GameBuilder开发游戏应用系列之100行代码实现贪吃蛇

在线预览：http://osgames.duapp.com/apprun.html?appid=osgames1-801422234293697
在线编辑：http://osgames.duapp.com/gamebuilder.php?appid=osgames1-801422234293697
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运行截图：

除了重力感应游戏，GameBuilder开发传统的游戏也毫不逊色，作为一个怀旧的人，总是对这类游戏情有独钟。

贪吃蛇主要靠一个[UICanvas]来实现，前面一片博客GameBuilder开发游戏应用系列之100行代码实现别踩白块有介绍过，配合四个UIButton来控制方向。

食物生成

win.makeFoodBlock = function(num) {
    var bl = win.blockList;
    var fl = win.foodList;
    Math.min(48 * 72 - bl.length - fl.length, num);
    var x, y;
    for(var i = 0; i < num; i++) {
        var block = {x:0, y:0};
        do {
            x = Math.floor(Math.random() * 48);
            y = Math.floor(Math.random() * 72);
            block.x = x; block.y = y;
        } while(win.blockInList(block, win.blockList) || win.blockInList(block, win.foodList));
        win.foodList.push(block);
    }
};

方向控制

实现UIButton的onClick事件。

var win = this.getWindow();
win.changeDirection(win.DIR_UP);
//播放音效
this.playSoundEffect("disappear.mp3");

win.changeDirection = function(dir) {
    switch(win.direction) {
        case win.DIR_RIGHT:
            if(dir == win.DIR_LEFT) {
                return;
            }
            break;
        case win.DIR_UP:
            if(dir == win.DIR_DOWN) {
                return;
            }
            break;
        case win.DIR_LEFT:
            if(dir == win.DIR_RIGHT) {
                return;
            }
            break;
        case win.DIR_DOWN:
            if(dir == win.DIR_UP) {
                return;
            }
            break;
    }
    win.direction = dir;
};

计算蛇头下一个位置

win.nextFirst = function (first) {
    var nextFirst = {x:0, y:0};
    switch(win.direction) {
        case win.DIR_RIGHT:
            nextFirst.x = (first.x + 1) % 48;
            nextFirst.y = first.y;
            break;
        case win.DIR_UP:
            nextFirst.y = (first.y === 0) ? 71 : first.y - 1;
            nextFirst.x = first.x;
            break;
        case win.DIR_LEFT:
            nextFirst.x = (first.x === 0) ? 47 : first.x - 1;
            nextFirst.y = first.y;
            break;
        case win.DIR_DOWN:
            nextFirst.y = (first.y + 1) % 72;
            nextFirst.x = first.x;
    }
    return nextFirst;
};

贪吃蛇主要逻辑

win.updateList = function() {
    var last = win.blockList[win.blockList.length - 1];
    var first = win.blockList[0];
    var nf = win.nextFirst(first);
    //吃到食物了
    if(win.blockInList(nf, win.foodList)) {
        win.removeBlockFromFL(nf);
        win.blockList.unshift(nf);
        win.find("ui-sound-effects").play("disappear.mp3");
        win.makeFoodBlock(1);
        if(48 * 72 === win.blockList.length) {
            win.openWindow("win-result", function(ret){}, false, win.blockList.length);
            win.initGame();
        }
    } else if(win.blockInList(nf, win.blockList) && !win.checkEqual(nf, last)) {
        //蛇头碰到蛇身，游戏结束!
        win.openWindow("win-result", function(ret){}, false, win.blockList.length);
        win.initGame();
        console.log("Game Over");
    } else {
        //正常行进
        win.blockList.pop();
        win.blockList.unshift(nf);
    }
    setTimeout(win.updateList, 150);
};

绘制贪吃蛇

实现UICanvas的onPaint接口。

var win = this.getWindow();
var bl = win.blockList;
var fl = win.foodList;
var ctx = canvas2dCtx;
for(var i = 0; bl !== null && i < bl.length; i++) {
    ctx.strokeStyle = "white";
    ctx.fillStyle = "block";
    ctx.strokeRect(bl[i].x * 10, bl[i].y * 10, 10, 10);
    ctx.fillRect(bl[i].x * 10, bl[i].y * 10, 10, 10);
}
for(var i = 0; fl !== null && i < fl.length; i++) {
    ctx.strokeRect(fl[i].x * 10, fl[i].y * 10, 10, 10);
    ctx.fillRect(fl[i].x * 10, fl[i].y * 10, 10, 10);    
}

之所以用了100行代码，是因为食物是一个列表，而不是传统的一个食物，这样会多费一些代码维护食物列表。