Wayland Window Management Proposal

Kristian Høgsberg krh at bitplanet.net
Tue May 10 18:05:00 PDT 2011

On Tue, May 10, 2011 at 8:35 PM, Bill Spitzak <spitzak at gmail.com> wrote:
> With all the discussion about client side decorations, I thought I would try
> to write how window management could actually be done in Wayland. This is a
> really serious attempt to get the simplest system I could come up with,
> while still allowing for some of the legitimate gripes, in particular to
> make it not be impossible to do tiled window management.

I had a quick read through this and there is a lot of overlap with how
Wayland works today... are you proposing to change how Wayland works
or are you not familiar with what's already in place?

Anyway, for decorations and tiling window managers, bear in mind that
CSD is not about insisting that clients always draws decorations, but
about making clients draw the decorations *when* decorations are


> This I hope is in enough detail that it that it is not ambiguous whether
> this design does something or fails to do it. Too much of the client side
> decoration argument is making false assumptions about what the system will
> do.
> = Wayland Window Management proposal =
> == Object Parent ==
> All Wayland objects have a single "parent", which is another object or
> NULL. When an object is first created it's parent is NULL, but it can
> be set to any other object afterwards. If the attempt to set the
> parent produces a loop that is an error and the parent is
> unchanged. If a parent is deleted the child's parent is set to
> NULL. All parent changes produce events.
> The purpose is to build hierarchies that task managers need in order
> to display everything in a useful way to users. This has no effect on
> the display or how windows act.
> == Object Name ==
> All objects have a single UTF-8 string attached to them that is the
> "name". The purpose of the name is to provide something to show the
> user when a program can't or does not want to display an image.
> == Task objects ==
> Task objects are windows but their purpose is to appear in a "task
> list". They probably don't have an actual image allocated.
> There is a global task created by the compositor, tasks that should be
> visible are attached to this as children. Below that can be a
> hierarchy of more tasks and then actual windows (i'm not sure if there
> will need to be a way to distinguish tasks from windows).
> The image that appears in the task list may be the surface attached to
> the task object, or maybe some children with specific names. Not sure
> exactly how to do this but it would be nice if clients could control
> this to draw indicators, etc. Compositors can fall back to showing the
> name if no other image is found.
> == Multiple-surface windows ==
> What appears to be a single window to the user may be several Wayland
> windows. In particlar a video-playback program may have a YUV surface
> resized on screen to zoom the pixels, overlaid with a "frame" window
> which is an unscaled RGBA image of all the controls around and
> overlaid on the video. It is important that window management support
> this and them move and resize in exact lock.
> To indicate this the YUV surface should be a child of the frame
> and below the frame.
> == Client side decorations ==
> The client is responsible for drawing every single pixel in a window
> that the user would click on and expect to go to the client. This
> includes the window title and the borders on all sides of the window.
> Non-rectangular windows are done by leaving the portion between the
> window and the rectangle transparent black (all zero).
> "shadows" are done by the compositor as the pixels they occupy belong
> to the windows the shadows fall on. It can produce shadows for
> non-rectangular windows by using the alpha to create the shadow.
> "blurry opacity" is done by the compositor. It must not blur video
> playback children and not blur 100% transparent areas or the
> antialiased edges of these areas. I don't know how clients can control
> the blur, but perhaps color values greater than alpha can indicate
> blurring.
> == Compositor Window Management ==
> The compositor can produce events that clients are expected to respond
> to and update their windows appropriately. The compositor *NEVER*
> moves or does anything to the windows, as this would produce
> asynchronous updates. The clients must do this so they can immediatly
> draw the new contents.
> These events are produced by task manager windows, or by Alt+mouse
> style overrides, NOT by the user clicking on the window borders or
> contents. Clicks actually in the windows are expected to be handled by
> the clients or by the filtering described below.
> === Close ===
> Sent to a task or window indicating that the user wants it to go
> away. A typical response is to ask the user if they are sure, to
> destroy or unmap the window, to destroy or unmap other child windows,
> and for the client to exit.
> === Hide ===
> Sent to a task or window indicating that the user wants it off the
> screen but wants to bring it back later. Typical response is to unmap
> windows.
> === Show ===
> Sent to a task or window indicating that the user wants it on the
> screen. Typical response is to map windows.
> === Activate ===
> Sent to a task or window, includes a non-pointer input device (usually
> the keyboard). Indicates that the device's events will be sent to that
> task or window. Typical response is to change the graphics to show
> this and to make toolboxes appear. Note that the events may be sent to
> the task, not a visible window, the client is responsible for figuring
> out where they should go.
> === Deactivate ===
> Sent to a task or window that got Activate before when another object
> is sent Activate. Might not be sent until the other object confirms it
> took the event. Typical response is to change the graphics to show this
> and make toolboxes disappear.
> === Raise/Lower ===
> Sent to a task or window. An id of a visible object is passed that
> this object should be placed under, or None if it should be placed on
> top. May include a hint as to whether this is a raise or
> lower. Typical response is to reorder the window to that position,
