On 2014-07-03 12:33+0930 Jonathan Woithe wrote: > Hi all > > I have a relatively simple Qt program which utilises the PlPlot Qt widget > (QtExtWidget). QtExtWidget is a component of the main application window > and as such is constructed during program startup, prior to the calling of > QApplication::exec() and before any GUI elements have been made visible with > show(). I have noticed that during program startup I will sometimes get the > following warnings: > > QColor::setRgb: RGB parameters out of range > > This doesn't appear all the time and seems to be fairly sensitive to timing, > making it difficult to debug. However, after much trial and error I have > determined that the warning is triggered from the QtExtWidget constructor. > Further exploration showed it was coming from QtPLWidget's constructor > (from which QtExtWidget is derived). > > Looking at the source of QtPLWidget::QtPLWidget() in plqt.cpp, I noticed a > call to QApplication::processEvents() which didn't seem right to me. > Commenting this out resolves the warning. Importantly, the warning remains > when any of the other Qt functions (such as resize(), QPen()) are commented > out. > > The reason I'm suspicious of this call is that there is no guarantee that > any event loop has even been initialised at the time the constructors are > called. Certainly in my case the event loop isn't running because > QApplication::exec() has not yet been called at the time of construction. > Similarly, the widget tree is not visible at event creation time, so it > seems reasonable that some parts of the GUI environment (such as QColor > objects) might not have been allocated yet. At a fundamental level, I > expect that the processEvents() call could be triggering a draw of the as > yet incompletely constructed widget. I also recall reading in the past that > draw actions cannot be triggered in constructors due to the incomplete > nature of the widget being built. > > Regardless, I can't think of any reason for calling > QApplication::processEvents() in the constructor of a Qt widget. Does > anyone know why this call is being made in QtPLWidget's constructor? Based > on tests here and the reasons given above I think it should be removed. The > trivial patch to do this is included at the end of this email. > > What do others think?
I don't understand Qt that well. However, my own tests with the test_interactive target indicate your change is fine so I have committed it (revision 13137) with appropriate commentary to the svn trunk version (which will end up as our next release). @Hazen: I thought I better commit this before it got lost. However, as our Qt expert feel free to revert this change, if you prefer some different solution. Alan __________________________ Alan W. Irwin Astronomical research affiliation with Department of Physics and Astronomy, University of Victoria (astrowww.phys.uvic.ca). Programming affiliations with the FreeEOS equation-of-state implementation for stellar interiors (freeeos.sf.net); the Time Ephemerides project (timeephem.sf.net); PLplot scientific plotting software package (plplot.sf.net); the libLASi project (unifont.org/lasi); the Loads of Linux Links project (loll.sf.net); and the Linux Brochure Project (lbproject.sf.net). __________________________ Linux-powered Science __________________________ ------------------------------------------------------------------------------ _______________________________________________ Plplot-devel mailing list Plplot-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/plplot-devel
