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add pre-multiplied mode for `{get,set}-argb-pixels'

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This commit is contained in:
Matthew Flatt 2011-05-18 12:24:25 -07:00
parent 006d5ef45a
commit b6445880e2
5 changed files with 73 additions and 20 deletions
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10
collects/racket/draw/private/bitmap-dc.rkt
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@ -132,20 +132,22 @@
[exact-nonnegative-integer? w]
[exact-nonnegative-integer? h]
[bytes? bstr]
[any? [set-alpha? #f]])
[any? [set-alpha? #f]]
[any? [pre-mult? #f]])
(let ([bm (internal-get-bitmap)])
(when bm
(send bm set-argb-pixels x y w h bstr set-alpha?))))
(send bm set-argb-pixels x y w h bstr set-alpha? pre-mult?))))
(def/public (get-argb-pixels [exact-nonnegative-integer? x]
[exact-nonnegative-integer? y]
[exact-nonnegative-integer? w]
[exact-nonnegative-integer? h]
[bytes? bstr]
[any? [get-alpha? #f]])
[any? [get-alpha? #f]]
[any? [pre-mult? #f]])
(let ([bm (internal-get-bitmap)])
(when bm
(send bm get-argb-pixels x y w h bstr get-alpha?))))
(send bm get-argb-pixels x y w h bstr get-alpha? pre-mult?))))
(def/public (draw-bitmap-section-smooth [bitmap% src]
[real? dest-x]

18
collects/racket/draw/private/bitmap.rkt
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@ -572,7 +572,8 @@
[exact-nonnegative-integer? w]
[exact-nonnegative-integer? h]
[bytes? bstr]
[any? [get-alpha? #f]])
[any? [get-alpha? #f]]
[any? [pre-mult? #f]])
(unless ((bytes-length bstr) . >= . (* w h 4))
(raise-mismatch-error (method-name 'bitmap% 'get-argb-pixels)
"byte string is too short: "
@ -581,10 +582,10 @@
(if alt?
(call-with-alt-bitmap
x y w h
(lambda (bm) (send bm get-argb-pixels 0 0 w h bstr get-alpha?)))
(do-get-argb-pixels x y w h bstr get-alpha?))))
(lambda (bm) (send bm get-argb-pixels 0 0 w h bstr get-alpha? pre-mult?)))
(do-get-argb-pixels x y w h bstr get-alpha? pre-mult?))))
(define/private (do-get-argb-pixels x y w h bstr get-alpha?)
(define/private (do-get-argb-pixels x y w h bstr get-alpha? pre-mult?)
;; Fill range that is beyond edge of picture:
(if get-alpha?
(for* ([i (in-range width (+ x w))]
@ -603,7 +604,7 @@
(cairo_surface_flush s)
(let ([data (cairo_image_surface_get_data s)]
[row-width (cairo_image_surface_get_stride s)]
[use-alpha? (or alpha-channel? b&w?)]
[use-alpha? (or (and alpha-channel? (not pre-mult?)) b&w?)]
[set-alpha? alpha-channel?])
(let ([w2 (+ x (min (- width x) w))])
(for* ([j (in-range y (min (+ y h) height))])
@ -652,7 +653,8 @@
[exact-nonnegative-integer? w]
[exact-nonnegative-integer? h]
[bytes? bstr]
[any? [set-alpha? #f]])
[any? [set-alpha? #f]]
[any? [pre-mult? #f]])
(unless ((bytes-length bstr) . >= . (* w h 4))
(raise-mismatch-error (method-name 'bitmap% 'set-argb-pixels)
"byte string is too short: "
@ -687,7 +689,9 @@
(if alpha-channel?
(let ([a (bytes-ref bstr pi)]
[pm (lambda (a v)
(quotient (* a v) 255))])
(if pre-mult?
(min a v)
(quotient (* a v) 255)))])
(bytes-set! data (+ ri A) a)
(bytes-set! data (+ ri R) (pm a (bytes-ref bstr (+ pi 1))))
(bytes-set! data (+ ri G) (pm a (bytes-ref bstr (+ pi 2))))

6
collects/scribblings/draw/bitmap-class.scrbl
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@ -63,7 +63,8 @@ When a @scheme[bits] byte string is provided: Creates a monochrome
[width exact-nonnegative-integer?]
[height exact-nonnegative-integer?]
[pixels (and/c bytes? mutable?)]
[alpha? any/c #f])
[just-alpha? any/c #f]
[pre-multiplied? any/c #f])
void?]{
Produces the same result as @xmethod[bitmap-dc% get-argb-pixels], but the
@ -264,7 +265,8 @@ A monochrome bitmap saved as @scheme['png] without a mask bitmap
[width exact-nonnegative-integer?]
[height exact-nonnegative-integer?]
[pixels bytes?]
[alpha? any/c #f])
[just-alpha? any/c #f]
[pre-multiplied? any/c #f])
void?]{
The same as @xmethod[bitmap-dc% set-argb-pixels], but the

