Question

enter image description here

上面只是图像以获得小提琴的链接，其角色无关紧要。

我试图沿圆圈移动一个物体（实际上是一个边框半径= 100％的矩形画布，因此表现为圆形）。但只能移动它而不能重新阻止圆圈中的移动）

这是我的JS Fiddle Link。 注意：请在js代码中向下滚动，查看以下评论中编写的唯一代码

//---- Code of interest begins-----//至// ---感兴趣的代码结束--- //

我的所需输出就像这个轮子farbtastic。虽然它是开源的但我无法在我的色轮中使用它的鼠标移动事件代码

尝试搜索时我发现Canvas move object in circle 但我不能使用它因为我不知道d而且不知道across是什么。所以无法通过arccos(1-(d/r)^2/2)

获取theta

Answer 1

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。

我在这里举例说明..

阅读评论，特别是关于rotate（）函数

http://jsfiddle.net/Z37FF/3/

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)
    })
})

围绕圈子javascript移动对象

1 个答案: