GameScreen类的主要工作是负责显示几种游戏不同状态下的界面

这个分屏分别是:准备游戏，游戏中，游戏暂停，游戏结束

package com.badlogic.androidgames.mrnom;

import java.util.List;

import android.graphics.Color;

import com.badlogic.androidgames.framework.Game;
import com.badlogic.androidgames.framework.Graphics;
import com.badlogic.androidgames.framework.Input.TouchEvent;
import com.badlogic.androidgames.framework.Pixmap;
import com.badlogic.androidgames.framework.Screen;

//枚举游戏的四种状态，准备游戏，游戏中，游戏暂停，游戏结束
public class GameScreen extends Screen {
    enum GameState {
        Ready,
        Running,
        Paused,
        GameOver
    }
    
    GameState state = GameState.Ready;
    World world;
    int oldScore = 0;
    String score = "0";
    
    public GameScreen(Game game) {
        super(game);
        world = new World();
    }

    @Override
    public void update(float deltaTime) {
        List<TouchEvent> touchEvents = game.getInput().getTouchEvents();
        game.getInput().getKeyEvents();
        
        if(state == GameState.Ready)
            updateReady(touchEvents);
        if(state == GameState.Running)
            updateRunning(touchEvents, deltaTime);
        if(state == GameState.Paused)
            updatePaused(touchEvents);
        if(state == GameState.GameOver)
            updateGameOver(touchEvents);        
    }

    //在准备游戏状态，触碰屏幕就进入游戏
    private void updateReady(List<TouchEvent> touchEvents) {
        if(touchEvents.size() > 0)
            state = GameState.Running;
    }

    //游戏中状态
    private void updateRunning(List<TouchEvent> touchEvents, float deltaTime) {        
        int len = touchEvents.size();
        for(int i = 0; i < len; i++) {
            TouchEvent event = touchEvents.get(i);
            if(event.type == TouchEvent.TOUCH_UP) {
            	//如果碰到暂停按钮
                if(event.x < 64 && event.y < 64) {
                    if(Settings.soundEnabled)
                        Assets.click.play(1);
                    state = GameState.Paused;
                    return;
                }
            }
            if(event.type == TouchEvent.TOUCH_DOWN) {
            	//如果碰到逆时钟转向按钮
                if(event.x < 64 && event.y > 416) {
                    world.snake.turnLeft();
                }
                //如果碰到顺时钟转向按钮
                if(event.x > 256 && event.y > 416) {
                    world.snake.turnRight();
                }
            }
        }
        
        world.update(deltaTime);
        //游戏结束
        if(world.gameOver) {
            if(Settings.soundEnabled)
                Assets.bitten.play(1);
            state = GameState.GameOver;
        }
        //累加游戏得分,并播放吃中目标的音效
        if(oldScore != world.score) {
            oldScore = world.score;
            score = "" + oldScore;
            if(Settings.soundEnabled)
                Assets.eat.play(1);
        }
    }

    private void updatePaused(List<TouchEvent> touchEvents) {
        int len = touchEvents.size();
        for(int i = 0; i < len; i++) {
            TouchEvent event = touchEvents.get(i);
            if(event.type == TouchEvent.TOUCH_UP) {
                if(event.x > 80 && event.x <= 240) {
                	//如果选择恢复游戏
                    if(event.y > 100 && event.y <= 148) {
                        if(Settings.soundEnabled)
                            Assets.click.play(1);
                        state = GameState.Running;
                        return;
                    }                   
                    //如果选择退出
                    if(event.y > 148 && event.y < 196) {
                        if(Settings.soundEnabled)
                            Assets.click.play(1);
                        game.setScreen(new MainMenuScreen(game)); 
                        return;
                    }
                }
            }
        }
    }

    private void updateGameOver(List<TouchEvent> touchEvents) {
        int len = touchEvents.size();
        for(int i = 0; i < len; i++) {
            TouchEvent event = touchEvents.get(i);
            if(event.type == TouchEvent.TOUCH_UP) {
            	//如果选择退出
                if(event.x >= 128 && event.x <= 192 &&
                   event.y >= 200 && event.y <= 264) {
                    if(Settings.soundEnabled)
                        Assets.click.play(1);
                    game.setScreen(new MainMenuScreen(game));
                    return;
                }
            }
        }
    }

