MainWindow/PluginRoot classes mixed

[klayoutmatthias]

As internally KLayout internally identifies MainWindow with PluginRoot, but does not expose this identity as an implementation detail, the Python class mapping is getting messed up.

One symptom is the result of

pya.PluginRoot.instance()

which is a MainWindow object, but does not implementat the PluginRoot object. The other way has been reported too: "pya.MainWindow.instance()" apparently returns a "PluginRoot" object as well (https://www.klayout.de/forum/discussion/1140/the-return-type-of-pya-mainwindow-instance-is-sometimes-wrong#latest).

[klayoutmatthias]

There is one more issue found during this fix was PluginRoot#get_config which is broken.

The workaround is to use "Application#get_config" which is the more popular method anyway.

[klayoutmatthias]

See pull request #192

[klayoutmatthias]

I now better understood what's going on and there is a workaround.

Actually, the wrong class gets assigned because the first time, a C++ object is bound in Python space, the type will be assigned. In this case, there are two types that apply (MainWindow and PluginRoot). So if the MainWindow object is bound the first time in MainWindow context (i.e. through "pya.MainWindow.instance()", it gets MainWindow class. If it's bound the first time in "PluginRoot" context, it gets "PluginRoot" class. The latter happens implicitly for example for the "root" parameter in "PluginFactory.create_plugin".

Consider this code from https://www.klayout.de/forum/discussion/1151/capture-a-mouse-click-and-its-location#latest:

class SetOriginOnMouseClickPluginFactory(pya.PluginFactory):

  def __init__(self):
    super(SetOriginOnMouseClickPluginFactory, self).__init__()
    pya.MainWindow.instance()  # (workaround for bug 191)
    self.register(-1000, "set_origin", "Cell Origin")
    
  def create_plugin(self, manager, root, view):
    return SetOriginOnMouseClickPlugin()

When the plugin is created, the "root" argument of "create_plugin" will bind the MainWindow object to PluginRoot unless it was bound otherwise. Hence there is a simple workaround by explicitly binding before "create_plugin" is called:

class SetOriginOnMouseClickPluginFactory(pya.PluginFactory):

  def __init__(self):
    super(SetOriginOnMouseClickPluginFactory, self).__init__()

    # (workaround for bug 191)
    # will bind the MainWindow object to the MainWindow class before anything bad happens
    pya.MainWindow.instance()  

    self.register(-1000, "set_origin", "Cell Origin")
    
  def create_plugin(self, manager, root, view):
    return SetOriginOnMouseClickPlugin()

Please note that this is only because of the ambiguity of MainWindow/PluginRoot. All other objects are not affected by this issue.

Matthias

[klayoutmatthias]

Fixed in master branch. Will be released with 0.25.6.