added a checkbox to simplify using elliptic tangents

[marc-frank]

As stated here https://stackoverflow.com/questions/14169234/the-relation-of-the-bezier-curve-and-ellipse when tangent_length = 0.55228474983, a bezier curve closely matches an ellipse.

This can be useful for planform design and with this checkbox, the value doesn't have to be entered manually.

It also locks the Field_Widgets to protect against accidental modification. The Field_Widgets can be unlocked again, by unchecking the checkbox.

[jxjo]

Hi Marc, ... super - thanks!

I made some changes to your request to adapt it to the special framework concept (sorry ;-):

Instead of using a checkbox, I took a button. The user will still be able to move the tangent points via mouse. So disabling the input fields wouldn't be enough ...

self.add(Button_Widget (self,r,1, lab='Set elliptical', width=110, columnspan=2, 
                            style=SUPTLE, set=self.set_elliptical, padx=2, pady=(5,15)))

The buttons calls back a local proxy method which handles the changes. I do not use the tkinter 'active variables'. So the widgets have to be updated by a push refresh call.

    def set_elliptical (self): 
        """ set bezier planform t be elliptical"""
        self.planform().set_elliptical()            # the 'logic' is handled in model object Planform_Bezier
        self.refresh ()                             # refresh all widgets of self (push)
        fireEvent (self.ctk_root, CHORD_CHANGED)    # refresh diagram (separated from edit frames)

The Bezier 'set to elliptical' is done in the model

    def set_elliptical (self):
        """ sets the tangents so that planform becoms elliptical """
        # see https://stackoverflow.com/questions/14169234/the-relation-of-the-bezier-curve-and-ellipse

        tangent_length = 0.55228474983
        self.set_tangentLength_root(tangent_length)
        self.set_tangentLength_tip(tangent_length)
        self.set_tangentAngle_root(0)

That's it ...