Thanks for the additional details. I’m now able to reproduce the issue.
The fact that this issue is only triggered when the menu is transparent makes me think that this issue may share a root cause with the issue discussed here:
Investigating these issues is now at the top of my to-do list. However, I’ve already spent a little time investigating the other issue without making much progress, so I’m not feeling particularly optimistic at the moment.
In general it’s best to avoid creating additional windows in your plugin editor. This is especially true for AUv3, and to a lesser extent, AU plugins.
Another option would be to set your plugin editor as the parent of your PopupMenu (see PopupMenu::Options::withParentComponent). This way, your menu will be restricted to the editor’s viewport, but transparency effects and rounded corners will work as expected. This approach is less likely to cause problems in AU versions of you plugin, such as the menu window opening behind the plugin editor window.
In particular, consider the official guidance from Apple for supporting out-of-process audio units:
- If custom, free-floating dialogs don’t work as you expect, add them as a subwindow to the main window — this includes custom tooltip and drop-down menu implementations.