Re: [PATCH] User-defined fringe tooltips (a request for review)

[Vladimir Kazanov <vekazanov@gmail.com>]

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Thanks for looking into this!

> The code in note_mouse_highlight examines
> the buffer text and overlays for text properties whose meaning is to
> display a help-echo string, so why cannot you do the same to look for
> a 'display' property of this specific structure, and extract the
> help-echo directly from there at mouse-highlight time instead of at
> glyph-generation time?

Yes, having Lispy stuff in the glyph_row struct doesn't make sense,
and this is why I was in doubt.

Anyway, a new patch is attached with the approach you suggested (the
way I understood it). I use "struct it" to iterate over the line for
which the fringe indicator is defined, in note_mouse_highlight. The
iterator then pulls out the display spec and saves the last left/right
fringe captions it walked over.

Does that feel right?

Thank you,
Vlad

On Wed, 20 Dec 2023 at 12:32, Eli Zaretskii <eliz@gnu.org> wrote:
>
> > From: Vladimir Kazanov <vekazanov@gmail.com>
> > Date: Tue, 19 Dec 2023 19:38:09 +0000
> >
> > Recently I've been looking into implementing a suggestion from
> > etc/TODO related to fringe indicator tooltips:
> >
> > > ** Allow fringe indicators to display a tooltip
> > > Provide a help-echo property?
> >
> > Attached is a quick and dirty proof-of-concept. The patch extends the
> > display specification with an optional string that would be displayed
> > through either tooltips or the echo area:
> >
> > (overlay-put (make-overlay (point) (point))
> >    'before-string (propertize "x" 'display `(left-fringe right-arrow
> > nil "left fringe test tooltip")))
> >
> > Moving a mouse pointer to the fringe would then display the string in
> > a tooltip on a relevant line.
>
> Thanks.
>
> > To make this work I've extended "struct it" and "struct glyphs_row"
> > with pointers to strings, and added some mouse hover handling in the
> > "note_mouse_highlight function". Obviously, the code needs more checks
> > but I want to confirm the approach with emacs-devel@ first.
> >
> > Happy to hear comments and suggestions about the path taken!
>
> I'm not sure I like to have Lisp_Object members in 'struct glyph_row'.
> I also don't think I understand why you needed to copy the hel-echo
> string to the glyph row.  The code in note_mouse_highlight examines
> the buffer text and overlays for text properties whose meaning is to
> display a help-echo string, so why cannot you do the same to look for
> a 'display' property of this specific structure, and extract the
> help-echo directly from there at mouse-highlight time instead of at
> glyph-generation time?



-- 
Regards,

Vladimir Kazanov

[-- Attachment #2: add-user-fringe-indicator-tooltips.patch --]
[-- Type: text/x-patch, Size: 4078 bytes --]

diff --git a/src/dispextern.h b/src/dispextern.h
index 3a4d6095f73..e8f984e1a71 100644
--- a/src/dispextern.h
+++ b/src/dispextern.h
@@ -2801,6 +2801,12 @@ #define OVERLAY_STRING_CHUNK_SIZE 16
      is in effect, and only in hscrolled windows.  */
   int stretch_adjust;
 
+  /* Left fringe caption (Qnil or a stringp) */
+  Lisp_Object left_user_fringe_caption;
+
+  /* Right fringe caption  (Qnil or a stringp)*/
+  Lisp_Object right_user_fringe_caption;
+
   /* Left fringe bitmap number (enum fringe_bitmap_type).  */
   unsigned left_user_fringe_bitmap : FRINGE_ID_BITS;
 
diff --git a/src/xdisp.c b/src/xdisp.c
index 75d769600c4..5c5d39acde1 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -3265,6 +3265,10 @@ init_iterator (struct it *it, struct window *w,
   /* Clear IT, and set it->object and other IT's Lisp objects to Qnil.
      Other parts of redisplay rely on that.  */
   memclear (it, sizeof *it);
+
+  it->left_user_fringe_caption = Qnil;
+  it->right_user_fringe_caption = Qnil;
+
   it->current.overlay_string_index = -1;
   it->current.dpvec_index = -1;
   it->base_face_id = remapped_base_face_id;
@@ -6127,6 +6131,13 @@ handle_single_display_spec (struct it *it, Lisp_Object spec, Lisp_Object object,
 		face_id = face_id2;
 	    }
 
