Selecting the cursor type when using an overlay 'cursor property

Question

The documentation for the 'cursor overlay property does not discuss methods for altering the type of cursor that is used when point is on a particular overlay: https://www.gnu.org/software/emacs/manual/html_node/elisp/Special-Properties.html The default overlay cursor type is hollow.

Is there a way for a user to select the type of cursor that is displayed when point is on a particular overlay? E.g., box; bar; (bar . [WIDTH]); hbar; (hbar . [WIDTH])

The following example creates an overlay using an xpm image at the end of the current line, which requires an Emacs version that supports xpm images. The test was performed with a default Emacs installation -- i.e., a white buffer background and a black cursor color -- the hollow cursor outline can be easily seen in this example.

(let ((xpm--pilcrow
       (propertize " " 'cursor t 'display
         `(image :type xpm :mask nil :ascent center :data
         "/* XPM */
         static char * pilcrow_plain_xpm[] = {
         \"11 20 2 1\",
         \". c white\",
         \"+ c cyan\",
         \"...........\",
         \"...........\",
         \"...........\",
         \"...........\",
         \"...++++++..\",
         \"..++++.+...\",
         \"..++++.+...\",
         \"..++++.+...\",
         \"...+++.+...\",
         \".....+.+...\",
         \".....+.+...\",
         \".....+.+...\",
         \".....+.+...\",
         \".....+.+...\",
         \"...........\",
         \"...........\",
         \"...........\",
         \"...........\",
         \"...........\",
         \"...........\"};"))))
  (overlay-put (make-overlay (point-at-eol) (point-at-eol)) 'after-string xpm--pilcrow))

Answer 1

The following is a partial workaround to prevent the hollow outline around the primary xpm; and, it serves to create the visual appearance of a cursor-type 'bar. It is achieved by creating an xpm image that is one (1) pixel in width and whatever the chosen height happens to be (in this example 20 pixels high). The color of the one-pixel wide image should match the buffer background -- this effectively creates a very thin xpm image that is invisible because it blends in with the buffer's background. The result is a visual vertical bar when the cursor touches it and it works with a blinking cursor. The concatenated xpm does not get a hollow cursor. This example reduces the concatenated image by one (1) pixel in width to compensate for the new xpm that is added to the left.

(let* (
    (xpm--cursor-vbar
      (propertize " " 'cursor t 'display
        `(image :type xpm :mask nil :ascent center :data
        "/* XPM */
        static char * cursor_vbar_xpm[] = {
        \"1 20 1 1\",
        \"+ c white\",
        \"+\",
        \"+\",
        \"+\",
        \"+\",
        \"+\",
        \"+\",
        \"+\",
        \"+\",
        \"+\",
        \"+\",
        \"+\",
        \"+\",
        \"+\",
        \"+\",
        \"+\",
        \"+\",
        \"+\",
        \"+\",
        \"+\",
        \"+\"};")))
    (xpm--pilcrow
      (propertize " " 'cursor t 'display
        `(image :type xpm :mask nil :ascent center :data
        "/* XPM */
        static char * pilcrow_plain_xpm[] = {
        \"10 20 2 1\",
        \". c white\",
        \"+ c cyan\",
        \"..........\",
        \"..........\",
        \"..........\",
        \"..........\",
        \"..++++++..\",
        \".++++.+...\",
        \".++++.+...\",
        \".++++.+...\",
        \"..+++.+...\",
        \"....+.+...\",
        \"....+.+...\",
        \"....+.+...\",
        \"....+.+...\",
        \"....+.+...\",
        \"..........\",
        \"..........\",
        \"..........\",
        \"..........\",
        \"..........\",
        \"..........\"};"))) )
  (overlay-put (make-overlay (point-at-eol) (point-at-eol)) 'after-string
    (concat xpm--cursor-vbar xpm--pilcrow)) )