added bitmap/url to 2htdp/image

collects/2htdp/image.rkt

@@ -128,7 +128,8 @@ and they all have good sample contracts. (It is amazing what we can do with kids
          step-count?
          save-image
          
-         freeze)
+         freeze
+         bitmap/url)
 
 (provide bitmap
          empty-image)

collects/2htdp/private/image-more.rkt

@@ -11,7 +11,8 @@
          racket/math
          (for-syntax racket/base
                      racket/list)
-         lang/posn)
+         lang/posn
+         net/url)
 
 ;; for testing
 ; (require racket/gui/base)
@@ -98,12 +99,6 @@
 ;                                         ;;   
                                                                             
 
-;; bitmap : string -> image
-;; gets one of the bitmaps that comes with drracket, scales it down by 1/8 or something
-;; so that later scaling /translation/whatever will look reasonable.
-;; (the error message for a bad argument will list all of the currently installed example images;
-;; we may want to have some way teachers can stick new ones in there)
-
 ;; scale : number image -> image
 (define/chk (scale factor image)
   (scale-internal factor factor image))
@@ -1273,6 +1268,16 @@
   ;; the rotate does a coercion to a 2htdp/image image
   (rotate 0 (make-object image-snip% (make-object bitmap% arg 'unknown/mask))))
 
+(define/chk (bitmap/url string)
+  ;; the rotate does a coercion to a 2htdp/image image
+  (rotate
+   0
+   (call/input-url (string->url string)
+                   get-pure-port
+                   (λ (port)
+                     (make-object bitmap% port 'unknown #f #t)))))
+                      
+
 (define/chk (image->color-list image)
   (let* ([w (image-width image)]
          [h (image-height image)]
@@ -1443,6 +1448,7 @@
          color-list->bitmap
          
          bitmap
+         bitmap/url
          
          swizzle
          

collects/teachpack/2htdp/scribblings/image.scrbl

@@ -1110,6 +1110,14 @@ more expensive than with the other shapes.
                   (bitmap icons/b-run.png)]
 }
 
+@defproc[(bitmap/url [url string?]) image?]{
+  Goes out on the web and downloads the image at @racket[url].
+
+  Downloading the image happens each time this function is called, so
+  you may find it simpler to download the image once with a browser 
+  and then paste it into your program or download it and use @racket[bitmap].
+}
+                                 
 @defproc[(image->color-list [image image?]) (listof color?)]{
   Returns a list of colors that correspond to the colors in the
   image, reading from left to right, top to bottom.