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

[Po Lu]

Moritz Maxeiner <mm@ucw.sh> writes:

> I'm not clear on why that would make it wrong (as in incorrect semantics). 
> It's definitely inefficient (though I've not noticed the overhead in 
> practice), 
> which is why I asked if there's a more elegant solution.

The overhead is apparent when options such as
`mouse-drag-and-drop-region' are enabled and the connection to the X
server is slow.

> Which this is, thank you very much for pointing that out. I've changed that 
> part of the patch accordingly, though this does unfortunately mean that a new 
> function is required, due to multiple places setting the glyph rectangle as 
> it 
> relates to dragging.

I find that difficult to believe.  Would you please describe the other
callers of `remember_mouse_glyph' that make adjustments there
impossible?

I asked you to make the change in `remember_mouse_glyph' because that
would avoid the need to modify each of the *term.[cm] files
individually.  Replacing it with a different function would miss the
point of the change.

> Assuming this version of the implementation meets muster I will work
> on the etc/NEWS entry and can look into adding something to
> (elisp)Accessing Mouse, as well.

Several other comments below:

> +/* Function to bisect `glyph` into left and right halves, then
> +   replace it with the half in which `x` is.  */
> +
> +static void
> +x_vertical_bisect_glyph(XRectangle *glyph, int x)
> +{
> +  int halfwidth = glyph->width / 2;
> +  glyph->width = halfwidth;
> +
> +  int bisection = glyph->x + halfwidth;
> +  if (x > bisection)
> +    glyph->x = bisection;
> +}

Please follow the GNU coding standards for both function declarators and
comments, by capitalizing (not quoting) arguments which appear in the
commentary, and placing a space between the identifier name and the
opening parentheses of the parameter type list.  Also, use the active
voice when describing the behavior of a function within its commentary:

/* Replace *GLYPH, a rectangle containing the bounds of a glyph, with
   the half of the rectangle containing the position X.  */

static void
x_vertical_bisect_glyph (XRectangle *glyph, int x)
{
  /* ... */
}

In addition, we don't use Markdown style quotes for code.  When quoting
identifier names in the future, either write:

  /* `foo' is used to perform ...  */

or

  /* 'foo' is used to perform ...  */

>  /* Function to report a mouse movement to the mainstream Emacs code.
>     The input handler calls this.
>  
> @@ -14218,6 +14232,8 @@ x_note_mouse_movement (struct frame *frame, const 
> XMotionEvent *event,
>        note_mouse_highlight (frame, event->x, event->y);
>        /* Remember which glyph we're now on.  */
>        remember_mouse_glyph (frame, event->x, event->y, r);
> +      if (mouse_prefer_closest_glyph)
> +        x_vertical_bisect_glyph(r, event->x);
>        dpyinfo->last_mouse_glyph_frame = frame;
>        return true;
>      }
> @@ -14382,6 +14398,8 @@ x_fast_mouse_position (struct frame **fp, int insist, 
> Lisp_Object *bar_window,
>         remember_mouse_glyph (f1, win_x, win_y,
>                               &dpyinfo->last_mouse_glyph);
>         dpyinfo->last_mouse_glyph_frame = f1;
> +       if (mouse_prefer_closest_glyph)
> +         x_vertical_bisect_glyph(&dpyinfo->last_mouse_glyph, win_x);
>  
>         *bar_window = Qnil;
>         *part = scroll_bar_nowhere;
> @@ -14733,6 +14751,8 @@ XTmouse_position (struct frame **fp, int insist, 
> Lisp_Object *bar_window,
>           dpyinfo = FRAME_DISPLAY_INFO (f1);
>           remember_mouse_glyph (f1, win_x, win_y, &dpyinfo->last_mouse_glyph);
>           dpyinfo->last_mouse_glyph_frame = f1;
> +         if (mouse_prefer_closest_glyph)
> +           x_vertical_bisect_glyph(&dpyinfo->last_mouse_glyph, win_x);

Please place a space between the identifier name and the opening brace
of each function call.

However, implementing this feature shouldn't need changes to xterm.c at
all.  Please make the change in `remember_mouse_glyph', not in window
system specific code.