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fix alpha mult in `set-argb-pixels'

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This commit is contained in:
Matthew Flatt 2011-08-26 07:06:31 -06:00
parent 290fe066b6
commit cc82506be5
1 changed files with 20 additions and 15 deletions
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25
collects/racket/draw/private/bitmap.rkt
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@ -64,6 +64,13 @@
(define fx+ unsafe-fx+) (define fx+ unsafe-fx+)
(define fx* unsafe-fx*) (define fx* unsafe-fx*)
(define (alpha-mult al v)
(unsafe-fl->fx
(unsafe-flround
(unsafe-fl/
(unsafe-fx->fl (fx* al v))
255.0))))
(define png-convertible<%> (define png-convertible<%>
(interface* () (interface* ()
([prop:convertible ([prop:convertible
@ -422,12 +429,7 @@
255)] 255)]
[premult (lambda (al v) [premult (lambda (al v)
(if pre? (if pre?
(unsafe-fl->fx (alpha-mult al v)
(unsafe-flround
(unsafe-fl/
(unsafe-fx->fl (fx* al v))
255.0)))
#;(unsafe-fxquotient (fx* al v) 255)
v))]) v))])
(unsafe-bytes-set! dest (fx+ pos A) al) (unsafe-bytes-set! dest (fx+ pos A) al)
(unsafe-bytes-set! dest (fx+ pos R) (premult al (unsafe-bytes-ref r spos))) (unsafe-bytes-set! dest (fx+ pos R) (premult al (unsafe-bytes-ref r spos)))
@ -633,9 +635,12 @@
255 255
;; `min' shouldn't be necessary, but it's ;; `min' shouldn't be necessary, but it's
;; just in case the data is ill-formed ;; just in case the data is ill-formed
(unsafe-fxmin 255 (unsafe-fxquotient (unsafe-fxmin 255
(unsafe-fx* v 255) (unsafe-fl->fx
a))) (unsafe-flround
(unsafe-fl/
(unsafe-fx->fl (fx* 255 v))
(unsafe-fx->fl a))))))
v)])]) v)])])
(when set-alpha? (when set-alpha?
(unsafe-bytes-set! bstr pi a)) (unsafe-bytes-set! bstr pi a))
@ -696,7 +701,7 @@
[pm (lambda (a v) [pm (lambda (a v)
(if pre-mult? (if pre-mult?
(min a v) (min a v)
(quotient (* a v) 255)))]) (alpha-mult a v)))])
(bytes-set! data (+ ri A) a) (bytes-set! data (+ ri A) a)
(bytes-set! data (+ ri R) (pm a (bytes-ref bstr (+ pi 1)))) (bytes-set! data (+ ri R) (pm a (bytes-ref bstr (+ pi 1))))
(bytes-set! data (+ ri G) (pm a (bytes-ref bstr (+ pi 2)))) (bytes-set! data (+ ri G) (pm a (bytes-ref bstr (+ pi 2))))