本文实例为大家分享了JS实现圆形进度条拖拽滑动的具体代码，供大家参考，具体内容如下
效果展示
半圆进度条效果
圆形进度条
代码实现
<!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1" />
<title> 圆形进度条拖拽滑动 </title>
</head>
<body>
<canvas id="canvasId" width="400" height="400"></canvas>
<script type="text/javascript">
var canvas = document.getElementById("canvasId");
var ctx = canvas.getContext("2d");
var ox = 200;
var oy = 200;
var or = 180;
var br = 15;
var moveFlag = false;
function offset(r,d) {//根据弧度与距离计算偏移坐标
return {x: -Math.sin(r)*d, y: Math.cos(r)*d};
};
function draw(n) {
ctx.clearRect(0,0,canvas.width,canvas.height);
ctx.strokeStyle = "#99a";
ctx.lineWidth = 5;
ctx.beginPath();
ctx.arc(ox,oy,or,0,Math.PI,true);//半圆
// ctx.arc(ox,oy,or,0,2*Math.PI,true);//整圆
ctx.stroke();
ctx.strokeStyle = "#69f";
ctx.lineWidth = 5;
ctx.beginPath();
ctx.arc(ox,oy,or,Math.PI,(n*2+0.5)*Math.PI,false);
// ctx.arc(ox,oy,or,0.5*Math.PI,(n*2+0.5)*Math.PI,false);
ctx.stroke();
ctx.fillStyle = "#69f";
ctx.font = "80px Arial";
ctx.textAlign = "center";
ctx.textBaseline = "middle";
ctx.fillText(Math.round(n*100-25)+"%",ox,oy);
ctx.fillStyle = "#00f";
ctx.beginPath();
var d = offset(n*2*Math.PI,or);
ctx.arc(ox+d.x,oy+d.y,br,0,2*Math.PI,true);
ctx.fill();
}
var on = ("ontouchstart" in document)? {
start: "touchstart", move: "touchmove", end: "touchend"
} : {
start: "mousedown", move: "mousemove", end: "mouseup"
};
function getXY(e,obj) {
var et = e.touches? e.touches[0] : e;
var x = et.clientX;
var y = et.clientY;
return {
x : x - obj.offsetLeft + (document.body.scrollLeft || document.documentElement.scrollLeft),
y : y - obj.offsetTop + (document.body.scrollTop || document.documentElement.scrollTop)
}
}
canvas.addEventListener(on.start, function(e) {
moveFlag = true;
}, false);
canvas.addEventListener(on.move, function(e) {
if (moveFlag) {
var k = getXY(e,canvas);
var r = Math.atan2(k.x-ox, oy-k.y);
var hd = (Math.PI+r)/(2*Math.PI);
// 半圆的滑动范围判断
if (hd <= 0.75 && hd >= 0.25) {
draw(hd);
}
}
}, false);
canvas.addEventListener(on.end, function(e) {
moveFlag = false;
}, false);
draw(0.25);
</script>
</body>
</html>
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