On Mon, Dec 27, 2010 at 7:58 AM, Robby Findler
<ro...@eecs.northwestern.edu> wrote:
> [ sorry -- hit send too soon. ]
>
> I like your idea for alphas in colors. I'll add that, hopefully today.
I've added that now (just now pushed) and below is the revised version
of the map-image function to take advantage of it. The example
map-image demonstrate how using the alpha values can improve the
output.
(Still missing good error checking, tho.)
Robby
#lang racket/base
(require racket/draw
racket/snip
racket/class
2htdp/image
(only-in mrlib/image-core render-image))
(define (map-image img f)
(define w (image-width img))
(define h (image-height img))
(define bm (make-bitmap w h))
(define bdc (make-object bitmap-dc% bm))
(render-image img bdc 0 0)
(send bdc set-bitmap #f)
(define bytes (make-bytes (* w h 4)))
(send bm get-argb-pixels 0 0 w h bytes)
(for ([i (in-range 0 (* w h 4) 4)])
(define nc
(f (make-color (bytes-ref bytes (+ i 1))
(bytes-ref bytes (+ i 2))
(bytes-ref bytes (+ i 3))
(bytes-ref bytes i))))
(bytes-set! bytes i (color-alpha nc))
(bytes-set! bytes (+ i 1) (color-red nc))
(bytes-set! bytes (+ i 2) (color-green nc))
(bytes-set! bytes (+ i 3) (color-blue nc)))
(send bm set-argb-pixels 0 0 w h bytes)
(make-object image-snip% bm))
(define i
(overlay (rectangle 100 10 "solid" "red")
(circle 20 "solid" "lightblue")
(rectangle 10 100 "solid" "forestgreen")))
(define (grey c)
(define avg (floor (/ (+ (color-red c)
(color-blue c)
(color-green c))
3)))
(color avg avg avg))
(define (grey/alpha c)
(define avg (floor (/ (+ (color-red c)
(color-blue c)
(color-green c))
3)))
(color avg avg avg (color-alpha c)))
i
(map-image i grey)
(map-image i grey/alpha)
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