Question

我很难弄清楚该怎么做，我一直在寻找解决方案，但似乎无所适从。我曾尝试从互联网上的工作示例中复制代码，但是每当我将其放入自己的代码中时，它似乎都无法正常工作。

当您在画布上绘画时，我只是在寻找，然后单击下载，它将您在画布上绘制的内容保存到本地存储中。

有人可以帮我吗？下面是我的代码

<!DOCTYPE html>
<html>
<head>
<title>Page Title</title>


<style>
canvas { border: 5px solid blue }


</style>

</head>
<body>
<canvas id="c" width="500" height="300"></canvas>
<h1>This is a Heading</h1>
<p>This is a paragraph.</p>


<script>
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 = 50;
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);
    }

function download() {
var download = document.getElementById("download");
var image = document.getElementById("c").toDataURL("image/png")
    .replace("image/png", "image/octet-stream");
download.setAttribute("href", image);
//download.setAttribute("download","archive.png");
}

</script>


<form id ="search">
<input type = "text" name="message" id="user_input">
<input type = "submit" value="Clear Sketchpad" id="clearbutton" 
onclick="clearCanvas(canvas,ctx);">
</form>
<a id="download" download="triangle.png">
<button type="button" onClick="download()">Download</button>
</a>

<p><span id='display'></span></p>
</body>
</html>

Answer 1

似乎在使用“ onclick”时未定义函数下载。 Uncaught ReferenceError: function is not defined with onclick

与其在HTML上进行onclick操作，不如将其绑定到具有addEventListener的javascript中。

var d = document.getElementById("download");
d.addEventListener("click",function(){
var image = document.getElementById("c").toDataURL("image/png")
    .replace("image/png", "image/octet-stream");
d.setAttribute("href", image);
})

https://jsfiddle.net/8sa3ugcm/

Answer 2

<form id ="search">
<input type = "text" name="message" id="user_input">
<input type = "submit" value="Clear Sketchpad" id="clearbutton" 
  onclick="clearCanvas(canvas,ctx);">
 </form>
 <a id="download" download="triangle.png">
 <button type="button" onClick="download()">Download</button>
 </a>

第一个onclick具有小写的“ c”。第二个具有大写字母“ C”。

第一个是正确的。

如何通过单击按钮

2 个答案: