GNU bug report logs - #43379
[PATCH] Double-click events can occur without preceding single-click events

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Daniel Koning <dk <at> danielkoning.com>
To: bug-gnu-emacs <at> gnu.org
Subject: [PATCH] Double-click events can occur without preceding
 single-click events
Date: Sun, 13 Sep 2020 12:00:10 -0500

[Message part 1 (text/plain, inline)]

According to the documentation (21.7.7 of the Lisp ref, "Repeat Events"), a
double-click binding should "assume that the single-click command has already
run," since Emacs only produces a double-click event after an equivalent
single-click event. But (so long as 'double-click-time' is set generously
enough) it's easy to trigger a double-click event without a corresponding
single-click event, because the event handling primitives aren't quite
particular enough about what they count as a repeat.

For one thing, the code ignores whether the modifier keys of one input action
differ from the next. So the sequence "M-mouse-1 mouse-1" produces <M-mouse-1>
<double-mouse-1>. This is no good: <M-mouse-1> is likely bound to something
different from <mouse-1>, so the <double-mouse-1> command will run under false
premises.

It also uses just one repeat click counter, despite the fact that down/up click
event pairs can be interleaved. The counter increments when a button-down
matches the last button-up, and it carries over to whatever button-up comes in
next. Therefore, the mouse sequence

    down on mouse-1
    down on mouse-3
    up on mouse-1
    down on mouse-1
    up on mouse-3

produces a <double-mouse-3> event with no preceding <mouse-3>.

The function 'make_lispy_event', which translates raw events to Lisp objects, is
responsible for tagging a mouse event (button-down, click, drag, or wheel) as a
double. This patch against master revises that function to avoid creating "bare"
double mouse events. It does so by consolidating the scattered repeat-tracking
logic into its own function, where more relevant state can be maintained without
any extra global cruft. (With less cruft, in fact: 'button_down_time' is no
longer punned as an interrupt flag, wheel event codes need not be coerced to
negative to stuff them into the same variable as clicks, etc.)

Just as before, a repeat mouse event has to use the same button, happen in
roughly the same place, happen at roughly the same time, and so on. Aside from
the specific deliberate narrowing I've described, I believe this code duplicates
the logic of the old code exactly. That includes nuances that strike me as
strange. For instance,

    down on mouse-1
    up on mouse-1
    down on mouse-1
    keystroke
    up on mouse-1
    down on mouse-1

finishes with <double-mouse-1> <down-mouse-1>, even though it would make more
sense to me if the keystroke reset the count right away. But that's how it was
before.

There is still at least one fringy situation in which a <double-mouse-1> command
could run without the <mouse-1> command running first: when the first and second
click land in different windows. I would have liked to add a test for this, but
I don't fully understand the type constraint on the 'frame_or_window' member of
struct input_event (specifically when it's a mouse event). 'make_lispy_event'
seems to assume it's a frame: it does an XFRAME without a check. But then the
comparison against 'double-click-fuzz', which I folded into the new function,
tries both possibilities. I left the more cautious code in place, and I haven't
added any more logic related to windows.

This also has no effect on xterm-mouse-mode, which doesn't interact with the C
event translator at all. It just takes key sequences which have already passed
through 'make_lispy_event' and translates them to mouse-event lists.
xterm-mouse-mode has some major inconsistencies with the GUI repeat-handling
behavior, but it doesn't seem to exhibit the bug this report describes.

This patch rewords the docs slightly to say explicitly that modifier keys make a
difference. It also makes a small tweak to the criteria for drag events, and
another tweak to the Cocoa-specific trackpad code to fix a conspicuous bug
caused by a similar oversight. Namely, newly pressed modifier keys can attach to
invisible so-called "momentum" events generated by a swipe on the trackpad that
has already ended. One result is that if a Cocoa user scrolls up to the top of
the buffer and immediately presses (say) C-e, Emacs gets barraged with
<C-wheel-up> events and scales the buffer text up to a ridiculous size.

Daniel

[repeat-events.patch (text/x-patch, attachment)]

Message #8 received at 43379 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Daniel Koning <dk <at> danielkoning.com>
Cc: 43379 <at> debbugs.gnu.org
Subject: Re: bug#43379: [PATCH] Double-click events can occur without preceding
 single-click events
Date: Sun, 13 Sep 2020 20:30:26 +0300

> From: Daniel Koning <dk <at> danielkoning.com>
> Date: Sun, 13 Sep 2020 12:00:10 -0500
> 
> ++++
> +** Repeat events are now produced only when the modifier keys are the same.

