function clearArcFun(x,y,r,cxt){ //(x,y)为要清除的圆的圆心,r为半径,cxt为context var stepClear=1;//别忘记这一步 clearArc(x,y,r); function clearArc(x,y,radius){ var calcWidth=radius-stepClear; var calcHeight=Math.sqrt(radius*radius-calcWidth*calcWidth); var posX=x-calcWi