5、GameScreen.java
GameScreen使用了一個低級應用編程接口Canvas屏幕，和Image、Graphics類來繪制游戲面板、棋子，以及游戲的最終結果狀態。要獲取更詳細的信息，請參閱各種繪畫方法和drawCircle、drawCross、drawPiece、drawPlayerCursor、drawBoard等方法。這個屏幕使用MIDlet的quit回調方法來指示游戲結束。
此屏幕可適應各種可用顯示性能(高、寬、色彩等)。此外還要注意到可以使用四向導航鍵，也可以使用雙向導航鍵來移動光標。
它使用了封裝了主游戲程序邏輯的Game類。
package example.tictactoe;
import java.util.Random;
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
class GameScreen extends Canvas implements CommandListener {
private static final int BLACK = 0x00000000;
private static final int WHITE = 0x00FFFFFF;
private static final int RED = 0x00FF0000;
private static final int BLUE = 0x000000FF;
private static final int NO_MOVE = -1;
private final TicTacToeMIDlet midlet;
private final Game game;
private final Command exitCommand;
private final Command newGameCommand;
private final Random random = new Random();
private int screenWidth, screenHeight;
private int boardCellSize, boardSize, boardTop, boardLeft;
private boolean playerIsCircle;
private boolean computerIsCircle;
private int preCursorPosition, cursorPosition;
private int computerMove = NO_MOVE;
private int playerMove = NO_MOVE;
private int computerGamesWonTally = 0;
private int playerGamesWonTally = 0;
private boolean isRestart;
public GameScreen(TicTacToeMIDlet midlet, boolean playerIsCircle) {
this.midlet = midlet;
this.playerIsCircle = playerIsCircle;
computerIsCircle = !playerIsCircle;
game = new Game(random);
initializeBoard();
// configure Screen commands
exitCommand = new Command("Exit", Command.EXIT, 1);
newGameCommand = new Command("New", Command.SCREEN, 2);
addCommand(exitCommand);
addCommand(newGameCommand);
setCommandListener(this);
// begin the game play initialize();
}
// Initialize the Game and Game screen. Also used for game restarts.
private void initialize() {
game.initialize();
preCursorPosition = cursorPosition = 0;
playerMove = NO_MOVE;
boolean computerFirst = ((random.nextInt() & 1) == 0);
if (computerFirst) {
computerMove = game.makeComputerMove();
}
else
{
computerMove = NO_MOVE;
}
isRestart = true;
repaint();
}
public void paint(Graphics g) {
if (game.isGameOver()) {
paintGameOver(g);
}
else {
paintGame(g);
}
}
private void paintGame(Graphics g) {
if (isRestart) {
// clean the canvas
g.setColor(WHITE);
g.fillRect(0, 0, screenWidth, screenHeight);
drawBoard(g);
isRestart = false;
}
drawCursor(g);
if (playerMove != NO_MOVE) {
drawPiece(g, playerIsCircle, playerMove);
}
if (computerMove != NO_MOVE) {
drawPiece(g, computerIsCircle, computerMove);
}
}
private void paintGameOver(Graphics g)
{
String statusMsg = null;
if(game.isComputerWinner()) {
statusMsg = "I win !";
computerGamesWonTally++;
}
else if (game.isPlayerWinner()) {
statusMsg = "You win";
playerGamesWonTally++;
}
else {
statusMsg = "Stalemate";
}
String tallyMsg = "You:" + playerGamesWonTally + " Me:" + computerGamesWonTally;
Font font = Font.getFont(Font.FACE_SYSTEM, Font.STYLE_PLAIN, Font.SIZE_MEDIUM);
int strHeight = font.getHeight();
int statusMsgWidth = font.stringWidth(statusMsg);
int tallyMsgWidth = font.stringWidth(tallyMsg);
int strWidth = tallyMsgWidth;
if (statusMsgWidth > tallyMsgWidth)
{
strWidth = statusMsgWidth;
}
// Get the
{
x, y
}
position for painting the strings. int x = (screenWidth - strWidth) / 2;
x = x < 0 ？ 0 : x;
int y = (screenHeight - 2 * strHeight) / 2;
y = y < 0 ？ 0 : y;
// clean the canvas
g.setColor(WHITE);
g.fillRect(0, 0, screenWidth, screenHeight);
// paint the strings' text
