Add lisp/face-remap.el and associated documentation

Revision: emacs@sv.gnu.org/emacs--devo--0--patch-1200

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+;;; face-remap.el --- Functions for managing `face-remapping-alist'
+;;
+;; Copyright (C) 2008 Free Software Foundation, Inc.
+;;
+;; Author: Miles Bader <miles@gnu.org>
+;; Keywords: faces face display user commands
+;;
+;; This file is part of GNU Emacs.
+;;
+;; GNU Emacs 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 3 of the License, or
+;; (at your option) any later version.
+;;
+;; GNU Emacs 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 GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
+;;
+
+;;; Commentary:
+
+;;
+;; This file defines some simple operations that can be used for
+;; maintaining the `face-remapping-alist' in a cooperative way.  This is
+;; especially important for the `default' face.
+;;
+;; Each face-remapping definition in `face-remapping-alist' added by
+;; this code uses the form:
+;;
+;;   (face RELATIVE_SPECS_1 RELATIVE_SPECS_2 ... BASE_SPECS)
+;;
+;; The "specs" values are a lists of face names or face attribute-value
+;; pairs, and are merged together, with earlier values taking precedence.
+;;
+;; The RELATIVE_SPECS_* values are added by `add-relative-face-remapping'
+;; (and removed by `remove-relative-face-remapping', and are intended for
+;; face "modifications" (such as increasing the size).  Typical users of
+;; relative specs would be minor modes.
+;;
+;; BASE_SPECS is the lowest-priority value, and by default is just the
+;; face name, which causes the global definition of that face to be used.
+;;
+;; A non-default value of BASE_SPECS may also be set using
+;; `set-base-face-remapping'.  Because this _overwrites_ the default
+;; value inheriting from the global face definition, it is up to the
+;; caller of set-base-face-remapping to add such inheritance if it is
+;; desired.  A typical use of set-base-face-remapping would be a major
+;; mode setting face remappings, e.g., of the default face.
+;;
+;; All modifications cause face-remapping-alist to be made buffer-local.
+;;
+
+
+;;; Code:
+
+
+;; ----------------------------------------------------------------
+;; Utility functions
+
+;;;### autoload
+(defun add-relative-face-remapping (face &rest specs)
+  "Add a face remapping entry of FACE to SPECS in the current buffer.
+
+Return a cookie which can be used to delete the remapping with
+`remove-relative-face-remapping'.
+
+SPECS can be any value suitable for the `face' text property,
+including a face name, a list of face names, or a face-attribute
+property list.  The attributes given by SPECS will be merged with
+any other currently active face remappings of FACE, and with the
+global definition of FACE, with the most recently added relative
+remapping taking precedence.
+
+The base (lowest priority) remapping may be set to a specific
+value, instead of the default of the global face definition,
+using `set-base-face-remapping'."
+  (make-local-variable 'face-remapping-alist)
+  (let ((entry (assq face face-remapping-alist)))
+    (when (null entry)
+      (setq entry (list face face))	; explicitly merge with global def
+      (push entry face-remapping-alist))
+    (setcdr entry (cons specs (cdr entry)))
+    (cons face specs)))
+
+(defun remove-relative-face-remapping (cookie)
+  "Remove a face remapping previously added by `add-relative-face-remapping'.
+COOKIE should be the return value from that function."
+  (let ((remapping (assq (car cookie) face-remapping-alist)))
+    (when remapping
+      (let ((updated-entries (remq (cdr cookie) (cdr remapping))))
+	(unless (eq updated-entries (cdr remapping))
+	  (setcdr remapping updated-entries)
+	  (when (or (null updated-entries)
+		    (and (eq (car-safe updated-entries) (car cookie))
+			 (null (cdr updated-entries))))
+	    (setq face-remapping-alist
+		  (remq remapping face-remapping-alist)))
+	  (cdr cookie))))))
+
+;;;### autoload
+(defun set-default-base-face-remapping (face)
+  "Set the base remapping of FACE to inherit from FACE's global definition."
+  (let ((entry (assq face face-remapping-alist)))
+    (when entry
+      ;; If there's nothing except a base remapping, we simply remove
+      ;; the entire remapping entry, as setting the base to the default
+      ;; would be the same as the global definition.  Otherwise, we
+      ;; modify the base remapping.
+      (if (null (cddr entry))		; nothing except base remapping
+	  (setq face-remapping-alist	; so remove entire entry
+		(remq entry face-remapping-alist))
+	(setcar (last entry) face)))))  ; otherwise, just inherit global def
+
+;;;### autoload
+(defun set-base-face-remapping (face &rest specs)
+  "Set the base remapping of FACE in the current buffer to SPECS.
+If SPECS is empty, the default base remapping is restored, which
+inherits from the global definition of FACE; note that this is
+different from SPECS containing a single value `nil', which does
+not inherit from the global definition of FACE."