What will this do if the modifier key is "simulated" using "C-x @"?

More generally, for a change this deep and wide, I'd like to
understand better what exactly are the problems being solved, and also
how can we be sure (by testing or otherwise) we are not getting
regressions in some use cases.  Could you please clarify that?

> +Before, when the user pressed the same mouse button repeatedly within
> +the bounds specified by 'double-click-fuzz' and 'double-click-time',
> +it always produced a 'double-' or 'triple-' event, even if the user
> +was holding down modifier keys on one click and not another.  This
> +meant that it was possible for Emacs to read a double-click event
> +without reading the same kind of single-click event first.  Emacs now
> +looks at modifier keys to determine if a mouse event is a repeat.

Beyond theoretical (un)cleanliness, what other practical problems did
you find with the current code and fix in these patches?

>  This variable is also the threshold for motion of the mouse to count
> -as a drag.
> +as a drag.  (But if the mouse moves from one screen position to
> +another while the button is held down, it always counts as a drag, no
> +matter the value of @code{double-click-fuzz}.)

Isn't this an incompatible change?

Thanks.

Message #11 received at 43379 <at> debbugs.gnu.org (full text, mbox):

From: Daniel Koning <dk <at> danielkoning.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 43379 <at> debbugs.gnu.org
Subject: Re: bug#43379: [PATCH] Double-click events can occur without
 preceding single-click events
Date: Sun, 13 Sep 2020 15:20:35 -0500

Eli Zaretskii <eliz <at> gnu.org> writes:

>> From: Daniel Koning <dk <at> danielkoning.com>
>> Date: Sun, 13 Sep 2020 12:00:10 -0500
>>
>> ++++
>> +** Repeat events are now produced only when the modifier keys are the same.
>
> What will this do if the modifier key is "simulated" using "C-x @"?

As before, you can't get a repeat tag on an event with a simulated
modifier key, because the raw keyboard events representing "C-x @" break
the chain, and double and triple modifiers get set before a keymap can
see events and reinterpret them. Kind of a shame, but better than
getting spurious tags. I guess you could change simple.el to do
something akin to what xterm-mouse-mode does, but it doesn't strike me
as necessary.

"C-x @ m mouse-1 mouse-1" *will* call the commands for <M-mouse-1> and
<double-mouse-1>. As with the case of clicks in different windows, even
though my patch doesn't concern itself with this, I do think it's a
flaw worth fixing at some point.

> More generally, for a change this deep and wide, I'd like to
> understand better what exactly are the problems being solved,

That the program's actual behavior doesn't match the documentation,
which describes behavior that reflects how double clicks work on every
other GUI I've ever used.

The docs could just be rewritten to match the program, but imagine what
they'd look like: "Design the command binding of the double click event
to assume that the single-click command has already run, or at least
*some* single-click command using the same mouse button but potentially
different modifier keys, or if not that, then a single-click command for
a different mouse button which is now being held down but hasn't been
held down for as long as this button has. But one of those for sure!"

> and also how can we be sure (by testing or otherwise) we are not
> getting regressions in some use cases. Could you please clarify that?

Unfortunately, I don't think it's possible to add automated regression
tests for this stuff, at least not with ERT. You'd need to have some
programmatic way of generating events from Lisp that get fed into the
src/keyboard.c functions. Without serious additions to the underlying C
layer (or maybe a module?), I don't see how that could happen. And in
general, I think that's a sensible limitation; what if event X got
mapped to a Lisp command which generated a fake event X, which generated
another etc. etc.?

Here's how I've been testing it manually: feed Emacs (patched and
unpatched) as many combinations of mouse actions as I can think up, then
check the lossage file to see if it's interpreting them right. Or better
yet, visit *scratch* in a split frame with another buffer called
*Events*, and eval this form:

    (cl-loop
     (let ((event (read-event)))
       (with-current-buffer "*Events*"
         (insert (prin1-to-string event) "\n\n")
         (goto-char (point-min))))))

You'll see the full (pre-keymap, pre-input-method) event representation
appear immediately for everything you do. Bind 'double-click-time' and
'double-click-fuzz' around it as you please for more test cases.

(If you click around in the continually updating *Events* window, you'll
get a lot of drags, because the text is moving under the cursor between
down and release. This is not new, and a preexisting comment says it's
by design.)

There's no way around the fact that it needs line-by-line scrutiny. But
I went to great lengths to make it lucid and direct so that it won't be
onerous to give it that scrutiny.

