Add book-reader: two-page image book viewer

Browser viewer for books stored as folders of page images: two-page
spreads with a GPU-composited 3D page turn, keyboard/wheel/click
navigation, fit-height and fit-width (scroll then flip) modes, a library
of every image folder under the configured root, and per-book reading
progress in localStorage.

rc.book-reader serves it with python3 http.server on 127.0.0.1 from a
runtime dir of symlinks, so the library is never written to. It can be
copied to /etc/rc.d: started as root it re-executes itself as RUNAS.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

4 files changed, 732 insertions, 0 deletions

diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..9efa6fb
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,338 @@
+                    GNU GENERAL PUBLIC LICENSE
+                       Version 2, June 1991
+
+ Copyright (C) 1989, 1991 Free Software Foundation, Inc.,
+ <https://fsf.org/>
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
+                            Preamble
+
+  The licenses for most software are designed to take away your
+freedom to share and change it.  By contrast, the GNU General Public
+License is intended to guarantee your freedom to share and change free
+software--to make sure the software is free for all its users.  This
+General Public License applies to most of the Free Software
+Foundation's software and to any other program whose authors commit to
+using it.  (Some other Free Software Foundation software is covered by
+the GNU Lesser General Public License instead.)  You can apply it to
+your programs, too.
+
+  When we speak of free software, we are referring to freedom, not
+price.  Our General Public Licenses are designed to make sure that you
+have the freedom to distribute copies of free software (and charge for
+this service if you wish), that you receive source code or can get it
+if you want it, that you can change the software or use pieces of it
+in new free programs; and that you know you can do these things.
+
+  To protect your rights, we need to make restrictions that forbid
+anyone to deny you these rights or to ask you to surrender the rights.
+These restrictions translate to certain responsibilities for you if you
+distribute copies of the software, or if you modify it.
+
+  For example, if you distribute copies of such a program, whether
+gratis or for a fee, you must give the recipients all the rights that
+you have.  You must make sure that they, too, receive or can get the
+source code.  And you must show them these terms so they know their
+rights.
+
+  We protect your rights with two steps: (1) copyright the software, and
+(2) offer you this license which gives you legal permission to copy,
+distribute and/or modify the software.
+
+  Also, for each author's protection and ours, we want to make certain
+that everyone understands that there is no warranty for this free
+software.  If the software is modified by someone else and passed on, we
+want its recipients to know that what they have is not the original, so
+that any problems introduced by others will not reflect on the original
+authors' reputations.
+
+  Finally, any free program is threatened constantly by software
+patents.  We wish to avoid the danger that redistributors of a free
+program will individually obtain patent licenses, in effect making the
+program proprietary.  To prevent this, we have made it clear that any
+patent must be licensed for everyone's free use or not licensed at all.
+
+  The precise terms and conditions for copying, distribution and
+modification follow.
+
+                    GNU GENERAL PUBLIC LICENSE
+   TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
+
+  0. This License applies to any program or other work which contains
+a notice placed by the copyright holder saying it may be distributed
+under the terms of this General Public License.  The "Program", below,
+refers to any such program or work, and a "work based on the Program"
+means either the Program or any derivative work under copyright law:
+that is to say, a work containing the Program or a portion of it,
+either verbatim or with modifications and/or translated into another
+language.  (Hereinafter, translation is included without limitation in
+the term "modification".)  Each licensee is addressed as "you".
+
+Activities other than copying, distribution and modification are not
+covered by this License; they are outside its scope.  The act of
+running the Program is not restricted, and the output from the Program
+is covered only if its contents constitute a work based on the
+Program (independent of having been made by running the Program).
+Whether that is true depends on what the Program does.
+
+  1. You may copy and distribute verbatim copies of the Program's
+source code as you receive it, in any medium, provided that you
+conspicuously and appropriately publish on each copy an appropriate
+copyright notice and disclaimer of warranty; keep intact all the
+notices that refer to this License and to the absence of any warranty;
+and give any other recipients of the Program a copy of this License
+along with the Program.
+
+You may charge a fee for the physical act of transferring a copy, and
+you may at your option offer warranty protection in exchange for a fee.
