JavaScript HTML5-Canvas-使用SetInterval绘制弧会导致锯齿状边缘 | 使用SetInterval绘制弧会导致锯齿状边缘

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问题描述

我正在尝试绘制一个甜甜圈图，到目前为止，我已经成功了。问题是，当尝试通过将 stroke（）与 setInterval（）组合来为圆弧设置动画时，它可以工作，但是它看起来不光滑，并产生锯齿状的边缘。动画制作完成后，我尝试使用 clearRect（）清除画布并重新添加动画的最终版本，但是我必须一直使用 clearRect（）错误，因为它什么也没做。如果您对如何使它看起来更好有任何想法，我将非常感激。

I'm trying to draw a donut chart, and so far I've been successful. The problem is that when trying to animate the arc by combining stroke() with setInterval(), it works, but it does not look smooth, and produces jagged edges. I tried using clearRect() to clear the canvas after the animation was done and re-add the final version of the animation, but I must have been using clearRect() wrong, because it did nothing. If you have any ideas on how to get this looking good, I'd really appreciate it.

您可以在jsfiddle上看到我当前的代码：及以下版本：

You can see my current code on jsfiddle: http://jsfiddle.net/4mJCy/ and below:

正文：

<canvas id="Donutchart" width="215" height="500" style="border:1px solid #000;">
Your browser does not support the HTML5 canvas tag.  Please Upgrade to the latest version of Chrome, Firefox, or Safari.</canvas>

JavaScript：

JavaScript:

var canvas=document.getElementById("Donutchart");
var maincircle=canvas.getContext("2d");
maincircle.beginPath();
maincircle.arc(107,107,100,0,2*Math.PI);
maincircle.fillStyle="#FF0000";
maincircle.fill();



var currentEndAngle = 1.5;
var currentStartAngle = 1.5;

var pie1 = setInterval(draw, 15);

var counter = 0;

function draw(){


    if(counter >= 101){



    } else {

        var startAngle = currentStartAngle * Math.PI;
        var endAngle = (currentEndAngle) * Math.PI;

        currentEndAngle = currentEndAngle + 0.01;

        var counterClockwise = false;


        var donutslice1=canvas.getContext("2d");
        donutslice1.beginPath();
        donutslice1.arc(107,107,75,startAngle,endAngle);
        donutslice1.lineWidth = 50;
        donutslice1.strokeStyle="#222";
        donutslice1.stroke();

    }



    counter++;

}


var innercircle=canvas.getContext("2d");
innercircle.beginPath();
innercircle.arc(107,107,50,0,2*Math.PI);
innercircle.fillStyle="#FFF";
innercircle.fill();

推荐答案

锯齿是由反复覆盖弧线引起的

The jaggies are caused by repeatedly over-writing your arcs.

相反，重构代码以在每个动画循环中清除画布。

Instead, refactor your code to clear the canvas with each animation loop.

演示：

类似这样的东西：

<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>
<style>
    body{ background-color: white; }
    canvas{border:1px solid red;}
</style>
<script>
$(function(){

    var canvas=document.getElementById("canvas");
    var ctx=canvas.getContext("2d");

    var currentEndAngle = 1.5;
    var currentStartAngle = 1.5;

    var pie1 = setInterval(draw, 15);

    var counter = 0;

    function draw(){

      if(counter >= 101){

      } else {

        var startAngle = currentStartAngle * Math.PI;
        var endAngle = (currentEndAngle) * Math.PI;

        currentEndAngle = currentEndAngle + 0.01;

        var counterClockwise = false;

        ctx.clearRect(0,0,canvas.width,canvas.height);
        // red
        drawCircle(75,"#FF0000");
        // gray
        drawDonut(startAngle,endAngle);

      }

      counter++;
    }

    //
    function drawDonut(startAngle,endAngle){
        ctx.beginPath();
        ctx.arc(107,107,75,startAngle,endAngle);
        ctx.lineWidth = 50;
        ctx.strokeStyle="#444";
        ctx.stroke();
    }
    //
    function drawCircle(radius,color){
        ctx.beginPath();
        ctx.arc(107,107,radius,0,2*Math.PI);
        ctx.lineWidth = 50;
        ctx.strokeStyle=color;
        ctx.stroke();
    }

}); // end $(function(){});
</script>
</head>
<body>
    <canvas id="canvas" width=300 height=300></canvas>
</body>
</html>

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