X-Git-Url: https://code.delx.au/gnu-emacs/blobdiff_plain/db4613576d3115aa320f0293d081ce98baa06acd..7095596ac3ece75b7fb98be7a47e4715a54842c2:/lisp/face-remap.el

diff --git a/lisp/face-remap.el b/lisp/face-remap.el
index 3ec074b559..9c2cae14b3 100644
--- a/lisp/face-remap.el
+++ b/lisp/face-remap.el
@@ -1,6 +1,6 @@
 ;;; face-remap.el --- Functions for managing `face-remapping-alist'  -*- lexical-binding: t -*-
 ;;
-;; Copyright (C) 2008-2015 Free Software Foundation, Inc.
+;; Copyright (C) 2008-2016 Free Software Foundation, Inc.
 ;;
 ;; Author: Miles Bader <miles@gnu.org>
 ;; Keywords: faces, face remapping, display, user commands
@@ -187,7 +187,7 @@ of face attribute/value pairs, like in a `face' text property.
 
 If SPECS is empty, call `face-remap-reset-base' to use the normal
 definition of FACE as the base remapping; note that this is
-different from SPECS containing a single value `nil', which means
+different from SPECS containing a single value nil, which means
 not to inherit from the global definition of FACE at all."
   (while (and (consp specs) (not (null (car specs))) (null (cdr specs)))
     (setq specs (car specs)))
@@ -256,6 +256,23 @@ disable `text-scale-mode' as necessary)."
 						text-scale-mode-amount))))
   (force-window-update (current-buffer)))
 
+(defun text-scale-min-amount ()
+  "Return the minimum amount of text-scaling we allow."
+  ;; When the resulting pixel-height of characters will become smaller
+  ;; than 1 pixel, we can expect trouble from the display engine.
+  ;; E.g., it requires that the character glyph's ascent is
+  ;; non-negative.
+  (log (/ 1.0 (frame-char-height)) text-scale-mode-step))
+
+(defun text-scale-max-amount ()
+  "Return the maximum amount of text-scaling we allow."
+  ;; The display engine uses a 16-bit short for pixel-width of
+  ;; characters, thus the 0xffff limitation.  It also makes no sense
+  ;; to have characters wider than the display.
+  (log (/ (min (display-pixel-width) #xffff)
+          (frame-char-width))
+       text-scale-mode-step))
+
 ;;;###autoload
 (defun text-scale-set (level)
   "Set the scale factor of the default face in the current buffer to LEVEL.
@@ -266,7 +283,8 @@ Each step scales the height of the default face by the variable
 `text-scale-mode-step' (a negative number decreases the height by
 the same amount)."
   (interactive "p")
-  (setq text-scale-mode-amount level)
+  (setq text-scale-mode-amount
+        (max (min level (text-scale-max-amount)) (text-scale-min-amount)))
   (text-scale-mode (if (zerop text-scale-mode-amount) -1 1)))
 
 ;;;###autoload
@@ -279,8 +297,13 @@ Each step scales the height of the default face by the variable
 height by the same amount).  As a special case, an argument of 0
 will remove any scaling currently active."
   (interactive "p")
-  (setq text-scale-mode-amount
-	(if (= inc 0) 0 (+ (if text-scale-mode text-scale-mode-amount 0) inc)))
+  (let* ((current-value (if text-scale-mode text-scale-mode-amount 0))
+         (new-value (if (= inc 0) 0 (+ current-value inc))))
+    (if (or (> new-value (text-scale-max-amount))
+            (< new-value (text-scale-min-amount)))
+        (user-error "Cannot %s the default face height more than it already is"
+                    (if (> inc 0) "increase" "decrease")))
+    (setq text-scale-mode-amount new-value))
   (text-scale-mode (if (zerop text-scale-mode-amount) -1 1)))
 
 ;;;###autoload
@@ -330,7 +353,7 @@ a top-level keymap, `text-scale-increase' or
               ((or ?+ ?=) inc)
               (?- (- inc))
               (?0 0)
-              (t inc))))
+              (_ inc))))
       (text-scale-increase step)
       ;; (unless (zerop step)
       (message "Use +,-,0 for further adjustment")