[Possible bug or strange behaviour] On 2nd run the libui window is black

[rubyFeedback]

Hey there kojix2,

I may have found a bug or at the least a weird behaviour.

First let me show the image - it shows a black window:

https://i.imgur.com/Sng4FNl.png

Next, here is how you can reproduce the behaviour:

First I took the code you showcase in the examples. I will copy/paste it next,
the only change I made was adding "class Button" so I can run this via
"Button.new":

    require 'libui'

    UI = LibUI

    UI.init

    class Button

      def initialize
        main_window = UI.new_window('hello world', 300, 200, 1)
        button = UI.new_button('Button')
        UI.button_on_clicked(button) do
          UI.msg_box(main_window, 'Information', 'You clicked the button')
        end
        UI.window_on_closing(main_window) do
          puts 'Bye Bye'
          UI.control_destroy(main_window)
          UI.quit
          0
        end
        UI.window_set_child(main_window, button)
        UI.control_show(main_window)
        UI.main
        UI.quit
      end

    end

Next, start irb. Do a:

require './button.rb'

or require_relative.

Then do:

Button.new

This is now important! On the first run it works fine. No error.

But!

After you close the window, and do:

Button.new

again, then this black window shows up. It looks to me as if it is
re-using some old data perhaps? Otherwise I would not know
why the second time it is run is different to the first run.

How did I discover this behaviour?

In one of my projects I use libui. I start it via a REPL, similar
to irb. First run is fine but second run always has this black
window. Perhaps I did something wrong, but the behaviour
by libui is quite strange - for instance, via ruby-gtk3 it works
just as expected, I always get the same widget when I run
it without any black window suddenly.

[kojix2]

Hi. @rubyFeedback

Thank you for your Feedback.

Sorry, I forgot about this problem for so long. When I first saw it, I thought it looked difficult and forgot about it.
Today I noticed this issue left behind.

I am only connecting the C libui to the Ruby language interface and do not have a deep understanding of libui. I'm sure everyone has already noticed that I'm not that familiar with the C language. But even if I didn't know much about it, there are things I could figure out by looking at the code. My guess is that it is due to calling UI.quit twice.

You say that's not true?

Indeed UI.quit is called twice, once in the block of the window_on_closing method, and then once in the last line of initialize method.

Although libui looks like one library, it is actually a collection of three different libraries that behave in a similar way. For Unix, for macOS, and for Windows. Let's take a look at the Unix code. uiQuit is here.

void uiQuit(void)
{
	gdk_threads_add_idle(quit, NULL);
}

Here the quit function is added to the thread. The quit function waits for the end of main.
Since you called UI.quit twice, there are two callbacks waiting for main to exit. But actually main has only been called once. So there is one callback remaining. This may be causing the problem. If you delete the last line of UI.quit, it works as expected.

Button.new Button.new Button.new ...

Sorry if my explanation above is wrong. Read the libui code and find out for yourself. If you can read Ruby, you can read C.
If you think you can't read C, it's just a self-suggestion.

But in any case, if you're going to create a Window more than once, I'd suggest you delete the UI.quit on the last line.

Best regards

[AndyObtiva]

I am re-opening this issue because I encountered it too, but only on Linux.

I reported it at the c libui project, but they were not able to reproduce it there, so it must be a Ruby libui binding issue:
libui-ng/libui-ng#205

If I try to run this example (which simply duplicates the code of basic window twice), it runs on the Mac, but it fails to launch a window twice on Ubuntu Linux 22:

require 'libui'

UI = LibUI

puts 'Run 1'

UI.init

main_window = UI.new_window('hello world', 300, 200, 1)

UI.control_show(main_window)

UI.window_on_closing(main_window) do
  puts 'Bye Bye'
  UI.control_destroy(main_window)
  UI.quit
  0
end

UI.main
UI.quit

puts 'Run 2'

UI.init

main_window = UI.new_window('hello world', 300, 200, 1)

UI.control_show(main_window)

UI.window_on_closing(main_window) do
  puts 'Bye Bye'
  UI.control_destroy(main_window)
  UI.quit
  0
end

UI.main
UI.quit

It was reported to me by 2 users:

• Multiple executions in IRB causes error AndyObtiva/glimmer-dsl-libui#45
• Launching window twice causes segfault AndyObtiva/glimmer-dsl-libui#48

This is an important feature to have to be able to conditionally open and close windows within the same application. It is useful for example in IRB or girb (Glimmer IRB).

