[PyQt] Re: Segfaults on MacOS

[Michael Held]

sorry for the spam, it was all my mistake! the underlying data from
which the QImage was generated was moved to the garbage, which caused
the seg fault (looks like QImage is accessing the data by reference
instead value)

michael


Michael Held wrote:
> ok, maybe my debugging is helpful and I am really PyQt newbie, but a
> mutex helped the seg fault.
> I guess this is some kind of concurrency issue of QImage.pixel
> 
> so my new version runs stable (although I am not sure if am really
> supposed to an mutex myself ;-) )
> 
> cheers,
> michael
> 
> 
> class ImageViewer(QScrollArea):
> 
>     def __init__(self, parent):
>         super(ImageViewer, self).__init__(parent)
>         self.setBackgroundRole(QPalette.Dark)
>         self.setHorizontalScrollBarPolicy(Qt.ScrollBarAsNeeded)
>         self.setVerticalScrollBarPolicy(Qt.ScrollBarAsNeeded)
>         self.label = QLabel(self)
>         self.label.setBackgroundRole(QPalette.Base)
>         self.setAlignment(Qt.AlignHCenter|Qt.AlignVCenter)
>         self.label.installEventFilter(self)
>         self.label.show()
>         self.label.setMouseTracking(True)
>         self.setWidget(self.label)
>         self._qimage = None
>         self.connect(self, SIGNAL('MouseMovedOverImage'),
>                      self._on_move)
>         self._mutex = mutex.mutex()
> 
>     def from_numpy(self, data):
>         self._qimage = numpy_to_qimage(data)
>         self._update()
> 
>     def from_qimage(self, qimage):
>         self._qimage = qimage
>         self._update()
> 
>     def _on_move(self, pos):
>         if self._mutex.testandset():
>             print pos, self._qimage.pixel(pos)
>             self._mutex.unlock()
> 
> 
>     def eventFilter(self, obj, ev):
>         if ev.type() == QEvent.MouseMove and obj == self.label:
>             self.emit(SIGNAL('MouseMovedOverImage'),
>                       ev.pos())
>             return True
>         else:
>             return super(ImageViewer, self).eventFilter(obj, ev)
> 
>     def _update(self):
>         self.label.setPixmap(QPixmap.fromImage(self._qimage))
>         self.label.resize(self.label.pixmap().size())
>         #self.setMaximumSize(self.label.pixmap().size()+QSize(15,15))
> 
> 
> Michael Held wrote:
>> hi,
>>
>> I am building an image viewer with PyQt and wanted to display the pixel
>> color under the cursor for mouseMoveEvent - everything fine so far.
>> using the eventFilter I was able circumvent QLabel sub-classing.
>>
>> *BUT* printing the pixel value crashes my program with a seg fault (I am
>> just moving a bit over the image and BANG...)
>> my silly attempt to delay the event-response with time.sleep(0.5) did
>> also not work.
>>
>> I was using Stackless Python 2.6.2 before but the same error happened
>> for the normal Python 2.6.2
>> MacOS 10.5.7
>> PyQt-mac-gpl-4.5.2-snapshot-20090627
>> sip-4.8.1
>>
>> thanks a lot!
>> michael
>>
>>
>> class ImageViewer(QScrollArea):
>>
>>     def __init__(self, parent):
>>         super(ImageViewer, self).__init__(parent)
>>         self.setBackgroundRole(QPalette.Dark)
>>         self.setHorizontalScrollBarPolicy(Qt.ScrollBarAsNeeded)
>>         self.setVerticalScrollBarPolicy(Qt.ScrollBarAsNeeded)
>>         self.label = QLabel(self)
>>         self.label.setBackgroundRole(QPalette.Base)
>>         self.setAlignment(Qt.AlignHCenter|Qt.AlignVCenter)
>>         self.label.installEventFilter(self)
>>         self.label.show()
>>         self.label.setMouseTracking(True)
>>         self.setWidget(self.label)
>>         self._qimage = None
>>         self.connect(self, SIGNAL('MouseMovedOverImage'),
>>                      self._on_move)
>>
>>     def from_numpy(self, data):
>>         self._qimage = numpy_to_qimage(data)
>>         self._update()
>>
>>     def from_qimage(self, qimage):
>>         self._qimage = qimage
>>         self._update()
>>
>>     def _on_move(self, pos):
>>         print pos, self._qimage.pixel(pos)
>>         time.sleep(0.5)
>>
>>     def eventFilter(self, obj, ev):
>>         if ev.type() == QEvent.MouseMove and obj == self.label:
>>             self.emit(SIGNAL('MouseMovedOverImage'),
>>                       ev.pos())
>>             return True
>>         else:
>>             return False
>>
>>     def _update(self):
>>         self.label.setPixmap(QPixmap.fromImage(self._qimage))
>>         self.label.resize(self.label.pixmap().size())
>>
>