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improved docs for overlay/xy a little

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svn: r10622
This commit is contained in:
Robby Findler 2008-07-05 18:42:16 +00:00
parent 5f581afc58
commit 84600d6b99
1 changed files with 21 additions and 4 deletions
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collects/teachpack/htdp/scribblings/image.scrbl
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@ -153,10 +153,27 @@ first image.
@defproc[(overlay/xy [img image?] [delta-x number?] [delta-y number?] [other image?]) image?]{
Creates an image by adding the pixels of @scheme[other] to
@scheme[img]. Instead of lining up on the pinhole, @scheme[other]'s pinhole
is lined up with an offset of (@scheme[delta-x],@scheme[delta-y]) from the
pinhole of @scheme[img]. The pinhole of the resulting image is the same
place as the pinhole in the first image.}
@scheme[img].
Instead of lining the two images up on their pinholes,
@scheme[other]'s pinhole is lined up on the point:
@schemeblock[
(make-posn (+ (pinhole-x img) delta-x)
(+ (pinhole-y img) delta-y))
]
The pinhole of the resulting image is the same
place as the pinhole in the first image.
The same effect can be had by combining
@scheme[move-pinhole] and @scheme[overlay],
@schemeblock[
(overlay img
(move-pinhole other
(- delta-x)
(- delta-y)))]
}
@defproc[(image-inside? [img image?] [other image?]) boolean?]{
Determines whether the pixels of the second image appear in the first.