Wayland compositors try to make of most of the hardware by displaying directly without any copy pixel buffers coming from clients such as games, browsers and video players. This lowers battery usage, improves latency and leaves the 3D engine free for clients to use. The display engines found in modern GPUs often can support this zero-copy mechanism only if the buffers have been allocated in a special fashion. However, buffers allocated this way won't be optimal for rendering, and only a handful of buffers can be directly displayed.

As a result, a trade-off between zero-copy display and optimal rendering needs to be made. The compositor is the natural place where a decision can be made, because it has a global view of all apps which need to be presented. Once the compositor has taken a decision, it needs to be communicated to the clients. The brand new linux-dmabuf feedback protocol enables this negotiation between the compositor and the clients.

If you're up for some window system integration madness, grab some popcorn and come enjoy the show!