学习html5 canvas 圆环

从Joy ho 处借用

<!DOCTYPE html>
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=utf-8" />
<meta http-equiv="Cache-Control" content="no-cache" />
<meta name="viewport" content="width=device-width,initial-scale=1.0,maximum-scale=1.0,minimum-scale=1.0,user-scalable=no" />
<meta name="MobileOptimized" content="320"/>
<title>多色圆环进度</title>
</head>
<body>
<canvas id="procanvas" class="procanvas" value="100%"></canvas>
<script>
function process(canvasid,op,stylewidth,styleheight){
var canvas = document.getElementById(canvasid);
var canvasvalue = canvas.getAttribute("value");
var process = canvasvalue.substring(0, canvasvalue.length-1);
var oProcess = op;
var context = canvas.getContext('2d');
var scale = window.devicePixelRatio;
var center = [stylewidth/2*scale,styleheight/2*scale];
canvas.style.width = stylewidth + "px";
canvas.style.height = styleheight + "px";
canvas.width = stylewidth*scale;
canvas.height = styleheight*scale;

//开始画一个灰色的圆
context.beginPath();
context.moveTo(center[0], center[1]);
context.arc(center[0], center[1], center[0], 0, Math.PI * 2, false);
context.closePath();
context.fillStyle = '#e6e5e5';
context.fill();

// 画进度(红色)
if(process != 0 && process != 100){
context.beginPath();
context.moveTo(center[0], center[1]);
if(process <25){
context.arc(center[0], center[1], center[0], Math.PI*1.5, Math.PI*(1.5+0.5*(process/25)), false);//设置圆弧的起始于终止点
}
else{
context.arc(center[0], center[1], center[0], Math.PI*1.5, Math.PI*2* ((process / 100)-0.25), false);//设置圆弧的起始于终止点
}
context.closePath();
context.fillStyle = '#db3030';
context.fill();
}
else if(process == 100){
context.beginPath();
context.moveTo(center[0], center[1]);
context.arc(center[0], center[1], center[0], 0, Math.PI*2, false);//设置圆弧的起始于终止点
context.closePath();
context.fillStyle = '#db3030';
context.fill();
}

//画进度(橙色)
if(oProcess != 0 && oProcess !=100){
context.beginPath();
context.moveTo(center[0], center[1]);
context.arc(center[0], center[1], center[0], Math.PI*1.5,Math.PI*1.5-(oProcess/25)*Math.PI*0.5, true);//设置圆弧的起始于终止点
context.closePath();
context.fillStyle = '#fb7d32';
context.fill();
//Math.PI*1.5-((oProcess+25)/100*Math.PI)
}
else if(oProcess == 100){
context.beginPath();
context.moveTo(center[0], center[1]);
context.arc(center[0], center[1], center[0], 0,Math.PI*2, true);//设置圆弧的起始于终止点
context.closePath();
context.fillStyle = '#fb7d32';
context.fill();
}

// 画内部空白
context.beginPath();
context.moveTo(center[0], center[1]);
context.arc(center[0], center[1], 21*scale, 0, Math.PI * 2, true);
context.closePath();
context.fillStyle = 'rgba(255,255,255,1)';
context.fill();
}

var vu=50;//可以用变量
process("procanvas",vu,52,52);//10是橙色
</script>
</body>
</html>