如何使用javascript / jquery旋转由点组成的半圆

Question

我有这个代码来创建一个小圆圈的半圆，但我不知道如何旋转它，以便半圆开始在圆的顶部而不是侧面（向左旋转45º）。

var items = 9;

for (var i = 0; i < items; i++) {

  var x = 200 + 50 * Math.cos(1.1 * Math.PI * i / items);
  var y = 100 + 50 * Math.sin(1.1 * Math.PI * i / items);

  $("body").append("<div class='point' style='left:" + x + "px;top:" + y + "px'></div>");

}

.point {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: white;
  border: 1px solid black;
  position: absolute;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

Current Output，Desired Output

谢谢！

Answer 1

我相信这就是你想要的：

var items = 8;

for(var i = 0; i < items; i++) {

    var x = 200 + 50 * Math.cos(Math.PI * i / items);
    var y = 100 + 50 * Math.sin(Math.PI * i / items); 
    
    $("#center").append("<div class='point' style='left:"+ x +"px;top:"+ y +"px'></div>");

}

#location {
  
    width:200px;
    height:200px;
    /* border-radius:100px; */
    background: black;
    position:relative;
    left:200px;
    top:100px;
    
}

#center {
  transform: rotateZ(-80deg);
}

.point {
  
    width:8px;
    height:8px;
    border-radius:50%;
    background: white;
    border: 1px solid black;
    position:absolute;
    
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="center"></div>

Answer 2

只需反转顶部/左侧的x / y值：

var items = 9;
for (var i = 0; i < items; i++) {

  var x = 100 + 50 * Math.cos(1.1 * Math.PI * i / items);
  var y = 200 + 50 * Math.sin(1.1 * Math.PI * i / items);

  $("body").append("<div class='point' style='left:" + y + "px;top:" + x + "px'></div>");

}

.point {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: white;
  border: 1px solid black;
  position: absolute;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

Answer 3

你可以交换sin和cos电话。与您的问题无关，但也许您更喜欢添加元素的jQuery样式：

var items = 9;
for (var i = 0; i < items; i++) {
  var x = 200 + 50 * Math.sin(1.1 * Math.PI * i / items);
  var y = 100 + 50 * Math.cos(1.1 * Math.PI * i / items);
  $("body").append($("<div>").addClass("point").css({left: x, top: y}));
}

.point {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: white;
  border: 1px solid black;
  position: absolute;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>