Hi, I am using Elementary OS Juno which is based on Ubuntu 18.04 LTS. I downloaded the Moodle Desktop AppImage (3.7.0.472) from https://download.moodle.org/desktop. But when I open it, I can only 'see' a transparent window. I can see it in the dock, I can Alt+Tab to it and it gets focus when I do that (I can see it if I use my screenshot tool to capture active window). However the window remains transparent.

System specification

Elementary OS Juno x64
elementary GTK+ theme (default)
[AppImageLauncher |https://github.com/TheAssassin/AppImageLauncher]

Steps to reproduce

1. Double-click the AppImage
2. Run Once / Integrate and Run 

Logs

These are the output when I run the AppImage via terminal:

(AppImageLauncher:29344): Gtk-CRITICAL **: 09:18:47.363: Unable to load resource for composite template for type 'GtkDialog': The resource at “/org/gtk/libgtk/ui/gtkdialog.ui” failed to decompress

(AppImageLauncher:29344): Gtk-CRITICAL **: 09:18:47.363: gtk_widget_class_bind_template_child_full: assertion 'widget_class->priv->template != NULL' failed

(AppImageLauncher:29344): Gtk-CRITICAL **: 09:18:47.363: gtk_widget_class_bind_template_child_full: assertion 'widget_class->priv->template != NULL' failed

(AppImageLauncher:29344): Gtk-CRITICAL **: 09:18:47.364: gtk_widget_class_bind_template_child_full: assertion 'widget_class->priv->template != NULL' failed

(AppImageLauncher:29344): Gtk-CRITICAL **: 09:18:47.364: gtk_widget_class_bind_template_child_full: assertion 'widget_class->priv->template != NULL' failed

(AppImageLauncher:29344): Gtk-CRITICAL **: 09:18:47.364: gtk_widget_class_bind_template_callback_full: assertion 'widget_class->priv->template != NULL' failed

Hotfixes that worked for me

1. Switching GTK+ theme to anything else 

            - I can switch back to elementary without issues once the window appears.

            - It seems that switching theme redraws the window.

            - However on the Arc and Adwaita theme, the issue does occur at all. The window loads fine on first run. 

            - The error messages are shown even for the Arc/Adwaita theme where the issue does not occur.

        2. Un-maximizing the window (I have hot corners enabled. Thus, I could toggle maximise eventhough the window is invisible)

            - This seems to redraw the window as well.

Troubleshooting

1. Ran the Moodle Desktop AppImage using different GTK+ themes

            Works: Arc, Adwaita

            Does not work: Elementary, High Contrast

        2. Built the Moodle Desktop app from [source|https://github.com/moodlehq/moodlemobile2] as a Debian package as well as AppImage. Both of them failed to open (invisible) when using GTK+ themes from above.The hotfixes worked for both.

        3. Tested on a fresh user with and without AppImageLauncher installed. The issue remains the same. And the hotfixes work.

The issue seems to only affect certain GTK+ themes but since we cannot control what themes users will use, I suppose we should force a redraw through Electron?

Resolution

I sort of fixed it by commenting out line 57 in desktop/electron.js

mainWindow.maximize();

I'm not sure if there would be any repercussions from doing that but I'd be happy to test any other possible fixes.