> Beyond theoretical (un)cleanliness, what other practical problems did
> you find with the current code and fix in these patches?

I didn't change the code in order to make it cleaner; if I'd needed to
make it dirtier in order to fix the bug, that's what I would have done.
It just happened that the most straightforward approach to fixing it
meant making it cleaner, which I think is nice. (Modifying the code in
place is not straightforward, since the pertinent sections of the
switch/case labyrinth -- which are almost but not quite identical --
inevitably end up having to interact with each other when the more
stringent criteria come into play. File-level static variables start
multiplying out of control at that point.)

As for patch #1, the big one, I explained what it addresses above:
Emacs was doing the wrong thing both according to its documentation and
according to my intuition. Now it does the right thing for modifier keys
and interleaved clicks, and (I contend) it does everything else the same
as before.

Here's what the other five patches address, in order:

2/6 mentions an existing limitation on 'double-click-fuzz' in that
variable's manual entry.

3/6 changes some expressions to use the POSN_WINDOW and POSN_POSN
macros that are defined to expand to the same things. (Not very
important, but it makes the expressions readable instead of opaque.)

4/6 closes a weird loophole in the detection of drag events, surely
unintended. See discussion below.

5/6 fixes the Cocoa bug where trackpad swipes got retroactively modified
by keys that weren't pressed yet when the user swiped.

6/6 is a small elaboration on an existing FIXME comment to explain why
the issue is hard to fix. (Also not too important.)

All the patches are self-contained. They can be applied in any
combination.

>
>>  This variable is also the threshold for motion of the mouse to count
>> -as a drag.
>> +as a drag.  (But if the mouse moves from one screen position to
>> +another while the button is held down, it always counts as a drag, no
>> +matter the value of @code{double-click-fuzz}.)
>
> Isn't this an incompatible change?

It's not a change; it already worked that way. And it makes sense that
it works that way -- otherwise, if you had 'double-click-fuzz' set too
high, you couldn't drag to select a region of two adjacent characters.
But the exception to the rule isn't obvious without looking at the code.

My related change (4/6) was to look at windows per se as well as window
positions. Before, a drag starting at position 1 of one window, and
ending at position 1 of another window, wasn't tagged as a drag because
the position values were the same. I think this one should be
uncontroversial (as should the trackpad thing in src/nsterm.m, 5/6).

Daniel

Message #14 received at 43379 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Daniel Koning <dk <at> danielkoning.com>
Cc: 43379 <at> debbugs.gnu.org
Subject: Re: bug#43379: [PATCH] Double-click events can occur without
 preceding single-click events
Date: Wed, 21 Jul 2021 14:45:24 +0200

I've just read this thread and skimmed the patches, and they seem to
make sense to me.  However, when I tried to apply them to test, they
don't apply cleanly any more (since this was almost a year ago,
unfortunately).

Do you have updated versions of the patch sets?  If so, I can test and
get them pushed to Emacs 28.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

Message #17 received at 43379 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Daniel Koning <dk <at> danielkoning.com>
Cc: 43379 <at> debbugs.gnu.org
Subject: Re: bug#43379: [PATCH] Double-click events can occur without
 preceding single-click events
Date: Fri, 12 Nov 2021 09:22:50 +0100

Lars Ingebrigtsen <larsi <at> gnus.org> writes:

> I've just read this thread and skimmed the patches, and they seem to
> make sense to me.  However, when I tried to apply them to test, they
> don't apply cleanly any more (since this was almost a year ago,
> unfortunately).
>
> Do you have updated versions of the patch sets?  If so, I can test and
> get them pushed to Emacs 28.

I've respun the patches below -- some of the code has changed
considerably, so it may not be 100% correct any more.

However, I can't reproduce the original bug report (in either emacs-28
or the current trunk).  Here's the test case:

(let ((double-click-time 500))
  (require 'cl-lib)
  (pop-to-buffer "*Events*")
  (cl-loop
   (let ((event (read-event)))
     (with-current-buffer "*Events*"
       (insert (replace-regexp-in-string
		" .*" ""
		(prin1-to-string event))
	       "\n")
       (goto-char (point-min))))))

I can't get a single instance of a double-mouse-x without a mouse-x
happening before, even with long double-click-times.