+
+  2. You may modify your copy or copies of the Program or any portion
+of it, thus forming a work based on the Program, and copy and
+distribute such modifications or work under the terms of Section 1
+above, provided that you also meet all of these conditions:
+
+    a) You must cause the modified files to carry prominent notices
+    stating that you changed the files and the date of any change.
+
+    b) You must cause any work that you distribute or publish, that in
+    whole or in part contains or is derived from the Program or any
+    part thereof, to be licensed as a whole at no charge to all third
+    parties under the terms of this License.
+
+    c) If the modified program normally reads commands interactively
+    when run, you must cause it, when started running for such
+    interactive use in the most ordinary way, to print or display an
+    announcement including an appropriate copyright notice and a
+    notice that there is no warranty (or else, saying that you provide
+    a warranty) and that users may redistribute the program under
+    these conditions, and telling the user how to view a copy of this
+    License.  (Exception: if the Program itself is interactive but
+    does not normally print such an announcement, your work based on
+    the Program is not required to print an announcement.)
+
+These requirements apply to the modified work as a whole.  If
+identifiable sections of that work are not derived from the Program,
+and can be reasonably considered independent and separate works in
+themselves, then this License, and its terms, do not apply to those
+sections when you distribute them as separate works.  But when you
+distribute the same sections as part of a whole which is a work based
+on the Program, the distribution of the whole must be on the terms of
+this License, whose permissions for other licensees extend to the
+entire whole, and thus to each and every part regardless of who wrote it.
+
+Thus, it is not the intent of this section to claim rights or contest
+your rights to work written entirely by you; rather, the intent is to
+exercise the right to control the distribution of derivative or
+collective works based on the Program.
+
+In addition, mere aggregation of another work not based on the Program
+with the Program (or with a work based on the Program) on a volume of
+a storage or distribution medium does not bring the other work under
+the scope of this License.
+
+  3. You may copy and distribute the Program (or a work based on it,
+under Section 2) in object code or executable form under the terms of
+Sections 1 and 2 above provided that you also do one of the following:
+
+    a) Accompany it with the complete corresponding machine-readable
+    source code, which must be distributed under the terms of Sections
+    1 and 2 above on a medium customarily used for software interchange; or,
+
+    b) Accompany it with a written offer, valid for at least three
+    years, to give any third party, for a charge no more than your
+    cost of physically performing source distribution, a complete
+    machine-readable copy of the corresponding source code, to be
+    distributed under the terms of Sections 1 and 2 above on a medium
+    customarily used for software interchange; or,
+
+    c) Accompany it with the information you received as to the offer
+    to distribute corresponding source code.  (This alternative is
+    allowed only for noncommercial distribution and only if you
+    received the program in object code or executable form with such
+    an offer, in accord with Subsection b above.)
+
+The source code for a work means the preferred form of the work for
+making modifications to it.  For an executable work, complete source
+code means all the source code for all modules it contains, plus any
+associated interface definition files, plus the scripts used to
+control compilation and installation of the executable.  However, as a
+special exception, the source code distributed need not include
+anything that is normally distributed (in either source or binary
+form) with the major components (compiler, kernel, and so on) of the
+operating system on which the executable runs, unless that component
+itself accompanies the executable.
+
+If distribution of executable or object code is made by offering
+access to copy from a designated place, then offering equivalent
+access to copy the source code from the same place counts as
+distribution of the source code, even though third parties are not
+compelled to copy the source along with the object code.
+
+  4. You may not copy, modify, sublicense, or distribute the Program
+except as expressly provided under this License.  Any attempt
+otherwise to copy, modify, sublicense or distribute the Program is
+void, and will automatically terminate your rights under this License.
+However, parties who have received copies, or rights, from you under
+this License will not have their licenses terminated so long as such
+parties remain in full compliance.
+
+  5. You are not required to accept this License, since you have not
+signed it.  However, nothing else grants you permission to modify or
+distribute the Program or its derivative works.  These actions are
+prohibited by law if you do not accept this License.  Therefore, by
+modifying or distributing the Program (or any work based on the
+Program), you indicate your acceptance of this License to do so, and
+all its terms and conditions for copying, distributing or modifying
+the Program or works based on it.
+
+  6. Each time you redistribute the Program (or any work based on the
+Program), the recipient automatically receives a license from the
+original licensor to copy, distribute or modify the Program subject to
+these terms and conditions.  You may not impose any further
+restrictions on the recipients' exercise of the rights granted herein.
