Saving an Image drawn on a Canvas

Question

I have a simple HTML app where I can draw on a HTML5 canvas. I have a save button where I capture the image using canvas.todataURL . When I open this link in a web browser, the full drawing isn't shown -- only a subsection of the drawing. Below is my code. Try it out, it doesn't make sense.

JSFIDDLE: https://jsfiddle.net/v0a2Lfsk/1/

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.4.1/jquery.js"></script>

<script>
var mousePressed = false;
var lastX, lastY;
var ctx;

$(window).on('load', function() { 
  canv = document.getElementById('myCanvas');
  ctx = canv.getContext("2d");
  canv.width  = $(window).width();
  canv.height = 1000;

  $('#myCanvas').mousedown(function (e) {
    mousePressed = true;
    //Draw(e.pageX - $(this).offset().left, e.pageY - $(this).offset().top, false);
    Draw(e.pageX, e.pageY, false);
  });

  $('#myCanvas').mousemove(function (e) {
    if (mousePressed) {
      //Draw(e.pageX - $(this).offset().left, e.pageY - $(this).offset().top, true);
      Draw(e.pageX , e.pageY , true);
    }
  });

  $('#myCanvas').mouseup(function (e) {
    mousePressed = false;
  });
  $('#myCanvas').mouseleave(function (e) {
    mousePressed = false;
  });


});

function Draw(x, y, isDown) {
  if (isDown) {
    ctx.beginPath();
    ctx.strokeStyle = "blue";
    ctx.lineWidth = $('#selWidth').val();
    ctx.lineJoin = "round";
    ctx.moveTo(lastX, lastY);
    ctx.lineTo(x, y);
    ctx.closePath();
    ctx.stroke();
  }
  lastX = x; lastY = y;
}

function next(){

    var canvas = document.getElementById('myCanvas');

    var image = canvas.toDataURL("image/png");  // here is the most important part because if you dont replace you will get a DOM 18 exception.
    console.log(image);

    // html2canvas(document.querySelector("#myCanvas")).then(canvas => {
    //     document.body.appendChild(canvas);
    //     alert("dasds");
    // });

}

function clearArea() {
  // Use the identity matrix while clearing the canvas
  ctx.setTransform(1, 0, 0, 1, 0, 0);
  ctx.clearRect(0, 0, ctx.canvas.width, ctx.canvas.height);
}
</script>
<body>
 <canvas id="myCanvas"></canvas>
  <div class="controls">     
    <button onclick="javascript:clearArea();return false;">Clear Area</button>
    <button onclick="javascript:next();return false;">Save (Print to Console Log)</button>
    <!-- Line width : <select id="selWidth">
    <option value="1">1</option>
    <option value="3">3</option>
    <option value="5" selected="selected">5</option>
    <option value="7">7</option>
    <option value="9">9</option>
    <option value="11">11</option>
    </select>
    Color : <select id="selColor">
    <option value="black">black</option>
    <option value="blue" selected="selected">blue</option>
    <option value="red">red</option>
    <option value="green">green</option>
    <option value="yellow">yellow</option>
    <option value="gray">gray</option>
    </select> -->
  </div>

</body>
  <style>
body{
  overflow:hidden;
}
#mycanvas
{
  background-color:#fff;
  position:absolute;
*/  background-repeat:   no-repeat;
}
.controls
{
  position:absolute;
  top:0px;
  right:0px;
  width: 600px;
  background-color:#2277dd;
  padding:5px;
  margin:2px;
  color:#fff;
  -webkit-border-radius: 3px;
  border-radius: 3px;
}
</style>

Answer 1

Make sure that you press the "Show More" button in the Console Tab of Developer Tools, otherwise you may copy only part of the output string (as per asdadsads's comment).

In some cases, showing a cut-off base64 string will lead to an error message, while in others (such as yours), a part of the image will be displayed.

Alternatively, just use the "Copy" button, which will copy the entire output.

Saving an Image drawn on a Canvas

Question

1 answers

solution1
1 ACCPTED 2019-05-30 23:42:28

Saving an Image drawn on a Canvas

Question

1 answers

solution1 1 ACCPTED 2019-05-30 23:42:28

solution1
1 ACCPTED 2019-05-30 23:42:28