Tetris

he Tetris game is one of the most popular computer games ever created. The original game was designed and programmed by a Russian programmer Alexey Pajitnov in 1985. Since then, Tetris is available on almost every computer platform in lots of variations.

Tetris is called a falling block puzzle game. In this game, we have seven different shapes calledtetrominoes: an S-shape, a Z-shape, a T-shape, an L-shape, a Line-shape, a MirroredL-shape, and a Square-shape. Each of these shapes is formed with four squares. The shapes are falling down the board. The object of the Tetris game is to move and rotate the shapes so that they fit as much as possible. If we manage to form a row, the row is destroyed and we score. We play the Tetris game until we top out.

Figure: Tetrominoes

PyQt4 is a toolkit designed to create applications. There are other libraries which are targeted at creating computer games. Nevertheless, PyQt4 and other application toolkits can be used to create simple games.

Creating a computer game is a good way for enhancing programming skills.

The development

We do not have images for our Tetris game, we draw the tetrominoes using the drawing API available in the PyQt4 programming toolkit. Behind every computer game, there is a mathematical model. So it is in Tetris.

Some ideas behind the game:

• We use a QtCore.QBasicTimer() to create a game cycle.
• The tetrominoes are drawn.
• The shapes move on a square by square basis (not pixel by pixel).
• Mathematically a board is a simple list of numbers.

The code consists of four classes: Tetris, Board, Tetrominoe and Shape. The Tetris class sets up the game. The Board is where the game logic is written. The Tetrominoe class contains names for all tetris pieces and the Shape class contains the code for a tetris piece.

#!/usr/bin/python
# -*- coding: utf-8 -*-

"""
ZetCode PyQt4 tutorial 

This is a Tetris game clone.

author: Jan Bodnar
website: zetcode.com
last edited: October 2013
"""

import sys, random
from PyQt4 import QtCore, QtGui

class Tetris(QtGui.QMainWindow):

    def __init__(self):
        super(Tetris, self).__init__()

        self.initUI()

    def initUI(self):    

        self.tboard = Board(self)
        self.setCentralWidget(self.tboard)

        self.statusbar = self.statusBar()
        self.tboard.msg2Statusbar[str].connect(self.statusbar.showMessage)

        self.tboard.start()

        self.resize(180, 380)
        self.center()
        self.setWindowTitle('Tetris')
        self.show()

    def center(self):

        screen = QtGui.QDesktopWidget().screenGeometry()
        size = self.geometry()
        self.move((screen.width()-size.width())/2,
            (screen.height()-size.height())/2)

class Board(QtGui.QFrame):

    msg2Statusbar = QtCore.pyqtSignal(str)

    BoardWidth = 10
    BoardHeight = 22
    Speed = 300

    def __init__(self, parent):
        super(Board, self).__init__(parent)

        self.initBoard()

    def initBoard(self):     

        self.timer = QtCore.QBasicTimer()
        self.isWaitingAfterLine = False

        self.curX = 0
        self.curY = 0
        self.numLinesRemoved = 0
        self.board = []

        self.setFocusPolicy(QtCore.Qt.StrongFocus)
        self.isStarted = False
        self.isPaused = False
        self.clearBoard()

    def shapeAt(self, x, y):
        return self.board[(y * Board.BoardWidth) + x]

    def setShapeAt(self, x, y, shape):
        self.board[(y * Board.BoardWidth) + x] = shape

    def squareWidth(self):
        return self.contentsRect().width() / Board.BoardWidth

    def squareHeight(self):
        return self.contentsRect().height() / Board.BoardHeight

    def start(self):

        if self.isPaused:
            return

        self.isStarted = True
        self.isWaitingAfterLine = False
        self.numLinesRemoved = 0
        self.clearBoard()

        self.msg2Statusbar.emit(str(self.numLinesRemoved))

        self.newPiece()
        self.timer.start(Board.Speed, self)

    def pause(self):

        if not self.isStarted:
            return

        self.isPaused = not self.isPaused

        if self.isPaused:
            self.timer.stop()
            self.msg2Statusbar.emit("paused")

        else:
            self.timer.start(Board.Speed, self)
            self.msg2Statusbar.emit(str(self.numLinesRemoved))

