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add some color to the image guide's fractals

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and use local instead of internal define to
be more HtDP friendly
This commit is contained in:
Robby Findler 2012-12-31 11:42:26 -06:00
parent 8f300b9e73
commit 2a83c2147c
1 changed files with 42 additions and 14 deletions
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56
collects/teachpack/2htdp/scribblings/image-guide.scrbl
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@ -29,6 +29,9 @@
(interaction-eval-show #:eval guide-eval exp) (interaction-eval-show #:eval guide-eval exp)
(guide-eval '(extra-margin 0)))) (guide-eval '(extra-margin 0))))
@(interaction-eval #:eval guide-eval
(require racket/list racket/local))
@title[#:tag "image-guide"]{Image Guide} @title[#:tag "image-guide"]{Image Guide}
@ -219,28 +222,53 @@ library, e.g.:
@image-interaction[(define (sierpinski-carpet n) @image-interaction[(define (sierpinski-carpet n)
(cond (cond
[(zero? n) (square 2 "solid" "black")] [(zero? n) (square 1 "solid" "black")]
[else [else
(define c (sierpinski-carpet (- n 1))) (local [(define c (sierpinski-carpet (- n 1)))
(define i (square (image-width c) "solid" "white")) (define i (square (image-width c) "solid" "white"))]
(above (beside c c c) (above (beside c c c)
(beside c i c) (beside c i c)
(beside c c c))]))] (beside c c c)))]))]
@image-interaction[(sierpinski-carpet 4)] @image-interaction[(sierpinski-carpet 5)]
We can adjust the carpet to add a little color:
@image-interaction[(define (colored-carpet colors)
(cond
[(empty? (rest colors))
(square 1 "solid" (first colors))]
[else
(local [(define c (colored-carpet (rest colors)))
(define i (square (image-width c) "solid" (car colors)))]
(above (beside c c c)
(beside c i c)
(beside c c c)))]))]
@image-interaction[(colored-carpet
(list (color #x33 #x00 #xff)
(color #x66 #x00 #xff)
(color #x99 #x00 #xff)
(color #xcc #x00 #xff)
(color #xff #x00 #xff)
(color 255 204 0)))]
The Koch curve can be constructed by simply placing four
curves next to each other, rotated appropriately:
@image-interaction[(define (koch-curve n) @image-interaction[(define (koch-curve n)
(cond (cond
[(zero? n) (square 1 "solid" "black")] [(zero? n) (square 1 "solid" "black")]
[else [else
(define smaller (koch-curve (- n 1))) (local [(define smaller (koch-curve (- n 1)))]
(beside/align "bottom" (beside/align "bottom"
smaller smaller
(rotate 60 smaller) (rotate 60 smaller)
(rotate -60 smaller) (rotate -60 smaller)
smaller)]))] smaller))]))
(koch-curve 5)]
@image-interaction[(koch-curve 5)] And then put three of them together to form the Koch snowflake.
@image-interaction[(above @image-interaction[(above
(beside (beside