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ex099.rkt
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;; The first three lines of this file were inserted by DrRacket. They record metadata
;; about the language level of this file in a form that our tools can easily process.
#reader(lib "htdp-beginner-reader.ss" "lang")((modname ex099) (read-case-sensitive #t) (teachpacks ((lib "image.rkt" "teachpack" "2htdp") (lib "universe.rkt" "teachpack" "2htdp") (lib "batch-io.rkt" "teachpack" "2htdp"))) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ((lib "image.rkt" "teachpack" "2htdp") (lib "universe.rkt" "teachpack" "2htdp") (lib "batch-io.rkt" "teachpack" "2htdp")) #f)))
; Constants
(define BASE-UNIT 5) ; 1 bu = 5 px
(define HEIGHT (* 40 BASE-UNIT))
(define WIDTH HEIGHT)
(define BACKGROUND
(overlay/align "center" "bottom"
(rectangle WIDTH BASE-UNIT "solid" "brown")
(empty-scene WIDTH HEIGHT "darkblue")))
(define UFO-RADIUS (* 2 BASE-UNIT))
(define UFO-WIDTH (* 4 UFO-RADIUS))
(define UFO-X-CENTER (/ UFO-WIDTH 2))
(define UFO
(overlay (rectangle UFO-WIDTH BASE-UNIT "solid" "green")
(circle UFO-RADIUS "solid" "green")))
(define TANK-HEIGHT (* 3 BASE-UNIT))
(define TANK-WIDTH (* 2 TANK-HEIGHT))
(define TANK-X-CENTER (/ TANK-WIDTH 2))
(define TANK-Y-CENTER (/ TANK-HEIGHT 2))
(define Y-TANK (- HEIGHT TANK-Y-CENTER BASE-UNIT))
(define TANK (rectangle TANK-WIDTH TANK-HEIGHT "solid" "darkgreen"))
(define MISSILE-SIZE (* 2 BASE-UNIT))
(define MISSILE-CENTER (/ MISSILE-SIZE 2))
(define MISSILE-LAUNCH-Y (- Y-TANK TANK-Y-CENTER MISSILE-CENTER))
(define MISSILE (triangle MISSILE-SIZE "solid" "red"))
(define EXPLOSION-INNER (* 2 BASE-UNIT))
(define EXPLOSION-OUTER (* 2 EXPLOSION-INNER))
(define EXPLOSION
(overlay (radial-star 15 EXPLOSION-INNER EXPLOSION-OUTER "outline" "red")
(radial-star 15 EXPLOSION-INNER EXPLOSION-OUTER "solid" "yellow")))
(define MESSAGE-HEIGHT (* 10 BASE-UNIT))
(define MESSAGE-TEXT-SIZE 16)
(define MESSAGE-VICTORY "VICTORY!")
(define MESSAGE-DEFEAT "DEFEAT!")
(define VX-TANK 3) ; The UFO moves at a speed of 3 px/tick
(define VY-UFO BASE-UNIT) ; The UFO descends at a speed of 1 bu/tick
(define VY-MISSILE (* 2 VY-UFO)) ; The missile ascends at 2x the UFO's speed
; A UFO is a Posn.
; interpretation (make-posn x y) is the UFO's location
; (using the top-down, left-to-right convention)
(define-struct tank [loc vel])
; A Tank is a structure:
; (make-tank Number Number).
; interpretation (make-tank x dx) specifies the position:
; (x, Y-TANK) and the tank's speed: dx pixels/tick
; A Missile is a Posn.