        self.update()

    def paintEvent(self, event):

        painter = QtGui.QPainter(self)
        rect = self.contentsRect()

        boardTop = rect.bottom() - Board.BoardHeight * self.squareHeight()

        for i in range(Board.BoardHeight):
            for j in range(Board.BoardWidth):
                shape = self.shapeAt(j, Board.BoardHeight - i - 1)

                if shape != Tetrominoe.NoShape:
                    self.drawSquare(painter,
                        rect.left() + j * self.squareWidth(),
                        boardTop + i * self.squareHeight(), shape)

        if self.curPiece.shape() != Tetrominoe.NoShape:

            for i in range(4):

                x = self.curX + self.curPiece.x(i)
                y = self.curY - self.curPiece.y(i)
                self.drawSquare(painter, rect.left() + x * self.squareWidth(),
                    boardTop + (Board.BoardHeight - y - 1) * self.squareHeight(),
                    self.curPiece.shape())

    def keyPressEvent(self, event):

        if not self.isStarted or self.curPiece.shape() == Tetrominoe.NoShape:
            super(Board, self).keyPressEvent(event)
            return

        key = event.key()

        if key == QtCore.Qt.Key_P:
            self.pause()
            return

        if self.isPaused:
            return

        elif key == QtCore.Qt.Key_Left:
            self.tryMove(self.curPiece, self.curX - 1, self.curY)

        elif key == QtCore.Qt.Key_Right:
            self.tryMove(self.curPiece, self.curX + 1, self.curY)

        elif key == QtCore.Qt.Key_Down:
            self.tryMove(self.curPiece.rotateRight(), self.curX, self.curY)

        elif key == QtCore.Qt.Key_Up:
            self.tryMove(self.curPiece.rotateLeft(), self.curX, self.curY)

        elif key == QtCore.Qt.Key_Space:
            self.dropDown()

        elif key == QtCore.Qt.Key_D:
            self.oneLineDown()

        else:
            super(Board, self).keyPressEvent(event)

    def timerEvent(self, event):

        if event.timerId() == self.timer.timerId():

            if self.isWaitingAfterLine:
                self.isWaitingAfterLine = False
                self.newPiece()
            else:
                self.oneLineDown()

        else:
            super(Board, self).timerEvent(event)

    def clearBoard(self):

        for i in range(Board.BoardHeight * Board.BoardWidth):
            self.board.append(Tetrominoe.NoShape)

    def dropDown(self):

        newY = self.curY

        while newY > 0:

            if not self.tryMove(self.curPiece, self.curX, newY - 1):
                break

            newY -= 1

        self.pieceDropped()

    def oneLineDown(self):

        if not self.tryMove(self.curPiece, self.curX, self.curY - 1):
            self.pieceDropped()

    def pieceDropped(self):

        for i in range(4):

            x = self.curX + self.curPiece.x(i)
            y = self.curY - self.curPiece.y(i)
            self.setShapeAt(x, y, self.curPiece.shape())

        self.removeFullLines()

        if not self.isWaitingAfterLine:
            self.newPiece()

    def removeFullLines(self):

        numFullLines = 0
        rowsToRemove = []

        for i in range(Board.BoardHeight):

            n = 0
            for j in range(Board.BoardWidth):
                if not self.shapeAt(j, i) == Tetrominoe.NoShape:
                    n = n + 1

            if n == 10:
                rowsToRemove.append(i)

        rowsToRemove.reverse()

        for m in rowsToRemove:

            for k in range(m, Board.BoardHeight):
                for l in range(Board.BoardWidth):
                        self.setShapeAt(l, k, self.shapeAt(l, k + 1))

        numFullLines = numFullLines + len(rowsToRemove)

        if numFullLines > 0:

            self.numLinesRemoved = self.numLinesRemoved + numFullLines
            self.msg2Statusbar.emit(str(self.numLinesRemoved))

            self.isWaitingAfterLine = True
            self.curPiece.setShape(Tetrominoe.NoShape)
            self.update()

    def newPiece(self):

        self.curPiece = Shape()
        self.curPiece.setRandomShape()
        self.curX = Board.BoardWidth / 2 + 1
        self.curY = Board.BoardHeight - 1 + self.curPiece.minY()

