Re: Calculating screen relative X when horizontal scrolling.

[Keith David Bershatsky]

I apologize for having misspoken about using the 3rd argument of 
draw_window_cursor to control the relative x coordinate of the fake cursor.  I 
had forgotten that I actually temporarily hijack w->phys_cursor.x and assign my 
own relative x just prior to calling draw_window_cursor.  Here is a snippet 
from the relevant section of feature requests 17684 (crosshairs) and 22873 
(multiple fake cursors):

  /* Record some of the current values for the cursor and glyph_row. */
  bool phys_cursor_on_p = w->phys_cursor_on_p;
  struct glyph_row *glyph_row = MATRIX_ROW (w->current_matrix, vpos);
  bool cursor_in_fringe_p = glyph_row->cursor_in_fringe_p;
  bool reversed_p = glyph_row->reversed_p;
  ptrdiff_t phys_cursor_x = w->phys_cursor.x;
  ptrdiff_t phys_cursor_y = w->phys_cursor.y;
  ptrdiff_t phys_cursor_hpos = w->phys_cursor.hpos;
  ptrdiff_t phys_cursor_vpos = w->phys_cursor.vpos;
  ptrdiff_t phys_cursor_ascent = w->phys_cursor_ascent;
  ptrdiff_t phys_cursor_height = w->phys_cursor_height;
  ptrdiff_t phys_cursor_width = w->phys_cursor_width;
  enum text_cursor_kinds phys_cursor_type = w->phys_cursor_type;
  /* Hijack w->phys_cursor. */
  w->phys_cursor.x = x;
  w->phys_cursor.y = glyph_row->y;
  w->phys_cursor.hpos = hpos;
  w->phys_cursor.vpos = vpos;
  w->phys_cursor_type = cursor_type;
  w->phys_cursor_ascent = glyph_row->ascent;
  w->phys_cursor_height = glyph_row->height;
  w->phys_cursor_width = cursor_width;

  FRAME_RIF (f)->draw_window_cursor (w, glyph_row, x, y, cursor_type, 
cursor_width, true, active_cursor_p);

  /* Restore the previous values for w->phys_cursor and glyph_row. */
  w->phys_cursor_on_p = phys_cursor_on_p;
  w->phys_cursor.x = phys_cursor_x;
  w->phys_cursor.y = phys_cursor_y;
  w->phys_cursor.hpos = phys_cursor_hpos;
  w->phys_cursor.vpos = phys_cursor_vpos;
  w->phys_cursor_type = phys_cursor_type;
  glyph_row->cursor_in_fringe_p = cursor_in_fringe_p;
  glyph_row->reversed_p = reversed_p;
  w->phys_cursor_ascent = phys_cursor_ascent;
  w->phys_cursor_height = phys_cursor_height;
  w->phys_cursor_width = phys_cursor_width;

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> Date: [10-17-2018 09:25:41] <17 Oct 2018 19:25:41 +0300>
> From: Eli Zaretskii <address@hidden>
> To: Keith David Bershatsky <address@hidden>
> CC: address@hidden
> Subject: Re: Calculating screen relative X when horizontal scrolling.
> 
> > Date:  Tue, 16 Oct 2018 08:41:00 -0700
> > From:  Keith David Bershatsky <address@hidden>
> > Cc:  address@hidden
> >
> > The x coordinate sought will be used as the 3rd argument to 
> > draw_window_cursor in conjunction with feature requests 17684 (crosshairs) 
> > and 22873 (multiple fake cursors).
> >
> > The method of calculation used in the initial post is off by a few pixels 
> > when dealing with each of the fact patterns described.  Here is a sample 
> > _current_ line (miscellaneous characters of varying pixel widths) where my 
> > calculations go awry:
> 
> I'm sorry, I still don't have a clear understanding of the issue.  In
> particular, the implementations of draw_window_cursor method don't use
> the 3rd argument for positioning the cursor.  So I still don't
> understand what you mean by "relative x".