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

From: Keith David Bershatsky <[email-masked]>
Date: Mon, 08 Apr 2019 21:03:20 -0700

This is version 018.000 of a proof concept for multiple fake cursors and crosshairs.

Special thanks to Eli Z. and Alan T. for helping me out on numerous issues over the past few months -- greatly appreciated!!!

VERSION:

- 018.000 [04/08/2019]

CHANGELOG:

- Creation of fake cursors now immediately follows calls to `draw_glyphs'.

- Removal of fake cursors occurs prior to Emacs scrolling the text on the glass
  directly and at the outset of `update_window'.

- The NS port now automatically redraws fake cursors that got erased because they
  were left/right overwritten glyphs, but work still needs to be done on the w32
  and X ports.  The future plan of attack for the w32 and X ports is probably
  similar to the NS port; i.e., left/right overwritten glyphs have their strings
  tagged during `mc_draw_glyphs' and are dealt with on a per port basis when
  FRAME_RIF (f)->mc_scribe_string is called.

- Semi-duplicate functions have been created so as to reduce the number of entry
  points into the core code base of Emacs.  [This approach enables semi- worry
  free tinkering without the risk of breaking something important.]

- Removal of scroll bars no longer erase fake cursors when windows are resized
  or deleted on the NS and w32 ports.  [I didn't see any issues on an X11 build.]

- Numerous bug fixes, some minor and some major.

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:

- 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 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.