g.setColor(BLACK);
g.drawString(statusMsg, x, y, (Graphics.TOP | Graphics.LEFT));
g.drawString(tallyMsg, x, (y + 1 + strHeight), (Graphics.TOP | Graphics.LEFT));
}
public void commandAction(Command c, Displayable d) {
if (c == exitCommand) {
midlet.quit();
}
else if (c == newGameCommand) {
initialize();
}
}
private void initializeBoard() {
screenWidth = getWidth();
screenHeight = getHeight();
if (screenWidth > screenHeight) {
boardCellSize = (screenHeight - 2) / 3;
boardLeft = (screenWidth - (boardCellSize * 3)) / 2;
boardTop = 1;
}
else {
boardCellSize = (screenWidth - 2) / 3;
boardLeft = 1;
boardTop = (screenHeight - boardCellSize * 3) / 2;
}
}
protected void keyPressed(int keyCode) {
// can't continue playing until the player restarts
if (game.isGameOver()) {
return;
}
int gameAction = getGameAction(keyCode);
switch (gameAction) {
case FIRE: doPlayerMove();
break;
case RIGHT: doMoveCursor(1, 0);
break;
case DOWN: doMoveCursor(0, 1);
break;
case LEFT: doMoveCursor(-1, 0);
break;
case UP: doMoveCursor(0, -1);
break;
default: break;
}
}
private void doPlayerMove() {
if (game.isFree(cursorPosition)) {
// player move game.
makePlayerMove(cursorPosition);
playerMove = cursorPosition;
// computer move
if (!game.isGameOver()) {
computerMove = game.makeComputerMove();
}
repaint();
}
}
private void doMoveCursor(int dx, int dy) {
int newCursorPosition = cursorPosition + dx + 3 * dy;
if ((newCursorPosition >= 0) && (newCursorPosition < 9))
{
preCursorPosition = cursorPosition;
cursorPosition = newCursorPosition;
repaint();
}
}
// Draw a CIRCLE or CROSS piece on the board
private void drawPiece(Graphics g, boolean isCircle, int pos) {
int x = ((pos % 3) * boardCellSize) + 3;
int y = ((pos / 3) * boardCellSize) + 3;
if (isCircle) {
drawCircle(g, x, y);
}
else {
drawCross(g, x, y);
}
}
// Draw blue CIRCLE onto the board image
private void drawCircle(Graphics g, int x, int y) {
g.setColor(BLUE);
g.fillArc(x + boardLeft, y + boardTop, boardCellSize - 4, boardCellSize - 4, 0, 360);
g.setColor(WHITE);
g.fillArc(x + 4 + boardLeft, y + 4 + boardTop, boardCellSize - 4 - 8, boardCellSize - 4 - 8, 0, 360);
}
// Draw red CROSS onto the board image
private void drawCross(Graphics g, int x, int y) {
g.setColor(RED);
for (int i = 0;
i < 4;
i++) {
g.drawLine(x + 1 + i + boardLeft, y + boardTop, x + boardCellSize - 4 - 4 + i + boardLeft, y + boardCellSize - 5 + boardTop);
g.drawLine(x + 1 + i + boardLeft, y + boardCellSize - 5 + boardTop, x + boardCellSize - 4 - 4 + i + boardLeft, y + boardTop);
}
}
// Visually indicates a Player selected square on the board image
private void drawCursor(Graphics g) {
// draw cursor at selected Player square.
g.setColor(WHITE);
g.drawRect(((preCursorPosition % 3) * boardCellSize) + 2 + boardLeft, ((preCursorPosition/3) * boardCellSize) + 2 + boardTop, boardCellSize - 3, boardCellSize - 3);
// draw cursor at selected Player square.
g.setColor(BLACK);
g.drawRect(((cursorPosition % 3) * boardCellSize) + 2 + boardLeft, ((cursorPosition/3) * boardCellSize) + 2 + boardTop, boardCellSize - 3, boardCellSize - 3);
}
private void drawBoard(Graphics g) {
// clean the board
g.setColor(WHITE);
g.fillRect(0, 0, screenWidth, screenHeight);
// draw the board
g.setColor(BLACK);
for (int i = 0;
i < 4;
i++) {
g.fillRect(boardLeft, boardCellSize * i + boardTop, (boardCellSize * 3) + 2, 2);
g.fillRect(boardCellSize * i + boardLeft, boardTop, 2, boardCellSize * 3);
}
}
}
