Re: Obtain X / HPOS with move_it_to at eol when buffer-display-table line-feed

[Keith David Bershatsky <esq@lawlist.com>]

Fake cursors are created/erased by hijacking w->phys_cursor.x/y/hpos/vpos and calling either erase_phys_cursor or draw_window_cursor.  The creation of a glyph/character on top of the cursor is optional so that a floating cursor anywhere is possible if so desired.

With respect to eol pilcrows, move_it_to gives X and HPOS coordinates for an invisible \n to the right of the pilcrow.  We essentially have ¶\n, and IT cannot see the pilcrow.  The X and HPOS returned by move_it_to gives us ¶|\n instead of |¶\n.  Stated another way, X and HPOS are reported as being on the end of the pilcrow, instead of the beginning of the pilcrow.

My preference would be to continue using the built-in method for drawing/erasing cursors -- i.e., let erase_phys_cursor and draw_window_cursor do all the work for us, and we only need to give them precise coordinates (x/y/hpos/vpos).

Perhaps there is some way to help move_it_to see the pilcrow, or at least pretend that it exists?

  /* EXAMPLES of (aref buffer-display-table ?\n):  [(182 . 127) 10]; [182 10]; [10] */
  Lisp_Object buffer_display_table = BVAR (b, display_table);
  bool buffer_display_table_p = !NILP (buffer_display_table);
  Lisp_Object line_feed_vector;
  if (buffer_display_table_p)
    line_feed_vector = Faref (buffer_display_table, make_number (10));
  /* Reset it.current_x and it.hpos to the desired locations. */
  if (FETCH_BYTE (IT_BYTEPOS (it)) == '\n'
      && buffer_display_table_p
      && VECTORP (line_feed_vector)
      && ASIZE (line_feed_vector) > 1)
   {
     it.current_x = ABRACADABRA_X;
     it.hpos = ABRACADABRA_HPOS;
   }

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DATE:  [08-30-2017 09:51:56] <30 Aug 2017 19:51:56 +0300>
FROM:  Eli Zaretskii <eliz@gnu.org>
> 
> * * *
> 
> When you say "X POS for any particular eol pilcrow", do you mean the x
> coordinate of the beginning of the pilcrow or of its end?
> 
> And what do you get instead when you use move_it_to like you show?
> 
> Also, why do you care about the exact coordinate of the pilcrow?  You
> could simply reach it and then do there whatever you want, no matter
> what is the coordinate.
> 
> * * *