Override escape key behavior

[lee-deraud]

I have a visualization.gui-base app with a keystroke callback on the SceneWidget. The callback sees both the UP and DOWN events for the escape key, reports both as CONSUMED, yet the window still closes. I've also tried attaching a key event handler to the top-level window (Application.instance) with more or less the same result.

I would like to handle the escape key myself, (1) to use it as a 'reset' key for an operation, and (2) because it's just too easy to hit accidently and lose work. This is on WIndows 11, open3d 0.19.0, Python 3.12.X. Any suggestions?

[joseph-sch]

In my experience, it is impossible to catch the Escape keypress and prevent it from closing the window. I've run into the same problem as you for the same reasons.

FWIW, I've personally come to the conclusion that Open3D's GUI capabilities are too limited and too idiosyncratic, without upsides, for my use case. Within a day, I had Codex implement an export of my scene to a JSON format, and a Three.js-based web viewer with all the features I previously had in the Open3D GUI visualizer. Admittedly, I don't have at this stage callbacks - nor have I tested it yet on very large scenes, for which I will probably have to switch to binary serialization.

[lee-deraud]

Thanks. I was starting to lean toward "can't br done in open3d" as the answer, but clearly "end program" is not a normal behavior for the escape key on most Windows apps. Not sure about Mac/Linux, but I doubt it would be acceptable there either.
If nothing better comes up, I'll probably submit it as a bug/enhancement-request...vaguely surprised it wasn't on the to-be-fixed list years ago.

[victor-flindt]

Use the "set_on_close" callback, docs.

Example,

        ## callbacks
        self._quitting = False
        self.main_window.set_on_layout(self._on_window_layout_event)
        self.main_window.set_on_key(self._on_key_event)
        self.main_window.set_on_close(self._on_close)

Here main_window is a window created via gui.Application.instance.create_window()

    def _on_close(self):
        """Called on ANY close attempt (ESC, X button etc.)"""
        if self._quitting:
            return True
        self._show_quit_confirmation() 
        return False

Here i have implemented a dialog that ask the users if they are sure they want to close, but you can do whatever you want.

[lee-deraud]

Problem is, that doesn't work: see #4597. The return value from _on_close() is ignored, unless something changed since I last looked at it in February.
It's an easy fix (just comment out the change from #3992), but as of a couple weeks ago the main branch has other issues that have not been fully resolved yet. I'm leaving it be until the dust settles and 1.20.0 is official.

[victor-flindt]

Maybe i am misunderstanding your problem then, can you try to run the following and let me know which part is not letting you re-program the esc key.

import open3d.visualization.gui as gui
import open3d.visualization.rendering as rendering

class MainWindow:
    def __init__(self, title="esc key example"):

        self.exit_counter = 0
        # Create the app
        self.app = gui.Application.instance
        self.app.initialize()

        self.main_window = self.app.create_window(title, 1350, 950)
        self.em = self.main_window.theme.font_size

        # Create the scene window (3D view)
        self.scene_window = gui.SceneWidget()
        self.scene_window.scene = rendering.Open3DScene(self.main_window.renderer)
        self.scene_window.scene.set_background([0.2, 0.2, 0.2, 1])  # background
        self.scene_window.frame = gui.Rect(0, self.main_window.content_rect.y,
                                            0, self.main_window.content_rect.height)
        
        ## ADD CHILDREN
        self.main_window.add_child(self.scene_window)
        
        ## callbacks
        self._quitting = False
        self.main_window.set_on_key(self._on_key_event)
        self.main_window.set_on_close(self._on_close)
        

    def _on_close(self):
        """Called on ANY close attempt (ESC, X button etc.)"""
        if self._quitting:
            return True
        if self.exit_counter >= 5:
            self._quitting = True
        return False

    def _on_key_event(self, event):
        if event.type == gui.KeyEvent.DOWN:
            if event.key == 27:
                ## Put custom logic here
                print(f"Key 'esc' pressed DOWN {self.exit_counter=}")
                self.exit_counter += 1 

    def run(self):
        self.app.run()


# Run the viewer
if __name__ == '__main__':
    viewer = MainWindow()
    viewer.run()

This works to overwrite the default esc key behavior, a mechanism needs to be implemented to then handle the closing of the window, in this example its just a simple counter but more usable would probably just be another key / key combination.

Tested on Windows 11 & open3d == 0.19.0

[lee-deraud]

Ok, that appears to work. The only difference I can see between my code and yours is that I have the key callback attached to the SceneWidget rather than the main window. I can move it to the main window for now, but eventually I'll have multiple widgets/windows that will each need their own key callbacks.

What's puzzling is that the "default" ESC behavior (close app) occurs regardless of whether the callback returns CONSUMED or HANDLED (I tried both), which makes me think that the event is getting passed up to the parent/main window despite being handled at the SceneWidget level.

I'll pursue this a bit more when (if?) circumstances allow...it may be awhile though: life happens. Thanks.

(Re "but more usable would probably just be another key / key combination", note that another reason I think #3992's "fix" is a bad idea is that there are already multiple ways to close the main window and kill the app. The 'X' button and the Alt-F4 combination do the same thing, at least in Windows and Linux...not sure about Mac but I'd be astonished if the there isn't an equivalent keyboard shortcut there also.)

[lee-deraud]

UPDATE: Ok, tried it in my app and attaching the key callback to the main window successfully traps the ESC key and keeps it from closing the app. I'm baffled as to why events are being propogated upward in the widget heirarchy despite being consumed by the lower-level widget (SceneWidget in this case), but I'll declare victory for now and chase that as a separate discussion.

Thanks for the assist.