问题
Does anyone know how to define an animated arc / circle in SVG, such that the arc starts at 0 degrees and ends at 360 degrees?
回答1:
you can paint it "by hand" using path's lineto and calculate the position of the arc:
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" version="1.1"
viewBox="0 0 1200 800"
preserveAspectRatio="xMidYMid"
style="width:100%; height:100%; position:absolute; top:0; left:0;"
onload="drawCircle();">
<script>
function drawCircle() {
var i = 0;
var circle = document.getElementById("arc");
var angle = 0;
var radius = 100;
window.timer = window.setInterval(
function() {
angle -=5;
angle %= 360;
var radians= (angle/180) * Math.PI;
var x = 200 + Math.cos(radians) * radius;
var y = 200 + Math.sin(radians) * radius;
var e = circle.getAttribute("d");
if(i==0) {
var d = e+ " M "+x + " " + y;
}
else {
var d = e+ " L "+x + " " + y;
}
if (angle === -5 && i !== 0) {
window.clearInterval(window.timer);
}
circle.setAttribute("d", d);
i++;
}
,10)
}
</script>
<path d="M200,200 " id="arc" fill="none" stroke="blue" stroke-width="2" />
</svg>
http://jsfiddle.net/k99jy/138/
回答2:
One way is to use a circle, and animate the stroke-dashoffset (you need 'stroke-dasharray' too). An example of such an animation (not with a circle, but the same principle applies) can be seen here.
The other option is to use a path animation, and arc path segments, for animating/morphing between paths see this example.
回答3:
You can also draw the SVG by hand using a circle and the following technique:
- Give the
circleastroke. - Make the
strokedashedwith a dash length equal to the circle's circumference. - Offset the
strokeby a length equal to the circle's circumference. - Animate the stroke.
HTML:
<svg width="200" height="200">
<circle class="path" cx="100" cy="100" r="96" stroke="blue" stroke-width="4" fill="none" />
</svg>
CSS:
circle {
stroke-dasharray: /* circumference */;
stroke-dashoffset: /* circumference */;
animation: dash 5s linear forwards;
}
@keyframes dash {
to {
stroke-dashoffset: /* length at which to stop the animation */;
}
}
jsfiddle
source: https://css-tricks.com/svg-line-animation-works/
回答4:
Or perhaps you could uncover a pre-drawn circle to give the required effect:
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 1000 1000" width="400" height="400">
<rect x="0" y="0" width="1000" height="1000"/>
<circle cx="500" cy="500" r="500" fill="red"/>
<rect x="0" y="500" width="1000" height="500"/>
<rect x="0" y= "0" width="1000" height="500">
<animateTransform attributeName="transform" type="rotate" begin="0s" dur="5s" fill="freeze" from="0,500,500" to="180,500,500"/>
</rect>
</svg>
回答5:
I was also a bit disapointed to not be able to simply make an circle's arc with a percent, or an angle.
Nowadays, when I need an arc which is not part of a longer path, I use a circle and strokeDasharray trick to show just a part of this circle.
svg {
outline: solid;
height: 100px;
width: 100px;
}
.arc {
fill: transparent;
stroke-width: 5;
stroke: red;
stroke-dasharray: 94.24778 219.91149;
}<svg viewport="0 0 100 100">
<circle cx="50" cy="50" r="50" class="arc"></circle>
</svg>You can see an improved version here which use Sass to make the calculations.
回答6:
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<title></title>
<link rel="stylesheet" href="">
</head>
<body>
</body>
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" version="1.1"
viewBox="0 0 1200 800"
preserveAspectRatio="xMidYMid"
style="width:100%; height:100%; position:absolute; top:0; left:0;"
onload="drawCircle();">
<script>
function drawCircle() {
// center point
var cX = 300,
cY = 300;
radius = 300,
p1 = {x: cX+radius, y: cY},
p2 = {x: cX-radius, y: cY},
circle = document.getElementById("arc"),
angle = 0;
window.timer = window.setInterval(
function() {
angle -= 5;
angle %= 360;
var radians= (angle/180) * Math.PI;
var x = cX + Math.cos(radians) * radius;
var y = cY + Math.sin(radians) * radius;
if (Math.abs(angle) < 180 && angle != 0)
d= 'M ' + p1.x + ',' + p1.y + ' A' + radius+ ',' + radius+ (Math.abs(angle)==180?' 0 1 0 ':' 0 0 0 ')+x+' '+y;
else
d= 'M ' + p1.x + ',' + p1.y + ' A' + radius+ ',' + radius+ ' 0 1 0 '+p2.x+' '+p2.y +
' M ' + p2.x + ',' + p2.y + ' A' + radius+ ',' + radius+ (Math.abs(angle)==0?' 0 1 0 ':' 0 0 0 ')+x+' '+y;
circle.setAttribute("d", d);
if (Math.abs(angle) == 0)
window.clearInterval(window.timer);
}
,10)
}
</script>
<path d="" id="arc" fill="none" stroke="blue" stroke-width="2" />
</svg>
</html>回答7:
Thanks for the answers - here is a little more information regarding why I want to animate a circle in SVG:
We have a server-client application. I plan to generate SVG images to represent charts (pie charts / bar charts) on the server and send the SVG to the clients. We have Java and .NET clients. I will write client-side code to parse and render the SVG images received from the server. I plan to use only a subset of the SVG format - not more than what we need to represent our charts, but animation is a requirement.
Long-term it would be nice to have an ajax client - that will run on browsers without java or .NET runtime. That is why I have chosen the SVG format.
For a short term solution I now think I will add my own element to the SVG, defining an arc using start and sweep angles. Then I can easily define the animation I require by animating the sweep angle, and makes my implementation simple.
Long term - if we really get around to imlpementing an AJAX/HTML client - I will have to re-implement and stick to the SVG standard.
来源：https://stackoverflow.com/questions/3256943/define-a-circle-arc-animation-in-svg