f15c6b4dbbc Apparently, to make it work with the Qt4 backend, one simply has to add: QtGui.QApplication.processEvents() to the method 'FigureCanvasQt.draw_idle' (matplotlib/backends/backend_qt4.py). I did not look further to see if this QApplication.processEvents call is affecting Matplotlib's performance in any way, but I guess that it won't make a big difference. Cheers, Pierre PS: I know that this example of animation is clearly not the most efficient way to animate a Matplotlib figure (and that it's very ugly from a GUI programming point of view!): the 'animation_blit_qt4.py' example is probably the recommended way but the simple example above is some much simpler for beginners. -- Beautiful is writing same markup. Internet Explorer 9 supports standards for HTML5, CSS3, SVG 1.1, ECMAScript5, and DOM L2 L3. Spend less time writing and rewriting code and more time creating great experiences on the web. Be a part of the beta today http://p.sf.net/sfu/msIE9-sfdev2dev ___ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
Re: [Matplotlib-users] Simple animation with Qt4 backend
On Sun, Nov 21, 2010 at 10:36 AM, Pierre Raybaut pierre.rayb...@gmail.com wrote: Hi all, Following a discussion with a Spyder user regarding simple animations with Matplotlib, I took a very quick look at the Qt4's backend source code to see if it was possible to make the following code work (which is working with the TkAgg backend but not the Qt4 backend): http://www.scipy.org/Cookbook/Matplotlib/Animations#head-e50abcca4333d3d76b3f2bb66ef00f15c6b4dbbc Apparently, to make it work with the Qt4 backend, one simply has to add: QtGui.QApplication.processEvents() to the method 'FigureCanvasQt.draw_idle' (matplotlib/backends/backend_qt4.py). I did not look further to see if this QApplication.processEvents call is affecting Matplotlib's performance in any way, but I guess that it won't make a big difference. From http://www.mail-archive.com/matplotlib-de...@lists.sourceforge.net/msg05606.html , discussion of why processEvents was originally removed from draw(): that line can not be added back in. When that line is in place, the backend attempts to process queued events before it is finished processing the current event. It was leading to segfaults in some cases. processEvents should not be called in the middle of processing an event. I am not familiar with draw_idle, and the documentation isn't helpful. Adding processEvents to that call looks similar to adding it to the end of the draw method itself. I'll argue strongly against such a change until it can be shown that the call to processEvents will never occur while processing a current event (I don't want to reintroduce segfaults in the programs I use at work.) Darren -- Beautiful is writing same markup. Internet Explorer 9 supports standards for HTML5, CSS3, SVG 1.1, ECMAScript5, and DOM L2 L3. Spend less time writing and rewriting code and more time creating great experiences on the web. Be a part of the beta today http://p.sf.net/sfu/msIE9-sfdev2dev ___ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
Re: [Matplotlib-users] Simple animation with Qt4 backend
On Sun, Nov 21, 2010 at 11:58:42AM -0500, Darren Dale wrote: Apparently, to make it work with the Qt4 backend, one simply has to add: QtGui.QApplication.processEvents() to the method 'FigureCanvasQt.draw_idle' (matplotlib/backends/backend_qt4.py). , discussion of why processEvents was originally removed from draw(): that line can not be added back in. When that line is in place, the backend attempts to process queued events before it is finished processing the current event. It was leading to segfaults in some cases. processEvents should not be called in the middle of processing an event. Yes, I can confirm that adding processEvents in places to facilitate redraws is a good way to lead to segfaults. I have seen this in many places other than matplotlib. The reason Tk does not have this problem is that it deals with event loops in a fundementally different way that Wx or Qt. I am not sure what the difference is exactly, but I seem to remember that the Tk event loop is more or less hard-wired in Python, and (maybe ?) lives in a different C-level thread. The problem with animations in the example linked by Pierre is that there is no redraw triggered, because the redraw needs to be done in the event loop. The question that needs to be answered to make it easier for people doing animations outside of the mainloop is rather: is there a way to force a redraw without returning in the mainloop. Chances are that there isn't, because the toolkit (Qt) is not thread safe. But the problem really boils down to the fact that the example is not the right way to write animations in GUI programming. However people do not want to learn event loop programming (I can understand them) and want to write for loops. In Mayavi, we provide a helper function that enables to put such a for loop in a generator and pass the generator to the event loop framework without having to worry about timer: http://code.enthought.com/projects/mayavi/docs/development/html/mayavi/auto/mlab_other_functions.html#animate While this function should work out of the box in Spyder, if the ETS_TOOLKIT variable is well set for Mayavi/Traits to use the Qt backend, it would also be fairly easy to port the main idea out of Mayavi and Traits, in matplotlib or spyder: https://svn.enthought.com/enthought/browser/Mayavi/trunk/enthought/mayavi/tools/animator.py My 2 cents, Gaël -- Beautiful is writing same markup. Internet Explorer 9 supports standards for HTML5, CSS3, SVG 1.1, ECMAScript5, and DOM L2 L3. Spend less time writing and rewriting code and more time creating great experiences on the web. Be a part of the beta today http://p.sf.net/sfu/msIE9-sfdev2dev ___ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
