javascript - 如何使javascript Canvas 绘制更快？-6ren

javascript - 如何使javascript Canvas 绘制更快？

转载作者：行者123 更新时间：2023-11-29 21:38:29

我有以下代码来显示ECG。我使用画布绘制图形背景（每个2.5毫米尺寸的网格）。稍后，我从数组array_1中获取y坐标（x坐标在程序中计算）。这种方法的问题是，由于数组array_1中有1250个值，因此绘制整个图形大约需要40秒。我可以做的是，我可以在循环中完成绘图部分，在这种情况下，页面加载后便会立即绘制整个图形。但是，我需要在5秒钟内完成绘图。不多。不低于。我将如何更改代码来做到这一点？请帮忙。

<!DOCTYPE html>
<html>
<head>
    <title></title>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
</head>
<body>
    <canvas id="canvas" width="1350" height="1300" style="background-color: white;"></canvas>
    <script type='text/javascript'>

    var canvas = document.getElementById("canvas");
    var ctxt = canvas.getContext("2d");
    var n1 = 1;
    var n1_x=49; //Graph x coordinate starting pixel.
    var n1_y=72;//Graph y coordinate starting pixel.
    var array_1 = []// array from which y coordinates are taken. Has 1250 elements
     var ctx = canvas.getContext("2d");
    var x=0;
    var y=0;
    var Line_position=-1;
    while(x<=1350)//graph width
    {
        ctxt.lineWidth = "0.5";
        Line_position=Line_position+1;
        if(Line_position%5==0)
        {
            ctxt.lineWidth = "1.5";
        }

        ctxt.strokeStyle = "black";
        ctxt.beginPath();
        ctxt.moveTo(x, 0);
        ctxt.lineTo(x, 1300);
        ctxt.stroke();
        x=x+9.43;

    }

    Line_position=-1;
    while(y<=1300)//graph height
    {
        ctxt.lineWidth = "0.5";
        Line_position=Line_position+1;
        if(Line_position%5==0)
        {
            ctxt.lineWidth = "1.5";
        }

        ctxt.strokeStyle = "black";
        ctxt.beginPath();
        ctxt.moveTo(0, y);
        ctxt.lineTo(1350,y);
        ctxt.stroke();
        y=y+9.43;
    }
   drawWave();
        function drawWave()
        {
          requestAnimationFrame(drawWave);
                ctx.lineWidth = "1";
                ctx.strokeStyle = 'blue';
               ctx.beginPath();
                ctx.moveTo(n1_x- 1, n1_y+array_1[n1-1]);//move to the pixel position
                ctx.lineTo(n1_x, n1_y+array_1[n1]);//Draw to the pixel position
                ctx.stroke();
                n1_x=n1_x+0.374;//Incrementing pixel so as to traverse x axis.
                n1++;
 }

