uploading canvas context as image using ajax and php

Question

I have a canvas and I want to upload the canvas context to the server using ajax and php. I want the final output to be an image stored on the server. I have done image uploading using form. But now I want to get the canvas context convert it to image and upload to the server!

So, how can i do that? Any suggestions, algos or solutions are appreciated!

Answer 1

This blog post aptly describes the method of saving canvases onto the server with AJAX queries, I guess this should be fitting for you.

Basically, you will need a var canvasData = testCanvas.toDataURL("image/png"); to retrieve the canvas' contents in JavaScript. This will be a Base64 encoded string, something like this: data:image/png;base64,fooooooooooobaaaaaaaaaaar==.

The following code will make sure the AJAX query sends the contents to the HTML:

var ajax = new XMLHttpRequest();
ajax.open("POST",'testSave.php',false);
ajax.setRequestHeader('Content-Type', 'application/upload');
ajax.send(canvasData);

On the server, in the PHP script, you will have a key named HTTP_RAW_POST_DATA in the $GLOBALS array, this will contain the data we just fetched.

// Remove the headers (data:,) part.
$filteredData=substr($GLOBALS['HTTP_RAW_POST_DATA'], strpos($GLOBALS['HTTP_RAW_POST_DATA'], ",")+1);

// Need to decode before saving since the data we received is already base64 encoded
$decodedData=base64_decode($filteredData);

$fp = fopen( 'test.png', 'wb' );
fwrite( $fp, $decodedData);
fclose( $fp );

Of course, test.png is the filename you will save. The first line is required to remove the data:image/png;base64, part of the encoded image, so that it can later be decoded by base64_decode(). It's output ($decodedData) will be saved to the file.