canvas 繪制圓形進度條
阿新 • • 發佈：2017-06-29
設置字體大小 文字 height center body 字體 指定位置 str n)
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>canvas 圓形進度條效果</title>
<style>
*{margin:0;padding:0;}
body{text-align:center;background-color:#000;}
</style>
</head>
<body>
<canvas id="canvas" width="500" height="500" style="background:#000;"></canvas>
<script>
window.onload = function(){
var canvas = document.getElementById(‘canvas‘), //獲取canvas元素
context = canvas.getContext(‘2d‘), //獲取畫圖環境，指明為2d
centerX = canvas.width/2, //Canvas中心點x軸坐標
centerY = canvas.height/2, //Canvas中心點y軸坐標
rad = Math.PI*2/100, //將360度分成100份，那麽每一份就是rad度
speed = 0.1; //加載的快慢就靠它了
//繪制藍色外圈
function blueCircle(n){
context.save();
context.strokeStyle = "#fff"; //設置描邊樣式
context.lineWidth = 5; //設置線寬
context.beginPath(); //路徑開始
context.arc(centerX, centerY, 100 , -Math.PI/2, -Math.PI/2 +n*rad, false); //用於繪制圓弧context.arc(x坐標，y坐標，半徑，起始角度，終止角度，順時針/逆時針)
context.stroke(); //繪制
context.closePath(); //路徑結束
context.restore();
}
//繪制白色外圈
function whiteCircle(){
context.save();
context.beginPath();
context.strokeStyle = "white";
context.arc(centerX, centerY, 100 , 0, Math.PI*2, false);
context.stroke();
context.closePath();
context.restore();
}
//百分比文字繪制
function text(n){
context.save(); //save和restore可以保證樣式屬性只運用於該段canvas元素
context.strokeStyle = "#fff"; //設置描邊樣式
context.font = "40px Arial"; //設置字體大小和字體
//繪制字體，並且指定位置
context.strokeText(n.toFixed(0)+"%", centerX-25, centerY+10);
context.stroke(); //執行繪制
context.restore();
}
//動畫循環
(function drawFrame(){
window.requestAnimationFrame(drawFrame, canvas);
context.clearRect(0, 0, canvas.width, canvas.height);
whiteCircle();
text(speed);
blueCircle(speed);
if(speed > 100) speed = 0;
speed += 0.1;
}());
}
</script>
</body>
</html>
有詳細解釋 練習demo
canvas 繪制圓形進度條