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added an example

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svn: r11835
This commit is contained in:
Matthias Felleisen 2008-09-22 18:07:36 +00:00
parent ce10c4a5fc
commit 52b9740042
1 changed files with 18 additions and 1 deletions
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19
collects/teachpack/htdp/scribblings/world.scrbl
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@ -71,7 +71,7 @@ pinholes are at position @scheme[(0,0)].
for describing students work. for describing students work.
} }
In addition, Example:
@schemeblock[ @schemeblock[
(define (create-UFO-scene height) (define (create-UFO-scene height)
(place-image UFO 50 height (empty-scene 100 100))) (place-image UFO 50 height (empty-scene 100 100)))
@ -174,6 +174,23 @@ A @tech{KeyEvent} represents key board events, e.g., keys pressed or
tick events, @tech{KeyEvent}s, or @tech{MouseEvent}s are forwarded to tick events, @tech{KeyEvent}s, or @tech{MouseEvent}s are forwarded to
the respective handlers. As a result, the canvas isn't updated either.} the respective handlers. As a result, the canvas isn't updated either.}
Example: The following examples shows that @scheme[(run-simulation 100 100
(/ 1 28) create-UFO-scene)] is a short-hand for three lines of code:
@schemeblock[
(define (create-UFO-scene height)
(place-image UFO 50 height (empty-scene 100 100)))
(define UFO
(overlay (circle 10 'solid 'green)
(rectangle 40 4 'solid 'green)))
(big-bang 100 100 (/1 28) 0)
(on-tick-event add1)
(on-redraw create-UFO-scene)
]
Exercise: Add a condition for stopping the flight of the UFO when it
reaches the bottom.
@section{Scenes and Images} @section{Scenes and Images}
For the creation of scenes from the world, use the functions from @secref["image"]. The following two For the creation of scenes from the world, use the functions from @secref["image"]. The following two