/**
 * 游戏开始菜单
 **/

var Menu = function(context) {
    this.ctx = context;
    this.x = 0;
    this.y = -SCREEN_HEIGHT;
    this.selectTank = new SelectTank();
    this.playNum = 1;
    this.times = 0;

    /**
     * 画菜单
     */
    this.draw = function() {

        this.times++;
        var temp = 0;
        if (parseInt(this.times / 6) % 2 == 0) {
            temp = 0;
        } else {
            temp = this.selectTank.size;
        }
        if (this.y >= 0) {
            this.y = 0;
        } else {
            this.y += 5;
        }
        this.ctx.clearRect(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT);
        this.ctx.save();
        //画背景
        this.ctx.drawImage(MENU_IMAGE, this.x, this.y);
            log(MENU_IMAGE,this.x,this.y);
        //画选择坦克
        this.ctx.drawImage(RESOURCE_IMAGE, POS["selectTank"][0], POS["selectTank"][1] + temp, this.selectTank.size, this.selectTank.size,
            this.selectTank.x, this.y + this.selectTank.ys[this.playNum - 1], this.selectTank.size, this.selectTank.size);
        this.ctx.restore();
    };

    /**
     * 选择坦克上下移动
     */
    this.next = function(n) {
        this.playNum += n;
        if (this.playNum > 2) {
            this.playNum = 1;
        } else if (this.playNum < 1) {
            this.playNum = 2;
        }
    };
};