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Beginnings of the Wayward Programmer



Another try with HTDP 2nd Edition

Posted by , in Scheme 08 January 2012 - - - - - - · 1,278 views

http://www.ccs.neu.e...e/prologue.html

(define BOARDWIDTH 200)
(define BOARDHEIGHT 200)
(define STARTPOSITION 50)
(define BOARDBKGR "blue")
(define GAMEBOARD (empty-scene BOARDWIDTH BOARDHEIGHT BOARDBKGR))
(define ROCKET .)
(define UFO (overlay (circle 10 "solid" "red")
				   (rectangle 40 4 "solid" "green")))
(define FLATBED (rectangle 60 10 "outline" "black"))
(define (SPACESHIP option)
  (cond
	[(= option 1) ROCKET]
	[(= option 2) UFO]))
(define SHOWNSHIP (SPACESHIP 1))
(define V 10) ;Velocity
(define A 1)  ;Acceleration
(define (distance t)  ;t = Time
  (- (* V t) (* 1/2 A (sqr t))))
(define SPACESHIP-BOTTOM (- BOARDHEIGHT (/ (image-height SHOWNSHIP) 2)))
(define (render-shownship x y)
  (place-image SHOWNSHIP x y GAMEBOARD))
(define (create-rocket-scene.v7 t)
  (cond
	[(<= (distance t) SPACESHIP-BOTTOM)
	 (render-shownship STARTPOSITION (distance t))]
	[(> (distance t) SPACESHIP-BOTTOM)
	 (render-shownship STARTPOSITION SPACESHIP-BOTTOM)]))
	

This code is based off of Chapter 1 of HTDP. I've gotten this far and it wasn't as bad as last time. And it's been 5 years (I can't believe it) since I've touched this language. The only issues I have really are two things.
  • I couldn't find a way to do one of the suggestions. Which was: How would change the program so that the rocket lands on a flat rock bed that is 10 pixels higher than the bottom of the scene? Don’t forget to change the scenery, too. When I tried adding another function call to render-shownship, I kept getting an error.
  • The spaceship goes down to the bottom of the screen, then accelerates up the screen. I'm a bit lost on why that is.

Outside of those two things. I'm quite happy with my progress. I've thankfully gotten over the prefix issue as well, lol.





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