+You are not responsible for enforcing compliance by third parties to
+this License.
+
+  7. If, as a consequence of a court judgment or allegation of patent
+infringement or for any other reason (not limited to patent issues),
+conditions are imposed on you (whether by court order, agreement or
+otherwise) that contradict the conditions of this License, they do not
+excuse you from the conditions of this License.  If you cannot
+distribute so as to satisfy simultaneously your obligations under this
+License and any other pertinent obligations, then as a consequence you
+may not distribute the Program at all.  For example, if a patent
+license would not permit royalty-free redistribution of the Program by
+all those who receive copies directly or indirectly through you, then
+the only way you could satisfy both it and this License would be to
+refrain entirely from distribution of the Program.
+
+If any portion of this section is held invalid or unenforceable under
+any particular circumstance, the balance of the section is intended to
+apply and the section as a whole is intended to apply in other
+circumstances.
+
+It is not the purpose of this section to induce you to infringe any
+patents or other property right claims or to contest validity of any
+such claims; this section has the sole purpose of protecting the
+integrity of the free software distribution system, which is
+implemented by public license practices.  Many people have made
+generous contributions to the wide range of software distributed
+through that system in reliance on consistent application of that
+system; it is up to the author/donor to decide if he or she is willing
+to distribute software through any other system and a licensee cannot
+impose that choice.
+
+This section is intended to make thoroughly clear what is believed to
+be a consequence of the rest of this License.
+
+  8. If the distribution and/or use of the Program is restricted in
+certain countries either by patents or by copyrighted interfaces, the
+original copyright holder who places the Program under this License
+may add an explicit geographical distribution limitation excluding
+those countries, so that distribution is permitted only in or among
+countries not thus excluded.  In such case, this License incorporates
+the limitation as if written in the body of this License.
+
+  9. The Free Software Foundation may publish revised and/or new versions
+of the General Public License from time to time.  Such new versions will
+be similar in spirit to the present version, but may differ in detail to
+address new problems or concerns.
+
+Each version is given a distinguishing version number.  If the Program
+specifies a version number of this License which applies to it and "any
+later version", you have the option of following the terms and conditions
+either of that version or of any later version published by the Free
+Software Foundation.  If the Program does not specify a version number of
+this License, you may choose any version ever published by the Free Software
+Foundation.
+
+  10. If you wish to incorporate parts of the Program into other free
+programs whose distribution conditions are different, write to the author
+to ask for permission.  For software which is copyrighted by the Free
+Software Foundation, write to the Free Software Foundation; we sometimes
+make exceptions for this.  Our decision will be guided by the two goals
+of preserving the free status of all derivatives of our free software and
+of promoting the sharing and reuse of software generally.
+
+                            NO WARRANTY
+
+  11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
+FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW.  EXCEPT WHEN
+OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES
+PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED
+OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  THE ENTIRE RISK AS
+TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.  SHOULD THE
+PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING,
+REPAIR OR CORRECTION.
+
+  12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
+REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
+INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING
+OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED
+TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY
+YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
+PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE
+POSSIBILITY OF SUCH DAMAGES.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+convey the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License along
+    with this program; if not, see <https://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+If the program is interactive, make it output a short notice like this
+when it starts in an interactive mode:
+
+    Gnomovision version 69, Copyright (C) year name of author
+    Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, the commands you use may
+be called something other than `show w' and `show c'; they could even be
+mouse-clicks or menu items--whatever suits your program.
+
+You should also get your employer (if you work as a programmer) or your
+school, if any, to sign a "copyright disclaimer" for the program, if
+necessary.  Here is a sample; alter the names:
+
+  Yoyodyne, Inc., hereby disclaims all copyright interest in the program
+  `Gnomovision' (which makes passes at compilers) written by James Hacker.
+
+  <signature of Moe Ghoul>, 1 April 1989
+  Moe Ghoul, President of Vice
+
+This General Public License does not permit incorporating your program into
+proprietary programs.  If your program is a subroutine library, you may
+consider it more useful to permit linking proprietary applications with the
+library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..5ad3942
--- /dev/null
+++ b/README.md
@@ -0,0 +1,82 @@
+# book-reader
+
+Browser viewer for books stored as folders of page images. Shows two pages
+side by side with a 3D page-turn animation, flips with keyboard, mouse wheel
+or click, and remembers where you stopped in each book.
