Support falling back to X11 from Wayland

[demurky]

Checklist

• I have searched the issue tracker for open issues that relate to the same feature, before opening a new one.
• This issue only relates to a single feature. I will open new issues for any other features.

Is your feature request related to a problem?

Adding Wayland support (-tags wayland) removes X11 support.

Is it possible to construct a solution with the existing API?

No response

Describe the solution you'd like to see.

Fyne apps built with Wayland support should try Wayland but fall back to X11 if Wayland is unavailable, so that a single binary is sufficient for one platform, regardless of the available display server.

[Jacalz]

Glfw v3.3 only has support for building against one display protocol at a time, not both, so we can't really do anything about this until we update to v3.4. The plan is to build for both X11 and Wayland by default once go-gl/glfw#400 is done and likely have -tags wayland be Wayland-only with an x11 tag for the opposite.

[heathcliff26]

It seems Glf v3.4 had been merged via go-gl/glfw#414

[andydotxyz]

Thanks to @alexballas for pulling that all together. I have tested both x11 and wayland modes and they work well with Fyne on develop.

However I was not able to figure out how to test the runtime switching. If I have x11 and wayland open it defaults to X11 (expected) but if I export DISPLAY= and then run the app I get an GLFW crash relating to X11 setup instead of a Wayland window.

Am I doing it wrong? :)

[alexballas]

Hey @andydotxyz
I think this is the part of the code you're looking for

https://github.com/go-gl/glfw/blob/master/v3.4/glfw/glfw/src/platform.c#L94-L97

if (strcmp(session, "wayland") == 0 && getenv("WAYLAND_DISPLAY"))
    desiredID = GLFW_PLATFORM_WAYLAND;
else if (strcmp(session, "x11") == 0 && getenv("DISPLAY"))
    desiredID = GLFW_PLATFORM_X11;

DISPLAY= still assumes X11

[andydotxyz]

Thanks for this hint. However this did not work either:

XDG_SESSION_TYPE=wayland DISPLAY= go run .

This could be down to Fyne needing changes to support auto-detecting - but I cannot see where, sorry.

[alexballas]

DIPLAY= is not unset DISPLAY. If you pass DISPLAY= it will break here https://github.com/go-gl/glfw/blob/master/v3.4/glfw/glfw/src/x11_init.c#L1296-L1307
GLFW only takes the forced Wayland path if WAYLAND_DISPLAY is also present