Can anybody else reproduce this problem?

diff --git a/doc/emacs/custom.texi b/doc/emacs/custom.texi
index d9d6a68005..92044309ea 100644
--- a/doc/emacs/custom.texi
+++ b/doc/emacs/custom.texi
@@ -2186,8 +2186,12 @@ Mouse Buttons
 
   The symbols for mouse events also indicate the status of the modifier
 keys, with the usual prefixes @samp{C-}, @samp{M-}, @samp{H-},
-@samp{s-}, @samp{A-}, and @samp{S-}.  These always precede @samp{double-}
-or @samp{triple-}, which always precede @samp{drag-} or @samp{down-}.
+@samp{s-}, @samp{A-}, and @samp{S-}.  These always precede
+@samp{double-} or @samp{triple-}, which always precede @samp{drag-} or
+@samp{down-}.  (Two clicks with different modifier keys can never
+produce a double event, no matter how close together the clicks are.
+Otherwise, Emacs could get a @code{double-mouse-1} event without getting
+a @code{mouse-1} event first.)
 
   A frame includes areas that don't show text from the buffer, such as
 the mode line and the scroll bar.  You can tell whether a mouse button
diff --git a/doc/lispref/commands.texi b/doc/lispref/commands.texi
index 6ed46fa6a2..d1471e9221 100644
--- a/doc/lispref/commands.texi
+++ b/doc/lispref/commands.texi
@@ -1717,9 +1717,12 @@ Repeat Events
 @cindex triple-click events
 @cindex mouse events, repeated
 
-If you press the same mouse button more than once in quick succession
-without moving the mouse, Emacs generates special @dfn{repeat} mouse
-events for the second and subsequent presses.
+Emacs generates special @dfn{repeat} mouse events to represent actions
+like double and triple clicks.  If you press a button twice in quick
+succession without moving the mouse in between, Emacs will designate the
+second event as a repeat.  (However, if you hold down any modifier keys
+during one press and not the other, Emacs will treat the two events as
+unconnected, and the second event will not be a repeat.)
 
 The most common repeat events are @dfn{double-click} events.  Emacs
 generates a double-click event when you click a button twice; the event
@@ -1793,7 +1796,10 @@ Repeat Events
 clicks to make a double-click.
 
 This variable is also the threshold for motion of the mouse to count
-as a drag.
+as a drag.  (But if the mouse moves from one window to another while
+the button is held down, or from one screen position to another, it
+always counts as a drag, no matter the value of
+@code{double-click-fuzz}.)
 @end defopt
 
 @defopt double-click-time
diff --git a/etc/NEWS b/etc/NEWS
index 0057fbdcbf..234059a781 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -138,6 +138,16 @@ LRI).  The new command 'highlight-confusing-reorderings' finds and
 highlights segments of buffer text whose reordering for display is
 suspicious and could be malicious.
 
++++
+** Repeat events are now produced only when the modifier keys are the same.
+Before, when the user pressed the same mouse button repeatedly within
+the bounds specified by 'double-click-fuzz' and 'double-click-time',
+it always produced a 'double-' or 'triple-' event, even if the user
+was holding down modifier keys on one click and not another.  This
+meant that it was possible for Emacs to read a double-click event
+without reading the same kind of single-click event first.  Emacs now
+looks at modifier keys to determine if a mouse event is a repeat.
+
 
 
 ** Emacs server and client changes.
diff --git a/src/keyboard.c b/src/keyboard.c
index de9805df32..c30b980ba2 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -351,6 +351,7 @@ #define READABLE_EVENTS_IGNORE_SQUEEZABLES	(1 << 2)
 static Lisp_Object read_char_x_menu_prompt (Lisp_Object,
                                             Lisp_Object, bool *);
 static Lisp_Object read_char_minibuf_menu_prompt (int, Lisp_Object);
+static intmax_t mouse_repeat_count (const struct input_event *);
 static Lisp_Object make_lispy_event (struct input_event *);
 static Lisp_Object make_lispy_movement (struct frame *, Lisp_Object,
                                         enum scroll_bar_part,
@@ -5062,18 +5063,6 @@ #define ISO_FUNCTION_KEY_OFFSET 0xfe00
    the down mouse event.  */
 static Lisp_Object frame_relative_event_pos;
 
-/* Information about the most recent up-going button event:  Which
-   button, what location, and what time.  */
-
-static int last_mouse_button;
-static int last_mouse_x;
-static int last_mouse_y;
-static Time button_down_time;
-
-/* The number of clicks in this multiple-click.  */
-
-static int double_click_count;
-
 /* X and Y are frame-relative coordinates for a click or wheel event.
    Return a Lisp-style event list.  */
 
