[ sorry -- hit send too soon. ]
I like your idea for alphas in colors. I'll add that, hopefully today.
In the meantime, here's map-image with the current colors.
#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-set! bytes i 255)
(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))
(overlay (rectangle 100 10 "solid" "purple")
(rectangle 10 100 "solid" "forestgreen"))
(map-image (overlay (rectangle 100 10 "solid" "purple")
(rectangle 10 100 "solid" "forestgreen"))
(λ (c)
(define avg (floor (/ (+ (color-red c)
(color-blue c)
(color-green c))
3)))
(make-color avg avg avg)))
On Mon, Dec 27, 2010 at 7:47 AM, Robby Findler
<[email protected]> wrote:
> On Mon, Dec 27, 2010 at 7:13 AM, Stephen Bloch <[email protected]> wrote:
>> I'm trying to port the picturing-programs teachpack to still work with 5.1.
>> (BTW, approximately how long do I have to do that before 5.1 is released?)
>
> We have not started the release process yet, but the release is
> sometime in Jan. Generally releases are every 3 months. Ryan should
> know the precise dates.
>
>> Right now it crashes because the API for make-bitmap has changed -- for the
>> better, I think, but I still need to fix things.
>
> Which make-bitmap would that be? Are you talking about the internal,
> private constructor?
>
>> I've got a "map-image" function that creates a [bitmap] image the same width
>> and height as an existing image by mapping a color->color function on its
>> pixels, and a "build-image" function that creates a [bitmap] image of a
>> specified width and height by mapping a specified function on the
>> coordinates of its pixels. I also wrote (but didn't really document) a
>> "map-masked-image" and "build-masked-image" which do the same, but the
>> mapped function is also allowed to return #f, in which case the specified
>> pixel is made transparent (i.e. alpha=0). I can tweak those to work with
>> the new make-bitmap, but the process got me wondering...
>>
>> It would be nice if I could allow students to generate alphas other than 1
>> and 0. It seems to me the cleanest way to do this is with an alpha-color
>> struct (which existed in htdp/image, but seems to be gone from 2htdp/image).
>> I can do that myself, putting in glue code between it and 2htdp/image to
>> convert back and forth among various color-like-things (color, alpha-color,
>> string, symbol, color%, and #f for transparency), but 2htdp/image is already
>> doing a lot of that, and it feels really inefficient to re-do it.
>>
>> What would you think of ALL "color" structs actually having an alpha
>> component, with the constructor allowing alpha to default to 1?
>
> I think you should be operating at the racket/draw bitmap level, not
> the 2htdp/image bitmap level. That is, use the render-image function
> to get a bitmap, and then make a loop that calls their function and
> fills in a bytes and then turn that bytes back into a bitmap. This
> will save creating a bunch of intermediate data and is a simpler
> function overall.
>
> Robby
>
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