CODEWITHSUNDEEP
javascripthtmlcanvas
Julian
Julian

Reputation: 4676

How can I put multiple canvas elements in to one canvas element?

I have multiple canvas elements created by JavaScript. My question is: "How can I put multiple canvas elements to one canvas element?".

Upvotes: 5

Views: 10554

Answers (3)

user1467267
user1467267

Reputation:

Here you go;

JSfiddle

  • It will grab each canvas and make them PNG's
  • Access the buffer canvas and write the PNG's on top of each other inside it
  • Write back the buffer canvas to PNG and send it to the IMG-tag

Just give the #buffer canvas element display: none; and everything will happen invisible (check here; http://jsfiddle.net/Allendar/UqxCY/2/).

HTML

<body onload="generatePNG()">
    <canvas id="c1"></canvas>
    <canvas id="c2"></canvas>
    <canvas id="c3"></canvas>

    <canvas id="buffer"></canvas>

    <div id="output">Empty</div>
</body>

CSS

canvas[id^=c], div[id=output] {
    border: 1px solid red;
}

canvas[id=buffer] {
    border: 1px dotted green;
}

#output {
    padding: 15px;
}

#output img {
    border: 1px dotted blue;
}

JavaScript

function generatePNG() {
    var b_canvas1 = document.getElementById("c1");
    var b_context1 = b_canvas1.getContext("2d");
    b_context1.fillRect(10, 50, 50, 50);
    var b_canvas2 = document.getElementById("c2");
    var b_context2 = b_canvas2.getContext("2d");
    b_context2.fillRect(80, 50, 50, 50);
    var b_canvas3 = document.getElementById("c3");
    var b_context3 = b_canvas3.getContext("2d");
    b_context3.fillRect(150, 50, 50, 50);

    var img1 = new Image();
    img1.src = b_canvas1.toDataURL("image/png");
    var img2 = new Image();
    img2.src = b_canvas2.toDataURL("image/png");
    var img3 = new Image();
    img3.src = b_canvas3.toDataURL("image/png");

    var buffer = document.getElementById("buffer");
    var buffer_context = buffer.getContext("2d");
    buffer_context.drawImage(img1, 0, 0);
    buffer_context.drawImage(img2, 0, 0);
    buffer_context.drawImage(img3, 0, 0);

    var buffer_img = new Image();
    buffer_img.src = buffer.toDataURL("image/png");

    var output = document.getElementById('output');
    output.innerHTML = '<img src="' + buffer_img.src + '" alt="Canvas Image" />';
}

Upvotes: 3

user368361
user368361

Reputation:

A canvas's drawImage method can actually take another canvas instead of an image - you don't need to convert the canvases to images first. (See the WhatWG's documentation.)

I've simplified Allendar's JSFiddle to demonstrate:

http://jsfiddle.net/7hEKL/

Basically, all you need to do is:

targetCanvas.drawImage(sourceCanvas, 0, 0);

and you should be good to go.

Upvotes: 2

Jan Jongboom
Jan Jongboom

Reputation: 27342

Perhaps something like this, export the source canvas to an image, paint that image to the target canvas (untested):

function drawCanvasOnOtherCanvas(src, target) {
  var img = new Image();
  img.onload = function() {
    target.drawImage(img, 0, 0);
  };
  img.src = src.toDataURL('image/png');
}

Upvotes: 0

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