bug#17331: 24.4.50; `display' text property with mouse movement - tooltip not updated

[Drew Adams]

Put these lines in a buffer.

;; AAAAAAAAAAAAAAAAAAAAA
;; BBBBBBBBBBBBBBBBBBBBB

Use these sexps to add a `help-echo' property, with point on the first
line for the first sexp and point on the second line for the second
sexp.

(add-text-properties
 (line-beginning-position) (line-end-position)
 '(mouse-face highlight help-echo "1111111111111111"))

(add-text-properties
 (line-beginning-position) (line-end-position)
 '(mouse-face highlight help-echo "2222222222222222"))

Now move the mouse over the first line, then the second line, without
moving it outside the line text (i.e., keep it within the mouse-face
area).

When you move the mouse between the lines, the tooltip text changes, as
it should.

Now do the same thing, but using these sexps:

(add-text-properties
 (line-beginning-position) (line-end-position)
 '(mouse-face highlight help-echo
   (propertize " " 'display "1111111111111111")))

(add-text-properties
 (line-beginning-position) (line-end-position)
 '(mouse-face highlight help-echo
   (propertize " " 'display "2222222222222222")))

The tooltip does not change as it should.  To get it to change, you need
to move the mouse outside of the current line's propertized text before
moving it over the other line's text.

This is a bug, IMO, and should be fixed.  Tooltip info can be important.
Among other use cases, consider a tooltip that displays a thumbnail
image upon mouseover of an image file in Dired.

If you will not consider this a bug, please consider it an enhancement
request.


Add a `help-echo' property to some text.  Add a different `help-echo'
property to some text that is contiguous with it, or is directly above
or below it (different line), so you can move the mouse from one to the
other without moving it over text that does not have property
`help-echo'.



In GNU Emacs 24.4.50.1 (i686-pc-mingw32)
 of 2014-04-21 on ODIEONE
Bzr revision: 117005 dancol@dancol.org-20140421180019-po4wdeg7gqvvlh5d
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --prefix=/c/Devel/emacs/snapshot/trunk
 --enable-checking=yes,glyphs 'CFLAGS=-O0 -g3'
 LDFLAGS=-Lc:/Devel/emacs/lib 'CPPFLAGS=-DGC_MCHECK=1
 -Ic:/Devel/emacs/include''