+
+Every folder under the library that contains images is a book, named after
+the folder. Pages are sorted in natural order (`2.jpg` before `10.jpg`).
+
+## Usage
+
+Create `~/.config/book-reader.conf`:
+
+```sh
+LIBRARY="/path/to/collection"
+PORT=8642
+```
+
+Then:
+
+```sh
+./rc.book-reader start    # prints the URL, e.g. http://127.0.0.1:8642/reader.html
+./rc.book-reader stop|restart|status
+```
+
+The server is Python's stdlib `http.server`, bound to 127.0.0.1. Its served
+root holds only symlinks to `reader.html` and the library, nothing is written
+into the library. Runtime files live in `/tmp/book-reader-$UID`.
+
+### Start at boot (Slackware)
+
+```sh
+cp rc.book-reader /etc/rc.d/ && chmod 755 /etc/rc.d/rc.book-reader
+```
+
+Set `RUNAS=` near the top of the copy to your user name, and add to the
+config the path of the viewer, since the copy no longer sits next to it:
+
+```sh
+READER="/path/to/book-reader/reader.html"
+```
+
+Then in `/etc/rc.d/rc.local`:
+
+```sh
+[ -x /etc/rc.d/rc.book-reader ] && /etc/rc.d/rc.book-reader start
+```
+
+and the same with `stop` in `/etc/rc.d/rc.local_shutdown`. Started as root,
+the script re-executes itself as `RUNAS`, so the server never runs as root and
+reads that user's config.
+
+Reading progress is kept in browser localStorage, which is per origin: keep
+`PORT` fixed or progress starts over.
+
+## Keys
+
+| Action | Keys |
+|---|---|
+| Next spread | Right, Space, PgDn (scroll first in fit-width), `l`, wheel down, click right half |
+| Previous spread | Left, PgUp, Shift+Space, Backspace, `h`, wheel up, click left half |
+| First / last | Home / End |
+| Toggle cover-alone offset | `c` |
+| Fit width / fit height | `w` (fit-width scrolls, wheel flips at the end of a spread) |
+| Library | `b` (Esc closes) |
+| Fullscreen | `f` |
+
+## License
+
+Copyright (C) 2026 Danilo M. <danix@danix.xyz>
+
+This program is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License version 2, as published by the
+Free Software Foundation. See [LICENSE](LICENSE).
+
+## Development Approach
+
+This project is developed using AI-assisted tools. Code is generated with the help of AI based on human-provided specifications, design decisions, and iterative feedback.
+
+All contributions are reviewed, tested, and curated by the maintainer before being included in the codebase. AI is used as a productivity and exploration tool, while human oversight remains central to all decisions.
+
+The goal is to combine the flexibility of AI-assisted development with standard open-source practices such as transparency, review, and accountability.
diff --git a/rc.book-reader b/rc.book-reader
new file mode 100755
index 0000000..5ba30a3
--- /dev/null
+++ b/rc.book-reader
@@ -0,0 +1,61 @@
+#!/bin/bash
+# rc.book-reader: start/stop the local server for book-reader.
+# Copyright (C) 2026 Danilo M. <danix@danix.xyz>
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Config (shell syntax): ${XDG_CONFIG_HOME:-~/.config}/book-reader.conf
+#   LIBRARY=/path/to/collection   # required; every folder with images inside is a book
+#   PORT=8642                      # keep it fixed: reading progress is stored per origin
+#   BIND=127.0.0.1
+#   READER=/path/to/book-reader/reader.html  # needed when this script is copied out of the repo
+#
+# Boot (Slackware): copy to /etc/rc.d, set RUNAS below, call "start" from
+# rc.local and "stop" from rc.local_shutdown. Run as root, the script
+# re-executes itself as RUNAS: the web server never runs as root.
