Don't block changes in mouse pointer inside 'track-mouse'

* etc/NEWS:
* doc/lispref/frames.texi (Mouse Tracking): Document the special
effect of setting 'track-mouse' to 'dragging'.

* lisp/textmodes/artist.el (artist-mouse-draw-continously):
* lisp/ruler-mode.el (ruler-mode-mouse-drag-any-column-iteration):
* lisp/mouse-drag.el (mouse-drag-throw):
* lisp/mouse.el (mouse-drag-line): Set 'track-mouse' to 'dragging'
to avoid changes in the shape of the mouse pointer.

* src/xdisp.c (define_frame_cursor1): Don't change the mouse
pointer shape when do_mouse_tracking has the value of 'dragging',
not just any non-nil value.  (Bug#20934)
(syms_of_xdisp): DEFSYM 'dragging'.

4 files changed, 11 insertions, 2 deletions

diff --git a/lisp/mouse-drag.el b/lisp/mouse-drag.el
index 88838edaaed..945c305db7d 100644
--- a/lisp/mouse-drag.el
+++ b/lisp/mouse-drag.el
@@ -222,6 +222,8 @@ To test this function, evaluate:
          (col-scrolling-p (mouse-drag-should-do-col-scrolling)))
     (select-window start-window)
     (track-mouse
+      ;; Don't change the mouse pointer shape while we drag.
+      (setq track-mouse 'dragging)
       (while (progn
                (setq event (read-event)
                      end (event-end event)
diff --git a/lisp/mouse.el b/lisp/mouse.el
index 7854d32eb20..9bb00cb105e 100644
--- a/lisp/mouse.el
+++ b/lisp/mouse.el
@@ -468,8 +468,10 @@ must be one of the symbols `header', `mode', or `vertical'."
                   (setq dragged t)
                   (adjust-window-trailing-edge window growth nil t))
                 (setq last-position position))))))
-      ;; Start tracking.
-      (setq track-mouse t)
+      ;; Start tracking.  The special value 'dragging' signals the
+      ;; display engine to freeze the mouse pointer shape for as long
+      ;; as we drag.
+      (setq track-mouse 'dragging)
       ;; Loop reading events and sampling the position of the mouse.
       (setq exitfun
             (set-transient-map
diff --git a/lisp/ruler-mode.el b/lisp/ruler-mode.el
index f0b012ed2f1..4f68909ed4c 100644
--- a/lisp/ruler-mode.el
+++ b/lisp/ruler-mode.el
@@ -437,6 +437,8 @@ the mouse has been clicked."
   (let ((drags 0)
         event)
     (track-mouse
+      ;; Signal the display engine to freeze the mouse pointer shape.
+      (setq track-mouse 'dragging)
       (while (mouse-movement-p (setq event (read-event)))
         (setq drags (1+ drags))
         (when (eq window (posn-window (event-end event)))
diff --git a/lisp/textmodes/artist.el b/lisp/textmodes/artist.el
index 14cf402a971..a29418e6f84 100644
--- a/lisp/textmodes/artist.el
+++ b/lisp/textmodes/artist.el
@@ -4965,6 +4965,9 @@ The event, EV, is the mouse event."
         (artist-no-rb-set-point1 x1 y1))
     (unwind-protect
         (track-mouse
+          ;; We don't want flickering of mouse pointer shape while we
+          ;; drag the mouse.
+          (setq track-mouse 'dragging)
           (while (or (mouse-movement-p ev)
                      (member 'down (event-modifiers ev)))
             (setq ev-start-pos (artist-coord-win-to-buf