>> > But then we are back at the problem which the buffer-position check
>> > tries to address:
>> >
>> >                        /* 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
>> >                           a click.  */
>> >
>> > IOW, just testing the screen coordinates is not enough.
>> 
>> In my "in short is approximately" I used `mouse_has_moved` but that
>> was an oversimplification: in the new code `mouse_has_moved` doesn't
>> revert to "false" when the mouse returns to the original position,
>> contrary to what happen in the current code.
>
> How exactly does that happen?

Because as soon as `note_mouse_highlight` receives information that the
mouse is outside of the fuzz, the var is set to `false` [ And it's only
set to true when we get the mouse-down event ].

>> The comment above talks about buffer positions (i.e. the Fcar+Fcdr
>> part of the positions), whereas this `EQ` tests the windows, and the
>> only relevant comment I see is
>> 
>>     /* Different window */
>> 
>> which reminds the reader that it's comparing windows but doesn't say why.
>> Did I miss something?
>
> Yes: we can be at the same buffer position, but a different window.

Right, but what's the problem with that?

IIUC the current code can generate a drag between windows if the mouse
has moved to a new screen position, but we never generate a drag between
windows if the mouse ends at the same screen position as it started.

I see now that this was done (in commit
6e2d3bce087d30a535b1f01715d7820576ffe390) to handle the case where
a mouse click causes some window-shuffle, so the up event ends up
pointing into another window.  IOW, a similar problem to the
display-line-number one you just fixed.

I think my code is immune to this problem since with it we only ever
generate a drag event if the mouse actually moved.  Which leads to
a further simplification of the code, see patch below.


        Stefan