Fallback to maximized style if Gala bus is unavailable

[davidmhewitt]

Currently, if you run wingpanel on a compositor that doesn't have the Gala DBus interface for checking the wallpaper colour, it defaults to a fully transparent light style which may not be ideal depending on the wallpaper.

It would be better to just have to solid black maximized panel in cases where the Gala DBus interface isn't available. This would either be because the compositor isn't Gala and doesn't implement the interface, or because Gala crashed (and you've got bigger issues than the colour of your panel)

[bobby285271]

When packaging the latest updates I have a quick try for this PR (https://github.com/NixOS/nixpkgs/commit/3b27254b41ca122f4fd4848e7a1446dd71b1eeec), and noticed that wingpanel is no longer transparent for me on both the greeter and the lock screen after this change. Is there something I should do downstream to resolve this (or is this by design)?

Edit: This should be fixed in https://github.com/elementary/greeter/pull/606 (https://github.com/elementary/greeter/pull/606/commits/af6eb5689dbba6d91293e33c4a16fdea58b4e0d7), tested greeter and lock screen via VM https://github.com/NixOS/nixpkgs/commit/34547b6111ce3e6b1cc05fd3c60a63e4f037405f.

[davidmhewitt]

@bobby285271 Thanks for noticing this!

I guess this is an unintended effect of this PR. The greeter doesn't use Gala as a compositor, so is affected by this change.

It's just lucky (or intentional) that the default of wingpanel was previously the fully transparent style. So I guess we want to revert this PR, or implement a skeleton of the needed DBus interface in the greeter compositor, so it can control the colour of the panel itself, even if it is just hardcoded to transparent.

[danirabbit]

@davidmhewitt I'd like to revisit having a blurred version of the wallpaper as the background so I'm in favor of implementing the dbus in the greeter compositor :)