Disable the KMS/DRM backend by default

[madsmtm]

The backend was introduced in #135 to fix #42, but I feel like it's somewhat too niche for us to support as a "primary" platform.

In a sense, this is in preparation for some day dropping X11 as a default platform too (though that's years in the future, and should be coordinated with Winit).

Then again, maybe the cost of the extra drm-* dependencies isn't large enough that it really matters?

WDYT?

[ids1024]

Then again, maybe the cost of the extra drm-* dependencies isn't large enough that it really matters?

Not sure what the best tool is currently for measuring this, but drm-rs is a pure-Rust library that mostly provides thin wrappers around ioctls. So I'd expect the bloat this adds to the binary, after optimizing out all the functions that aren't used by softbuffer, is pretty trivial.

[madsmtm]

I guess the reason why I wanted to do this was also motivated by #323, because I felt that DRM being a tier 3 platform somewhat warranted that the user more explicitly opted in to it.

[ids1024]

On the other hand, if winit still has no kms/drm backend, there's probably not much benefit to having this enabled by default, even if there isn't much harm either. The backend will only be used by projects that explicitly use it, in which case they can enable the feature.

[madsmtm]

Yeah, that was my reasoning too.

[madsmtm]

Maybe part of my problem is that I don't understand when you'd ever want to use this backend? Can you even use it if the desktop has Wayland or X11 installed and running? Isn't DRM/KMS more like the implementation detail of a Wayland compositor, not something you can actually use in e.g. a Bevy game?

[ids1024]

You'd use the DRM/KMS backend if you're running an application on a tty without Wayland or X11. I think it's relatively common to use Qt like this in embedded contexts: https://doc.qt.io/qt-6/embedded-linux.html.

Though presumably most uses of softbuffer would want a winit backend as well. And in the mean time, a Wayland compositor like cage can be used to run a single application.

[notgull]

Fine with this. Given the lack of bug reports I am sure that 0 people are using the KMS backend.