; interpretation (make-posn x y) is the missile's place
; Example structures
(define t75 (make-tank 75 3))
(define t56 (make-tank 56 3))
(define t125 (make-tank 125 -3))
(define t170 (make-tank 170 -3))
(define u10x50y (make-posn 10 50))
(define u56x112y (make-posn 56 112))
(define u56x10y (make-posn 56 10))
(define u106x185y (make-posn 106 190))
(define m56xly (make-posn 56 MISSILE-LAUNCH-Y))
(define m56x112y (make-posn 56 112))
; Example images
(define tr75 (place-image TANK 75 Y-TANK BACKGROUND))
(define tr56 (place-image TANK 56 Y-TANK BACKGROUND))
(define tr125 (place-image TANK 125 Y-TANK BACKGROUND))
(define tr170 (place-image TANK 170 Y-TANK BACKGROUND))
(define ur10x50y (place-image UFO 10 50 BACKGROUND))
(define ur56x112y (place-image UFO 56 112 BACKGROUND))
(define ur56x10y (place-image UFO 56 10 BACKGROUND))
(define ur106x185y (place-image UFO 106 190 BACKGROUND))
(define mr56xly (place-image MISSILE 56 MISSILE-LAUNCH-Y BACKGROUND))
(define mr56x112y (place-image MISSILE 56 112 BACKGROUND))
(define-struct aim [ufo tank])
(define-struct fired [ufo tank missile])
; A SIGS is one of:
; – (make-aim UFO Tank)
; – (make-fired UFO Tank Missile)
; interpretation represents the complete state of a
; space invader game
; Example states
(define s1 (make-aim u10x50y t75))
(define s2 (make-aim u56x10y t56))
(define s3 (make-fired u56x10y t56 m56xly))
(define s4 (make-fired u56x112y t56 m56x112y))
(define s5 (make-fired u106x185y t125 m56x112y))
; SIGS -> Image
; renders the given game state on top of BACKGROUND
; for examples see figure 32
(define (si-render s)
(cond
[(aim? s)
(tank-render (aim-tank s)
(ufo-render (aim-ufo s) BACKGROUND))]
[(fired? s)
(tank-render
(fired-tank s)
(ufo-render (fired-ufo s)
(missile-render (fired-missile s)
BACKGROUND)))]))
(check-expect (si-render s1)
(tank-render t75 (ufo-render u10x50y BACKGROUND)))
(check-expect (si-render s2)
(tank-render t56 (ufo-render u56x10y BACKGROUND)))
(check-expect (si-render s3)
(tank-render t56
(ufo-render u56x10y
(missile-render m56xly BACKGROUND))))
(check-expect (si-render s4)
(tank-render t56
(ufo-render u56x112y
(missile-render m56x112y BACKGROUND))))
(check-expect (si-render s5)
(tank-render t125
(ufo-render u106x185y
(missile-render m56x112y BACKGROUND))))
; Tank Image -> Image
; adds t to the given image im
(define (tank-render t im)
(place-image TANK (tank-loc t) Y-TANK im))
(check-expect (tank-render t75 BACKGROUND) tr75)
(check-expect (tank-render t56 BACKGROUND) tr56)
(check-expect (tank-render t125 BACKGROUND) tr125)
(check-expect (tank-render t170 BACKGROUND) tr170)
; UFO Image -> Image
; adds u to the given image im
(define (ufo-render u im)
(place-image UFO (posn-x u) (posn-y u) im))
(check-expect (ufo-render u10x50y BACKGROUND) ur10x50y)
(check-expect (ufo-render u56x112y BACKGROUND) ur56x112y)
(check-expect (ufo-render u56x10y BACKGROUND) ur56x10y)
(check-expect (ufo-render u106x185y BACKGROUND) ur106x185y)
; Missile Image -> Image
; adds m to the given image im
(define (missile-render m im)
(place-image MISSILE (posn-x m) (posn-y m) im))
(check-expect (missile-render m56xly BACKGROUND) mr56xly)
(check-expect (missile-render m56x112y BACKGROUND) mr56x112y)
; Posn Posn -> Number
; calculates the distance between two positions
(define (distance-points a b)
(sqrt (+ (sqr (- (posn-x a) (posn-x b)))
(sqr (- (posn-y a) (posn-y b))))))
(check-expect (distance-points (make-posn 0 0) (make-posn 3 4)) 5)
(check-expect (distance-points (make-posn -2 -3) (make-posn 4 5)) 10)
; SIGS -> Boolean
; checks if the missile hit the UFO