+
+RUNAS=      # user to run as when started by root
+
+if [ "$(id -u)" = 0 ]; then
+  if [ -z "$RUNAS" ] || [ "$RUNAS" = root ]; then echo "set RUNAS in $0 to a non-root user" >&2; exit 1; fi
+  exec su - "$RUNAS" -s /bin/bash -c "$(printf '%q %q' "$(readlink -f "$0")" "$1")"
+fi
+
+LIBRARY= PORT=8642 BIND=127.0.0.1 READER=$(dirname "$(readlink -f "$0")")/reader.html
+CONF=${BOOK_READER_CONF:-${XDG_CONFIG_HOME:-$HOME/.config}/book-reader.conf}
+[ -r "$CONF" ] && . "$CONF"
+
+# fixed path: boot (no XDG_RUNTIME_DIR) and desktop sessions must share the pidfile
+RUN=/tmp/book-reader-$UID
+PIDFILE=$RUN/pid
+URL="http://$BIND:$PORT/reader.html"
+
+running() { [ -f "$PIDFILE" ] && kill -0 "$(cat "$PIDFILE")" 2>/dev/null; }
+
+start() {
+  if running; then echo "book-reader already running: $URL"; return 0; fi
+  if [ ! -d "$LIBRARY" ]; then echo "LIBRARY not set or missing (edit $CONF)" >&2; return 1; fi
+  if [ ! -r "$READER" ]; then echo "reader.html not found at $READER (set READER in $CONF)" >&2; return 1; fi
+  # Served root holds only symlinks: the viewer and the library, so neither dir gets touched.
+  mkdir -p -m 700 "$RUN" "$RUN/root"
+  find "$RUN/root" -mindepth 1 -maxdepth 1 -type l -delete
+  ln -s "$(readlink -f "$READER")" "$RUN/root/reader.html"
+  ln -s "$(readlink -f "$LIBRARY")" "$RUN/root/$(basename "$LIBRARY")"
+  setsid python3 -m http.server -b "$BIND" -d "$RUN/root" "$PORT" >"$RUN/log" 2>&1 &
+  echo $! >"$PIDFILE"
+  sleep 0.5
+  if ! running; then echo "book-reader failed to start:" >&2; tail -n 5 "$RUN/log" >&2; rm -f "$PIDFILE"; return 1; fi
+  echo "book-reader started: $URL"
+}
+
+stop() {
+  if running; then kill "$(cat "$PIDFILE")"; echo "book-reader stopped"; else echo "book-reader not running"; fi
+  rm -f "$PIDFILE"
+}
+
+case "$1" in
+  start) start ;;
+  stop) stop ;;
+  restart) stop; start ;;
+  status) if running; then echo "book-reader running: $URL"; else echo "book-reader stopped"; exit 3; fi ;;
+  *) echo "usage: $0 start|stop|restart|status" >&2; exit 1 ;;
+esac
diff --git a/reader.html b/reader.html
new file mode 100644
index 0000000..5bc7057
--- /dev/null
+++ b/reader.html
@@ -0,0 +1,251 @@
+<!doctype html>
+<!--
+  book-reader: two-page image book viewer.
+  Copyright (C) 2026 Danilo M. <danix@danix.xyz>
+  SPDX-License-Identifier: GPL-2.0-only
+-->
+<html lang="en">
+<head>
+<meta charset="utf-8">
+<meta name="viewport" content="width=device-width,initial-scale=1">
+<title>Reader</title>
+<style>
+:root { --ar: .707; --dur: 650ms; --accent: #e8b86a; }
+* { box-sizing: border-box; margin: 0; }
+html, body { height: 100%; overflow: hidden; }
+/* fit-width: pages span the screen, document scrolls vertically */
+html.wide { overflow-y: auto; scrollbar-width: none; }
+html.wide body { height: auto; min-height: 100%; overflow: visible; place-items: start center; }
+body {
+  background: #070607;
+  color: #ddd; font: 14px/1.4 system-ui, sans-serif; user-select: none;
+  display: grid; place-items: center;
+}
+/* own fixed layer: stays put while scrolling, no repaint (unlike background-attachment: fixed) */
+body::before {
+  content: ""; position: fixed; inset: 0; z-index: -1;
+  background: radial-gradient(ellipse at 50% 40%, #2a2522 0%, #121011 60%, #070607 100%);
+}
+#book {
+  position: relative; display: flex; perspective: 2800px;
+  filter: drop-shadow(0 30px 40px rgba(0,0,0,.6));
+}
+.page, #leaf { height: min(100vh, calc(50vw / var(--ar))); aspect-ratio: var(--ar); }
+.wide .page, .wide #leaf { height: calc(50vw / var(--ar)); }
+.page { position: relative; }
+.page img, .face img { width: 100%; height: 100%; object-fit: contain; display: block; }
+img:not([src]) { visibility: hidden; }
+/* spine shading */
+.page.left::after, .page.right::after { content: ""; position: absolute; inset: 0; pointer-events: none; }
+.page.left::after { background: linear-gradient(to left, rgba(0,0,0,.35), transparent 6%); }
+.page.right::after { background: linear-gradient(to right, rgba(0,0,0,.35), transparent 6%); }