    //初始化游戏背景等 
    @Override
    public void present(float deltaTime) {
        Graphics g = game.getGraphics();
        
        g.drawPixmap(Assets.background, 0, 0);
        drawWorld(world);
        if(state == GameState.Ready) 
            drawReadyUI();
        if(state == GameState.Running)
            drawRunningUI();
        if(state == GameState.Paused)
            drawPausedUI();
        if(state == GameState.GameOver)
            drawGameOverUI();
        
        drawText(g, score, g.getWidth() / 2 - score.length()*20 / 2, g.getHeight() - 42);
    }

    //根据world对象来画出游戏背景和人物
    private void drawWorld(World world) {
        Graphics g = game.getGraphics();
        Snake snake = world.snake;
        SnakePart head = snake.parts.get(0);
        Stain stain = world.stain;
        
        //画出"污渍"
        Pixmap stainPixmap = null;
        if(stain.type == Stain.TYPE_1)
            stainPixmap = Assets.stain1;
        if(stain.type == Stain.TYPE_2)
            stainPixmap = Assets.stain2;
        if(stain.type == Stain.TYPE_3)
            stainPixmap = Assets.stain3;
        int x = stain.x * 32;
        int y = stain.y * 32;      
        g.drawPixmap(stainPixmap, x, y);             
        //画出蛇的身体
        int len = snake.parts.size();
        for(int i = 1; i < len; i++) {
            SnakePart part = snake.parts.get(i);
            x = part.x * 32;
            y = part.y * 32;
            g.drawPixmap(Assets.tail, x, y);
        }
        //画出蛇头
        Pixmap headPixmap = null;
        if(snake.direction == Snake.UP) 
            headPixmap = Assets.headUp;
        if(snake.direction == Snake.LEFT) 
            headPixmap = Assets.headLeft;
        if(snake.direction == Snake.DOWN) 
            headPixmap = Assets.headDown;
        if(snake.direction == Snake.RIGHT) 
            headPixmap = Assets.headRight;        
        x = head.x * 32 + 16;
        y = head.y * 32 + 16;
        g.drawPixmap(headPixmap, x - headPixmap.getWidth() / 2, y - headPixmap.getHeight() / 2);
    }
    //画出准备游戏界面
    private void drawReadyUI() {
        Graphics g = game.getGraphics();
        
        g.drawPixmap(Assets.ready, 47, 100);
        g.drawLine(0, 416, 480, 416, Color.BLACK);
    }
    //画出游戏中画面
    private void drawRunningUI() {
        Graphics g = game.getGraphics();

        g.drawPixmap(Assets.buttons, 0, 0, 64, 128, 64, 64);
        g.drawLine(0, 416, 480, 416, Color.BLACK);
        g.drawPixmap(Assets.buttons, 0, 416, 64, 64, 64, 64);
        g.drawPixmap(Assets.buttons, 256, 416, 0, 64, 64, 64);
    }
    //画出游戏暂停画面
    private void drawPausedUI() {
        Graphics g = game.getGraphics();
        
        g.drawPixmap(Assets.pause, 80, 100);
        g.drawLine(0, 416, 480, 416, Color.BLACK);
    }
    //画出游戏结束画面
    private void drawGameOverUI() {
        Graphics g = game.getGraphics();
        
        g.drawPixmap(Assets.gameOver, 62, 100);
        g.drawPixmap(Assets.buttons, 128, 200, 0, 128, 64, 64);
        g.drawLine(0, 416, 480, 416, Color.BLACK);
    }
    //画出游戏的当前得分
    public void drawText(Graphics g, String line, int x, int y) {
        int len = line.length();
        for (int i = 0; i < len; i++) {
            char character = line.charAt(i);

            if (character == ' ') {
                x += 20;
                continue;
            }

            int srcX = 0;
            int srcWidth = 0;
            if (character == '.') {
                srcX = 200;
                srcWidth = 10;
            } else {
                srcX = (character - '0') * 20;
                srcWidth = 20;
            }

            g.drawPixmap(Assets.numbers, x, y, srcX, 0, srcWidth, 32);
            x += srcWidth;
        }
    }

    //判断游戏状态，把状态置为暂停,并把得分保存到文件中
    @Override
    public void pause() {
        if(state == GameState.Running)
            state = GameState.Paused;
        
        if(world.gameOver) {
            Settings.addScore(world.score);
            Settings.save(game.getFileIO());
        }
    }

    @Override
    public void resume() {
        
    }

    @Override
    public void dispose() {
        
    }
}