How to Upload HTML Canvas Data to PHP Server
Last time, I shared my experience about how to use JavaScript saving HTML canvas data to local disk in Chrome. In this tutorial, I would like to share how to save HTML canvas data to remote service with JavaScript and PHP.
Uploading canvas data is a little bit complicated comparing to file upload. If you want to learn how to upload a file, you can read the tutorial PHP File Upload.
Let’s get started to create a project, which includes two files upload.html and upload_data.php. In addition, you need to create a folder upload for receiving files.
upload.html:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Upload Canvas Data to PHP Server</title>
</head>
<body>
<h1>Upload Canvas Data to PHP Server</h1>
<canvas width="80" height="80" id="canvas">canvas</canvas>
<script type="text/javascript">
window.onload = function() {
var canvas = document.getElementById("canvas");
var context = canvas.getContext("2d");
context.rect(0, 0, 80, 80);
context.fillStyle = 'yellow';
context.fill();
}
</script>
<div>
<input type="button" onclick="uploadEx()" value="Upload" />
</div>
<form method="post" accept-charset="utf-8" name="form1">
<input name="hidden_data" id='hidden_data' type="hidden"/>
</form>
<script>
function uploadEx() {
var canvas = document.getElementById("canvas");
var dataURL = canvas.toDataURL("image/png");
document.getElementById('hidden_data').value = dataURL;
var fd = new FormData(document.forms["form1"]);
var xhr = new XMLHttpRequest();
xhr.open('POST', 'upload_data.php', true);
xhr.upload.onprogress = function(e) {
if (e.lengthComputable) {
var percentComplete = (e.loaded / e.total) * 100;
console.log(percentComplete + '% uploaded');
alert('Succesfully uploaded');
}
};
xhr.onload = function() {
};
xhr.send(fd);
};
</script>
</body>
</html>
- Create a canvas tag, and draw a rectangle on canvas when the whole page has been loaded.
- Create a button for triggering uploading event.
- Create a form with a hidden input tag, which is used to save the data URL.
- Use XMLHttpRequest to asynchronously upload form data to PHP service.
upload_data.php:
<?php
$upload_dir = "upload/";
$img = $_POST['hidden_data'];
$img = str_replace('data:image/png;base64,', '', $img);
$img = str_replace(' ', '+', $img);
$data = base64_decode($img);
$file = $upload_dir . mktime() . ".png";
$success = file_put_contents($file, $data);
print $success ? $file : 'Unable to save the file.';
?>
Now deploy the whole project to a web server, such as nginx, Apache and so forth. Visit localhost:port/upload.html, click the button, and open the file folder to check whether the image is there.
Anything unclear? Please feel free to contact me at {desmond at Dynamsoft dot com}.