线段长度计算以及相交、平移和旋转算法

线段平移。

    function Line(from, to, color, dasharray){        this.from = from;        this.to = to;        this.color = typeof(color)=='undefined'?'black':color;        this.dasharray = typeof(dasharray)=='undefined'?false:dasharray;    }

移动方法

    Line.prototype.move = function(d){        var r = Math.atan2(this.to.x-this.from.x, this.to.y-this.from.y)+Math.PI/2;        var x = Math.sin(r)*d, y = Math.cos(r)*d;        var x1 = this.from.x+x, y1 = this.from.y+y;        var x2 = this.to.x+x, y2 = this.to.y+y;        return new Line(new Point(x1, y1),new Point(x2, y2));    };

旋转

    Line.prototype.rotate = function(alpha){        var l = Math.round(Math.sqrt(            Math.pow((this.to.y-this.from.y), 2) +            Math.pow((this.to.x-this.from.x), 2)));        var r = Math.atan2(this.to.y-this.from.y, this.to.x-this.from.x)+Math.PI*alpha/180;        var x = Math.cos(r)*l, y = Math.sin(r)*l;        //var x2 = this.        console.log('r:' + r + ', beta: ' + Math.round(180*(r/Math.PI)) + ', length: ' + l);        var x2 = this.from.x+x, y2 = this.from.y+y;        return new Line(this.from, new Point(x2, y2));    };

根据起点和角度、长度创建线段

    var LineMaker = {        make: function(from, alpha, l){            var to = new Point(                from.x+l*Math.cos(Math.PI*alpha/180),                from.y+l*Math.sin(Math.PI*alpha/180)            );            return new Line(from, to);        }    }