@@ -5388,6 +5377,139 @@ make_scroll_bar_position (struct input_event *ev, Lisp_Object type)
 		builtin_lisp_symbol (scroll_bar_parts[ev->part]));
 }
 
+/* Whether the next click (or wheel event) should be treated as a
+   single no matter what, even if a matching prior event would make it
+   a repeat.  This gets flipped on when a keystroke or drag event
+   comes in: double clicks can't extend across one of those.  */
+
+static bool interrupt_next_repeat_click;
+
+/* If EVENT is a repeat, return the number of consecutive mouse events
+   so far.  Return 1 otherwise.  In the background, keep a record of
+   where we are in the current sequence of repeats.
+
+   This should only receive a pointer to an event of an applicable
+   kind -- namely, a button-down, button-up, or wheel event.  */
+
+static intmax_t
+mouse_repeat_count (const struct input_event *event)
+{
+  /* Keep persistent information about any chain of repeat events we
+     might be in the middle of.  */
+
+  static ENUM_BF (event_kind) kind;
+  static unsigned code;
+  static unsigned keys;
+  static unsigned wheel_dir;
+
+  static Time timeout_start;
+  static EMACS_INT x, y;
+
+  static intmax_t count;
+
+  /* Analyze the new event that came in.  */
+
+  unsigned new_keys = event->modifiers & CHAR_MODIFIER_MASK;
+  unsigned new_wheel_dir;
+
+  Time interval;
+  EMACS_INT new_x, new_y, offset;
+
+  bool is_wheel = (event->kind == WHEEL_EVENT
+                   || event->kind == HORIZ_WHEEL_EVENT);
+  bool is_button = !is_wheel;
+  bool is_button_up = (is_button && (event->modifiers & up_modifier));
+
+  if (is_wheel)
+    new_wheel_dir = (event->modifiers & (down_modifier | up_modifier));
+  else
+    new_wheel_dir = 0;
+
+  /* We need to update timestamp and position after both repeat and
+     non-repeat events.  Make the relevant comparisons in advance,
+     then do the update immediately.  */
+
+  interval = event->timestamp - timeout_start;
+  if (!is_button_up)
+    timeout_start = event->timestamp;
+
+  new_x = XFIXNUM (event->x);
+  new_y = XFIXNUM (event->y);
+  offset = max (eabs (new_x - x), eabs (new_y - y));
+  x = new_x;
+  y = new_y;
+
+  /* Is this a repeat?  Start checking for conditions that imply
+     otherwise.  */
+
+  if (interrupt_next_repeat_click && !is_button_up)
+    {
+      interrupt_next_repeat_click = false;
+      goto not_a_repeat;
+    }
+
+  if (event->kind != kind || event->code != code || new_keys != keys
+      || new_wheel_dir != wheel_dir)
+    goto not_a_repeat;
+
+  if (is_button_up)
+    /* That's it for button-up events.  At this point, we declare that
+       it's a repeat that should inherit the count of the preceding
+       button-down.  */
+    return count;
+
+  if (FIXNATP (Vdouble_click_time))
+    {
+      if (interval >= XFIXNAT (Vdouble_click_time))
+        goto not_a_repeat;
+    }
+  else if (!EQ (Vdouble_click_time, Qt))
+    goto not_a_repeat;
+
+  {
+    /* On window-system frames, use the value of 'double-click-fuzz'
+       as is.  On other frames, interpret it as a multiple of 1/8
+       characters.  */
+    struct frame *f;
+    intmax_t fuzz;
+
+    if (WINDOWP (event->frame_or_window))
+      f = XFRAME (XWINDOW (event->frame_or_window)->frame);
+    else if (FRAMEP (event->frame_or_window))
+      f = XFRAME (event->frame_or_window);
+    else
+      emacs_abort ();
+
+    if (FRAME_WINDOW_P (f))
+      fuzz = double_click_fuzz;
+    else
+      fuzz = double_click_fuzz / 8;
+
+    if (offset > fuzz)
+      goto not_a_repeat;
+  }
+
+  /* We've ruled out everything that could disqualify it as a repeat,
+     so treat it as one.  */
+  count++;
+  return count;
+
+ not_a_repeat:
+  /* Base a new repeat chain off of this event.  */
+  count = 1;
+  kind = event->kind;
+  code = event->code;
+  keys = new_keys;
+  wheel_dir = new_wheel_dir;
+
+  if (is_button_up)
+    /* A button-up event should cut off a chain when it doesn't match
+       the last event, but it shouldn't start its own chain.  */
+    interrupt_next_repeat_click = true;
+
+  return count;
+}
+
 /* Given a struct input_event, build the lisp event which represents
    it.  If EVENT is 0, build a mouse movement event from the mouse
    movement buffer, which should have a movement event in it.
@@ -5512,7 +5634,7 @@ make_lispy_event (struct input_event *event)
 	if ((event->code) == 040
 	    && event->modifiers & shift_modifier)
 	  c |= shift_modifier;
-	button_down_time = 0;
+	interrupt_next_repeat_click = true;
 	XSETFASTINT (lispy_c, c);
 	return lispy_c;
       }
@@ -5531,7 +5653,7 @@ make_lispy_event (struct input_event *event)
       /* A function key.  The symbol may need to have modifier prefixes
 	 tacked onto it.  */
     case NON_ASCII_KEYSTROKE_EVENT:
-      button_down_time = 0;
+      interrupt_next_repeat_click = true;
 
