Tetris Game -- First Interactive Application

tetris-1.rkt

;; A tetris game -- partial implementation, part 1

;; Copyright (c) 2020 Alex Harsányi (AlexHarsanyi@gmail.com)

;; Permission is hereby granted, free of charge, to any person obtaining a
;; copy of this software and associated documentation files (the "Software"),
;; to deal in the Software without restriction, including without limitation
;; the rights to use, copy, modify, merge, publish, distribute, sublicense,
;; and/or sell copies of the Software, and to permit persons to whom the
;; Software is furnished to do so, subject to the following conditions:

;; The above copyright notice and this permission notice shall be included in
;; all copies or substantial portions of the Software.

;; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
;; IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
;; FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
;; AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
;; LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
;; FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
;; DEALINGS IN THE SOFTWARE.
#lang racket/gui
(require pict racket/draw racket/contract)

(module+ test
  (require rackunit)
  #;(printf "*** Will run tests~%"))


;;.................................................... Block Definitions ....

;; A tetris block is defined as a list of 4 strings, providing a nice visual
;; representation of the block inside the program code.  Each string can
;; contain one of the following characters: "." represents a space (we could
;; have used a space here, but the dot is easier to see and align).  One of
;; the letters IQLJTZS, we will use the letters to give each block a unique
;; color.

(define I-Block
  '(".I.."
    ".I.."
    ".I.."
    ".I.."))

(define Q-Block
  '("...."
    ".QQ."
    ".QQ."
    "...."))   

(define L-Block
  '("LL.."
    ".L.."
    ".L.."
    "...."))   

(define J-Block
  '(".JJ."
    ".J.."
    ".J.."
    "...."))   

(define T-Block
  '(".T.."
    "TTT."
    "...."
    "...."))

(define Z-Block
  '(".Z.."
    "ZZ.."
    "Z..."
    "...."))   

(define S-Block
  '("S..."
    "SS.."
    ".S.."
    "...."))   

;; A list of all the tetris blocks.  This will be used in the game to randomly
;; pick the next block, but also in our testing when we need to check a
;; function against all the tetris blocks.
(define all-blocks (list I-Block Q-Block L-Block J-Block T-Block Z-Block S-Block))

;; Return true if ROW is a valid block row, which means that it is a 4
;; character string, containing only the valid characters for tetris blocks.
(define (valid-block-row? row)
  (and (string? row)                     ; a row is a string
       (= (string-length row) 4)         ; of 4 characters
       (for/and ([item (in-string row)]) ; containing only valid characters
         (and (member item '(#\. #\I #\Q #\L #\J #\T #\Z #\S)) #t))))

;; Return true if BLOCK is a valid tetris block, meaning that it is a list
;; containing four rows which pass the VALID-BLOCK-ROW? test.
(define (valid-block? block)
  (and (list? block)                      ; a block is a list
       (= (length block) 4)               ; ... of 4 items
       (andmap valid-block-row? block)))  ; ... each element is a valid row

(module+ test
  (check-false (valid-block-row? 1))        ; not a string
  (check-false (valid-block-row? "......")) ; more than 4 characters
  (check-false (valid-block-row? "X..."))   ; containing invalid characters

  ;; First, let's verify that VALID-BLOCK? can actually detect invalid blocks
  (check-false (valid-block? "hello"))  ; not a list
  (check-false (valid-block? (append L-Block T-Block))) ; more than 4 items
  (check-false (valid-block? (list "...." "...." "...." 1))) ; not a list of strings
  (check-false (valid-block? (list "X..." "...." "...." "...."))) ; contains invalid characters

  ;; Verify that all our blocks are correctly defined
  (for ([block (in-list all-blocks)])
    (check-pred valid-block? block)))


;;.................................................... Displaying Blocks ....

(define square-size 20)                 ; size of a block square in pixels

;; Map each letter that can be present in a tetris block to a color, this will
;; be used to color each tetris block with a unique color.  Any colors can be
;; used for this purpose, these ones are from Paul Tol's Vibrant Qualitative
;; color scheme https://personal.sron.nl/~pault/
(define colors
  (hash
   #\I (make-color 0 119 187)
   #\Q (make-color 51 187 238)
   #\L (make-color 0 153 136)
   #\J (make-color 238 119 51)
   #\T (make-color 204 51 17)
   #\Z (make-color 238 51 119)
   #\S (make-color 136 34 85)))

;; Produce a pict from a string containing valid Tetris color codes (see
;; `colors`) table above.  Note that we don't restrict the argument to be a
;; valid block row, as this function will also be used to produce the filled
;; lines from blocks that accumulate at the bottom of the playing field.
;;
;; Sample use: (row->squares ".LL.")
(define/contract (row->squares row)
  (-> string? pict?)
  (define items
    (for/list ([char (in-string row)])
      (define color (hash-ref colors char #f))
      (if color
          (filled-rectangle square-size square-size #:color color)
          (rectangle square-size square-size))))
  (apply hc-append items))

;; Produce a PICT corresponding to the tetris BLOCK.
;;
;; Sample use:
;; (block->pict L-Block)
;; (map block->pict all-blocks)
(define/contract (block->pict block)
  (-> valid-block? pict?)
  (apply vc-append (map row->squares block)))


;;....................................................... Block Rotation ....