+#leaf {
+  position: absolute; top: 0; transform-style: preserve-3d; visibility: hidden;
+  will-change: transform;
+}
+.face { position: absolute; inset: 0; backface-visibility: hidden; }
+.back { transform: rotateY(180deg); }
+.shade { position: absolute; inset: 0; background: #000; opacity: 0; pointer-events: none; }
+
+#hud {
+  position: fixed; left: 50%; bottom: 14px; transform: translateX(-50%);
+  display: flex; gap: 14px; align-items: center; padding: 8px 14px;
+  background: rgba(20,18,18,.75); backdrop-filter: blur(8px); border-radius: 999px;
+  border: 1px solid rgba(255,255,255,.08); transition: opacity .4s;
+}
+body.idle #hud { opacity: 0; }
+body.idle { cursor: none; }
+#bar { width: min(30vw, 260px); height: 4px; background: rgba(255,255,255,.12); border-radius: 2px; overflow: hidden; }
+#fill { height: 100%; width: 0; background: var(--accent); transition: width .3s; }
+button { background: none; border: 0; color: inherit; font: inherit; cursor: pointer; padding: 2px 6px; border-radius: 6px; }
+button:hover, button:focus-visible { background: rgba(255,255,255,.1); outline: none; }
+
+#shelf {
+  position: fixed; inset: 0; padding: 6vh 6vw; overflow-y: auto;
+  background: rgba(8,7,8,.88); backdrop-filter: blur(14px);
+  opacity: 0; pointer-events: none; transition: opacity .25s;
+}
+#shelf.open { opacity: 1; pointer-events: auto; }
+#shelf h1 { font-weight: 300; letter-spacing: .08em; margin-bottom: 24px; }
+#grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(160px, 1fr)); gap: 28px; }
+.card { text-align: left; padding: 0; transition: transform .2s; }
+.card:hover, .card:focus-visible { transform: translateY(-4px); background: none; }
+.card img { width: 100%; aspect-ratio: var(--ar); object-fit: cover; border-radius: 4px; box-shadow: 0 10px 25px rgba(0,0,0,.6); }
+.card.current img { outline: 2px solid var(--accent); outline-offset: 3px; }
+.card b { display: block; margin-top: 8px; font-weight: 500; }
+.card small { color: #999; }
+.card .p { height: 3px; background: rgba(255,255,255,.12); margin-top: 6px; }
+.card .p i { display: block; height: 100%; background: var(--accent); }
+#help { color: #888; margin-top: 30px; }
+@media (prefers-reduced-motion: reduce) { :root { --dur: 0ms; } }
+</style>
+</head>
+<body>
+<div id="book">
+  <div class="page left"><img alt=""></div>
+  <div class="page right"><img alt=""></div>
+  <div id="leaf">
+    <div class="face front"><img alt=""><i class="shade"></i></div>
+    <div class="face back"><img alt=""><i class="shade"></i></div>
+  </div>
+</div>
+
+<div id="hud">
+  <button id="books" title="Books (B)">☰</button>
+  <span id="title"></span>
+  <div id="bar"><div id="fill"></div></div>
+  <span id="count"></span>
+  <button id="fit" title="Fit width / height (W)">↔</button>
+  <button id="fs" title="Fullscreen (F)">⛶</button>
+</div>
+
+<div id="shelf">
+  <h1>Library</h1>
+  <div id="grid"></div>
+  <p id="help">→ / Space / PgDn / wheel down: next · ← / PgUp / wheel up: previous · Home / End ·
+    W: fit width / height (wheel and ↑↓ scroll, flip at page end) · C: toggle cover offset · F: fullscreen · B: library · click left/right half to flip</p>
+</div>
+
+<script>
+const $ = s => document.querySelector(s);
+const IMG = /\.(jpe?g|png|webp|gif|avif)$/i;
+const coll = new Intl.Collator(undefined, { numeric: true });
+const dec = s => decodeURIComponent(s);
+
+let store = { pos: {}, last: null, cover: true, wide: false };
+try { Object.assign(store, JSON.parse(localStorage.getItem('reader')) || {}); } catch {}
+const save = () => { try { localStorage.setItem('reader', JSON.stringify(store)); } catch {} };
+
+let books = [], book = null, s = 0, cur = null;
+const L = $('.left img'), R = $('.right img'), leaf = $('#leaf');
+const F = $('.front img'), B = $('.back img'), shades = document.querySelectorAll('.shade');
+
+// Every directory holding images is a book, named after its folder. Needs a server that lists dirs (rc.book-reader).
