Support for (box . SIZE) 'cursor-type'

This allows control of the minimum size of a masked image under
which the box cursor becomes hollow.
* buffer.c (cursor-type): Add commentary about (box . SIZE)
'cursor-type'.
* xdisp.c (get_specified_cursor_type): Check for 'cursor-type'
of the form (box . SIZE).
(get_window_cursor_type): Check masked image size for
(box . SIZE) 'cursor-type'.

* doc/emacs/display.texi (Cursor Display):
* doc/emacs/display.texi (Cursor Parameters): Add description
of (box . SIZE) 'cursor-type'.

* etc/NEWS: Mention the new (box . SIZE) 'cursor-type'.

1 files changed, 6 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 6ab6a8aab3b..2c5133e1d24 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -64,6 +64,12 @@ It was declared obsolete in Emacs 27.1.
 
 * Changes in Emacs 28.1
 
+** Support for '(box . SIZE)' cursor-type.
+By default, 'box' cursor always has a filled box shape.  Unless you
+specify cursor-type to be '(box . SIZE)'.  In such case, cursor
+becomes a hollow box if the point is under masked image larger than
+'SIZE' pixels in any dimension.
+
 
 * Editing Changes in Emacs 28.1