以上只是获取小提琴链接的图片，它的作用是没有问题的。
我正在尝试沿圆形移动一个对象（实际上是一个边框半径=100% 的矩形画布，因此表现为圆形）。但只能移动它，不能限制圆圈的移动）
这是我的JS Fiddle Link。 注意：请在js代码中向下滚动查看唯一写在以下cmets下的代码
//---- Code of interest begins-----// 到 //---感兴趣的代码结束---//
我的想要的输出会像这个轮子farbtastic。虽然它是开源的，但我一直无法在我的色轮中使用它的鼠标移动事件代码
在尝试搜索时，我找到了Canvas move object in circle
但我不能使用它，因为我不知道d，也不知道across 是什么。所以无法通过arccos(1-(d/r)^2/2)获得theta
【问题讨论】：
标签： javascript math drag-and-drop logic farbtastic
我认为最简单的方法是计算角度并将 css3 旋转变换应用于元素。
我在这里给你举个例子..
读取 cmets，特别是在 rotate() 函数上
HTML
<body>
<div id="circle">
<div id="circle-in"></div>
<div id="picker">
<div id="picker-circle"></div>
</div>
</div>
</body>
CSS
#circle{
position: relative;
width: 300px;
height: 300px;
border-radius: 50%;
background: #000;
}
#circle-in{
position: absolute;
top: 35px;
left: 35px;
width: 230px;
height: 230px;
border-radius: 50%;
background: #fff;
}
#picker{
position: absolute;
top: 50%;
left: 50%;
height: 30px;
margin-top: -15px;
width: 50%;
/* important: sets the transform origin to the center of the circle */
transform-origin: center left;
}
#picker-circle{
width: 30px;
height: 30px;
border-radius: 50%;
background: #fff;
margin: 0 3px 0 auto;
cursor: move;
}
JS
document.addEventListener('DOMContentLoaded', function(){
var circle = document.getElementById('circle'),
picker = document.getElementById('picker'),
pickerCircle = picker.firstElementChild,
rect = circle.getBoundingClientRect(),
center = {
x: rect.left + rect.width / 2,
y: rect.top + rect.height / 2
},
rotate = function(x, y){
var deltaX = x - center.x,
deltaY = y - center.y,
// The atan2 method returns a numeric value between -pi and pi representing the angle theta of an (x,y) point.
// This is the counterclockwise angle, measured in radians, between the positive X axis, and the point (x,y).
// Note that the arguments to this function pass the y-coordinate first and the x-coordinate second.
// atan2 is passed separate x and y arguments, and atan is passed the ratio of those two arguments.
// * from Mozilla's MDN
// Basically you give it an [y, x] difference of two points and it give you back an angle
// The 0 point of the angle is right (the initial position of the picker is also right)
angle = Math.atan2(deltaY, deltaX) * 180 / Math.PI
// Math.atan2(deltaY, deltaX) => [-PI +PI]
// We must convert it to deg so...
// / Math.PI => [-1 +1]
// * 180 => [-180 +180]
return angle
},
// DRAGSTART
mousedown = function(event){
event.preventDefault()
document.body.style.cursor = 'move'
mousemove(event)
document.addEventListener('mousemove', mousemove)
document.addEventListener('mouseup', mouseup)
},
// DRAG
mousemove = function(event){
picker.style.transform = 'rotate(' + rotate(event.x, event.y) + 'deg)'
},
// DRAGEND
mouseup = function(){
document.body.style.cursor = null;
document.removeEventListener('mouseup', mouseup)
document.removeEventListener('mousemove', mousemove)
}
// DRAG START
pickerCircle.addEventListener('mousedown', mousedown)
// ENABLE STARTING THE DRAG IN THE BLACK CIRCLE
circle.addEventListener('mousedown', function(event){
if(event.target == this) mousedown(event)
})
})
【讨论】：