Question

我尝试使用canvas html5绘制ecg系统。

几乎我接近完成我的波动正在移动，但不是连续不断重复，但我想画波是从左到右连续移动？

以下链接就是示例。

例：https://www.youtube.com/watch?v=wuwBfSpVEgw

我每1秒收到一次数据。

Data Ex：

var ydata = [
                    148,149,149,150,150,150,143,82,82,82,82,82,82,82,
                    148,149,149,150,150,150,143,82,82,82,82,82,82,82,
                    148,149,149,150,150,150,143,82,82,82,82,82,82,82,
                    148,149,149,150,150,150,143,82,82,82,82,82,82,82,
                    148,149,149,150,150,150,143,82,82,82,82,82,82,82,
                    148,149,149,150,150,150,143,82,82,82,82,82,82,82,
                    148,149,149,150,150,150,143,82,82,82,82,82,82,82,
                    148,149,149,150,150,150,143,82,82,82,82,82,82,82,
                    148,149,149,150,150,150,143,82,82,82,82,82,82,82,
                    148,149,149,150,150,150,143,82,82,82,82,82,82,82,
                ];

这是我的代码：

<!DOCTYPE html>
<html>
    <head>
        <title></title>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    </head>
    <body>
        <canvas id="canvas" width="160" height="160" style="background-color: black;"></canvas>
        <script type='text/javascript'>

            var canvas = document.getElementById("canvas");
            var ctx = canvas.getContext("2d");
            ctx.fillStyle = "#dbbd7a";
            ctx.fill();

            var fps = 60;
            var n = 1;


            var data = [
                148, 149, 149, 150, 150, 150, 143, 82, 82, 82, 82, 82, 82, 82,
                148, 149, 149, 150, 150, 150, 143, 82, 82, 82, 82, 82, 82, 82,
                148, 149, 149, 150, 150, 150, 143, 82, 82, 82, 82, 82, 82, 82,
                148, 149, 149, 150, 150, 150, 143, 82, 82, 82, 82, 82, 82, 82,
                148, 149, 149, 150, 150, 150, 143, 82, 82, 82, 82, 82, 82, 82,
                148, 149, 149, 150, 150, 150, 143, 82, 82, 82, 82, 82, 82, 82,
                148, 149, 149, 150, 150, 150, 143, 82, 82, 82, 82, 82, 82, 82,
                148, 149, 149, 150, 150, 150, 143, 82, 82, 82, 82, 82, 82, 82,
                148, 149, 149, 150, 150, 150, 143, 82, 82, 82, 82, 82, 82, 82,
                148, 149, 149, 150, 150, 150, 143, 82, 82, 82, 82, 82, 82, 82, ];


            drawWave();

            function drawWave() {
                setTimeout(function() {
                    requestAnimationFrame(drawWave);
                    ctx.lineWidth = "2";
                    ctx.strokeStyle = 'green';

                    // Drawing code goes here
                    n += 1;
                    if (n >= data.length) {
                        ctx.clearRect(0, 0, canvas.width, canvas.height);
                        n = 1;
                    }
                    ctx.beginPath();
                    ctx.moveTo(n - 1, data[n - 1]);
                    ctx.lineTo(n, data[n]);
                    ctx.stroke();

                }, 1000 / fps);
            }

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

Answer 1

如果您想让它看起来像视频，请不要在每次通过结束时清除帧，只需将其清除到路径末尾的右侧。

                // Drawing code goes here
                n += 1;
                if (n >= data.length) {
                    n = 1;
                }
                ctx.beginPath();
                ctx.moveTo(n - 1, data[n - 1]);
                ctx.lineTo(n, data[n]);
                ctx.stroke();

                ctx.clearRect(n+1, 0, 10, canvas.height);

演示：http://jsfiddle.net/Shp4X/

这就是你想要的吗？

Answer 2

setTimeout()只运行一次回调你从未告诉过你的代码不止一次运行。

每次浏览器渲染帧时，都应调用requestAnimationFrame()来运行动画然后，您需要检查自上一帧以来经过的时间，并以适当的距离更新动画。

Answer 3

var EcgData=[];    
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var w = canvas.width,
    h = canvas.height,
    speed = 1,
    scanBarWidth = 20,
    i=0,
    data = EcgData[0].split(','),
    color='#00ff00';
var px = 0;
var opx = 0;
var py = h/2;
var opy = py;
ctx.strokeStyle = color;
ctx.lineWidth = 3;
ctx.setTransform(1,0,0,-1,0,h);

drawWave();

function drawWave() {
     px += speed;
     ctx.clearRect( px,0, scanBarWidth, h);
     ctx.beginPath();
     ctx.moveTo( opx,  opy);
     ctx.lineJoin= 'round';
     py=(data[++i>=data.length? i=0 : i++]/450+10);
     ctx.lineTo(px, py);
     ctx.stroke();
     opx = px;
     opy = py;
     if (opx > w) {px = opx = -speed;}

     requestAnimationFrame(drawWave);
 }

演示：https://jsfiddle.net/majidagt/hc18mvbw/

Answer 4

我创建了最易于使用的Web组件来显示来自蓝牙心率监视器或外部api的数据。您要做的就是在每个出现的节拍上拨打bang()。

document.body.innerHTML += '<ecg-line></ecg-line>';
ecgLine((bang) => setInterval(() => bang(), 1000));

源代码已发布here。我认为它看起来比提出的替代方案好很多

如何使用HTML5在画布上绘制ecg监视器？

4 个答案: