Commit 0e7bcec1 authored by Eli Zaretskii's avatar Eli Zaretskii

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)
parent 85f257c9
......@@ -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
......
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