>Here you're wrong. Twice. Both X11 and Wayland provide that information.
Nope. X protocol knows nothing about subpixel order. Wayland does.
Xranrd in this case is a cop-out because it's not universally available.
>But the fun part: it is useless in Wayland. By design. Because in Wayland your surface could be rotated, stretched or somehow transformed, so that subpixel information is completely useless there.
Wayland exposes the surface orientation to applications (surprise!), while X doesn't. So applications can adapt their rendering settings if they can.
And of course, there are compositing managers in X that can mutilate the image in various ways.