+	  Lisp_Object caption = Qnil;
+          if (CONSP (XCDR (XCDR (XCDR (spec)))))
+            {
+              caption = XCAR (XCDR (XCDR (XCDR (spec))));
+            }
+
+
 	  /* Save current settings of IT so that we can restore them
 	     when we are finished with the glyph property value.  */
 	  push_it (it, position);
@@ -6150,11 +6161,13 @@ handle_single_display_spec (struct it *it, Lisp_Object spec, Lisp_Object object,
 	    {
 	      it->left_user_fringe_bitmap = fringe_bitmap;
 	      it->left_user_fringe_face_id = face_id;
+              it->left_user_fringe_caption = caption;
 	    }
 	  else
 	    {
 	      it->right_user_fringe_bitmap = fringe_bitmap;
 	      it->right_user_fringe_face_id = face_id;
+              it->right_user_fringe_caption = caption;
 	    }
 	}
 #endif /* HAVE_WINDOW_SYSTEM */
@@ -35720,10 +35733,50 @@ note_mouse_highlight (struct frame *f, int x, int y)
       }
     else
       cursor = FRAME_OUTPUT_DATA (f)->nontext_cursor;
-  else if (part == ON_LEFT_FRINGE || part == ON_RIGHT_FRINGE
-	   || part == ON_VERTICAL_SCROLL_BAR
+  else if (part == ON_LEFT_FRINGE || part == ON_RIGHT_FRINGE) {
+      cursor = FRAME_OUTPUT_DATA (f)->nontext_cursor;
+
+      if (NILP (help_echo_string)) {
+	  /* Translate windows coordinates into vertical window
+             position. */
+	  int hpos, vpos, area;
+	  x_y_to_hpos_vpos (w, x, y, &hpos, &vpos, 0, 0, &area);
+
+	  /* Figure out where the window starts - will need to get to
+             the fringe line */
+	  struct text_pos start_pos;
+	  SET_TEXT_POS_FROM_MARKER (start_pos, w->start);
+
+	  /* Need an iterator to walk through all the properties on
+             the line. Find the line first, reset text from previous
+             lines and then collect the properties on it. */
+	  struct it it;
+	  init_iterator (&it, w, CHARPOS(start_pos), BYTEPOS (start_pos),
+			 NULL, DEFAULT_FACE_ID);
+
+	  /* Walk to the fringe line and reset captions found on the
+             way*/
+	  move_it_by_lines(&it, vpos);
+	  it.left_user_fringe_caption = Qnil;
+	  it.right_user_fringe_caption = Qnil;
+
+	  /* Reset and go through the line. */
+	  move_it_by_lines (&it, 1);
+
+	  /* Output through whatever the user prefers, most likely a
+             tooltip */
+	  if (part == ON_LEFT_FRINGE
+	      && !NILP(it.left_user_fringe_caption))
+	      help_echo_string = it.left_user_fringe_caption;
+	  else if (part == ON_RIGHT_FRINGE
+		   && !NILP(it.right_user_fringe_caption))
+              help_echo_string = it.right_user_fringe_caption;
+      }
+
+  }
+  else if (part == ON_VERTICAL_SCROLL_BAR
 	   || part == ON_HORIZONTAL_SCROLL_BAR)
-    cursor = FRAME_OUTPUT_DATA (f)->nontext_cursor;
+      cursor = FRAME_OUTPUT_DATA (f)->nontext_cursor;
   else
     cursor = FRAME_OUTPUT_DATA (f)->text_cursor;
 #endif