> reorder other surfaces to be adjacent, and to raise, if necessary,
> toolboxes so they are atop the window.
> To avoid blinking the client should raise the top-most window first
> and place each lower window below it. Lowering must be done in the
> opposite order. It may be useful for Wayland to provide a "put A below
> B if not above B" api to avoid a lot of round-trip queries to
> determine if it needs to move a window.
> === Move/Resize ===
> Sent only to windows. Includes the rectangle the entire window contents
> is expected to fit into, and also four "edge" flags, and a "title" flag.
> Expected result is that the client resizes the window to the desired
> size, though it can choose a smaller size that fits in the area as
> long as opposite "edge" flags are not on, and it moves and resizes
> other windows, such as the multiple surface windows I described
> above.
> The "edge" flags indicate if the border should not be drawn on that
> side. It indicates alignment with some graphic the compositor draws
> (as in a tiled window manager) or with a screen edge. The client can
> then skip drawing this border, making the contents go all the way to
> the edge of the window. It can also shift the opposite edge of the
> window over (provided it does have the edge flag set) so that the
> contents do not change size.
> The "title" flag indicates that the client should not draw a title
> bar. Note that in typical window designs the top of the window has a
> flat area that is this title bar, outside of which is a few pixels of
> shaded top border that the edge controls.
> == Client Window Management ==
> Clients can directly do anything they want to their
> windows. Compositors should be prepared for this.
> To allow cooperation a client can also send a few messages to the
> compositor so that the compositor does not have to guess what happened.
> === Close ===
> Clients can send this with a task or window to indicate the close
> action was performed. This includes an internal pop up of an "are your
> sure" that the user dismissed, ie the program did not really
> close. May be useful if the compositor keeps track of close attempts.
> === Hide/Show ===
> Clients can send this with a task or window to indicate they performed
> the results of that message. Allows direct control over the state of
> tasks, rather than the compositor guessing it from the visibility of
> windows.
> === Activate ===
> Indicate that the client is in control of a given input device. The
> compositor will send the Deactivate to whatever had it before.
> A client supports click-to-type by sending an activate when the mouse
> is clicked in their window.
> To support point-to-type it sends an activate when the mouse enters
> the window. It can also warp the mouse to point at the correct window
> when it receives an activate event, and warp the mouse out when it
> receives a deactivate, so the mouse always matches the activation.
> Note that both policies can co-exist and applications can choose.
> This does not guarantee that the compositor will send events to this
> client.
> === Deactivate ===
> Done with an input device. The compositor should find some other
> object to activate if it can.
> === Resize ===
> Clients can send the same resize event they receive. The purpose is to
> tell the compositor the settings of the edge and title flags. This is
> needed so that fullscreen can be distinguished from maximize.
> === Move/Resize Interaction ===
> A client can tell the compositor to take control of the mouse or other
> input device and to start a move/resize action. This should be very
> similar to how drag & drop is initiated.
> The purpose is so that snapping and preview and tiling effects can be
> done by the compositor. The client will start this up in response to
> clicks on the borders and titles and resize handles, and perhaps on
> inactive areas of the contents. It then will handle incoming
> Move/Resize/Raise events from the compositor.
> There are 4 flags indicating what edges are being moved. None
> indicates a move. One edge indicates a one-direction resize. Two
> adjacent edges represent a corner. Other combinations should produce
> some reasonable result but the exact meaning is left up to the
> compositor. There is a fifth title flag to indicate whether the click
> was on a "titlebar" or on the contents of the window.
> == Event Filtering ==
> When the compositor sends events to the client, it can look for a
> response back. This response indicates whether the client "ignored"
> the event. If so the compositor can use it for another purpose.
> The main reason for this is so that global shortcuts can require less
> complex shift combinations, by giving clients the opportunity to use
> the key if it wants (Compositors are also free to not send the event
> in the first place if they don't want clients to override it).
> Ignored mouse clicks should be treated as the above mouse grab where
> the click is in the contents.
> Ignored raise/lower/map/etc can be faked. All child windows
> should have the same action done to them as the main window so they
> all move as a unit.
> Ignored resize probably should not change the size, just move the
> window. Move lower children the same way.
> Ignored close should kill the program (note that the client asking the
> user if they want to quit means the client did use the close event).
> Ignored activate means maybe it should try another window. (?)
> Ignored deactive may want to unmap higher child windows as these are
> probably modal dialogs.
> == Fallback Window Management ==
> After a timeout if the client does not send the response back, the
> compositor can assume the client is locked up. The compositor can then
> indicate this state (by changing the cursor to a wait indicator, or
> graying the window, etc). It can then handle the event as though the
> client ignored it (except any events this produced should immediatly
> be acted on as though ignored, rather than sent).
> If the user clicks enough times without the program responding, or if
> a close event is ignored, it should pop up a dialog offering to kill
> the process.
> == END ==
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