+async function walk(path) {
+  const html = await (await fetch(path || './')).text();
+  const hrefs = [...new DOMParser().parseFromString(html, 'text/html').querySelectorAll('a[href]')]
+    .map(a => a.getAttribute('href')).filter(h => !/^([?\/#]|\.\.|[a-z]+:)/i.test(h));
+  const pages = hrefs.filter(h => IMG.test(h)).sort((a, b) => coll.compare(dec(a), dec(b))).map(h => path + h);
+  const out = pages.length ? [{ id: path, name: dec(path.slice(0, -1)).split('/').pop(), pages }] : [];
+  for (const d of hrefs.filter(h => h.endsWith('/')).sort((a, b) => coll.compare(dec(a), dec(b))))
+    out.push(...await walk(path + d));
+  return out;
+}
+
+const align = i => i - ((i + (store.cover ? 1 : 0)) % 2);   // left index of spread containing page i (may be -1)
+const src = (img, i) => book.pages[i] ? img.src = book.pages[i] : img.removeAttribute('src');
+const first = () => store.cover ? -1 : 0;
+
+function show() {
+  src(L, s); src(R, s + 1);
+  const n = book.pages.length, a = Math.max(s, 0) + 1, b = Math.min(s + 2, n);
+  $('#title').textContent = book.name;
+  $('#count').textContent = (a === b ? a : `${a}–${b}`) + ` / ${n}`;
+  $('#fill').style.width = (b / n * 100) + '%';
+  store.pos[book.id] = Math.max(s, 0); store.last = book.id; save();
+  for (let i = s - 2; i < s + 6; i++) if (book.pages[i]) new Image().src = book.pages[i]; // preload
+}
+
+function finish() { if (cur) { cur.forEach(a => a.cancel()); cur = null; leaf.style.visibility = 'hidden'; show(); } }
+
+function go(t) {
+  finish();
+  t = Math.max(first(), Math.min(align(t), align(book.pages.length - 1)));
+  if (t === s) return;
+  const fwd = t > s, old = s; s = t;
+  scrollTo(0, fwd ? 0 : document.documentElement.scrollHeight);   // back: land at the bottom of the spread
+  // base shows the halves that stay put during the turn; the leaf carries the turning page
+  if (fwd) { src(R, t + 1); src(F, old + 1); src(B, t); }
+  else     { src(L, t);     src(F, old);     src(B, t + 1); }
+  Object.assign(leaf.style, { left: fwd ? '50%' : '0', transformOrigin: fwd ? 'left' : 'right', visibility: 'visible' });
+  const opt = { duration: parseFloat(getComputedStyle(document.documentElement).getPropertyValue('--dur')) || 0,
+                easing: 'cubic-bezier(.645,.045,.355,1)', fill: 'forwards' };
+  cur = [
+    leaf.animate([{ transform: 'rotateY(0)' }, { transform: `rotateY(${fwd ? -180 : 180}deg)` }], opt),
+    shades[0].animate([{ opacity: 0 }, { opacity: .5 }], opt),
+    shades[1].animate([{ opacity: .5 }, { opacity: 0 }], opt),
+  ];
+  cur[0].onfinish = finish;
+}
+
+function open(b) {
+  finish(); book = b; $('#shelf').classList.remove('open');
+  const probe = new Image();
+  probe.onload = () => document.documentElement.style.setProperty('--ar', probe.naturalWidth / probe.naturalHeight);
+  probe.src = b.pages[0];
+  s = align(store.pos[b.id] ?? 0); show();
+}
+
+function shelf() {
+  const g = $('#grid'); g.replaceChildren();
+  for (const b of books) {
+    const c = document.createElement('button'), img = new Image(), name = document.createElement('b'),
+          sm = document.createElement('small'), p = document.createElement('div'), pi = document.createElement('i');
+    const at = Math.min((store.pos[b.id] ?? -1) + 2, b.pages.length);
+    c.className = 'card' + (b === book ? ' current' : '');