28
collects/scribblings/draw/bitmap-dc-class.scrbl
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@ -54,7 +54,8 @@ In older versions, this method smoothed drawing more than
[width exact-nonnegative-integer?]
[height exact-nonnegative-integer?]
[pixels (and/c bytes? (not/c immutable?))]
[alpha? any/c #f])
[just-alpha? any/c #f]
[pre-multiplied? any/c #f])
void?]{
Gets a rectangle of pixels in the bitmap, subject to the same rules
@ -73,15 +74,20 @@ The pixel RGB values are copied into @scheme[pixels]. The first byte
DC. The pixels are in row-major order, left to right then top to
bottom.
If @scheme[alpha?] is false, if the bitmap does not have an alpha
If @scheme[just-alpha?] is false, if the bitmap does not have an alpha
channel, then the alpha value for each pixel is set to 255. If
@scheme[alpha?] is true, then @italic{only} the alpha value is set
@scheme[just-alpha?] is true, then @italic{only} the alpha value is set
for each pixel; if the bitmap has no alpha channel, then the alpha
value is based on each pixel's inverted RGB average. Thus, when a
bitmap has a separate mask bitmap, the same @scheme[pixels] byte
string is in general filled from two bitmaps: one (the main image)
for the pixel values and one (the mask) for the alpha values.
If @racket[pre-multiplied?] is true, @scheme[just-alpha?] is false,
and the bitmap has an alpha channel, then RGB values in the result
are scaled by the corresponding alpha value (i.e., multiplied by the
alpha value and then divided by 255).
}
@defmethod[(get-bitmap)
@ -110,7 +116,8 @@ result is @scheme[#f].
[width exact-nonnegative-integer?]
[height exact-nonnegative-integer?]
[pixels bytes?]
[alpha? any/c #f])
[just-alpha? any/c #f]
[pre-multiplied? any/c #f])
void?]{
@ -126,8 +133,9 @@ The pixel RGB values are taken from @scheme[pixels]. The first byte
determine the new pixel values in the DC. The pixels are in row-major
order, left to right then top to bottom.
If @scheme[alpha?] is false, then the alpha value for each pixel is
used only if the DC's current bitmap has an alpha channel. If @scheme[alpha?] is true, then each
If @scheme[just-alpha?] is false, then the alpha value for each pixel is
used only if the DC's current bitmap has an alpha channel. If
@scheme[just-alpha?] is true and the bitmap has no alpha channel, then each
pixel is set based @italic{only} on the alpha value, but inverted to serve
as a mask. Thus, when working with bitmaps that have an associated mask
bitmap instead of an alpha channel, the same
@ -135,6 +143,14 @@ If @scheme[alpha?] is false, then the alpha value for each pixel is
(the main image) for the pixel values and one (the mask) for the
alpha values.
If @racket[pre-multiplied?] is true, @scheme[just-alpha?] is false,
and the bitmap has an alpha channel, then RGB values in
@racket[pixels] are interpreted as scaled by the corresponding alpha value
(i.e., multiplied by the alpha value and then divided by 255). If an
R, G, or B value is greater than its corresponding alpha value (which
is not possible if the value is properly scaled), then it is effectively
reduced to the alpha value.
}
@defmethod[(set-bitmap [bitmap (or/c (is-a?/c bitmap%) false/c)])

31
collects/tests/gracket/dc.rktl
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@ -364,6 +364,7 @@
(mk #"\377\377\377\377\377\377\377\377\377\0\0\0\377\0\0\0" 'opaque black white #t))
;; ----------------------------------------
;; check get-alpha mode of `get-argb-pixels'
(let ()
(define (get-column-alpha bm x y)
@ -378,7 +379,7 @@
(bytes-ref bstr 2))
3)))
(send abm set-argb-pixels 0 0 2 2 #"0123456789abcdef")
(send nbm set-argb-pixels 0 0 2 2 #"0123456789abcdef")
(send nbm set-argb-pixels 0 0 2 2 #"0123456789abcdef") ; alphas ignored
(test (bytes (char->integer #\0) 0 0 0) 'a0+0 (get-column-alpha abm 0 0))
(test (bytes (char->integer #\4) 0 0 0) 'a1+0 (get-column-alpha abm 1 0))
@ -390,6 +391,34 @@
(test (bytes (avg #"9ab") 0 0 0) 'n0+1 (get-column-alpha nbm 0 1))
(test (bytes (avg #"def") 0 0 0) 'n1+1 (get-column-alpha nbm 1 1)))
;; ----------------------------------------
;; check pre-mult mode of `{get,set}-argb-pixels'
(let ()
(define abm (make-object bitmap% 2 2 #f #t))
(define nbm (make-object bitmap% 2 2 #f #f))
(send abm set-argb-pixels 0 0 2 2 #"30127456b89afcde" #f #t)
(send nbm set-argb-pixels 0 0 2 2 #"0123456789abcdef" #f #t) ; alphas ignored
(define (get-pixels bm pre-mult?)
(define bs (make-bytes 16))
(send bm get-argb-pixels 0 0 2 2 bs #f pre-mult?)
bs)
(define (unmul b)
(define (um v) (quotient (* v 255) (bytes-ref b 0)))
(bytes (bytes-ref b 0)
(um (bytes-ref b 1))
(um (bytes-ref b 2))
(um (bytes-ref b 3))))
(test #"\xFF123\xFF567\xFF9ab\xFFdef" 'no-alpha (get-pixels nbm #f))
(test #"\xFF123\xFF567\xFF9ab\xFFdef" 'no-alpha (get-pixels nbm #t))
(test (apply bytes-append (map unmul '(#"3012" #"7456" #"b89a" #"fcde")))
'alpha-normal (get-pixels abm #f))
(test #"30127456b89afcde" 'alpha-premult (get-pixels abm #t)))
;; ----------------------------------------