    </script>
</body>
</html>

这是数组：
array_1 = [69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69 ，69,69,69,69,69,69,69,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20 ，20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20 ，20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20 ，20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20 ，20,20,20,20,20,20,20,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69 ，69,72,72,72,72,72,72,72,73,73,74,74,74,74,74,74,74,73,73,73,73,74,74,74,74 ，73,73,73,73,73,73,73,73,73,73,73,73,73,74,74,74,73,73,73,72,73,73,73,73,73 ，73,73,73,73,73,73,73,73,73,73,72,72,72,71,72,72,72,73,73,73,72,72,72,73,73 ，73,74,73,73,72,72,72,72,72,73,73,73,73,73,72,72,72,72,73,73,73,72,72,72,72,71,101 ，71,70,70,70,69,68,68,67,67,66,66,67,67,69,70,72,72,72,73,73,74,73,73,73,73 ，73,73,73,73,73,74,76,77,76,70,57,40,22,11,11,22,40,57,69,73,73,71,71,71,72 ，72,73,73,74,74,74,73,72,72,72,72,72,72,72,72,72,72,72,72,71,71,70,70,71,71 ，71,71,70,70,6 9,69,69,69,69,69,69,68,68,68,67,67,66,66,65,65,64,63,63,62,62,62,62,62,62， 62,62,63,63,64,65,66,67,68,68,69,70,71,72,72,72,73,73,73,73,72,72,72,73,73， 73,73,73,73,73,73,73,73,73,73,73,73,73,72,72,72,73,73,73,73,72,73,73,73,73， 73,73,73,73,73,73,72,72,72,72,72,72,73,73,74,74,74,74,74,74,73,73,72,73,73， 73,74,73,73,72,72,72,73,73,73,72,72,73,73,74,74,73,73,73,73,73,73,73,73,73， 73,73,73,73,73,73,73,73,73,72,72,71,70,70,70,70,70,69,69,68,67,67,67,67,68， 69,71,72,72,73,73,73,73,74,74,74,74,74,73,73,73,73,75,77,78,76,67,53,35,18， 8,10,23,41,58,69,73,72,71,70,71,72,73,73,73,73,73,73,73,73,72,72,73,73,73， 73,72,71,71,70,70,71,71,71,71,71,71,71,71,71,70,70,69,69,69,69,68,68,67,67,67， 67,67,66,65,65,65,64,63,62,61,61,61,60,60,60,59,60,60,60,61,62,63,65,66,66， 67,68,69,70,71,72,72,72,72,73,73,73,72,72,72,72,72,72,72,73,73,73,73,73,73， 72,72,73,73,73,73,73,73,73,73,73,73,73,73,73,72,72,71,71,72,72,73,73,73,73,72， 72,72,72,72,72,73,73,73,73,73,73,73,73,73,72,73,73,73,73,73,73,72,73,73,73， 73,73,73,73,72,72,72,73,73， 73,73,73,73,73,73,73,73,73,73,73,73,73,73,73,73,73,73,72,71,71,70,70,69,69， 69,68,67,67,66,65,66,66,68,69,70,71,72,72,73,73,73,73,73,73,74,74,74,74,74， 74,76,78,78,74,64,48,29,13,5,10,26,45,62,71,73,72,71,71,72,73,73,73,73,73， 74,74,74,73,72,72,72,73,73,73,73,73,73,73,72,72,72,72,71,71,71,71,71,71,71,71， 71,71,70,70,69,69,69,69,68,67,66,66,66,66,65,65,64,63,62,62,61,61,60,60,60， 60,61,62,62,63,64,65,66,67,68,70,71,72,72,72,72,72,72,73,73,73,73,73,73,73， 74,74,75,75,74,74,74,73,73,73,74,73,73,73,73,73,74,74,74,74,74,73,73,73,73， 73,73,73,73,73,73,73,73,73,73,72,72,73,73,74,74,74,73,73,73,73,73,73,73,73， 73,73,72,72,72,72,73,73,72,72,73,73,73,73,73,73,73,73,73,73,73,73,73,73,73， 73,73,73,73,73,73,72,72,73,73,72,72,71,70,70,70,69,69,68,68,67,67,66,67,67， 68,69,70,71,72,73,73,74,74,73,73,73,74,75,75,74,73,73,74,76,78,75,67,52,32， 15,5,8,22,41,59,69,73,72,71,70,71,72,72,73,73,73,73,73,73,73,73,73,72,72， 72,72,72,72,72,72,72,72,71,71,71,70,70,70,70,70,70,70,69,69,69,69,69,68,68,68， 68,67,67,66,65,65,64,64,64,6 3,62,61,60,60,60,60,60,61,61,62,62,63,64,65,65,66,67,68,69,70,71,71,71,71， 71,71,72,72,73,73,73,72,72,73,73,73,73,73,73,73,73,73,73,73,73,73,72,72,72， 72,72,72,72,71,71,71,71,71,71,71,72,72,72,72,72,72,72,72,72,71,71,71,71,72,72， 73,73,72,72,72,72,72,73,73,73,73,73,72,72,72,72,72,73,73,73,73,73,72,72,72,72， 73,73,74,73,73,73,73,73,73,73,73,73,73,73,73,72,72,72,72,71,71,71,70,70,70， 70,69,69,68,67,67,68,69,71,72,73,73,73,73,73,73,73,73,74,75,75,75,74,74,74， 75,77,77,75,67,52,34,18,10,12,26,45,62,71,74,73,72,72,72,73,74,74,74,75,75， 74,74,74,74,74,74,74,74,74,73,73,73,73,74,74,73,73,73,73,73,73,73,72,72,71， 71,71,71,71,70,70,70,69,69,69,68,68,68,68,67,66,65,64,63,63,62,62,62,63,63， 63,63,64,65,66,67,69,69,70,71,72,72,73,73,74,74,74,74,75,75,76,76,74,72,70， 70,69,69];

