while(true){
	1 更新数据和对象状态
	2 渲染可视化UI
}
( 而在需要异步的地方,HTML是提供了异步机制的,例如网络传输 事件响应 )

while(true){
	处理用户输入
	更新数据和对象状态
	渲染游戏画面
}

while(true){
	1 更新数据和对象状态
	2 渲染可视化UI
}

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function segmentsIntr(a, b, c, d){

/** 1 解线性方程组, 求线段交点. **/
// 如果分母为0 则平行或共线, 不相交
    var denominator = (b.y - a.y)*(d.x - c.x) - (a.x - b.x)*(c.y - d.y);
    if (denominator==0) {
        return false;
    }
 
// 线段所在直线的交点坐标 (x , y)    
    var x = ( (b.x - a.x) * (d.x - c.x) * (c.y - a.y) 
                + (b.y - a.y) * (d.x - c.x) * a.x 
                - (d.y - c.y) * (b.x - a.x) * c.x ) / denominator ;
    var y = -( (b.y - a.y) * (d.y - c.y) * (c.x - a.x) 
                + (b.x - a.x) * (d.y - c.y) * a.y 
                - (d.x - c.x) * (b.y - a.y) * c.y ) / denominator;

/** 2 判断交点是否在两条线段上 **/
    if (
        // 交点在线段1上
        (x - a.x) * (x - b.x) <= 0 && (y - a.y) * (y - b.y) <= 0
        // 且交点也在线段2上
         && (x - c.x) * (x - d.x) <= 0 && (y - c.y) * (y - d.y) <= 0
        ){

        // 返回交点p
        return {
                x :  x,
                y :  y
            }
    }
    //否则不相交
    return false

}

var nx=b.y - a.y, 
    ny=a.x - b.x;
var normalLine = {  x: nx, y: ny };

var dist= normalLine.x*c.x + normalLine.y*c.y;

function segmentsIntr(a, b, c, d){

    //线段ab的法线N1
    var nx1 = (b.y - a.y), ny1 = (a.x - b.x);

    //线段cd的法线N2
    var nx2 = (d.y - c.y), ny2 = (c.x - d.x);
    
    //两条法线做叉乘, 如果结果为0, 说明线段ab和线段cd平行或共线,不相交
    var denominator = nx1*ny2 - ny1*nx2;
    if (denominator==0) {
        return false;
    }
    
    //在法线N2上的投影
    var distC_N2=nx2 * c.x + ny2 * c.y;
    var distA_N2=nx2 * a.x + ny2 * a.y-distC_N2;
    var distB_N2=nx2 * b.x + ny2 * b.y-distC_N2;

    // 点a投影和点b投影在点c投影同侧 (对点在线段上的情况,本例当作不相交处理);
    if ( distA_N2*distB_N2>=0  ) {
        return false;
    }
    
    //
    //判断点c点d 和线段ab的关系, 原理同上
    //
    //在法线N1上的投影
    var distA_N1=nx1 * a.x + ny1 * a.y;
    var distC_N1=nx1 * c.x + ny1 * c.y-distA_N1;
    var distD_N1=nx1 * d.x + ny1 * d.y-distA_N1;
    if ( distC_N1*distD_N1>=0  ) {
        return false;
    }

    //计算交点坐标
    var fraction= distA_N2 / denominator;
    var dx= fraction * ny1,
        dy= -fraction * nx1;
    return { x: a.x + dx , y: a.y + dy };
}

var triArea=( (a.x - c.x) * (b.y - c.y) - (a.y - c.y) * (b.x - c.x) ) /2 ;

function segmentsIntr(a, b, c, d){

    // 三角形abc 面积的2倍
    var area_abc = (a.x - c.x) * (b.y - c.y) - (a.y - c.y) * (b.x - c.x);

    // 三角形abd 面积的2倍
    var area_abd = (a.x - d.x) * (b.y - d.y) - (a.y - d.y) * (b.x - d.x); 

    // 面积符号相同则两点在线段同侧,不相交 (对点在线段上的情况,本例当作不相交处理);
    if ( area_abc*area_abd>=0 ) {
        return false;
    }

    // 三角形cda 面积的2倍
    var area_cda = (c.x - a.x) * (d.y - a.y) - (c.y - a.y) * (d.x - a.x);
    // 三角形cdb 面积的2倍
    // 注意: 这里有一个小优化.不需要再用公式计算面积,而是通过已知的三个面积加减得出.
    var area_cdb = area_cda + area_abc - area_abd ;
    if (  area_cda * area_cdb >= 0 ) {
        return false;
    }

    //计算交点坐标
    var t = area_cda / ( area_abd- area_abc );
    var dx= t*(b.x - a.x),
        dy= t*(b.y - a.y);
    return { x: a.x + dx , y: a.y + dy };

}

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• —软件人才免语言低担保 赴美带薪读研！—

• —软件人才免语言低担保 赴美带薪读研！—

• —软件人才免语言低担保 赴美带薪读研！—

• —软件人才免语言低担保 赴美带薪读研！—

• —软件人才免语言低担保 赴美带薪读研！—