weston/TODO

Core wayland protocol

 - generate pointer_focus (and drag focus) on raise/lower, move
   windows, all kinds of changes in surface stacking.

 - glyph cache

 - dnd, figure out large object transfer: through wayland protocol or
   pass an fd through the compositor to the other client and let them
   sort it out?

 - DnD issues:

   How to roboustly handle failing drag, ie the case where an
   application gets a button event, tries to activate a drag, but when
   the server gets the drag request, the button has already been
   released and the grab is no longer active.  What's the concern:

    - Application may set a drag cursor that doesn't revert back,
      since a failed drag doesn't result in a pointer_focus event to
      give focus back to the surface.  We could just do that: if the
      pointer_focus is the same surface as we tried to start a grab
      for, just remove and give back pointer_focus.

      Alternatively, set drag cursors only in response to drag events,
      like drag focus.  But drag_focus and drag_motion are sent to the
      drag target, so the source surface won't always get those.  We
      may also end up setting the cursor after the drag ends, but in
      this case the drag started and ended and we'll get a
      pointer_focus event, which will make the application reset the
      pointer image.  Could introduce a drag start event that
      indicates that the drag active.

   How to handle drop decline (accept with type=NULL)

    - Targets must send a NULL type in accept if they don't accept a
      drop at the drag_focus/drag_motion position.  Root window will
      send a NULL type or x-wayland/root-something type if the source
      offers that.

   Races between pointer motion, ending the drag, the target sending
   accept request and the source receiving the target event.

    - We've sent a drag focus or motion event to the source, but
      haven't received an accept request corresponding to that event
      and now the button is release.  The compositor could wait for
      the source to reply to outstanding focus/motion events before
      sending the finish event to the source.  Or we could send the
      finish event through the source so that it needs to reply to the
      finish event too.  Either way, the state of the drag blocks on
      the client.  What if we drag to a client that doesn't doo dnd?

   How do we animate the drag icon back to the drag origin in case of
   a failed drag?

   How to handle surfaces from clients that don't know about dnd or
   don't care?  Maybe the dnd object should have a
   dnd.register_surface() method so clients can opt-in the surfaces
   that will participate in dnd.  Or just assume client is not
   participating until we receive an accept request.

   May need to look at all offer events before we can decide which one
   to go with.  Problem is, we don't know when we've seen that last
   offer event.

 - copy-n-paste, store data in server (only one mime-type available)
   or do X style (content mime-type negotiation, but data goes away
   when client quits).

 - Optional pointer images.

 - Discard buffer, as in "wayland discarded your buffer, it's no
   longer visible, you can stop updating it now.", reattach, as in "oh
   hey, I'm about to show your buffer that I threw away, what was it
   again?".  for wayland system compositor vt switcing, for example,
   to be able to throw away the surfaces in the session we're
   switching away from.  for minimized windows that we don't want live
   thumb nails for. etc.

 - Initial placement of surfaces.  Guess we can do, 1)
   surface-relative (menus), 2) pointer-relative (tooltips and
   right-click menus) or 3) server-decides (all other top-levels).

 - When a surface is the size of the screen and on top, we can set the
   scanout buffer to that surface directly.  Like compiz unredirect
   top-level window feature.  Except it won't have any protocol state
   side-effects and the client that owns the surface won't know.  We
   lose control of updates.  Should work well for X server root window
   under wayland.  Should be possible for yuv overlays as well.

    - what about cursors then?  maybe use hw cursors if the cursor
      satisfies hw limitations (64x64, only one cursor), switch to
      composited cursors if not.

    - clients needs to allocate the surface to be suitable for
      scanout, which they can do whenever they go fullscreen.

 - multihead, screen geometry and crtc layout protocol, hotplug

 - input device discovery, hotplug

    - Advertise axes as part of the discovery, use something like
      "org.wayland.input.x" to identify the axes.

    - keyboard state, layout events at connect time and when it
      changes, keyboard leds

    - relative events

    - multi touch?

