Wednesday, February 1, 2012

Wayland, Android and desktop Linux - a marriage made in heaven?

I noticed today that Wayland is rapidly reaching 1.0. It's no secret that many people (Canonical for one) see this as being the desktop graphics solution for the future...but I got to thinking; what if it could help us get proper Linux like Ubuntu onto Android devices too?

See, Android has its own userland, wildly different from a normal Linux system. I'd personally much rather be able to have the normal Posix/GNU/Linux API and utilities available to me, along with all that lovely desktop open-source software  (which is why I was rather upset when Nokia canned http://en.wikipedia.org/wiki/MeeGo). The kernel is GPLed, so we generally have the ability enforced by law to build Linux kernels for these devices, and for most devices it's possible to take the ICS source and combine it with the binary blobs from the OEM and install your own version of Android, so you'd think bringing up something like Ubuntu on the phone or tablet of your choice would be simple enough. Sadly this turns out not to be the case, and the main problem is the graphics drivers.

Sadly, essentially all Android devices have closed-source graphics hardware. The support for it is provided in the form of a binary userspace library that provides OpenGL ES and is linked with Bionic, Android's stripped-down libc, and not glibc. That means for Linux programs to use it they have to use Android's userspace; so getting X11 running on an Android device would a) mean porting it to bionic (and it would not surprise me if bionic is missing some Posix stuff X would like) and b) using OpenGL ES as its driver backend, which to my knowledge noone has done. So while you do see Ubuntu running on Android tablets, the usual method is to run Ubuntu in a chroot with an X11 server running as an unaccelerated VNC server, then running an Android VNC viewer to actually see the desktop. No hardware acceleration whatsoever and an extra trip over the network to boot.

Ugh. This is bad enough in performance with an 800x480 phone. With a tablet it's untenable and will get worse when 'retina display' tablets become a thing. You pretty much need at least accelerated compositing and bitblt (for scrolling), which is why OEMs are required to provide hardware acceleration for 2d in ICS if they want Google certification.

However! Wayland is built to use OpenGL ES already, and it's small by design. So, what if we were to port Wayland to Bionic/Android and SurfaceFlinger? (while keeping the Wayland client libraries on glibc). The common cases of 'composite windows' and 'move windows around' becomes hardware accelerated, as it should be. You can build support for this into something like CyanogenMod and every CyanogenMod device can suddenly run Ubuntu, Debian and co. as a first class citizen. Or, you can not use the Android stuff and turn your Galaxy Tab or Nook Color into a proper Ubuntu tablet with just enough Android userland to run Wayland and deal with wifi, talking to the cellphone or anything else that needs a binary driver. Seems like a win-win to me.






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