使用 Canvas 为填充圆设置动画

Question

基本上我希望能够使用画布填充一个圆圈，但它会以一定的百分比进行动画处理。 即只有圆圈填满了 80% 的路径。

我的画布知识并不惊人，这是我在 Photoshop 中制作的图像以显示我想要的内容。

我希望圆圈开始为空，然后填充到圆圈的 70%。 如果可以的话，这对 Canvas 是否可行？任何人都可以阐明如何做到这一点？

这是我所管理的一个小提琴

http://jsfiddle.net/6Vm67/

 var canvas = document.getElementById('Circle');
 var context = canvas.getContext('2d');
 var centerX = canvas.width / 2;
 var centerY = canvas.height / 2;
 var radius = 80;

 context.beginPath();
 context.arc(centerX, centerY, radius, 0, 2 * Math.PI, false);
 context.fillStyle = '#13a8a4';
 context.fill();
 context.lineWidth = 10;
 context.strokeStyle = '#ffffff';
 context.stroke();

任何帮助将不胜感激

Answer 1

剪切区域使这变得非常容易。您所要做的就是制作一个圆形剪切区域，然后填充某个大小的矩形以获得“部分圆形”的填充值。这是一个例子：

var canvas = document.getElementById('Circle');
var context = canvas.getContext('2d');
var centerX = canvas.width / 2;
var centerY = canvas.height / 2;
var radius = 80;

var full = radius*2;
var amount = 0;
var amountToIncrease = 10;

function draw() {
    context.save();
    context.beginPath();
    context.arc(centerX, centerY, radius, 0, 2 * Math.PI, false);
    context.clip(); // Make a clipping region out of this path
    // instead of filling the arc, we fill a variable-sized rectangle
    // that is clipped to the arc
    context.fillStyle = '#13a8a4';
    // We want the rectangle to get progressively taller starting from the bottom
    // There are two ways to do this:
    // 1. Change the Y value and height every time
    // 2. Using a negative height
    // I'm lazy, so we're going with 2
    context.fillRect(centerX - radius, centerY + radius, radius * 2, -amount);
    context.restore(); // reset clipping region

    context.beginPath();
    context.arc(centerX, centerY, radius, 0, 2 * Math.PI, false);
    context.lineWidth = 10;
    context.strokeStyle = '#000000';
    context.stroke();

    // Every time, raise amount by some value:
    amount += amountToIncrease;
    if (amount > full) amount = 0; // restart
}

draw();
// Every second we'll fill more;
setInterval(draw, 1000);

http://jsfiddle.net/simonsarris/pby9r/

Answer 2

这是一个更动态的面向对象的版本，因此您可以配置选项为圆的半径、边框宽度、颜色、持续时间和动画的步长，您还可以将圆设置为一定百分比的动画。写这个很有趣。

<canvas id="Circle" width="300" height="300"></canvas>
<script>
    function Animation( opt ) {
        var context = opt.canvas.getContext("2d");
        var handle = 0;
        var current = 0;
        var percent = 0;

        this.start = function( percentage ) {
            percent = percentage;
            // start the interval
            handle = setInterval( draw, opt.interval );
        }

        // fill the background color
        context.fillStyle = opt.backcolor;
        context.fillRect( 0, 0, opt.width, opt.height );

        // draw a circle
        context.arc( opt.width / 2, opt.height / 2, opt.radius, 0, 2 * Math.PI, false );
        context.lineWidth = opt.linewidth;
        context.strokeStyle = opt.circlecolor;
        context.stroke();

        function draw() {
            // make a circular clipping region
            context.beginPath();
            context.arc( opt.width / 2, opt.height / 2, opt.radius-(opt.linewidth/2), 0, 2 * Math.PI, false );
            context.clip();

            // draw the current rectangle
            var height = ((100-current)*opt.radius*2)/100 + (opt.height-(opt.radius*2))/2;
            context.fillStyle = opt.fillcolor;
            context.fillRect( 0, height, opt.width, opt.radius*2 );

            // clear the interval when the animation is over
            if ( current < percent ) current+=opt.step;
            else clearInterval(handle);
        }
    }

    // create the new object, add options, and start the animation with desired percentage
    var canvas = document.getElementById("Circle");
    new Animation({
        'canvas': canvas,
        'width': canvas.width,
        'height': canvas.height,
        'radius': 100,
        'linewidth': 10,        
        'interval': 20,
        'step': 1,
        'backcolor': '#666',
        'circlecolor': '#fff',
        'fillcolor': '#339999'
    }).start( 70 );
</script>