27 lines
839 B
Scheme
27 lines
839 B
Scheme
#lang frtime
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(require frtime/animation)
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(define ufo-x
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(modulo
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(+ 200 ; center of window
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(floor
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(integral ; integrate over time
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(* .04 ; scale speed to appropriate # of pixels/ms
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(- 3 ; start off stationary
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; use left and right arrows to accelerate
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; (up to 3 in either direction)
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(range-control (key 'left) (key 'right) 6 3))))))
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450))
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(define ufo-y ; bob up and down 5 pixels around center of window
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(+ 200 (* 5 (sin (/ milliseconds 200)))))
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(define ufo-bright ; flash light and dark
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(/ (add1 (cos (/ milliseconds 100))) 3))
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(define ufo-color
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(make-rgb ufo-bright ufo-bright ufo-bright))
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(display-shapes
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(list
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(make-circle (make-posn ufo-x ufo-y) 10 ufo-color)
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(make-rect (make-posn (- ufo-x 20) (- ufo-y 2))
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40 4 ufo-color)))
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