    - synaptics, 3-button emulation, scim

 - Figure out if we need the batch/commit scheme and what to do
   instead.  Since dropping the "copy" request, we have a race between
   copy from back to front and reporting damage.  "copy" did this
   atomically, but copy is a rendering operation (wayland doesn't do
   rendering) and requires synchronization between server and client
   before client can reuse backbuffer.

   The race condition happens when a client copies new content into
   its window and then, before the client reports the damage, the
   compositor then does a partial repaint (triggered by another
   client) that only pulls in part of the repainted area.  It's only a
   one-frame glitch, as the client will submit the damage and the
   compositor will repaint the damaged area next frame.  And ideally
   clients should do all rendering as early in the frame as possible
   to avoid this race.

 - auth; We need to generate a random socket name and advertise that
   on dbus along with a connection cookie.  Something like a method
   that returns the socket name and a connection cookie.  The
   connection cookie is just another random string that the client
   must pass to the wayland server to become authenticated.  The
   Wayland server generates the cookie on demand when the dbus method
   is called and expires it after 5s or so.

    - or just pass the fd over dbus

 - drm bo access control, authentication, flink_to

 - Range protocol may not be sufficient... if a server cycles through
   2^32 object IDs we don't have a way to handle wrapping.  And since
   we hand out a range of 256 IDs to each new clients, we're just
   talking about 2^24 clients.  That's 31 years with a new client
   every minute...  Maybe just use bigger ranges, then it's feasible
   to track and garbage collect them when a client dies.

 - Add protocol to let applications specify the effective/logical
   surface rectangle, that is, the edge of the window, ignoring drop
   shadows and other padding.  The compositor needs this for snapping
   and constraining window motion.  Also, maybe communicate the opaque
   region of the window (or just a conservative, simple estimate), to
   let the compositor reduce overdraw.

 - multi gpu, needs queue and seqno to wait on in requests

Clients and ports

 - port gtk+

    - eek, so much X legacy stuff there...

    - draw window decorations in gtkwindow.c

    - start from alexl's client-side-windows branch

    - Details about pointer grabs. wayland doesn't have active grabs,
      menus will behave subtly different.  Under X, clicking a menu
      open grabs the pointer and clicking outside the window pops down
      the menu and swallows the click.  without active grabs we can't
      swallow the click.  I'm sure there much more...

 - Port Qt?  There's already talk about this on the list.

 - X on Wayland

    - move most of the code from xf86-video-intel into a Xorg wayland
      module.

    - don't ask KMS for available output and modes, use the info from
      the wayland server.  then stop mooching off of drmmode.c.

    - map multiple wayland input devices to MPX in Xorg.

    - rootless; avoid allocating and setting the front buffer, draw
      window decorations in the X server (!), how to map input?

 - gnome-shell as a wayland session compositor

    - runs as a client of the wayland session compositor, uses
      clutter+egl on wayland

    - talks to an Xorg server as the compositing and window manager
      for that server and renders the output to a wayland surface.
      the Xorg server should be modified to take input from the system
      compositor through gnome-shell, but not allocate a front buffer.

    - make gnome-shell itself a nested wayland server and allow native
      wayland clients to connect and can native wayland windows with
      the windows from the X server.

 - qemu as a wayland client; session surface as X case

    - qemu has too simple acceleration, so a Wayland backend like the
      SDL/VNC ones it has now is trivial.

    - paravirt: forward wayland screen info as mmio, expose gem ioctls as mmio

    - mapping vmem is tricky, should try to only use ioctl (pwrite+pread)

    - not useful for Windows without a windows paravirt driver.

    - two approaches: 1) do a toplevel qemu window, or 2) expose a
      wayland server in the guest that forwards to the host wayland
      server, ie a "remote" compositor, but with the gem buffers
      shared.  could do a wl_connection directly on mmio memory, with
      head and tail pointers.  use an alloc_head register to indicate
      desired data to write, if it overwrites tail, block guest.  just
      a socket would be easier.

 - moblin as a wayland compositor

    - clutter as a wayland compositors

    - argh, mutter