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javascript - 如何将 html5 画布绘图下载为图像

问题描述

我最近刚刚将我的代码文件上传到服务器。我的网站是一个简单的 html5 绘图应用程序，用户可以在其中自由绘图。这部分我做得很好，但是我希望实现一个下载按钮，它可以简单地将用户绘制的任何图像直接下载到他们的设备，即电话、桌子、桌面。几个小时以来，我一直在寻找解决方案，但找不到任何东西。是我的服务器有问题吗？或类似的东西？任何帮助将非常感激。下面是我的代码

<!DOCTYPE html>
<html>
<head>
<title>Elemental</title>
<meta name="viewport" content="width=device-width, initial-scale=1">



<style type="text/css">

@import url('https://fonts.googleapis.com/css?family=Montserrat+Alternates');

@media screen and (max-width: 425px){

html,body{
overflow-x: hidden;
    width: 100%;
    margin: 0;
}






canvas { border: 3px solid #0BF446;
border-radius: 15px 0px 15px 0px;
display: block;
margin: 0 auto;
margin-top: 35px; 
background-color:#313131;
position: relative;}

#download{background-color:#04A12B ;
border-radius: 0 15px 0 15px;
padding: 20px 40px;
margin: 0 auto;
display: block;
font-size: 14px;
margin-top: 35px;
color: white;
font-family: 'Montserrat Alternates', sans-serif;}



#clearbutton{background-color:#04A12B ;
border-radius: 0 15px 0 15px;
padding: 20px;
margin: 0 auto;
display: block;
font-size: 14px;
color: white;
font-family: 'Montserrat Alternates', sans-serif;
margin-top: 35px;}






</style>

</head>
<body>
<body onload="init()">
<a href="../homepage.html"><img src="minilogo.png" id ="logo"></a>


<canvas id="c" width="350px" height="350px"></canvas>


<button id = "download">Download</button>


<input type = "submit" value="Clear Sketchpad" id="clearbutton" onclick="clearCanvas(canvas,ctx);">







<script>

function init() {
        // Get the specific canvas element from the HTML document
        canvas = document.getElementById('c');

      }



function midPointBtw(p1, p2) {
  return {
    x: p1.x + (p2.x - p1.x) / 2,
    y: p1.y + (p2.y - p1.y) / 2
  };
}

function getPattern() {
  return ctx.createPattern(img, 'repeat');
}


var el = document.getElementById('c');
var ctx = el.getContext('2d');

ctx.lineWidth = 30;
ctx.lineJoin = ctx.lineCap = 'round';

var img = new Image;
img.onload = function() {
  ctx.strokeStyle = getPattern();
};
img.src = "https://i.postimg.cc/rF2R0GRY/dick2.png";

var isDrawing, points = [];



var getXY = function(e) {
  var source = e.touches ? e.touches[0] : e;

  return {
    x: source.clientX,
    y: source.clientY
  };
};







var startDrawing = function(e) {
  isDrawing = true;
  points.push(getXY(e));
  event.preventDefault();


};


var keepDrawing = function(e) {
  if (!isDrawing) return;

  points.push(getXY(e));
  ctx.clearRect(0, 0, ctx.canvas.width, ctx.canvas.height);

  var p1 = points[0];
  var p2 = points[1];

  ctx.moveTo(p1.x, p1.y);

  for (var i = 1, len = points.length; i < len; i++) {
    var midPoint = midPointBtw(p1, p2);
    ctx.quadraticCurveTo(p1.x, p1.y, midPoint.x, midPoint.y);
    p1 = points[i];
    p2 = points[i + 1];
  }
  ctx.lineTo(p1.x, p1.y);
  ctx.stroke();
  event.preventDefault();
};


var stopDrawing = function() {
  isDrawing = false;
  points = [];

};






el.addEventListener('touchstart', startDrawing);
el.addEventListener('mousedown', startDrawing);

el.addEventListener('touchmove', keepDrawing);
el.addEventListener('mousemove', keepDrawing);

el.addEventListener('touchend', stopDrawing);
el.addEventListener('mouseup', stopDrawing);

function clearCanvas(canvas,ctx) {
        ctx.clearRect(0, 0, canvas.width, canvas.height);
        ctx.beginPath()
    }




</script>


</body>
</html>

标签： javascripthtmlcssdownloadhtml5-canvas

解决方案

您可以使用该Canvas#toDataURL方法生成包含画布当前图像的所有数据的 URL。然后可以使用它来代替任何 URL - 链接的href、 awindow.open等。对于下载链接，您可以使用download链接上的属性，这是 HTML5 的补充。该download属性的值是将用作默认保存文件名的文件名。

所以把所有这些放在一起：

<a id='downloadLink' download='myDrawing.png'>Download Image</a>
<script>
    function createDownload() {
        const downloadURL = document.getElementById('c').toDataURL();
        document.getElementById('downloadLink').href = downloadURL;
    }
</script>

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