       for (i = 0; i < ARRAYELTS (lispy_accent_codes); i++)
 	if (event->code == lispy_accent_codes[i])
@@ -5617,10 +5739,10 @@ make_lispy_event (struct input_event *event)
 #endif
       {
 	int button = event->code;
-	bool is_double;
 	Lisp_Object position;
 	Lisp_Object *start_pos_ptr;
 	Lisp_Object start_pos;
+	int repeat_count;
 
 	position = Qnil;
 
@@ -5709,57 +5831,20 @@ make_lispy_event (struct input_event *event)
 	    mouse_syms = larger_vector (mouse_syms, incr, -1);
 	  }
 
+	repeat_count = mouse_repeat_count (event);
+	if (repeat_count == 2)
+	  event->modifiers |= double_modifier;
+	else if (repeat_count >= 3)
+	  event->modifiers |= triple_modifier;
+
 	start_pos_ptr = aref_addr (button_down_location, button);
 	start_pos = *start_pos_ptr;
 	*start_pos_ptr = Qnil;
 
-	{
-	  /* On window-system frames, use the value of
-	     double-click-fuzz as is.  On other frames, interpret it
-	     as a multiple of 1/8 characters.  */
-	  struct frame *f;
-	  intmax_t fuzz;
-
-	  if (WINDOWP (event->frame_or_window))
-	    f = XFRAME (XWINDOW (event->frame_or_window)->frame);
-	  else if (FRAMEP (event->frame_or_window))
-	    f = XFRAME (event->frame_or_window);
-	  else
-	    emacs_abort ();
-
-	  if (FRAME_WINDOW_P (f))
-	    fuzz = double_click_fuzz;
-	  else
-	    fuzz = double_click_fuzz / 8;
-
-	  is_double = (button == last_mouse_button
-		       && (eabs (XFIXNUM (event->x) - last_mouse_x) <= fuzz)
-		       && (eabs (XFIXNUM (event->y) - last_mouse_y) <= fuzz)
-		       && button_down_time != 0
-		       && (EQ (Vdouble_click_time, Qt)
-			   || (FIXNATP (Vdouble_click_time)
-			       && (event->timestamp - button_down_time
-				   < XFIXNAT (Vdouble_click_time)))));
-	}
-
-	last_mouse_button = button;
-	last_mouse_x = XFIXNUM (event->x);
-	last_mouse_y = XFIXNUM (event->y);
-
 	/* If this is a button press, squirrel away the location, so
            we can decide later whether it was a click or a drag.  */
 	if (event->modifiers & down_modifier)
 	  {
-	    if (is_double)
-	      {
-		double_click_count++;
-		event->modifiers |= ((double_click_count > 2)
-				     ? triple_modifier
-				     : double_modifier);
-	      }
-	    else
-	      double_click_count = 1;
-	    button_down_time = event->timestamp;
 	    *start_pos_ptr = Fcopy_alist (position);
 	    frame_relative_event_pos = Fcons (event->x, event->y);
 	    ignore_mouse_drag_p = false;
@@ -5796,6 +5881,8 @@ make_lispy_event (struct input_event *event)
 		       && xdiff < double_click_fuzz
 		       && - double_click_fuzz < ydiff
 		       && ydiff < double_click_fuzz
+		       /* If we jumped windows, it has to be a drag.  */
+		       && EQ (POSN_WINDOW (start_pos), POSN_WINDOW (position))
 		       /* Maybe the mouse has moved a lot, caused scrolling, and
 			  eventually ended up at the same screen position (but
 			  not buffer position) in which case it is a drag, not
@@ -5812,7 +5899,7 @@ make_lispy_event (struct input_event *event)
 				   Fcar (position))))) /* Different window */
 		  {
 		    /* Mouse has moved enough.  */
-		    button_down_time = 0;
+		    interrupt_next_repeat_click = true;
 		    click_or_drag_modifier = drag_modifier;
 		  }
 		else if (((!EQ (Fcar (start_pos), Fcar (position)))
@@ -5853,14 +5940,8 @@ make_lispy_event (struct input_event *event)
 		  }
 	      }
 
