运用3角涵数在canvas上画虚线的方式

var context=document.getElementById("canvas").getContext("2d");
function drawDashedLine(context,x1,y1,x2,y2,dashlength){
    dashlength=dashlength===undefined?5:dashlength;
    var deltaX=x2-x1; //1条直角边的长
    var deltay=y2-y1; //另外一条指教边的长

    var numDashes=Math.floor(
        Math.sqrt(deltaX*deltaX+deltay*deltay)/dashlength  //Math.sqrt回到1个数的平方根  dashlength虚线每一个点的长度
    )

    var everydashLength_x=deltaX/numDashes  //明确X轴每条虚线点的起止点
    var everydashLength_y=deltay/numDashes  //明确Y轴每条虚线点的起止点

    for(var i=0;i<numDashes;i++){
        context[i%2===0?'moveTo':"lineTo"]
        (x1+everydashLength_x*i,y1+everydashLength_y*i)
    }
    context.stroke()

}
context.lineWidth=3
context.strokeStyle="blue"
drawDashedLine(context,20,20,context.canvas.width⑵0,20,20)