;; Rotate a tetris block clockwise by 90 degrees (a quarter of a circle),
;; returning the rotated tetris block.
(define/contract (rotate-clockwise block)
  (-> valid-block? valid-block?)
  (for/list ([a (in-string (first block))]
             [b (in-string (second block))]
             [c (in-string (third block))]
             [d (in-string (fourth block))])
    (string d c b a)))

;; Rotate a tetris BLOCK a number of TIMES (which can be 0) and return a new
;; tetris block.
(define/contract (rotate-clockwise* block times)
  (-> valid-block? exact-nonnegative-integer? valid-block?)
  (if (> times 0)
      (let ([rotated (rotate-clockwise block)])
        (rotate-clockwise* rotated (sub1 times)))
      block))

;; Rotate a tetris block counter-clockwise by 90 degrees (a quarter of a
;; circle), returning the rotated tetris block.  Rather than implementing a
;; block decomposition and building a new block, we simply rotate the block 3
;; times clockwise, which would bring it in the same position as one rotation
;; counter clockwise.
(define/contract (rotate-counter-clockwise block)
  (-> valid-block? valid-block?)
  (rotate-clockwise* block 3))

(module+ test
  (for ([block (in-list all-blocks)])
    ;; Rotating the block clockwise 4 times brings it in the same position as
    ;; where we started from.
    (check-equal? (rotate-clockwise* block 4) block)
    ;; Rotating a block once clockwise once counter-clockwise brings it back
    ;; into the initial position.
    (check-equal? (rotate-clockwise (rotate-counter-clockwise block)) block)))


;;......................................................... main program ....

;; A frame which intercepts keyboard input using the `on-subwindow-char`
;; method and passes it to `on-tetris-event` -- this is used to read keyboard
;; input from the user and move/rotate the current piece.
(define tetris-frame%
  (class frame%
    (init) (super-new)
    (define/override (on-subwindow-char receiver event)
      (define handled? (super on-subwindow-char receiver event))
      (if handled?
          #t                            ; one of the system events
          (on-tetris-event event)))))

;; The dimensions of the playing field, in squares
(define-values (field-width field-height) (values 12 24))
(define-values (window-width window-height)
  (values (* field-width square-size) (* field-height square-size)))

;; The toplevel window for the game
(define frame
  (new tetris-frame% [label "Tetris"] [width window-width] [height window-height]))

;; The current block and its x, y position on the playing field
(define-values (current-block block-x block-y) (values L-Block 0 0))

;; Display the playing field.  Currently, the current block is shown at its
;; X,Y location.
(define (on-tetris-paint canvas dc)
  (send dc clear)
  (define x (* block-x square-size))
  (define y (* block-y square-size))
  (draw-pict (block->pict current-block) dc x y))

;; A canvas which holds the drawing area for the game -- the on-tetris-paint
;; defined above is used to fill the canvas, and will be invoked when the
;; canvas is refreshed.
(define canvas (new canvas% [parent frame]
                    [min-width window-width]
                    [min-height window-height]
                    [stretchable-width #f]
                    [stretchable-height #f]
                    [paint-callback on-tetris-paint]))

;; Called at regular intervals to make pieces fall.  The function just
;; increments the blocks Y position, and if the Y position is larger than the
;; field height, it creates a new block.
(define (on-tetris-tick)
  (if (< block-y field-height)
      (set! block-y (add1 block-y))
      (spawn-new-block))
  (send canvas refresh))

;; Timer invokes `on-tetris-tick` periodically.  Changing the interval makes
;; the pieces fall slower or faster.
(define timer (new timer% [notify-callback on-tetris-tick] [interval 500]))

(define block-count -1)

;; Create a new block and place it a the top of the field.  For now, this
;; function just rotates through all blocks, but in the real game, blocks will
;; be randomly selected.
(define (spawn-new-block)
  (set! block-count (add1 block-count))
  (set! current-block (list-ref
                       all-blocks
                       (modulo block-count (length all-blocks))))
  (set! block-y 0)
  (set! block-x (exact-truncate (- (/ field-width 2) 2))))

;; Handle a keyboard event from the user.  Left-Right keys move a piece left
;; or right, while the up and down keys rotate the piece clockwise or
;; counter-clockwise
(define (on-tetris-event event)
  (case (send event get-key-code)
    ((left) (on-left-right-move sub1))
    ((right) (on-left-right-move add1))
    ((up) (on-rotation rotate-clockwise))
    ((down) (on-rotation rotate-counter-clockwise)))
  (send canvas refresh))

(define (on-rotation rotate-function)
  (set! current-block (rotate-function current-block)))

(define (on-left-right-move direction)
  (set! block-x (direction block-x)))

(define (start-game)
  (spawn-new-block)
  (send canvas focus)
  (send frame show #t)
  (send frame show #t))

(start-game)