Quoting the last commit:
wayland: Move surface texture ownership to MetaWaylandSurface Prior to this commit, MetaWaylandSurface held a reference to MetaWaylandBuffer, who owned the texture drawn by the surface. When switching buffer, the texture change with it. This is problematic when dealing with SHM buffer damage management, as when having one texture per buffer, damaged regions uploaded to one, will not follow along to the next one attached. It also wasted GPU memory as there would be one texture per buffer, instead of one one texture per surface. Instead, move the texture ownership to MetaWaylandSurface, and have the SHM buffer damage management update the surface texture. This ensures damage is processed properly, and that we won't end up with stale texture content when doing partial texture uploads. If the same SHM buffer is attached to multiple surfaces, each surface will get their own copy, and damage is tracked and uploaded separately. Non-SHM types of buffers still has their own texture reference, as the texture is just a representation of the GPU memory associated with the buffer. When such a buffer is attached to a surface, instead the surface just gets a reference to that texture, instead of a separately allocated one.