Allow unhandled key and mouse-wheel events to bubble up.

[rkern]

Fixes #550

Might have unintended consequences for existing applications, so consider it a WIP for testing.

When a Qt widget receives a QKeyEvent that it does not handle, it is supposed to call the ignore() method to allow the event to bubble up to the parent widget. KeyPress and KeyRelease events are accepted by default, so if not explicitly ignored, the in-focus Enable widget will swallow all of these QKeyEvents.

We should consider doing the same for wheelEvent(), as QWheelEvents have the same semantics. This has led to issues when Enable components are embedded in a scrolled group.

[jwiggins]

Basically LGTM. Can we try to test this and make a decision about wheelEvent in the next week or so? It would be good to get this into the 5.0.0 release.

[corranwebster]

Getting this in for 5.0.0 would mitigate the issues around potential breakage of existing code - it is a major release so some differences in behaviour are acceptable as long as we can highlight them.

[rkern]

I fixed a logic error (the _on_key_*() convenience methods don't actually return the handled flag) and added the wheelEvent modification.

[rkern]

Here's a simple manual test adapted from #550

Pressing d should print out keybinding hotkey pressed whether the Chaco plot has focus or not (click on the Chaco plot to give it focus).
Pressing n while the Chaco widget has focus should print out chaco hotkey pressed.
Scrolling with the mouse wheel should Just Work even when the mouse pointer crosses the Chaco plot (it will stop on the Chaco plot on master).

import os
import numpy as np

import logging
logging.basicConfig(level=logging.DEBUG)

from traits.api import Event, HasStrictTraits, Instance, Button
from traitsui.api import UItem, ModelView, VGroup, View
from traitsui.key_bindings import KeyBinding, KeyBindings
from chaco.api import ArrayPlotData, Plot
from enable.api import BaseTool, KeySpec, ComponentEditor


class HotkeyTool(BaseTool):
    key_pressed = Event

    next_key = Instance(KeySpec, args=("n",))

    def normal_key_pressed(self, event):
        if self.next_key.match(event):
            self.key_pressed = 'next'
            event.handled = True


class CustomView(ModelView):

    model = Instance(HasStrictTraits, ())

    dummy_button = Button('Do Nothing')

    image_plot = Instance(Plot)
    hotkey_tool = Instance(HotkeyTool)

    def _kb_hotkey_pressed(self, info=None):
        print('keybinding hotkey pressed')

    def _chaco_key_pressed(self, event):
        if event.new == 'next':
            print('chaco hotkey pressed')

    def _image_plot_default(self):
        plot_data = ArrayPlotData(
            intensity=np.random.randint(0, 255, size=(100, 100)))
        plot = Plot(plot_data)
        tool = HotkeyTool(plot)
        tool.observe(self._chaco_key_pressed, 'key_pressed')
        plot.tools.append(tool)
        plot.img_plot('intensity')
        return plot

    def default_traits_view(self):
        key_bindings = KeyBindings(
            KeyBinding(binding1='D',
                       description='Hotkey',
                       method_name='_kb_hotkey_pressed')
        )
        return View(
            VGroup(
                UItem('dummy_button'),
                # Make sure the image plot takes up some space.
                UItem('image_plot', editor=ComponentEditor(), height=-400),
                # Add a bunch of dummy spaces so we get a scrollbar to test the
                # wheel event handling.
                UItem('_'),
                UItem('_'),
                UItem('_'),
                UItem('_'),
                UItem('_'),
                UItem('_'),
                UItem('_'),
                UItem('_'),
                UItem('_'),
                UItem('_'),
                UItem('_'),
                UItem('_'),
                UItem('_'),
                UItem('_'),
                UItem('_'),
                UItem('_'),
                UItem('_'),
                UItem('_'),
                UItem('_'),
                UItem('_'),
                UItem('_'),
                UItem('_'),
                UItem('_'),
                UItem('_'),
                UItem('_'),
                scrollable=True,
            ),
            key_bindings=key_bindings,
            resizable=True,
        )


if __name__ == '__main__':
    from traits.etsconfig.api import ETSConfig
    config_dir = os.path.join(ETSConfig.application_data, 'traits')
    if os.path.exists(config_dir):
        for f in os.listdir(config_dir):
            if f.startswith('traits_ui.'):
                os.remove(os.path.join(config_dir, f))

    view = CustomView()
    view.configure_traits()

[jwiggins]

LGTM.

[rkern]

I'll leave merging to the team working on the 5.0.0 release.

[rahulporuri]

LGTM. I was able to use the provided manual script to verify that this change works as expected on pyqt and pyqt5 on windows.

@rkern Can you make time to add a regression test in this PR? I'm not sure how easy/difficult it will be to add the test.

[rahulporuri]

Thanks @rkern . I resolved the merge conflicts. Merging.