Display

This subsystem deals with the synchronization of the client's display and its configuration (ie: DPI, HDR, etc), in particular sending updated screen configuration whenever the number of monitors or their configuration changes.

The client may also apply scaling, which changes the display size exposed to the server.
This can be used to reduce the amount of pixels needed to cover a monitor.

Component	Link
client	xpra.client.subsystem.display
client connection	xpra.server.source.display
server	xpra.server.subsystem.display

Capability	Value	Information
desktop_size	width: int, height: int	The display size, covering all monitors
screen_sizes	list of screens	Geometry of all screens, scaled
screen_sizes.unscaled	list of screens	Unscaled geometry of all screens
monitors	list of monitors	Geometry of all monitors
dpi	dictionary	DPI configuration

Normally, every client that shares a session sees the same virtual display: its size is the largest width and height requested by any of them.

With --sharing=combine, the virtual display is instead made large enough to hold every client's monitors placed side by side, and each client is given its own area of it.

Each client is told that the display is exactly the size of its own area, and the server translates between the two coordinate spaces:

• the positions the server sends to a client (window-create, window-move-resize, window-initiate-moveresize, pointer-position) have the origin of that client's area subtracted
• the positions the client sends back are resolved from the monitor descriptor attached to its window-map, window-configure and pointer packets, which is offset by that same origin

This is why combine requires XPRA_BACKWARDS_COMPATIBLE=0: without those monitor relative coordinates, the absolute positions sent by two different clients would be indistinguishable and could not be mapped back onto the combined display. It also requires a seamless server whose virtual display can be re-configured with RandR 1.6 (the dummy driver with 16 outputs). When any of those requirements is not met, the server warns and shares the display as it would with sharing=yes.

Every window is still sent to every client, so that moving one from one user's screen to the next is just a metadata update rather than a new window: see window for how the windows outside a client's area are hidden.

Note that each user can only move a window within their own screen, which covers their own area of the display: a window can straddle the boundary between two areas (and is then shown by both clients), but pushing it all the way onto another client's area requires the application itself to move it, or a window manager request.

Packet Type	Direction	Arguments	Information
display-show-desktop	server to client	show : boolean	The server is requesting the client to show or hide the desktop
display-resized	server to client	width: int, height: int, max_w: int, max_h: int	The server has updated its display, the client may need to adjust its scaling properties
display-configure	client to server	monitor configuration dictionary	The client sends its updated monitor layout to the server
display-request-screenshot	client to server		The client requests a screenshot from the server
display-screenshot	server to client	w, h, encoding, rowstride, data	The server sends a screenshot in response to display-request-screenshot
display-request-icon	client to server		The client requests the session icon
display-icon	server to client	w, h, encoding, rowstride, data	The server sends the session icon