added bitmap/file

closes PR 12466

collects/2htdp/image.rkt

@@ -135,7 +135,8 @@ and they all have good sample contracts. (It is amazing what we can do with kids
          save-svg-image
          
          freeze
-         bitmap/url)
+         bitmap/url
+         bitmap/file)
 
 (provide bitmap
          empty-image)

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

@@ -1317,6 +1317,14 @@
                    (λ (port)
                      (make-object bitmap% port 'unknown #f #t)))))
                       
+(define/chk (bitmap/file filename)
+  (unless (file-exists? filename)
+    (error 'bitmap/file 
+           "could not find the file ~a" 
+           filename))
+  (rotate
+   0
+   (read-bitmap filename)))
 
 (define/chk (image->color-list image)
   (let* ([w (image-width image)]
@@ -1495,6 +1503,7 @@
          
          bitmap
          bitmap/url
+         bitmap/file
          
          swizzle
          

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

@@ -1247,6 +1247,16 @@ See also the @racketmodname[2htdp/planetcute] library.
   and then paste it into your program or download it and use @racket[bitmap].
 }
 
+@defproc[(bitmap/file [ps path-string?]) image?]{
+  Loads the image from @racket[ps].
+
+  If @racket[ps] is a relative path, the file is relative to
+  the current directory. (When running in DrRacket, the current
+  directory is set to the place where the definitions window is
+  saved, but in general this can be an arbitrary directory.)
+}
+
+
 @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.