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authorEli Zaretskii <eliz@gnu.org>2016-04-10 19:50:39 +0300
committerEli Zaretskii <eliz@gnu.org>2016-04-10 19:50:39 +0300
commit0e7bcec103073eceecc2621c19e4d290b2d97e8d (patch)
treec740216697d3c7f066b1dbe3b8a32ef2f4b32a72 /lisp/face-remap.el
parent85f257c9bc5b89043b2d7019e6763e552f4c89e7 (diff)
downloademacs-0e7bcec103073eceecc2621c19e4d290b2d97e8d.tar.gz
Avoid crashes due to unreasonably large or small text scaling
* lisp/face-remap.el (text-scale-min-amount) (text-scale-max-amount): New functions. (text-scale-set, text-scale-increase): Use them to limit the text scaling to a reasonable range of values. (Bug#23259)
Diffstat (limited to 'lisp/face-remap.el')
-rw-r--r--lisp/face-remap.el29
1 files changed, 26 insertions, 3 deletions
diff --git a/lisp/face-remap.el b/lisp/face-remap.el
index 0da6be7430b..9c2cae14b38 100644
--- a/lisp/face-remap.el
+++ b/lisp/face-remap.el
@@ -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