最佳答案

我可能会去做类似这样的任务。如评论中所提到的，我们需要每帧绘制多个数据点。我们绘制的数量取决于浏览器提供动画帧的速度。

我已经将值硬编码为4，因为这似乎可以在我的机器上使用，但是如果您不做更多的工作，您可能可以自己设置代码时间并即时调整该值，以使动画的运行时间接近可能达到目标时间。我走得很快，但结果糟透了，我将其留给读者作为研究或思考的练习。

通过跟踪当前“刷新周期”已经绘制了多少帧，我们知道要为每个帧绘制的第一个点索引到数组的距离。

我尝试过尽可能地对代码进行参数化，但是已经晚了，我很累，我可能在某处忽略了某些内容。

<!doctype html>
<html>
<head>
<script>
function byId(id,parent){return (parent == undefined ? document : parent).getElementById(id);}

window.addEventListener('load', onDocLoaded, false);
function onDocLoaded(evt)
{
    drawBkg(byId('canvas'), 9.43, 5, "0.5", "1.5", "black");
    drawCurFrame();
}

var dataSamples = [69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,20,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,69,72,72,72,72,72,72,72,73,73,74,74,74,74,74,74,74,73,73,73,73,74,74,74,74,73,73,73,73,73,73,73,73,73,73,73,73,73,74,74,74,73,73,73,72,73,73,73,73,73,73,73,73,73,73,73,73,73,73,73,72,72,72,71,72,72,72,73,73,73,72,72,72,73,73,73,74,73,73,72,72,72,72,72,73,73,73,73,73,72,72,72,72,73,73,73,72,72,72,71,101,71,70,70,70,69,68,68,67,67,66,66,67,67,69,70,72,72,72,73,73,74,73,73,73,73,73,73,73,73,73,74,76,77,76,70,57,40,22,11,11,22,40,57,69,73,73,71,71,71,72,72,73,73,74,74,74,73,72,72,72,72,72,72,72,72,72,72,72,72,71,71,70,70,71,71,71,71,70,70,69,69,69,69,69,69,69,68,68,68,67,67,66,66,65,65,64,63,63,62,62,62,62,62,62,62,62,63,63,64,65,66,67,68,68,69,70,71,72,72,72,73,73,73,73,72,72,72,73,73,73,73,73,73,73,73,73,73,73,73,73,73,73,72,72,72,73,73,73,73,72,73,73,73,73,73,73,73,73,73,73,72,72,72,72,72,72,73,73,74,74,74,74,74,74,73,73,72,73,73,73,74,73,73,72,72,72,73,73,73,72,72,73,73,74,74,73,73,73,73,73,73,73,73,73,73,73,73,73,73,73,73,73,73,72,72,71,70,70,70,70,70,69,69,68,67,67,67,67,68,69,71,72,72,73,73,73,73,74,74,74,74,74,73,73,73,73,75,77,78,76,67,53,35,18,8,10,23,41,58,69,73,72,71,70,71,72,73,73,73,73,73,73,73,73,72,72,73,73,73,73,72,71,71,70,70,71,71,71,71,71,71,71,71,70,70,69,69,69,69,68,68,67,67,67,67,67,66,65,65,65,64,63,62,61,61,61,60,60,60,59,60,60,60,61,62,63,65,66,66,67,68,69,70,71,72,72,72,72,73,73,73,72,72,72,72,72,72,72,73,73,73,73,73,73,72,72,73,73,73,73,73,73,73,73,73,73,73,73,73,72,72,71,71,72,72,73,