feat(nov): reading-view theme layer with palettes and font sizing

EPUB reading prefs were scattered: a hardcoded Merriweather/180 font-remap in calibredb-epub-config's nov hook, no color control (the old sepia foreground had been stripped), and a frame-global EBook fontaine preset as the only way to size up. That preset resized the font in every buffer in the frame, not just the book.

I pulled the reading view into its own layer, modules/nov-reading.el, on top of stock nov (no fork). It owns three things, all buffer-local: a reading palette (sepia/dark/light, each a face the dupre theme owns, sepia the default), the serif typography (family plus a defcustom base height replacing the hardcoded 180), and page font sizing (+/- bump the size live, = resets to the base). Width moves to { }. calibredb-epub-config keeps the library and width/centering layout. Its nov hook now calls into the layer.

The three palette faces register as a nov-reading app in theme-studio (face_data.py), so they're tunable there like any other app. I dropped the EBook fontaine preset, since reading size is buffer-local now.

1 files changed, 176 insertions, 0 deletions

diff --git a/modules/nov-reading.el b/modules/nov-reading.el
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+;;; nov-reading.el --- Reading-view theme layer for nov-mode EPUBs -*- lexical-binding: t; -*-
+;; author: Craig Jennings <c@cjennings.net>
+
+;;; Commentary:
+;;
+;; Layer: 4 (Added features).
+;; Category: O (optional commands + faces).
+;; Load shape: eager.
+;; Eager reason: defines the reading faces and commands the nov launch hook and
+;;   keymap reference; the faces must exist for theme-studio's inventory too.
+;; Top-level side effects: defface x3, defcustoms, a defgroup.
+;; Runtime requires: none (face-remap and text-scale are built in).
+;; Direct test load: yes.
+;;
+;; A small theme layer on top of the stock `nov' package (no fork): how an EPUB
+;; *reads*, kept buffer-local so it never disturbs the frame or other buffers.
+;; Two knobs:
+;;
+;;   - Reading palette -- the background + foreground, as sepia / dark / light,
+;;     each a face the dupre theme / theme-studio own (registered as the
+;;     "nov-reading" bespoke app in theme-studio's face_data.py).
+;;   - Typography -- a serif family and a base height, with +/-/= adjusting the
+;;     page font size live via a buffer-local text-scale on top of the base.
+;;
+;; calibredb-epub-config.el owns the library/calibre side and the text-width /
+;; centering layout; this module owns reading color and typography.  Its launch
+;; entry point `cj/nov-reading-setup' is called from that module's nov-mode hook.
+
+;;; Code:
+
+(defgroup cj/nov-reading nil
+  "Reading-view theming for nov-mode EPUBs."
+  :group 'cj)
+
+;; ----------------------------- Reading palettes ------------------------------
+;; nov renders through shr and defines no faces, so a palette is a buffer-local
+;; face-remap of `default'.  Each palette is one face carrying a :background and
+;; :foreground, so the theme owns the real colors (the hex defaults here are a
+;; starting point to tune in theme-studio).
+
+(defface cj/nov-reading-sepia
+  '((t :background "#1f1b16" :foreground "#c9b187"))
+  "Sepia reading palette for nov-mode: warm dark background, tan text."
+  :group 'cj/nov-reading)
+
+(defface cj/nov-reading-dark
+  '((t :background "#15140f" :foreground "#cfc8b8"))
+  "Dark reading palette for nov-mode: near-black background, light-gray text."
+  :group 'cj/nov-reading)
+
+(defface cj/nov-reading-light
+  '((t :background "#ece3cf" :foreground "#2a2622"))
+  "Light reading palette for nov-mode: cream background, near-black text."
+  :group 'cj/nov-reading)
+
+(defcustom cj/nov-reading-palettes
+  '(("sepia" . cj/nov-reading-sepia)
+    ("dark"  . cj/nov-reading-dark)
+    ("light" . cj/nov-reading-light))
+  "Alist of reading-palette NAME -> face for nov-mode.
+Each face supplies the reading view's :background and :foreground; the selector
+and cycle commands choose among these names.  Add an entry to add a palette."
+  :type '(alist :key-type string :value-type face)
+  :group 'cj/nov-reading)
+
+(defcustom cj/nov-reading-default-palette "sepia"
+  "Reading palette applied to a fresh nov-mode buffer.
+A key in `cj/nov-reading-palettes', or nil for the theme's normal rendering."
+  :type '(choice (const :tag "None (theme default)" nil) string)
+  :group 'cj/nov-reading)
+
+(defvar-local cj/nov--reading-remap-cookie nil
