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 use for showing charts on your website.
Download
Get the latest version of RGraph (version 6.19, 28th September 2024) from
the download page. You can read the changelog here. 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 (£129) commercial license available.The clearRect function
The clearRect
function can be used to return a section of the canvas
to transparency again - removing any drawing that might
be there. It can be used to clear the canvas
(assuming the dimensions are
correct) without affecting the transformation matrix
(ie any translate/scale/rotate/transform that you have done).
RGraph uses two functions to differentiate between using this function to
clear the canvas
and the way involving setting the
width to itself - a clear
function and a reset
function. The reset
function uses the width = width
method of clearing
the canvas
(which also removes any anti-aliasing translation that has been
done).
Arguments to the function
- The X coordinate
- The Y coordinate
- The width of the rectangle
- The height of the rectangle
An example
<script>
window.onload = function ()
{
var canvas = document.getElementById("cvs");
var context = canvas.getContext('2d');
var width = canvas.width;
var height = canvas.height;
// Clears the whole canvas
context.clearRect(0, 0, width, height);
}
</script>