73,73,72,72,72,72,72,72,73,73,73,73,73,73,73,73,73,72,73,73,73,73,73,73,72,73,73,73,73,73,73,73,72,72,72,73,73,73,73,73,73,73,73,73,73,73,73,73,73,73,73,73,73,73,73,72,71,71,70,70,69,69,69,68,67,67,66,65,66,66,68,69,70,71,72,72,73,73,73,73,73,73,74,74,74,74,74,74,76,78,78,74,64,48,29,13,5,10,26,45,62,71,73,72,71,71,72,73,73,73,73,73,74,74,74,73,72,72,72,73,73,73,73,73,73,73,72,72,72,72,71,71,71,71,71,71,71,71,71,70,70,69,69,69,69,68,67,66,66,66,66,65,65,64,63,62,62,61,61,60,60,60,60,61,62,62,63,64,65,66,67,68,70,71,72,72,72,72,72,72,73,73,73,73,73,73,73,74,74,75,75,74,74,74,73,73,73,74,73,73,73,73,73,74,74,74,74,74,73,73,73,73,73,73,73,73,73,73,73,73,73,73,72,72,73,73,74,74,74,73,73,73,73,73,73,73,73,73,73,72,72,72,72,73,73,72,72,73,73,73,73,73,73,73,73,73,73,73,73,73,73,73,73,73,73,73,73,73,72,72,73,73,72,72,71,70,70,70,69,69,68,68,67,67,66,67,67,68,69,70,71,72,73,73,74,74,73,73,73,74,75,75,74,73,73,74,76,78,75,67,52,32,15,5,8,22,41,59,69,73,72,71,70,71,72,72,73,73,73,73,73,73,73,73,73,72,72,72,72,72,72,72,72,72,72,71,71,71,70,70,70,70,70,70,70,69,69,69,69,68,68,68,68,67,67,66,65,65,64,64,64,63,62,61,60,60,60,60,60,61,61,62,62,63,64,65,65,66,67,68,69,70,71,71,71,71,71,71,72,72,73,73,73,72,72,73,73,73,73,73,73,73,73,73,73,73,73,73,72,72,72,72,72,72,72,71,71,71,71,71,71,71,72,72,72,72,72,72,72,72,72,71,71,71,72,72,73,73,72,72,72,72,72,73,73,73,73,73,72,72,72,72,72,73,73,73,73,73,72,72,72,73,73,74,73,73,73,73,73,73,73,73,73,73,73,73,72,72,72,72,71,71,71,70,70,70,70,69,69,68,67,67,68,69,71,72,73,73,73,73,73,73,73,73,74,75,75,75,74,74,74,75,77,77,75,67,52,34,18,10,12,26,45,62,71,74,73,72,72,72,73,74,74,74,75,75,74,74,74,74,74,74,74,74,74,73,73,73,73,74,74,73,73,73,73,73,73,73,72,72,71,71,71,71,71,70,70,70,69,69,69,68,68,68,68,67,66,65,64,63,63,62,62,62,63,63,63,63,64,65,66,67,69,69,70,71,72,72,73,73,74,74,74,74,75,75,76,76,74,72,70,70,69,69 ];

function drawBkg(canvasElem, squareSize, numSquaresPerBlock, minorLineWidthStr, majorLineWidthStr, lineColStr)
{
    var nLinesDone = 0;
    var i, curX, curY;
    var ctx = canvasElem.getContext('2d');
    ctx.clearRect(0,0,canvasElem.width,canvasElem.height);

