Category: Qt

Spherical Harmonics Explorer

I have written a neat little Spherical Harmonics explorer. Right now, the projection function has some weird bug still, but the basis functions, and arbitrary combinations of them can be viewed nicely. The tool is written in Python, using PyQt4 and PyOpenGL. Python is excellent for prototyping such a tool. It might not be as fast as C++, but the rendering speed using PyOpenGL is more than enough and very smooth. I might put the small 3D viewer widget online later, because it might be useful for many people. Here’s some eyecandy:

Update: Now the projection also works fine. See the example screenshot of an order 5 approximation. This still needs some more work, still using a very basic Monte Carlo sampling approach, which converges terribly slow. But I can already produce some results.

PyQt dynamic uic example

Here is a minimal example for PyQt4, to set up a main window and connect a simple action to some slot. The documentation on doing this is sparse to say the least. So I hope this is helpful for anyone trying something similar. I assume that you have created a ui_MainWindow.ui file with Qt Designer, which contains a form derived from QMainWindow.


import sys
from PyQt4 import QtCore, QtGui, uic

class MyMainWindow(QtGui.QMainWindow):

   def __init__(self):
      QtGui.QMainWindow.__init__(self)
      self.ui = uic.loadUi("ui_MainWindow.ui", self)
      self.connect(self.ui.actionOpen, QtCore.SIGNAL('triggered()'), self, QtCore.SLOT('open()'))
   
   @QtCore.pyqtSlot()
   def open(self):
      fileDialog = QtGui.QFileDialog(self, "Open file")
      fileDialog.show()

app = QtGui.QApplication(sys.argv)
mainWindow = MyMainWindow()
mainWindow.show()
sys.exit(app.exec_())

Not happy with Qt on OS X…

I really don’t get happy with Qt 4.6 on OS X 10.6. Nokia rates Qt on that platform as Tier 2. Which means, it is not fully supported. This results in stupid things happening. With Licq, I currently have the problem that the whole program crashes with the following message:

+[NSUndoManager(NSInternal) _endTopLevelGroupings] is only safe to invoke on the main thread.

The problem here is that Qt 4.6 for 64 Bit is (rightly so) built using the Cocoa API, instead of the C-only Carbon API. Now it seems that Qt uses the NSUndoManager, which in turn has an undocumented (?) function _endTopLevelGroupings. And as the above mentioned message tells you, it is only safe to call that function from the main thread. Since the qt4-gui plugin of Licq runs in a separate thread, this assertion fails, and the whole program crashes. So this basically means you cannot start up your GUI from a secondary thread with Cocoa based Qt. This, I think, constitutes a bug in Qt.
Update: I submitted a bug tracker item, and erijo is producing a minimal example that will hopefully show the bug in action. Now let’s wait and see.