[0815test]

I thought freesync support in modern GPUs meant that they weren't restricted to a fixed refresh rate anymore, and that pixels would then just be "composited" and appear on screen as quickly as possible regardless of their on-screen positioning. Then by using a single fixed buffer that covers the whole screen, this essentially gives you the equivalent to "compositing being disabled".

[Crinus]

The only way to avoid the composition latency is to have the entire composition be done when the GPU is sending the final image to the monitor (note that performing composition using the GPU via OpenGL or whatever is not the same thing even if both are done using the GPU), pretty much like what "hardware mouse cursor" gives you. This would require GPUs to support an arbitrary number of transformable overlapping surfaces (where a single surface=a single toplevel window) and applications being able to draw to these surfaces directly without any form of intermediate buffering (which is important to avoid the initial late frame latency).

Now, it isn't like it is impossible to make a GPU with this sort of functionality since GPUs already do some form of composition already, but AFAIK there isn't any GPU currently on the market that can do all the above. At best you get a few hardcoded planes so you can implement overlays for fullscreen content.

And of course none of the above mean that you have to use Wayland, the X server could perform toplevel window composition itself just fine.

[bitwize]

Some GPUs do support multiple layers which are composited together to form the final image.

This is one reason why the FBDev driver is deprecated: it only supports one framebuffer per output.