    // draw the vertical lines
    curX=0;
    ctx.strokeStyle = lineColStr;
    while (curX < canvasElem.width)
    {
        if (nLinesDone % numSquaresPerBlock == 0)
            ctx.lineWidth = majorLineWidthStr;
        else
            ctx.lineWidth = minorLineWidthStr;

        ctx.beginPath();
        ctx.moveTo(curX, 0);
        ctx.lineTo(curX, canvasElem.height);
        ctx.stroke();

        curX += squareSize;
        nLinesDone++;
    }

    // draw the horizontal lines
    curY=0;
    nLinesDone = 0;
    while (curY < canvasElem.height)
    {
        if (nLinesDone % numSquaresPerBlock == 0)
            ctx.lineWidth = majorLineWidthStr;
        else
            ctx.lineWidth = minorLineWidthStr;

        ctx.beginPath();
        ctx.moveTo(0, curY);
        ctx.lineTo(canvasElem.width, curY);
        ctx.stroke();

        curY += squareSize;
        nLinesDone++;
    }
}

// position that will be treated as 0,0 when drawing our points.
var originX=49;
var originY=72;

function drawSamples(nSamplesToDraw, firstSample, lineWidthStr, lineColourStr)
{
    var can = byId('canvas');
    var ctx = can.getContext('2d');

    ctx.strokeStyle = lineColourStr;
    ctx.lineWidth = lineWidthStr;
    console.log(firstSample);
    ctx.beginPath();

    ctx.moveTo( originX+firstSample-1, dataSamples[firstSample-1]+originY );
    for (var i=0; i<nSamplesToDraw; i++)
    {
        var curSample = dataSamples[i + firstSample];
        ctx.lineTo( originX+firstSample+i, curSample+originY );
    }
    ctx.stroke();
}

var curFrame=0;
var nPointsPerFrame = 4;
function drawCurFrame()
{
    if ((dataSamples.length - (nPointsPerFrame * curFrame)) < nPointsPerFrame)      // will we over-run the end of the array of datapoints?
    {
        curFrame = 0;                                                               // if so, reset
        drawBkg(byId('canvas'), 9.43, 5, "0.5", "1.5", "black");
    }
    drawSamples(nPointsPerFrame, nPointsPerFrame*curFrame, "1", "blue");
    curFrame++;
    requestAnimationFrame( drawCurFrame );
}
</script>

<style>
#canvas
{
    border: solid 1px black;
    background-color: #FFFFFF;
}
</style>

</head>
<body>
    <div id='txt'></div>
    <canvas id="canvas" width="1350" height="1300"></canvas>

</body>
</html>

关于javascript - 如何使javascript Canvas 绘制更快？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/34102126/

