Transparent fullscreen windows render black background

Affected version

• Archlinux and Fedora
• Mutter >= 43.1
• Wayland

Bug summary

Hello!
Applications that use background transparency in fullscreen mode (i.e. F11) render a black area instead of showing the wallpaper. This affects the terminals which apply background transparency through VTE3.

I'm not sure but guess that window-actor/wayland: Draw black background for fullscreen windows caused that.

Thank you for your work 🙂

PS: Not every VTE3-based terminal provides transparency by default. At least gnome-terminal requires additional patches. Fedora ships them by default. On Arch you can use another terminal like Tilix or the AUR package which I maintain from below.

Steps to reproduce

1. Install tilix, gnome-terminal (Fedora) or gnome-terminal-transparency (Arch)
2. Set background transparency in the preferences (profile -> colors), which works in windowed mode
3. Switch to fullscreen i.e. press F11

What happened

What did Mutter do that was unexpected?

Renders black background.

What did you expect to happen

Transparent background according to the setting.

Relevant logs, screenshots, screencasts etc.