Add a new write-up on making window focus consistent (see #152004)
2004-09-07 Elijah Newren <newren@math.utah.edu> Add a new write-up on making window focus consistent (see #152004) * doc/how-to-get-focus-right.txt: New document * rationales.txt: Remove references to focus bugs, instead point to doc/how-to-get-focus-right.txt
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Elijah Newren
Elijah Newren
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3 changed files with 209 additions and 15 deletions
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2004-09-07 Elijah Newren <newren@math.utah.edu>
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Add a new write-up on making window focus consistent (see #152004)
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* doc/how-to-get-focus-right.txt: New document
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* rationales.txt: Remove references to focus bugs, instead point
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to doc/how-to-get-focus-right.txt
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2004-09-06 Elijah Newren <newren@math.utah.edu>
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* rationales.txt: Add bugs regarding window focus
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199
doc/how-to-get-focus-right.txt
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199
doc/how-to-get-focus-right.txt
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To make choice of focus window consistent for each focus method, a
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number of guidelines should be followed. (For purposes of discussion
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here, I'm excluding things like the panel and the desktop from
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"windows". It is technically incorrect to do this, but I'm lazy and
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"windows" is shorter than something like "normal windows". See the
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end of the discussion for how these special cases are handled.) The
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basics are easy:
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Focus method Behavior
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click When a user clicks on a window, focus it
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sloppy When an EnterNotify is received, focus the window
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mouse Same as sloppy, but also defocus on LeaveNotify
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Note that these choices (along with the choice that clicking on a
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window raises it for the click focus method) introduces the following
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invariants for focus from mouse activity:
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Focus method Invariant
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click The window on top is focused
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sloppy If the mouse is in a window, then it is focused; if the
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mouse is not in a window, then the most recently used
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window is focused.
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mouse If the mouse is in a window, then it is focused; otherwise,
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the designated "no_focus_window" is focused
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However, there are a number of cases where the current focus window
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becomes invalid and another should be chosen. Some examples are when
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a focused window is closed or minimized, or when the user changes
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workspaces. In these cases, there needs to be a rule consistent with
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the above about the new window to choose.
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Focus method Behavior
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click Focus the most recently used window (same as the window
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on top)
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sloppy Focus the window containing the pointer if there is such
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a window, otherwise focus the most recently used window.
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mouse Focus the window containing the pointer if there is one,
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otherwise focus the designated "no_focus_window".
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Also, sometimes a new window will be mapped (e.g. unminimizing a
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window or launching a new application). Most users want to interact
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with new windows right away, so these should typically be focused.
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This does conflict with the invariants for sloppy and mouse focus
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modes, so this wouldn't be true for a strict-pointer-focus mode. For
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all other modes (non-strict-pointer-focus modes), there are only two
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cases in which a new window shouldn't be focused:
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1) If the window takes a while to launch and the user starts
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interacting with a different application, the new window should
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not take focus.
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2) If the window that will appear was not launched by the user
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(error dialogs, instant messaging windows, etc.), then the window
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should not take focus when it appears.
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To handle these cases, Metacity compares timestamps of the event that
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caused the launch and the timestamp of the last interaction with the
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focused window. (Case 2 is handled by providing a special timestamp
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of 0 for the launch time, which ensures that the window that appears
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doesn't get focus)
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If the newly launched window isn't focused, some things should be done
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to alert the user that there is a window to work with:
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1) The _NET_WM_DEMANDS_ATTENTION hint should be set
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2) If the new window isn't modal for the focused window, it should
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appear below the focused window so that it doesn't obscure the
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focused window that the user is interacting with.
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3) If the new window is modal to the focused window, the currently
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focused window should lose focus but the modal window should
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appear on top.
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Additionally, the user may decide to use the keyboard instead of the mouse
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to navigate between windows (referred to as "keynav"). This poses no
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problems for click-to-focus (because the same invariant can be
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maintained), but for sloppy and mouse focus it means that EnterNotify
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and LeaveNotify events should be ignored (they can be generated
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without using the mouse, for example, by grabs).