文章推荐： javascript - 正则表达式有问题

文章推荐： android - TouchDB - CouchbaseLite 库？

文章推荐： javascript - Rxjs 双工流

javascript - 执行存在于输入值字段中的 javascript - JavaScript
我有一个 html 格式的表单: 我需要得到 JavaScript在value input 字段执行，但只能通过表单的 submit .原因是页面是一个模板所以我不控制它(不能有
javascript - JavaScript 代码片段正在破坏其他 JavaScript
我管理的论坛是托管软件，因此我无法访问源代码，我只能向页面添加 JavaScript 来实现我需要完成的任务。我正在尝试用超链接替换所有页面上某些文本关键字的第一个实例。我还根据国家/地区代码对这些
javascript - JavaScript 如何使新页面包含更多 JavaScript？
我正在使用 JS 打开新页面并将 HTML 代码写入其中，但是当我尝试使用 document.write() 在新页面中编写 JS 时功能不起作用。显然，一旦看到，主 JS 就会关闭。用于即将打开的
javascript - Javascript 引擎如何在浏览器中执行 Javascript？
提问不是为了解决问题，提问是为了更好地理解系统专家!我知道每当你将 javascript 代码输入 javascript 引擎时，它会立即由 javascript 引擎执行。由于没有看过Engi
javascript - 如何将 JavaScript 变量从一个 JavaScript 文件传递到另一个 JavaScript 文件？
我在一个文件夹中有两个 javascript 文件。我想将一个变量的 javascript 文件传递到另一个。我应该使用什么程序？最佳答案 window.postMessage用于跨文档消息。使
javascript - javascript 中的 javascript 输入问题
我有一个练习，我需要输入两个输入并检查它们是否都等于一个。如果是 console.log 正则 console.log false 我试过这样的事情: function isPositive(fir
javascript - 在加载其他 javascript 库的页面上嵌入 Javascript？
我正在做一个Web应用程序，计划允许其他网站(客户端)在其页面上嵌入以下javascript: 我的网络应用程序位于 http://example.org 。我不能假设客户端网站的页面有 JQue
javascript - 从 Javascript 内部调用 Javascript
目前我正在使用三个外部 JS 文件。我喜欢将所有三个 JS 文件合而为一。尽一切可能。我创建 aio.js 并在 aio.js 中 src="https://code.jquery.com/
javascript - AngularJS/javascript javascript 对象的特殊排序顺序
我有例如像这样的数组: var myArray = []; var item1 = { start: '08:00', end: '09:30' } var item2 = {
javascript - 在 Javascript 内部执行 Javascript？
所以我正在制作一个 Chrome 扩展，它使用我制作的一些 TamperMonkey 脚本。我想要一个“主”javascript 文件，您可以在其中包含并执行其他脚本。我很擅长使用以下行将其他 jav
javascript - 如何将变量从 javascript 移动到 javascript？
我有 A、B html 和 A、B javascript 文件。并且，如何将 A JavaScript 中使用的全局变量直接移动到 B JavaScript 中？示例 JavaScript) va
javascript - 从 javascript 调用 javascript
我需要将以下整个代码放入名为 activate.js 的 JavaScript 中。你能告诉我怎么做吗？ var int = new int({ seconds: 30, mark
javascript - 将变量值从一个 JavaScript 传递到另一个 JavaScript
我已经为我的 .net Web 应用程序创建了母版页 EXAMPLE1.Master。他们的 I 将值存储在 JavaScript 变量中。我想在另一个 JS 文件中检索该变量。示例1.大师:-
javascript - 有没有开源库可以在浏览器中使用 Javascript 来整理 Javascript？
是否有任何库可以用来转换这样的代码: function () { var a = 1; } 像这样的代码: function () { var a = 1; } 在我的浏览器中。因为我在 Gi
javascript - javascript 中的参数列表后缺少语法 javascript 错误 )
我收到语法缺失 ) 错误 $(document).ready(function changeText() { var p = document.getElementById('bidp
javascript - 第一个 JavaScript 完成后启动第二个 JavaScript
我正在制作进度条。它有一个标签。我想调整某个脚本完成的标签。在找到可能的解决方案的一些答案后，我想出了以下脚本。第一个启动并按预期工作。然而，第二个却没有。它出什么问题了？代码如下: HTML:
javascript - 为什么外部 javascript 库会阻止我页面上的 javascript？
这里有一个很简单的问题，我简单的头脑无法回答:为什么我在外部库中加载时，下面的匿名和onload函数没有运行？我错过了一些非常非常基本的东西。 Library.js 只有一行:console.log(
javascript - 如何区分代码内 javascript 和客户端 javascript
我知道 javascript 是一种客户端语言，但如果实际代码中嵌入的 javascript 代码以某种方式与在控制台上运行的代码不同，我会尝试找到答案。让我用一个例子来解释它: 我想创建一个像 Mi
javascript - 将 Javascript 内联到不显眼的 JavaScript？
我如何将这个内联 javascript 更改为 Unobtrusive JavaScript？谢谢! 感谢您的回答，但它不起作用。我的代码是: PHP js文件 document.getElem
javascript - 如何将 JavaScript 对象导出为 JavaScript？
我正在寻找将简单的 JavaScript 对象“转储”到动态生成的 JavaScript 源代码中的最优雅的方法。目的:假设我们有 node.js 服务器生成 HTML。我们在服务器端有一个对象x。

行者123

个人简介

我是一名优秀的程序员,十分优秀！

作者热门文章

滴滴打车优惠券免费领取

全站热门文章

首页

博学

6Ren·AI

商城

javascript - 如何使javascript Canvas 绘制更快？