Fix keyboard event propagation when ImGui window has focus

[gaborpapp]

When an ImGui window has focus, all keyboard events are blocked from reaching the application, preventing other keyboard shortcuts handled in the app keyDown from working. This occurs because keyboard navigation is enabled by default, causing ImGui to capture all keyboard input for navigation purposes.

The proposed fix with the NavNoCaptureKeyboard flag prevents ImGui from setting WantCaptureKeyboard=true when only navigation is active (not text input). This allows the event handlers to correctly propagate keyboard events to the application when ImGui doesn't actually need them for text input.

[andrewfb]

Thanks for this, Gabor. This sounds promising but I was having trouble testing it meaning, I didn't see the behavior change I'd expect. Do you mind walking me through how to test it?

[gaborpapp]

I usually have Escape quitting the application:

void CinderApp::keyDown( KeyEvent event )
{   
    switch ( event.getCode() )
    {
        case KeyEvent::KEY_ESCAPE:
            quit();
            break;
    }
} 

Without this change, if the ImGui window is in focus Esc does not do anything. I mainly tested it on Linux and Mac, though.

[andrewfb]

Thanks for this - I tested it locally on both Linux and Windows. I don't believe MSW behavior changed, but the fix was apparent with Linux.