+  "The `face-remap-add-relative' cookie for the active reading palette, or nil.")
+
+(defvar-local cj/nov--reading-palette nil
+  "Name of the reading palette active in this buffer, or nil for none.")
+
+(defun cj/nov--reading-palette-face (name)
+  "Return the face for palette NAME, or nil when NAME is nil or unknown."
+  (cdr (assoc name cj/nov-reading-palettes)))
+
+(defun cj/nov--next-reading-palette (current names)
+  "Return the palette after CURRENT in the cycle NAMES then nil, wrapping.
+CURRENT nil is the no-palette state, and a returned nil means no palette.  An
+unknown CURRENT falls back to the first palette."
+  (let* ((cycle (append names (list nil)))
+         (tail (cdr (member current cycle))))
+    (car (or tail cycle))))
+
+(defun cj/nov--apply-reading-palette (name)
+  "Apply reading palette NAME buffer-local; NAME nil removes any palette.
+Removes the previous palette remap first so switching never stacks remaps, and
+leaves the typography remap (a separate `default' remap) untouched."
+  (when cj/nov--reading-remap-cookie
+    (face-remap-remove-relative cj/nov--reading-remap-cookie)
+    (setq cj/nov--reading-remap-cookie nil))
+  (let ((face (cj/nov--reading-palette-face name)))
+    (when face
+      (setq cj/nov--reading-remap-cookie
+            (face-remap-add-relative 'default face)))
+    (setq cj/nov--reading-palette (and face name))))
+
+(defun cj/nov-set-reading-palette (name)
+  "Choose reading palette NAME for this nov buffer; \"none\" clears it.
+Interactively prompts among `cj/nov-reading-palettes' plus \"none\"."
+  (interactive
+   (list (completing-read "Reading palette: "
+                          (cons "none" (mapcar #'car cj/nov-reading-palettes))
+                          nil t)))
+  (unless (derived-mode-p 'nov-mode)
+    (user-error "Not in a nov-mode buffer"))
+  (cj/nov--apply-reading-palette (unless (equal name "none") name))
+  (message "Reading palette: %s" (or cj/nov--reading-palette "none")))
+
+(defun cj/nov-cycle-reading-palette ()
+  "Cycle to the next reading palette, then the no-palette state, wrapping."
+  (interactive)
+  (unless (derived-mode-p 'nov-mode)
+    (user-error "Not in a nov-mode buffer"))
+  (let ((next (cj/nov--next-reading-palette
+               cj/nov--reading-palette
+               (mapcar #'car cj/nov-reading-palettes))))
+    (cj/nov--apply-reading-palette next)
+    (message "Reading palette: %s" (or next "none"))))
+
+;; ------------------------------- Typography ----------------------------------
+
+(defcustom cj/nov-reading-font-family "Merriweather"
+  "Variable-pitch serif family for the EPUB reading view."
+  :type 'string
+  :group 'cj/nov-reading)
+
+(defcustom cj/nov-reading-text-height 180
+  "Base `default'-face height (1/10 pt) a fresh nov buffer opens at.
+The +/-/= keys adjust the page size from here with a buffer-local text-scale;
+that adjustment resets to this base each time a book is opened."
+  :type 'integer
+  :group 'cj/nov-reading)
+
+(defun cj/nov-reading-apply-typography ()
+  "Apply the reading family and base height buffer-local.
+Remaps `variable-pitch', `default', and `fixed-pitch' so nov's shr output reads
+as a comfortably-sized serif page."
+  (face-remap-add-relative 'variable-pitch
+                           :family cj/nov-reading-font-family :height 1.0)
+  (face-remap-add-relative 'default
+                           :family cj/nov-reading-font-family
+                           :height cj/nov-reading-text-height)
+  (face-remap-add-relative 'fixed-pitch :height cj/nov-reading-text-height))
+
+(defun cj/nov-reading-text-bigger ()
+  "Increase the page font size (buffer-local), on top of the base height."
+  (interactive)
+  (text-scale-increase 1))
+
+(defun cj/nov-reading-text-smaller ()
+  "Decrease the page font size (buffer-local), on top of the base height."
+  (interactive)
+  (text-scale-decrease 1))
+
+(defun cj/nov-reading-text-reset ()
+  "Reset the page font size back to the base reading height (buffer-local)."
+  (interactive)
+  (text-scale-set 0))
+
+;; ------------------------------- Launch hook ---------------------------------
+
+(defun cj/nov-reading-setup ()
+  "Apply the reading view (typography + default palette) to this nov buffer.
+Called from the nov-mode launch hook in calibredb-epub-config.el."
+  (cj/nov-reading-apply-typography)
+  (when cj/nov-reading-default-palette
+    (cj/nov--apply-reading-palette cj/nov-reading-default-palette)))
+
+(provide 'nov-reading)
+;;; nov-reading.el ends here