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Finally, windows of type WM_DOCK or WM_DESKTOP (e.g. the desktop and
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the panel) present a special case. For all focus modes, we only focus
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these windows if the user clicks on them. (Well, erm, actually they
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can be focused in click and sloppy focus modes if no other window
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besides these are found, but there shouldn't be any difference in
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behavior between doing this and focusing the designated
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"no_focus_window")
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To read more about the bugs that inspired these choices:
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- When a focused window becomes invalid and another should be chosen
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http://bugzilla.gnome.org/show_bug.cgi?id=135810
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- When a new window is mapped
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http://bugzilla.gnome.org/show_bug.cgi?id=118372
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Also, the EWMH spec, especially the parts relating to _NET_WM_USER_TIME
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- Modal vs. non-modal dialogs that get denied focus when mapped
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http://bugzilla.gnome.org/show_bug.cgi?id=151996
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- Ignoring EnterNotify and LeaveNotify events during keynav
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http://bugzilla.gnome.org/show_bug.cgi?id=101190
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- Not focusing panels
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http://bugzilla.gnome.org/show_bug.cgi?id=120100 (maybe a different bug?)
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There were many bugs which had to be fixed to get all the above
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working; they helped form these policies and/or show the difficulties
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in implementing this policy (my apologies in advance for producing a
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list heavily lopsided to what I've done; it's just that these bugs are
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the ones I'm the most familiar with):
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bug 72314 ignore LeaveNotify events from grabs
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bug 82921 focus windows on map
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bug 87531 only show focus for sticky windows on active workspace (pager)
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bug 94545 focus window on workspace switch is non-deterministic
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bug 95747 should ignore EnterNotify events with NotifyInferior detail set
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bug 97635 sticky windows always keep focus when switching workspaces
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bug 102665 a window unminimized from the tasklist should be focused
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bug 108643 focus in MRU order instead of stack order
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bug 110970 moving a window to another workspace loses focus
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bug 112031 closing a dialog can result in a strange focus window
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bug 115650 add _NET_WM_USER_TIME support to gtk+ (see also 150502)
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bug 120100 panel shouldn't be focused after workspace applet usage
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bug 123803 need final EnterNotify after workspace switch (see also 124798)
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bug 124981 focus clicked window in pager only if on current workspace
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bug 128200 focus correct window on libwnck window minimize (see 107681 too)
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bug 131582 fix race condition on window minimize/close
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bug 133120 wrong window focused when changing workspaces
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bug 135024 _NET_ACTIVE_WINDOW messages need timestamps
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bug 135786 middle-clicking on focused window to lower it should defocus too
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bug 136581 window minimization vs. activation for mouse focus
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bug 144900 fix focus choice on "un-showing" the desktop
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bug 147475 don't lock keyboard on workspace change
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bug 148364 DEMANDS_ATTENTION support for metacity & libwnck (and other stuff)
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bug 149028 focus-stealing-prevention for metacity-dialog (and other stuff)
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bug 149366 windows denied focus on map occur in wrong order in alt-tab list
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bug 149543 consistent focus window when unshowing desktop
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bug 149589 race in focus choice from libwnck messages
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bug 150271 make sure "run application" dialog gets focused
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bug 150668 update gtk+ _NET_ACTIVE_WINDOW support
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bug 151245 application startup notification forwarding (partially rejected)
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bug 151984 Soeren's idea--backup timestamp when startup notification not used
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bug 151990 prevent focus inconsistencies by only providing one focus method
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bug 151996 modal dialogs denied focus should not be lowered
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bug 152000 fix race on window close followed by rapid mouse movement
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Addendum on sloppy and mouse focus
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You may occasionally hear people refer to sloppy or mouse focus
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modes as inherently buggy. This is what they mean by that:
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1) Keynav doesn't maintain the same invariants as mouse navigation
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for these focus modes; switching back and forth between
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navigation methods, therefore, may appear to have
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inconsistencies. Examples:
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a) If the user uses Alt-Tab to change the window with focus, then
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starts to move the mouse, at that moment the window where the
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mouse is does not have focus.
