clear Canvas and save Canvas - php

Question

I am just finishing web application for picture analysis and inpainting. And I need help with canvas. This is what I do:
EDIT:
<img id="imgEdit" src="<?php echo $imagename; ?>" border="0">
<canvas id="canvasPaint"
width="<?php echo $width; ?>"
height="<?php echo $height; ?>">
</canvas>
<input type="button" value="Clear" onClick="clearCanvas();" class="button">
<input type="button" value="Save" onClick="saveViaAJAX();" class="button">
<div id="debugFilenameConsole">Wait for a while after clicking the button and the filename of the image will be shown to you. </div>
But now I have problem with clearCanvas function. Because browsers cannot read property 'width'. This is my full source code. How, please can someone tell my what I doing wrong.
EDIT:
function clearCanvas()
{
var theCanvas = document.getElementById("canvasPaint");
if (theCanvas && theCanvas.getContext) {
var ctx = theCanvas.getContext("2d");
if (ctx) {
ctx.clearRect(0, 0, <?php echo $width; ?>, <?php echo $height; ?>);
var srcImg = document.getElementById("imgEdit");
ctx.drawImage(srcImg, 0,0);
clickX = new Array();
clickY = new Array();
clickDrag = new Array();
}}}
function saveViaAJAX()
{
var theCanvas = document.getElementById("canvasPaint");
var canvasData = theCanvas.toDataURL("image/jpg");
var postData = "canvasData="+canvasData;
var ajax = new XMLHttpRequest();
ajax.open("POST",'canvasSave.php',true);
ajax.setRequestHeader('Content-Type', 'canvas/upload');
ajax.send(postData);
}
I need to save canvas as jpeg image on local disk after user click 'save image'. That's mean, areas which are transparent in canvas become black background.
I need something like this:
http://i48.tinypic.com/2w5vhpv.jpg

Answer 1

You can save the canvas to an image file with the canvas.toDataUrl('image/jpg').
Regarding the first question: normally you clear the canvas with context.clearRect(0, 0, canvas.width, canvas.height) method. That being said, your code should work as expected if the canvas and context declarations have been made correctly.