+    img.loading = 'lazy'; img.src = b.pages[0]; img.alt = '';
+    name.textContent = b.name;
+    sm.textContent = `${b.pages.length} pages` + (store.pos[b.id] != null ? ` · at ${Math.max(at, 1)}` : '');
+    p.className = 'p'; pi.style.width = (store.pos[b.id] != null ? at / b.pages.length * 100 : 0) + '%';
+    p.append(pi); c.append(img, name, sm, p); c.onclick = () => open(b); g.append(c);
+  }
+  $('#shelf').classList.add('open'); g.querySelector('.current')?.focus();
+}
+
+const toggleShelf = () => $('#shelf').classList.contains('open') ? book && $('#shelf').classList.remove('open') : shelf();
+const fullscreen = () => document.fullscreenElement ? document.exitFullscreen() : document.documentElement.requestFullscreen();
+
+addEventListener('keydown', e => {
+  if (e.ctrlKey || e.metaKey || e.altKey) return;
+  if ($('#shelf').classList.contains('open')) { if (e.key === 'Escape' || e.key === 'b') toggleShelf(); return; }
+  const k = e.key, act = {
+    ArrowRight: () => go(s + 2), PageDown: () => page(1), ' ': () => page(e.shiftKey ? -1 : 1), l: () => go(s + 2),
+    ArrowLeft: () => go(s - 2), PageUp: () => page(-1), Backspace: () => go(s - 2), h: () => go(s - 2),
+    Home: () => go(first()), End: () => go(book.pages.length - 1),
+    c: () => { finish(); store.cover = !store.cover; s = align(Math.max(s, 0)); show(); },
+    f: fullscreen, b: toggleShelf, w: fit,
+  }[k];
+  if (act) { e.preventDefault(); act(); }
+});
+
+const atEdge = d => d > 0 ? scrollY + innerHeight >= document.documentElement.scrollHeight - 2 : scrollY <= 0;
+// fit-width: scroll a screen, flip only once the end of the spread is on screen
+function page(d) {
+  if (store.wide && !atEdge(d)) scrollBy({ top: d * innerHeight * .85, behavior: 'smooth' });
+  else go(s + 2 * d);
+}
+function fit() {
+  store.wide = !store.wide; save();
+  document.documentElement.classList.toggle('wide', store.wide); scrollTo(0, 0);
+}
+document.documentElement.classList.toggle('wide', store.wide);
+
+let lastWheel = 0, lastScroll = 0;
+addEventListener('scroll', () => lastScroll = performance.now());
+addEventListener('wheel', e => {
+  if ($('#shelf').classList.contains('open') || !book) return;
+  const now = performance.now();
+  // fit-width: native scroll; flip needs a fresh push after the edge was reached (stops momentum from flipping)
+  if (store.wide && (!atEdge(e.deltaY) || now - lastScroll < 400)) return;
+  e.preventDefault();
+  if (now - lastWheel < 350 || Math.abs(e.deltaY) < 4) return;   // ponytail: fixed throttle tames touchpad bursts
+  lastWheel = now; go(s + (e.deltaY > 0 ? 2 : -2));
+}, { passive: false });
+
+$('#book').onclick = e => go(s + (e.clientX > innerWidth / 2 ? 2 : -2));
+$('#books').onclick = toggleShelf; $('#fs').onclick = fullscreen; $('#fit').onclick = fit;
+
+let idle;
+addEventListener('mousemove', () => {
+  document.body.classList.remove('idle'); clearTimeout(idle);
+  idle = setTimeout(() => document.body.classList.add('idle'), 2500);
+});
+
+walk('').then(b => {
+  books = b;
+  if (!books.length) return $('#title').textContent = 'No images found under the library directory';
+  open(books.find(x => x.id === store.last) || books[0]);
+}).catch(() => $('#title').textContent = 'Directory listing failed: start rc.book-reader and open its URL, not file://');
+</script>
+</body>
+</html>