-	    /* Don't check is_double; treat this as multiple if the
-	       down-event was multiple.  */
-	    event->modifiers
-	      = ((event->modifiers & ~up_modifier)
-		 | click_or_drag_modifier
-		 | (double_click_count < 2 ? 0
-		    : double_click_count == 2 ? double_modifier
-		    : triple_modifier));
+	    event->modifiers = ((event->modifiers & ~up_modifier)
+				| click_or_drag_modifier);
 	  }
 	else
 	  /* Every mouse event should either have the down_modifier or
@@ -5880,7 +5961,7 @@ make_lispy_event (struct input_event *event)
 	  if (event->modifiers & drag_modifier)
 	    return list3 (head, start_pos, position);
 	  else if (event->modifiers & (double_modifier | triple_modifier))
-	    return list3 (head, position, make_fixnum (double_click_count));
+	    return list3 (head, position, make_fixnum (repeat_count));
 	  else
 	    return list2 (head, position);
 	}
@@ -5891,6 +5972,7 @@ make_lispy_event (struct input_event *event)
       {
 	Lisp_Object position;
 	Lisp_Object head;
+	int repeat_count;
 
 	/* Build the position as appropriate for this mouse click.  */
 	struct frame *f = XFRAME (event->frame_or_window);
@@ -5903,38 +5985,15 @@ make_lispy_event (struct input_event *event)
 	position = make_lispy_position (f, event->x, event->y,
 					event->timestamp);
 
-	/* Set double or triple modifiers to indicate the wheel speed.  */
 	{
-	  /* On window-system frames, use the value of
-	     double-click-fuzz as is.  On other frames, interpret it
-	     as a multiple of 1/8 characters.  */
-	  struct frame *fr;
-	  intmax_t fuzz;
 	  int symbol_num;
-	  bool is_double;
-
-	  if (WINDOWP (event->frame_or_window))
-	    fr = XFRAME (XWINDOW (event->frame_or_window)->frame);
-	  else if (FRAMEP (event->frame_or_window))
-	    fr = XFRAME (event->frame_or_window);
-	  else
-	    emacs_abort ();
-
-	  fuzz = FRAME_WINDOW_P (fr)
-	    ? double_click_fuzz : double_click_fuzz / 8;
 
 	  if (event->modifiers & up_modifier)
-	    {
 	      /* Emit a wheel-up event.  */
-	      event->modifiers &= ~up_modifier;
-	      symbol_num = 0;
-	    }
+	    symbol_num = 0;
 	  else if (event->modifiers & down_modifier)
-	    {
 	      /* Emit a wheel-down event.  */
-	      event->modifiers &= ~down_modifier;
-	      symbol_num = 1;
-	    }
+	    symbol_num = 1;
 	  else
 	    /* Every wheel event should either have the down_modifier or
 	       the up_modifier set.  */
@@ -5943,32 +6002,20 @@ make_lispy_event (struct input_event *event)
           if (event->kind == HORIZ_WHEEL_EVENT)
             symbol_num += 2;
 
-	  is_double = (last_mouse_button == - (1 + symbol_num)
-		       && (eabs (XFIXNUM (event->x) - last_mouse_x) <= fuzz)
-		       && (eabs (XFIXNUM (event->y) - last_mouse_y) <= fuzz)
-		       && button_down_time != 0
-		       && (EQ (Vdouble_click_time, Qt)
-			   || (FIXNATP (Vdouble_click_time)
-			       && (event->timestamp - button_down_time
-				   < XFIXNAT (Vdouble_click_time)))));
-	  if (is_double)
-	    {
-	      double_click_count++;
-	      event->modifiers |= ((double_click_count > 2)
-				   ? triple_modifier
-				   : double_modifier);
-	    }
+	  /* Set double or triple modifiers to indicate the wheel
+	     speed.  */
+	  repeat_count = mouse_repeat_count (event);
+	  if (repeat_count == 2)
+	    event->modifiers |= double_modifier;
+	  else if (repeat_count >= 3)
+	    event->modifiers |= triple_modifier;
 	  else
-	    {
-	      double_click_count = 1;
-	      event->modifiers |= click_modifier;
-	    }
+	    /* Non-repeat wheel events are tagged as clicks.  */
+	    event->modifiers |= click_modifier;
 
