读 Beginning Android Games 2nd Edition (十八) 贪食蛇类

作者的代码一看就懂,非常好理解.

污渍类,即贪食蛇吞噬的物体

package com.badlogic.androidgames.mrnom;

public class Stain {
    public static final int TYPE_1 = 0;
    public static final int TYPE_2 = 1;
    public static final int TYPE_3 = 2;
    public int x, y;
    public int type;

    public Stain(int x, int y, int type) {
        this.x = x;
        this.y = y;
        this.type = type;
    }
}

非常简单,有坐标,和类型(暂时不知道这个类型有什么用)
贪食蛇定义了两个类,一个是蛇类,一个是蛇身体元素(构成蛇的最小单位)

先看简单的身体元素类

package com.badlogic.androidgames.mrnom;

public class SnakePart {
    public int x, y;
    
    public SnakePart(int x, int y) {
        this.x = x;
        this.y = y;
    }
}

只有简简单单的一个坐标
蛇类就要复杂的多,有一系列的逻辑判断

package com.badlogic.androidgames.mrnom;

import java.util.ArrayList;
import java.util.List;

public class Snake {
    //逆时针,按上,左,下,右定义四个方向
    public static final int UP = 0;
    public static final int LEFT = 1;
    public static final int DOWN = 2;
    public static final int RIGHT = 3;
    //用一个集合来保存蛇的身体
    public List<SnakePart> parts = new ArrayList<SnakePart>();
    public int direction;    

    //初始化贪食蛇对象,移动方向为向上移动,身体长度为三节,同时定义了它们的坐标
    public Snake() {        
        direction = UP;
        parts.add(new SnakePart(5, 6));
        parts.add(new SnakePart(5, 7));
        parts.add(new SnakePart(5, 8));
    }

    //向左转,实际就是逆时针转动
    public void turnLeft() {
        direction += 1;
        if(direction > RIGHT)
            direction = UP;
    }
    
    //向右转,实际就是顺时针转动
    public void turnRight() {
        direction -= 1;
        if(direction < UP)
            direction = RIGHT;
    }

    //吃掉一个目标,身体长度增加
    public void eat() {
        SnakePart end = parts.get(parts.size()-1); 
        parts.add(new SnakePart(end.x, end.y));
    }

    public void advance() {
        SnakePart head = parts.get(0);               
        
        //无论往哪个方向移动,身体的部分一定会移到头部先前的位置,所以要把之前身体部分的坐标赋值给后面的部分
        int len = parts.size() - 1;
        for(int i = len; i > 0; i--) {
            SnakePart before = parts.get(i-1);
            SnakePart part = parts.get(i);
            part.x = before.x;
            part.y = before.y;
        }
        
        //按方向增减头部坐标
        if(direction == UP)
            head.y -= 1;
        if(direction == LEFT)
            head.x -= 1;
        if(direction == DOWN)
            head.y += 1;
        if(direction == RIGHT)
            head.x += 1;
        
        //头部坐标超过屏幕边界就重置坐标
        if(head.x < 0)
            head.x = 9;
        if(head.x > 9)
            head.x = 0;
        if(head.y < 0)
            head.y = 12;
        if(head.y > 12)
            head.y = 0;
    }

    //遍历贪食蛇的每个部分,如果是头部碰到自己的身体就判断咬到自己,游戏就要结束
    public boolean checkBitten() {
        int len = parts.size();
        SnakePart head = parts.get(0);
        for(int i = 1; i < len; i++) {
            SnakePart part = parts.get(i);
            if(part.x == head.x && part.y == head.y)
                return true;
        }        
        return false;
    }      
}