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guard against bad pre-mult ARGB

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Closes PR 11572
This commit is contained in:
Matthew Flatt 2010-12-28 20:03:56 -07:00
parent 1d89cfc9d7
commit 0476ab4fc4
1 changed files with 6 additions and 2 deletions
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8
collects/racket/draw/private/bitmap.rkt
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@ -614,9 +614,13 @@
[a (bytes-ref data (+ ri A))] [a (bytes-ref data (+ ri A))]
[unmult (lambda (a v) [unmult (lambda (a v)
(if use-alpha? (if use-alpha?
(if (zero? a) (if (unsafe-fx= 0 a)
255 255
(unsafe-fxquotient (fx* v 255) a)) ;; `min' shouldn't be necessary, but it's
;; just in case the data is ill-formed
(unsafe-fxmin 255 (unsafe-fxquotient
(unsafe-fx* v 255)
a)))
v))]) v))])
(when alpha-channel? (when alpha-channel?
(bytes-set! bstr pi a)) (bytes-set! bstr pi a))