(define (hit-ufo? s)
(and (fired? s) (<= (distance-points (fired-ufo s) (fired-missile s))
UFO-RADIUS)))
; SIGS -> Boolean
; checks if the UFO landed
(define (ufo-landed? s)
(or (and (fired? s) (<= (- HEIGHT BASE-UNIT (posn-y (fired-ufo s)))
UFO-RADIUS))
(and (aim? s) (<= (- HEIGHT BASE-UNIT (posn-y (aim-ufo s)))
UFO-RADIUS))))
; SIGS -> SIGS
; stops the game if the UFO lands or if the missile hits the UFO
(define (si-game-over? s)
(or (hit-ufo? s) (ufo-landed? s)))
(check-expect (si-game-over? s1) #false)
(check-expect (si-game-over? s2) #false)
(check-expect (si-game-over? s3) #false)
(check-expect (si-game-over? s4) #true)
(check-expect (si-game-over? s5) #true)
; String Color Image -> Image
; overlays text str of color c over the image im
(define (overlay-text str c im)
(overlay (overlay (text str MESSAGE-TEXT-SIZE c)
(rectangle WIDTH MESSAGE-HEIGHT "solid" (color 0 0 0 128)))
im))
; UFO Image -> Image
; places explosion on the UFO's position over image im
(define (ufo-explosion u im)
(place-image EXPLOSION (posn-x u) (posn-y u) im))
; SIGS -> Image
; renders the final image of the game, indicating victory or defeat
(define (si-render-final s)
(overlay-text (cond [(hit-ufo? s) MESSAGE-VICTORY]
[(ufo-landed? s) MESSAGE-DEFEAT])
(cond [(hit-ufo? s) "white"]
[(ufo-landed? s) "red"])
(cond [(hit-ufo? s) (ufo-explosion (fired-ufo s) (si-render s))]
[(ufo-landed? s) (si-render s)])))
(check-expect (si-render-final s4)
(overlay (overlay (text MESSAGE-VICTORY MESSAGE-TEXT-SIZE "white")
(rectangle WIDTH MESSAGE-HEIGHT
"solid" (color 0 0 0 128)))
(ufo-explosion u56x112y (si-render s4))))
(check-expect (si-render-final s5)
(overlay (overlay (text MESSAGE-DEFEAT MESSAGE-TEXT-SIZE "red")
(rectangle WIDTH MESSAGE-HEIGHT
"solid" (color 0 0 0 128)))
(si-render s5)))
; UFO -> Boolean
; checks if the UFO is close to the right and left edges of the frame
(define (ufo-close-to-edges? u)
(or (<= (posn-x u) UFO-RADIUS) (>= (posn-x u) (- WIDTH UFO-RADIUS))))
; UFO Number Number -> UFO
; moves UFO to the right dx pixels and down dy pixels, ensuring
; it doesn't move out of frame horizontally
(define (move-ufo u dx dy)
(make-posn (if (ufo-close-to-edges? u)
(posn-x u)
(+ (posn-x u) dx))
(+ (posn-y u) dy)))
; Missile Number -> Missile
; moves missile dy pixels upward
(define (move-missile m dy)
(make-posn (posn-x m) (- (posn-y m) dy)))
; Tank Number Number -> Tank
; moves tank to the left or right, according to its velocity
(define (move-tank t)
(make-tank (+ (tank-loc t) (tank-vel t)) (tank-vel t)))
; SIGS Number -> SIGS
; moves the space-invader objects; UFO moves horizontally by dx-u
(define (si-move-proper s dx-u)
(cond
[(aim? s)
(make-aim (move-ufo (aim-ufo s) dx-u VY-UFO)
(move-tank (aim-tank s)))]
[(fired? s)
(make-fired (move-ufo (fired-ufo s) dx-u VY-UFO)
(move-tank (fired-tank s))
(move-missile (fired-missile s) VY-MISSILE))]))
(check-expect (si-move-proper s1 3)
(make-aim (make-posn 10 55)
(make-tank 78 3)))
(check-expect (si-move-proper s2 3)
(make-aim (make-posn 59 15)
(make-tank 59 3)))
(check-expect (si-move-proper s3 -2)
(make-fired (make-posn 54 15)
(make-tank 59 3)
(make-posn 56 165)))
(check-expect (si-move-proper (make-aim u56x112y t125) 5)
(make-aim (make-posn 61 117)
(make-tank 122 -3)))
; Number -> Number
; produces random number in the interval [-n,n]
(define (random-interval-n n)
(- (random (+ (* 2 n) 1)) n))
; SIGS -> SIGS
; moves the space-invader objects after each tick; UFO makes random jumps
; to the left or right of at 1 BASE-UNIT
(define (si-move s)
(si-move-proper s (random-interval-n BASE-UNIT)))