        #print self.curY

        if not self.tryMove(self.curPiece, self.curX, self.curY):

            self.curPiece.setShape(Tetrominoe.NoShape)
            self.timer.stop()
            self.isStarted = False
            self.msg2Statusbar.emit("Game over")

    def tryMove(self, newPiece, newX, newY):

        for i in range(4):

            x = newX + newPiece.x(i)
            y = newY - newPiece.y(i)

            if x < 0 or x >= Board.BoardWidth or y < 0 or y >= Board.BoardHeight:
                return False

            if self.shapeAt(x, y) != Tetrominoe.NoShape:
                return False

        self.curPiece = newPiece
        self.curX = newX
        self.curY = newY
        self.update()

        return True

    def drawSquare(self, painter, x, y, shape):

        colorTable = [0x000000, 0xCC6666, 0x66CC66, 0x6666CC,
                      0xCCCC66, 0xCC66CC, 0x66CCCC, 0xDAAA00]

        color = QtGui.QColor(colorTable[shape])
        painter.fillRect(x + 1, y + 1, self.squareWidth() - 2,
            self.squareHeight() - 2, color)

        painter.setPen(color.light())
        painter.drawLine(x, y + self.squareHeight() - 1, x, y)
        painter.drawLine(x, y, x + self.squareWidth() - 1, y)

        painter.setPen(color.dark())
        painter.drawLine(x + 1, y + self.squareHeight() - 1,
            x + self.squareWidth() - 1, y + self.squareHeight() - 1)
        painter.drawLine(x + self.squareWidth() - 1,
            y + self.squareHeight() - 1, x + self.squareWidth() - 1, y + 1)

class Tetrominoe(object):

    NoShape = 0
    ZShape = 1
    SShape = 2
    LineShape = 3
    TShape = 4
    SquareShape = 5
    LShape = 6
    MirroredLShape = 7

class Shape(object):

    coordsTable = (
        ((0, 0),     (0, 0),     (0, 0),     (0, 0)),
        ((0, -1),    (0, 0),     (-1, 0),    (-1, 1)),
        ((0, -1),    (0, 0),     (1, 0),     (1, 1)),
        ((0, -1),    (0, 0),     (0, 1),     (0, 2)),
        ((-1, 0),    (0, 0),     (1, 0),     (0, 1)),
        ((0, 0),     (1, 0),     (0, 1),     (1, 1)),
        ((-1, -1),   (0, -1),    (0, 0),     (0, 1)),
        ((1, -1),    (0, -1),    (0, 0),     (0, 1))
    )

    def __init__(self):

        self.coords = [[0,0] for i in range(4)]
        self.pieceShape = Tetrominoe.NoShape

        self.setShape(Tetrominoe.NoShape)

    def shape(self):
        return self.pieceShape

    def setShape(self, shape):

        table = Shape.coordsTable[shape]

        for i in range(4):
            for j in range(2):
                self.coords[i][j] = table[i][j]

        self.pieceShape = shape

    def setRandomShape(self):
        self.setShape(random.randint(1, 7))

    def x(self, index):
        return self.coords[index][0]

    def y(self, index):
        return self.coords[index][1]

    def setX(self, index, x):
        self.coords[index][0] = x

    def setY(self, index, y):
        self.coords[index][1] = y

    def minX(self):

        m = self.coords[0][0]
        for i in range(4):
            m = min(m, self.coords[i][0])

        return m

    def maxX(self):

        m = self.coords[0][0]
        for i in range(4):
            m = max(m, self.coords[i][0])

        return m

    def minY(self):

        m = self.coords[0][1]
        for i in range(4):
            m = min(m, self.coords[i][1])

        return m

    def maxY(self):

        m = self.coords[0][1]
        for i in range(4):
            m = max(m, self.coords[i][1])

        return m

    def rotateLeft(self):

        if self.pieceShape == Tetrominoe.SquareShape:
            return self

        result = Shape()
        result.pieceShape = self.pieceShape

        for i in range(4):

            result.setX(i, self.y(i))
            result.setY(i, -self.x(i))

        return result

    def rotateRight(self):

        if self.pieceShape == Tetrominoe.SquareShape:
            return self

        result = Shape()
        result.pieceShape = self.pieceShape

        for i in range(4):

            result.setX(i, -self.y(i))
            result.setY(i, self.x(i))

        return result

def main():

    app = QtGui.QApplication([])
    tetris = Tetris()
    sys.exit(app.exec_())

if __name__ == '__main__':
    main()

