bug#22873: #22873 (multiple fake cursors); and, #17684 (crosshairs).

[Keith David Bershatsky <esq@lawlist.com>]

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VERSION:  019.002 [05/02/2019]


CHANGELOG:

- Eliminated the usage of a Lisp_Object within `mc_update_text_area' in favor of
  an array of structs.  [Every Lisp_Object that is eliminated will reduce the
  need for garbage collection.]

- Eliminated `mc/save-window-scroll' when using the multiple-crosshairs library
  written by Magnar Sveen.  [Said function caused non-selected windows to be
  updated during redisplay, resulting in undue slowdown.]

- Miscellaneous changes regarding when/what stderr messages are to appear when
  running M-x trace-redisplay; and, changed the name of the function responsible
  for erasing fake cursors and resetting the cache:  `mc_pre_scroll_clean'.
  Eliminated the message to run "M-x mc-install" when `crosshairs.el` loads.


SETUP:

Step 1:  git clone -b master git://git.sv.gnu.org/emacs.git

Step 2:  In the new emacs folder, go back to an Emacs version from 04/08/2019:

git reset --hard a038df77de7b1aa2d73a6478493b8838b59e4982

Step 3:  From within the new emacs folder created in Step 1, apply the patch:

git apply /path/to/the/patch.diff

Step 4:  ./autogen.sh

Step 5:  ./configure ... [your custom options]

Step 6:  make

Step 7:  make install


USAGE:

- For a minimal working example of built-in fake cursors, type:  M-x mc-test

  ;;; TURN ON FAKE CURSORS (buffer position, cursor-type, cursor color):

  (setq mc-conf '((1 "hbar" "magenta")
                  (2 "bar" "purple")
                  (3 "box" "#00FF00")
                  (4 "hollow" "#0000FF")
                  (5 ("hbar" 3) [1.0 0.0 1.0])
                  (6 ("bar" 3) [0.0 1.0 1.0])
                  (7 "framed" "OrangeRed"))))

  ;;; TURN OFF FAKE CURSORS:

  (setq mc-conf nil)

- To try out the crosshairs feature, type:  M-x +-mode

- To try out built-in fake cursors with Magnar Sveen's multiple-cursors package,
  install that package first.  [If the multiple-cursors package is installed, an
  eval-after-load "multiple-cursors-core" statement within `crosshairs.el` will
  redefine a couple of functions and set up a few keyboard shortcuts.]  If the
  multiple-cursors package by Magnar Sveen is not already installed, then here
  are two easy ways to install that package:

  Type:  M-x mc-install

  OR, evaluate the following snippet:

  (progn
    (require 'package)
    (add-to-list 'package-archives '("melpa" . "http://melpa.milkbox.net/packages/") t)
    (package-initialize)
    (package-refresh-contents)
    (package-install 'multiple-cursors))


TODO:

- Add support for `ch_inactive_windows' and `fc_inactive_windows'.

- When using the multiple fake cursors feature, a fake cursor does not show up at
  zv_p.

- Deal with left/right overwritten glyphs in the w32 and X ports of Emacs.

- Reduce the removal of fake cursors to the bare minimum when scrolling the text
  on the glass directly, and whenever `update_window' is called.

- When an idle-timer fires and point is at the end of a horizontally scrolled
  line in a narrow window, the temporary horizontal scroll is canceled.  Create
  an minimal working example and file a bug report.

- There is a bug affecting an older version of Emacs for the NS port that causes
  partial line flickering when the same characters are grouped together (;;;;;;)
  and MC_GLYPHLESS cursors are above or below -- having the same background color
  as the frame; e.g., black on black (used to erase a glyphless cursor).  The
  partial flickering is only noticeable with rapid fire; e.g., holding down the
  right/left arrow key.  When changing the color of the glyphless cursor, the
  issue is not present.  [@lawlist has verified that the X and HPOS coordinates
  are accurate.]

- There is a bug affecting the recorded `w->mc.lnum_pixel_width` that is
  observable when not running under gdb, but disappears when running under gdb.
  While viewing a folded org-mode buffer, the non-gdb instance had a visible
  line number pixel-width of 44, but Emacs treated it as fluctuating between
  44 and 55 as the cursor was moved to the end of line.  In the gdb instance,
  the visible line number pixel width was 55 with no fluctuation under the same
  conditions as the non-gdb instance.  This appears to be a different bug than
  bug#32177 (current line number shifts one column to the left) because the line
  number of the current line does not shift left, and changing the bidi settings
  did not correct the issue.

- The current test for `auto_hscroll_mode_p' only looks for `current_line` and
  all five related tests are based upon that assumption, which may not be true.

- Multiple Cursors:  If point is in the middle of a composite character, then
  select a fully composed character so that the fake cursor is visible.

- Implement functionality similar to the Lisp multiple-cursors by Magnar Sveen.

- Follow up with the Emacs team re bug#32177; i.e., (Current line number shifts
  one column to the left.)

- Follow up with the Emacs team re bug#32060; i.e., Horizontal Scrolling
  (Current Line):  Wrong line gets h-scrolled.

- Determine if bug #28936 needs to be fixed and help the Emacs team re same.


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