Manage correctly the key combination Ctrl + Tab under macOS

[Alzathar]

From qutebrowser/qutebrowser#2142 and specifically this comment:

The combination CTRL + Tab is specially handled by OSX/Cocoa text input method.

At least two solutions exists (here and there) to fix the problem. However, the first one use a private/undocumented API. The second is used by this PR.

NOTE: I am not the author of the proposed code.

[intrigus]

Do you have permission to use the code if you are not the author?
And is it compatible with glfw's license?

[Alzathar]

@intrigus I've sent an email to the original author to answer to your questions.

[tombsar]

It looks as though the code in this PR comes from QT, and is protected by a LGPL license. We can not simply copy the code without at minimum keeping the origin, authorship, and license intact. In my opinion (not a lawyer) we cannot include this code at all without explicit written permission from QT (and/or the original author) granting us an unrestricted license that does not carry with it the same responsibilities of the LGPL.

Are the comments included in the patch relevant to GLFW? I notice terms like performKeyEquivalent and QNSView that are unfamiliar, and I suspect may be referring to QT-specific code.

[Alzathar]

@tombsar performKeyEquivalent: is proposed by Apple in its AppKit API. This is a way to handle keyboard shortcut. You can replace QNSView by NSView (available in AppKit API) as the former inherits from the latter. I will modify the comment if the original author gives the permission to use its code.

[Alzathar]

Good news, we have the rights to use this code if Qt keeps the copyright!

I proposed to modify the proposed PR as following:

    // The Qt company has all the rights on the following code.
    // The GLFW project has the permission to use it in its source code
    // but the Qt company keeps the copyright
    // The original source code is here: https://codereview.qt-project.org/#/c/161214/1/src/plugins/platforms/cocoa/qnsview.mm
    // =========== QT COPYRIGHT BEGIN =========== //
    // At the moment the only reason we define this method
    // is Ctrl-tab key event never reaching any view at all.
    // ... 
    ...
   // =========== QT COPYRIGHT END =========== //

What do you think?

This PR will be very helpful for Dear ImGui to pass between windows with the CTRL + Tab shortcut. The following comment has a GIF to illustrate the behaviour: ocornut/imgui#787 (comment)