Multiple means about 4 (that's the number for Skylake & Kabylake gen Intel), and one of them is cursor plane. There might be also misc limitation regarding overlaps, so it might not be generally usable. Android in the earlier years used it for the notification area, as it basically split the screen vertically when the notification shade was moved.
Additionally, these buffers can be scaled at scan-out time. So what it is used for is emulating lower resolutions for Xrandr clients under XWayland (Wayland doesn't allow to switch resolutions to random apps).
Under MacOS, scaling at scan-out time is used for fractionally scaling of the entire framebuffer without using GPU.
Additionally, these buffers can be scaled at scan-out time. So what it is used for is emulating lower resolutions for Xrandr clients under XWayland (Wayland doesn't allow to switch resolutions to random apps).
Under MacOS, scaling at scan-out time is used for fractionally scaling of the entire framebuffer without using GPU.