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

From: Keith David Bershatsky <[email-masked]>
Date: Tue, 28 May 2019 01:31:55 -0700

VERSION:  020.000 [05/27/2019]

CHANGELOG:

- Consolidated all caches of fake cursors into one master window struct/matrix,
  which is uncoincidentally somewhat similar in design to the glyph_matrix.

- Removing and drawing fake cursors is now mostly limited to the ones that have
  changed since the previous redisplay.  A dry-run of what the prospective
  `w->current_matrix` will be at tail end of `update_window' is performed at the
  outset thereof -- without actually writing any glyphs to the glass.  During
  the dry-run, a new cache of fake cursors is created and it is compared to the
  old cache of fake cursors.  Anything that is different gets erased and just
  the new ones get drawn.  As to scrolling the text on the glass directly
  _before_ `update_window' is called -- `try_window_reusing_current_matrix' and
  `try_window_id' -- fake cursors are erased from min (r.current_y, r.desired_y)
  to the top of the mode-line, and any fake cursors above the min (supra) remain.

- The multiple fake cursors feature now includes a current column check for each
  visible cursor and odd/even column colors are assigned if the user has not
  specified a color preference in the `mc_conf' for the particular cursor being
  drawn.

- Miscellaneous bug fixes.

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:

- Free memory of w->mc_matrix whenever its associated window ceases to exist.

- Consider adding support for different colors when fake cursors are _at_ ZV
  versus _beyond_ ZV, including, but not limited to the right fringe bitmaps for
  a cursor at fringe and a cursor beyond the fringe.

- `mc_ns_clip_to_rect' is not working as expected.  `ns_draw_window_cursor' calls
  `ns_clip_to_rect', which does _not_ take `row->clip` into consideration when
  drawing cursors with `NSRectFill'.  When it comes time to draw glyphs on top of
  the box/hollow family of cursors, `row->clip` is taken into consideration by
  `get_glyph_string_clip'.  Fake cursors can be drawn even though the glyphs
  cannot, resulting in hollow/box family of cursors without text.  The issue can
  be reproduced by calling M-x mc-test and then moving the cursor left/right --
  a thick hbar-looking rectangle forms underneath the characters in the boxes.
  [Reproduction of the issue assumes `mc_ns_intersect_rectangles' is enabled.]
  https://lists.gnu.org/archive/html/emacs-devel/2019-04/msg00009.html

- `mc_ns_draw_overwritten' is not working as expected.  It appears that fake
  cursors are drawn outside of the area clipped, sometimes resulting in cursor
  fragments that are drawn in a different window; e.g., a top/bottom window split
  with the top window having crosshairs active.  Initial attempts at calling
  `mc_ns_clip_to_rect' from within `mc_ns_draw_overwritten' produced flickering
  of lines (presumably in the relevant vicinity).

- Add additional support for `ch_inactive_windows' and `fc_inactive_windows'
  when the variables have a `nil` value.  In such a case, the inactive windows
  should not display the crosshairs and/or visible fill column indicator.

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

- Is there any additional meaningful optimization that can be added to the
  three calls of `mc_pre_scroll_clean'?

- NOTE:  As to `mc_scrolling_window', it would appear that there is no tangible
  benefit to rotating the current/prospective cache of fake cursors to compare
  the data before removing the fake cursors.  When scrolling the display, only
  _some_ lines are copied to new locations.  Areas that are not overwritten may
  have fake cursors and those may not necessarily be removed if desired/current
  matrix glyphs are equal.  The test for `GLYPH_EQUAL_P' does not take into
  consideration the existence of a fake cursor, and the glyph (with a fake cursor)
  may not be updated as a result thereof.  As to lines that are not copied,
  portions may be updated and fake cursors would be removed thereby.

- 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.