A fix would be highly appreciated.

[kojix2]

I am a bit confused about this issue.

However, I still think that calling UI.quit twice is causing problems.
Cody's C code translated into Ruby's LibUI looks like this Here

libui-ng/libui-ng#205 (comment)

require "libui"

UI = LibUI

UI.init

# Create a new window
w = UI.new_window("hello world", 300, 30, 0)
UI.window_on_closing(w) { UI.quit; 1}
l = UI.new_label("Hello, World!")
UI.window_set_child(w, l)
UI.control_show(w)

UI.main

w = UI.new_window("hello world", 300, 30, 0)
UI.window_on_closing(w) { UI.quit; 1}
l = UI.new_label("Hello, World!")
UI.window_set_child(w, l)
UI.control_show(w)

UI.main

UI.uninit

uiQuit is called only once in each window, and uiUninit is called last instead of uiQuit.
Probably, this is the correct way to use libui(-ng).

So, the way I have been writing UI.quit at the end is not the correct way to write libui, or at least not the recommended way.

I started writing the LibUI samples based on the old Ruby binding using FFI created by jamescook, and you see the same usage here. This should also be written with reference to other libraries, and while it is one popular way of writing, I don't think it is the correct way.

I think this is the biggest point of this issue, but there could be other problems as well...

[kojix2]

I am planning to make a change in all the examples of LibUI.
Instead of calling uiQuit() twice, I intend to use uiInit() and uiUninit() to align with the C examples of libui. However, it should be noted that in LibUI, the UI.init function has been customized. The uiInitOptions structure is not protected and may be subject to garbage collection (GC). While there have been no known issues caused by this so far, it is necessary to understand the actual role of uiInitOptions before making any changes.

libui-ng/libui-ng#208

[AndyObtiva]

Hi, I experimented with using LibUI.uninit in order to start a window multiple times.

I encountered an issue when using a menu/quit-menu-item on the Mac.

LibUI code (attempts to start an app 3 times):

#!/usr/bin/ruby

require 'libui'

UI = LibUI

UI.init

menu = UI.new_menu('File')
UI.menu_append_quit_item(menu)

main_window = UI.new_window('hello world', 300, 200, 1)

UI.control_show(main_window)

UI.window_on_closing(main_window) do
  puts 'Bye Bye'
  UI.quit
  1
end

UI.main
UI.uninit

UI.init

main_window = UI.new_window('hello world', 300, 200, 1)

UI.control_show(main_window)

UI.window_on_closing(main_window) do
  puts 'Bye Bye'
  UI.quit
  1
end

UI.main
UI.uninit

UI.init

main_window = UI.new_window('hello world', 300, 200, 1)

UI.control_show(main_window)

UI.window_on_closing(main_window) do
  puts 'Bye Bye'
  UI.quit
  1
end

UI.main
UI.uninit

If you do not think this is an issue in the LibUI Ruby binding, yet an issue with the libui-ng C library, please confirm to me and I will report the issue at libui-ng.

[kojix2]

Hi @AndyObtiva
I ran your code on Ubuntu and the latest libui-ng, no error occurred.

If menus do not work properly in previous versions, this may be related to the following problem. Once a Menu was set, flags such as menusFinalized were set and UI.uninit did not restore the flags. This bug seems to have been fixed 4 months ago.

git clone https://github.com/kojix2/LibUI
cd LibUI
rm -f vendor/libui.*
# Download latest libui-ng binary
bundle exec rake vendor:kojix2:auto
# Or you can compile from source code 
bundle exec rake vendor:libui-ng:build

bundle exec ruby three_times_window.rb

I will check the behavior on Mac tomorrow.

[kojix2]

Updated:
Just confirmed that it works on M2 Mac mini.
But we need to release a LibUI gem with the latest libui-ng binaries to get a real solution...

[AndyObtiva]

Thank you for the update. I actually tested Linux from my side, and I didn't have the problem on Linux when using uninit. However, I do have the problem on MacOS as reported already.

I look forward to you making a new release with the latest libui-ng binaries to resolve the issue on the Mac.