+  (if (or (null specs)
+	  (and (eq (car specs) face) (null (cdr specs)))) ; default
+      ;; Set entry back to default
+      (set-default-base-face-remapping face)
+    ;; Set the base remapping
+    (make-local-variable 'face-remapping-alist)
+    (let ((entry (assq face face-remapping-alist)))
+      (if entry
+	  (setcar (last entry) specs)	; overwrite existing base entry
+	(push (list face specs) face-remapping-alist)))))
+  
+
+;; ----------------------------------------------------------------
+;; text-scale-mode
+
+(defcustom text-scale-mode-step 1.2
+  "Scale factor used by `text-scale-mode'.
+Each positive or negative step scales the default face height by this amount."
+  :group 'display
+  :type 'number)
+
+;; current remapping cookie for text-scale-mode
+(defvar text-scale-mode-remapping nil)
+(make-variable-buffer-local 'text-scale-mode-remapping)
+
+;; Lighter displayed for text-scale-mode in mode-line minor-mode list
+(defvar text-scale-mode-lighter "+0")
+(make-variable-buffer-local 'text-scale-mode-lighter)
+
+;; Number of steps that text-scale-mode will increase/decrease text height
+(defvar text-scale-mode-amount 0)
+(make-variable-buffer-local 'text-scale-mode-amount)
+
+(define-minor-mode text-scale-mode
+  "Minor mode for displaying buffer text in a larger/smaller font than usual.
+
+The amount of scaling is determined by the variable
+`text-scale-mode-amount':  one step scales the global default
+face size by the value of the variable `text-scale-mode-step' (a
+negative amount shrinks the text).
+
+The `increase-buffer-face-height' and
+`decrease-buffer-face-height' functions may be used to
+interactively modify the variable `text-scale-mode-amount' (they
+also enable or disable `text-scale-mode' as necessary."
+  :lighter (" " text-scale-mode-lighter)
+  (when text-scale-mode-remapping
+    (remove-relative-face-remapping text-scale-mode-remapping))
+  (setq text-scale-mode-lighter
+	(format (if (>= text-scale-mode-amount 0) "+%d" "%d")
+		text-scale-mode-amount))
+  (setq text-scale-mode-remapping
+	(and text-scale-mode
+	     (add-relative-face-remapping 'default
+					  :height
+					  (expt text-scale-mode-step
+						text-scale-mode-amount))))
+  (force-window-update (current-buffer)))
+
+;;;###autoload (global-set-key [(control =)] 'increase-buffer-face-height)
+;;;###autoload (global-set-key [(control +)] 'increase-buffer-face-height)
+;;;###autoload
+(defun increase-buffer-face-height (&optional inc)
+  "Increase the height of the default face in the current buffer by INC steps.
+If the new height is other than the default, `text-scale-mode' is enabled.
+
+Each step scales the height of the default face by the variable
+`text-scale-mode-step' (a negative number of steps decreases the
+height by the same amount).  As a special case, an argument of 0
+will remove any scaling currently active."
+  (interactive
+   (list
+    (cond ((eq current-prefix-arg '-) -1)
+	  ((numberp current-prefix-arg) current-prefix-arg)
+	  ((consp current-prefix-arg) -1)
+	  (t 1))))
+  (setq text-scale-mode-amount (if (= inc 0) 0 (+ text-scale-mode-amount inc)))
+  (text-scale-mode (if (zerop text-scale-mode-amount) -1 1)))
+
+;;;###autoload (global-set-key [(control -)] 'decrease-buffer-face-height)
+;;;###autoload
+(defun decrease-buffer-face-height (&optional dec)
+  "Decrease the height of the default face in the current buffer by DEC steps.
+See `increase-buffer-face-height' for more details."
+  (interactive
+   (list
+    (cond ((eq current-prefix-arg '-) -1)
+	  ((numberp current-prefix-arg) current-prefix-arg)
+	  ((consp current-prefix-arg) -1)
+	  (t 1))))
+  (increase-buffer-face-height (- dec)))
+
+
+;; ----------------------------------------------------------------
+;; variable-pitch-mode
+
+;; suggested key binding: (global-set-key "\C-cv" 'variable-pitch-mode)
+
+;; current remapping cookie for  variable-pitch-mode
+(defvar variable-pitch-mode-remapping nil)
+(make-variable-buffer-local 'variable-pitch-mode-remapping)
+
+(define-minor-mode variable-pitch-mode
+  "Variable-pitch default-face mode.  When active, causes the
+buffer text to be displayed using the `variable-pitch' face."
+  :lighter " VarPitch"
+  (when variable-pitch-mode-remapping
+    (remove-relative-face-remapping variable-pitch-mode-remapping))
+  (setq variable-pitch-mode-remapping
+	(and variable-pitch-mode
+	     (add-relative-face-remapping 'default 'variable-pitch)))
+  (force-window-update (current-buffer)))
+
+
+(provide 'face-remap)
+
+;; arch-tag: 5c5f034b-8d58-4967-82bd-d61fd364e686
+;;; face-remap.el ends here