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b) Users expect that a workspace they previously used will not
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change when the return to it. This means things like window
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position and stacking order, but also the focus window.
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Unfortunately, using the original focus window (which would be
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the most recently used window on that workspace) will
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sometimes conflict with the invariants for mouse and sloppy
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focus modes. Users are much more surprised by the invariant
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being broken than by having the focus window changed (see bug
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94545 and probably others), so we maintain the invariant.
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This only matters when using Ctrl-Alt-Arrow to switch
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workspaces instead of clicking in the workspace switcher, so
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this really is a keynav vs mouse issue. Either that, or a
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windows-are-being-mapped exception. ;-)
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c) Opening a menu, then moving the mouse to a different window,
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and then pressing escape to dismiss the menu will result in
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the window containing the mouse not being focused. This is
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actually correct behavior (because pressing escape shows that
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the user is using key navigation to interact with the window
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containing the menu) but is one of those hard-to-get-right
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keynav and mouse focus mixture cases. (See bug 101190 for
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more details)
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2) The sloppy/mouse invariants are often not strictly maintained;
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for example, we provide an exception to the invariant for newly
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mapped windows. (Most find that not allowing this exception is
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confusing)
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3) There are an awful lot of little cases to handle to get any focus
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mode right, even for click-to-focus. Since mouse and sloppy
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focus have sometimes been hard to even determine what correct
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behavior is, it is much harder to get them completely right.
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Plus mouse and sloppy focus users are a minority, decreasing the
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motivation of window manager implementors to get those focus
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modes right.
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4) Because of -1-, -2-, and -3-, implementations are often buggy or
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inconsistent and people form their opinions from usage of these
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implementations.
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5) Sloppy focus suffers from a bit of a discoverability problem (for
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example, I have seen a scientist sit down to a computer for which
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sloppy focus was in use and take a few minutes before figuring
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out how window activation worked; granted the layout of the
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windows in that situation was a bit unusual but it still
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illustrates that sloppy focus is harder than it should be to
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figure out). Mouse focus solves this problem; however, people
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that have experience with other computing environments are
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accustomed to being able to move their mouse outside the window
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they are working with and still continue interacting with that
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window, which conflicts with mouse focus.
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@ -2,12 +2,7 @@
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History
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====
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Focus windows on map:
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http://bugzilla.gnome.org/show_bug.cgi?id=118372
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http://bugzilla.gnome.org/show_bug.cgi?id=82921
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Choice of focus window (other than during a window map):
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http://bugzilla.gnome.org/show_bug.cgi?id=135810
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Focus issues: see doc/how-to-get-focus-right.txt
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Keep panel always on top: http://bugzilla.gnome.org/show_bug.cgi?id=81551
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Edge flipping: http://bugzilla.gnome.org/show_bug.cgi?id=82917
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@ -33,15 +28,6 @@ raise windows on click:
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http://bugzilla.gnome.org/show_bug.cgi?id=115072
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http://bugzilla.gnome.org/show_bug.cgi?id=115753
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Some discussion of how pointer focus is perhaps inherently problematic
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because of the "sometimes focus window that isn't under the mouse"
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heuristics (almost always involves some kind of use of keynav):
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http://bugzilla.gnome.org/show_bug.cgi?id=101190
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http://bugzilla.gnome.org/show_bug.cgi?id=145387
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http://bugzilla.gnome.org/show_bug.cgi?id=147699
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http://bugzilla.gnome.org/show_bug.cgi?id=124798
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http://bugzilla.gnome.org/show_bug.cgi?id=123803
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Tracking bugs
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====
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