The game is simplified a bit so that it is easier to understand. The game starts immediately after it is launched. We can pause the game by pressing the p key. The Space key will drop the tetris piece instantly to the bottom. The game goes at constant speed, no acceleration is implemented. The score is the number of lines that we have removed.

self.tboard = Board(self)
self.setCentralWidget(self.tboard)

An instance of the Board class is created and set to be the central widget of the application.

self.statusbar = self.statusBar()
self.tboard.msg2Statusbar[str].connect(self.statusbar.showMessage)

We create a statusbar where we will display messages. We will display three possible messages: the number of lines already removed, the paused message, or the game over message. The msg2Statusbaris a custom signal that is implemented in the Board class. The showMessage() is a built-in method that displays a message on a statusbar.

self.tboard.start()

This line initiates the game.

class Board(QtGui.QFrame):

    msg2Statusbar = QtCore.pyqtSignal(str)
...

A custom signal is created. The msg2Statusbar is a signal that is emitted when we want to write a message or the score to the statusbar.

BoardWidth = 10
BoardHeight = 22
Speed = 300

These are Board's class variables. The BoardWidth and the BoardHeight define the size of the board in blocks. The Speed defines the speed of the game. Each 300 ms a new game cycle will start.

...
self.curX = 0
self.curY = 0
self.numLinesRemoved = 0
self.board = []
...

In the initBoard() method we initialize some important variables. The self.board variable is a list of numbers from 0 to 7. It represents the position of various shapes and remains of the shapes on the board.

def shapeAt(self, x, y):
    return self.board[(y * Board.BoardWidth) + x]

The shapeAt() method determines the type of a shape at a given block.

def squareWidth(self):
    return self.contentsRect().width() / Board.BoardWidth

The board can be dynamically resized. As a consequence, the size of a block may change. ThesquareWidth() calculates the width of the single square in pixels and returns it. The Board.BoardWidth is the size of the board in blocks.

for i in range(Board.BoardHeight):
    for j in range(Board.BoardWidth):
        shape = self.shapeAt(j, Board.BoardHeight - i - 1)

        if shape != Tetrominoe.NoShape:
            self.drawSquare(painter,
                rect.left() + j * self.squareWidth(),
                boardTop + i * self.squareHeight(), shape)

The painting of the game is divided into two steps. In the first step, we draw all the shapes, or remains of the shapes that have been dropped to the bottom of the board. All the squares are remembered in the self.board list variable. The variable is accessed using the shapeAt() method.

if self.curPiece.shape() != Tetrominoe.NoShape:

    for i in range(4):

        x = self.curX + self.curPiece.x(i)
        y = self.curY - self.curPiece.y(i)
        self.drawSquare(painter, rect.left() + x * self.squareWidth(),
            boardTop + (Board.BoardHeight - y - 1) * self.squareHeight(),
            self.curPiece.shape())

The next step is the drawing of the actual piece that is falling down.

elif key == QtCore.Qt.Key_Right:
    self.tryMove(self.curPiece, self.curX + 1, self.curY)

In the keyPressEvent() method we check for pressed keys. If we press the right arrow key, we try to move the piece to the right. We say try because the piece might not be able to move.

elif key == QtCore.Qt.Key_Up:
    self.tryMove(self.curPiece.rotateLeft(), self.curX, self.curY)

The Up arrow key will rotate the falling piece to the left.

elif key == QtCore.Qt.Key_Space:
    self.dropDown()

The Space key will drop the falling piece instantly to the bottom.

elif key == QtCore.Qt.Key_D:
    self.oneLineDown()

Pressing the d key, the piece will go one block down. It can be used to accellerate the falling of a piece a bit.

