Re: Moving point after character when clicking latter half of it

[Eli Zaretskii]

> From: Moritz Maxeiner <mm@ucw.sh>
> Cc: emacs-devel@gnu.org
> Date: Sun, 09 Jul 2023 14:44:28 +0200
> 
> > The right place is in buffer_posn_from_coords.  The change will be
> > more complex there, but there's no way around this, since we want this
> > change to affect only mouse clicks.
> 
> I am not surprised, given that I know little about Emacs internals at this 
> time. Thank you for the explanation. After looking at it a bit more I'm not 
> sure if/how it can be accomplished without any modifications to 
> move_it_in_display_line_to, given that it uses/modifies the iterator in many 
> places and afaict we don't have access to glyph width outside of it.

That's not true.  buffer_posn_from_coords calls several functions of
the move_it_* family, including move_it_in_display_line_to itself, and
the information that your proposed patch accessed via it->pixel_width
is available to buffer_posn_from_coords through the 'struct it'
variable it passes to those move_it_* functions.  The only
complication is that you might need to call these functions more
times, to asses whether this or the next glyph are closer to the click
coordinates.

> Would adding another option to move_it_in_display_line_to be acceptable? That 
> way only functions that explicitly select the new halfway behavior, like I 
> did 
> with buffer_posn_from_coords in the new version of the poc patch.

I don't see how this would work.  buffer_posn_from_coords calls
move_it_to and move_it_in_display_line, it doesn't call
move_it_in_display_line_to directly.  Are you suggesting to copy all 3
of those functions, and only change them to account for this minor
quirk?  That would be a terribly inelegant solution, since those
functions are quite large and complex.

> That's good to hear. With respect to mouse dragging: Specifically in the case 
> that it's used to select text, yes, I would also like it to use the new 
> halfway behavior in that case, but I have not yet found where in emacs' 
> source 
> code that change would need to happen.

Dragging is handled by the same code: all we need is to know the
beginning and the end buffer position.  I was more asking about user
expectations: those could be different when clicking to move point and
when dragging.