About
RGraph is a JavaScript charts library based on
HTML5 SVG and canvas. RGraph is mature (over 15 years
old) and has a wealth of features making it an ideal
choice to show charts on your website.
Download
Get the latest version of RGraph (version 6.17) from
the download page. There's also older versions available,
minified files and links to cdnjs.com hosted libraries.
License
RGraph can be used for free under the GPL or if
that doesn't suit your situation there's an
inexpensive (£99) commercial license available.The getImageData function
The getImageData function allows to retrieve an ImageData object from your canvas. This allows you to manipulate it as
you wish and then you can add it back onto the canvas with the
putImageData function
(reference page for the putImageData function).
You can pass it the X/Y/W/H that you want to fetch as arguments.
Arguments to the function
- The X coordinate at which to fetch data
- The Y coordinate at which to fetch data
- The width to fetch
- The height to fetch
An example
<script>
window.onload = function ()
{
var canvas = document.getElementById('cvs');
var context = canvas.getContext('2d');
// Fetches image data from the canvas
var imgData = context.getImageData(0,0,600,250);
}
</script>