-	  button_down_time = event->timestamp;
-	  /* Use a negative value to distinguish wheel from mouse button.  */
-	  last_mouse_button = - (1 + symbol_num);
-	  last_mouse_x = XFIXNUM (event->x);
-	  last_mouse_y = XFIXNUM (event->y);
+	  /* The Lisp side expects to see direction information in
+	     'symbol_num', but not in the modifier bits.  */
+	  event->modifiers &= ~(down_modifier | up_modifier);
 
 	  /* Get the symbol we should use for the wheel event.  */
 	  head = modify_event_symbol (symbol_num,
@@ -5981,10 +6028,10 @@ make_lispy_event (struct input_event *event)
 	}
 
         if (NUMBERP (event->arg))
-          return list4 (head, position, make_fixnum (double_click_count),
+          return list4 (head, position, make_fixnum (repeat_count),
                         event->arg);
 	else if (event->modifiers & (double_modifier | triple_modifier))
-	  return list3 (head, position, make_fixnum (double_click_count));
+	  return list3 (head, position, make_fixnum (repeat_count));
 	else
 	  return list2 (head, position);
       }
diff --git a/src/nsterm.m b/src/nsterm.m
index 1f17a30272..b11fcb5ed5 100644
--- a/src/nsterm.m
+++ b/src/nsterm.m
@@ -291,6 +291,7 @@ - (NSColor *)colorUsingDefaultColorSpace
 static NSAutoreleasePool *outerpool;
 static struct input_event *emacs_event = NULL;
 static struct input_event *q_event_ptr = NULL;
+static int last_real_wheel_modifier_keys = 0;
 static int n_emacs_events_pending = 0;
 static NSMutableArray *ns_pending_files, *ns_pending_service_names,
   *ns_pending_service_args;
@@ -6559,8 +6560,13 @@ - (void)mouseDown: (NSEvent *)theEvent
           int lines = 0;
           int scrollUp = NO;
 
-          /* FIXME: At the top or bottom of the buffer we should
-           * ignore momentum-phase events.  */
+          /* FIXME: At the top or bottom of the buffer, we should
+           * ignore momentum-phase events that are bound to scrolling
+           * the buffer down or up respectively.  But since this code
+           * doesn't know about bindings and the keymap code doesn't
+           * know about wheel momentum, that doesn't seem to be
+           * possible yet.  */
+
           if (! ns_use_mwheel_momentum
               && [theEvent momentumPhase] != NSEventPhaseNone)
             return;
@@ -6645,6 +6651,21 @@ - (void)mouseDown: (NSEvent *)theEvent
           emacs_event->code = 0;
           emacs_event->modifiers = EV_MODIFIERS (theEvent) |
             (scrollUp ? up_modifier : down_modifier);
+
+          /* If this is a momentum-phase event, ignore the modifier
+           * keys it arrived with.  Inherit the modifier keys from the
+           * last non-momentum event in the sequence.  The user may be
+           * pressing or releasing modifier keys, intending to use
+           * them in the next event, while the wheel events are still
+           * firing.  */
+          if ([theEvent momentumPhase] != NSEventPhaseNone)
+            {
+              emacs_event->modifiers &= ~CHAR_MODIFIER_MASK;
+              emacs_event->modifiers |= last_real_wheel_modifier_keys;
+            }
+          else
+              last_real_wheel_modifier_keys =
+                emacs_event->modifiers & CHAR_MODIFIER_MASK;
 #if MAC_OS_X_VERSION_MIN_REQUIRED < 1070
         }
       else


-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

Message #22 received at 43379 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Daniel Koning <dk <at> danielkoning.com>
Cc: 43379 <at> debbugs.gnu.org
Subject: Re: bug#43379: [PATCH] Double-click events can occur without
 preceding single-click events
Date: Thu, 23 Dec 2021 11:32:33 +0100

Lars Ingebrigtsen <larsi <at> gnus.org> writes:

> I can't get a single instance of a double-mouse-x without a mouse-x
> happening before, even with long double-click-times.
>
> Can anybody else reproduce this problem?

There was no response within a month, so I'm guessing not, and I'm
closing this bug report.  If this is still an issue, please respond to
the debbugs address and we'll reopen.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

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