def tryMove(self, newPiece, newX, newY):

    for i in range(4):

        x = newX + newPiece.x(i)
        y = newY - newPiece.y(i)

        if x < 0 or x >= Board.BoardWidth or y < 0 or y >= Board.BoardHeight:
            return False

        if self.shapeAt(x, y) != Tetrominoe.NoShape:
            return False

    self.curPiece = newPiece
    self.curX = newX
    self.curY = newY
    self.update()
    return True

In the tryMove() method we try to move our shapes. If the shape is at the edge of the board or is adjacent to some other piece, we return False. Otherwise we place the current falling piece to a new position.

def timerEvent(self, event):

    if event.timerId() == self.timer.timerId():

        if self.isWaitingAfterLine:
            self.isWaitingAfterLine = False
            self.newPiece()
        else:
            self.oneLineDown()

    else:
        super(Board, self).timerEvent(event)

In the timer event, we either create a new piece after the previous one was dropped to the bottom or we move a falling piece one line down.

def clearBoard(self):

    for i in range(Board.BoardHeight * Board.BoardWidth):
        self.board.append(Tetrominoe.NoShape)

The clearBoard() method clears the board by setting Tetrominoe.NoShape at each block of the board.

def removeFullLines(self):

    numFullLines = 0
    rowsToRemove = []

    for i in range(Board.BoardHeight):

        n = 0
        for j in range(Board.BoardWidth):
            if not self.shapeAt(j, i) == Tetrominoe.NoShape:
                n = n + 1

        if n == 10:
            rowsToRemove.append(i)

    rowsToRemove.reverse()

    for m in rowsToRemove:

        for k in range(m, Board.BoardHeight):
            for l in range(Board.BoardWidth):
                    self.setShapeAt(l, k, self.shapeAt(l, k + 1))

    numFullLines = numFullLines + len(rowsToRemove)
 ...

If the piece hits the bottom, we call the removeFullLines() method. We find out all full lines and remove them. We do it by moving all lines above the current full line to be removed one line down. Notice that we reverse the order of the lines to be removed. Otherwise, it would not work correctly. In our case we use a naive gravity. This means that the pieces may be floating above empty gaps.

def newPiece(self):

    self.curPiece = Shape()
    self.curPiece.setRandomShape()
    self.curX = Board.BoardWidth / 2 + 1
    self.curY = Board.BoardHeight - 1 + self.curPiece.minY()

    if not self.tryMove(self.curPiece, self.curX, self.curY):

        self.curPiece.setShape(Tetrominoe.NoShape)
        self.timer.stop()
        self.isStarted = False
        self.msg2Statusbar.emit("Game over")

The newPiece() method creates randomly a new tetris piece. If the piece cannot go into its initial position, the game is over.

class Tetrominoe(object):

    NoShape = 0
    ZShape = 1
    SShape = 2
    LineShape = 3
    TShape = 4
    SquareShape = 5
    LShape = 6
    MirroredLShape = 7

The Tetrominoe class holds names of all possible shapes. We have also a NoShape for an empty space.

The Shape class saves information about a tetris piece.

class Shape(object):

    coordsTable = (
        ((0, 0),     (0, 0),     (0, 0),     (0, 0)),
        ((0, -1),    (0, 0),     (-1, 0),    (-1, 1)),
        ...
    )
...

The coordsTable tuple holds all possible coordinate values of our etris pieces. This is a template from which all pieces take their coordinate values.

self.coords = [[0,0] for i in range(4)]

Upon creation we create an empty coordinates list. The list will save the coordinates of the tetris piece.

Figure: Coordinates

The above image will help understand the coordinate values a bit more. For example, the tuples (0, -1), (0, 0), (-1, 0), (-1, -1) represent a Z-shape. The diagram illustrates the shape.

def rotateLeft(self):

    if self.pieceShape == Tetrominoe.SquareShape:
        return self

    result = Shape()
    result.pieceShape = self.pieceShape

    for i in range(4):

        result.setX(i, self.y(i))
        result.setY(i, -self.x(i))

    return result

The rotateLeft() method rotates a piece to the left. The square does not have to be rotated. That is why we simply return the reference to the current object. A new piece is created and its coordinates are set to the ones of the rotated piece.

Figure: Tetris